EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021Virtual Conference

In this lecture is made a brief route though the technology that has been the umbrella of all my academic life: powder metallurgy (PM). There are three main reasons to use this technology as an alternative to many others: 1) is a cost saving technology compared with alternative processes, 2) sometimes is a captive way to produce a part or a material and, 3) by the PM route is possible to obtain unique properties, better than any other alternatives. When I started my academic career, I did it working in my PhD thesis (1985), in PM low alloyed steels, materials that can be classified in the first group. In that time, the main questions to solve were why Cu swells during sintering and how was the role of carbon in this swelling. Many years after that, I am still working in answering those questions, but using much more efficient techniques to try to answer it. But I have also worked in materials of groups 2 and 3. As an example of the group 2 I go through one work where the aim is to replace Co as binder phase in harmetals, materials that only can be made by PM. And I also briefly report two examples of materials that can be considered from the group 3: new Co base superalloys for high temperature applications and high entropy alloys. In these later examples the main advantage of PM is the microstructural control and the ability of the technology to control the possible segregations and the grain size.
Aknowledgements.
I wish to acknowledge to all of those people who trusted on me, including those who has decided to award me with this Gold Medal, to all those academics who collaborate with me, and specially to my PhD students and all the students that walked with me part of the path.

Unproper disposal of non-biodegradable plastics and their accumulation on environment triggers the known white pollution. In turn, agrifood waste is a global concern since high foodstuffs amount ends as non-valued waste. To overcome these issues, ecology concepts as green manufacturing/circular economy are being pursued. Therefore, plastics with improved biodegradability, physicochemical, and mechanical profile are required.
From agrifood industries, biobased byproducts still containing valuable biomolecules of interest for the (bio)plastics manufacturing can be generated. From our most recent research, non-value potato washing slurries, potato peels, coffee silverskin, and eggshells revealed to be agrifood byproducts from which polysaccharides, proteins, lipids, phenolic compounds, and minerals can be recovered and further used in the development of starch-based bioplastics with improved physicochemical/mechanical performance and lightweight fillers for plastic materials. Most these formulations have shown compatibility with various plastic manufacturing technologies, namely solvent casting, extrusion, injection molding, and 3D printing by fused deposition modelling (FDM), and are capable of being transposed from lab to pilot scale. Complementary studies about the agrifood byproducts-derived (bio)plastics versatility are ongoing, targeting to exploit materials with a wide application range.
From an ecological and economic point of view, this circular economy strategy can bring sustainability and new business opportunities for both agrifood and plastic industries, and concomitantly contribute to fulfil the European Green Deal objectives.

Acknowledgments: Thanks are due to the University of Aveiro and FCT/MCTES for the financial support of CICECO (FCT Ref. UIDB/50011/2020 & UIDP/50011/2020). IG also acknowledge FCT for the Individual Call to Scientific Employment Stimulus (ref. CEECIND/00430/2017) and to the companies A Saloinha, FEB – Cafés S.A., and Derovo for providing the agrifood byproducts.

Controlling magnetic properties by tuning carrier concentration is a key feature of diluted ferromagnetic semiconductors, giving possibilities for multifunctional spintronic devices. Here, the evidence of the long-range magnetic order in V-doped WSe2 semiconductors will be presented. The magnetic domains of the long-range ferromagnetic order are observed by magnetic force microscopy at room temperature. More importantly, the magnetic domains can be modulated by a gate bias, which is concrete evidence for the ferromagnetic semiconducting characteristics. The mechanism behind the formation of the long-range order will be also discussed and investigated through scanning tunneling spectroscopy and density functional theory.
In addition, the giant Zeeman shift from the spin-polarized state in WSe2 doped with a small amount of vanadium atoms (~0.15%) by investigating resonant magnetotunneling spectroscopy of a vertical graphite/V-WSe2/graphite heterojunction will be discussed. The p-type character of the doping state is located near the valence band, substantially shifted under an external magnetic field at 7.8 meV/T with a giant g factor of approximately 135, an order of magnitude higher than that of other 2D magnetic semiconductors. The evidence of the spin-polarized band edges of V-doped WSe2 is also confirmed by circular-polarized photoluminescence.

In the quantum Hall (QH) regime, charge carriers flow in one dimensional quantum Hall edge channels (QHECs) and are topologically protected against backscattering. Due to its intrinsic two-dimensionality and the massless nature of its charge carriers, graphene constitutes a fascinating platform for studying QH effect. However, graphene edges are known to strongly harm the topological protection of QHECs. Local probe measurements have recently helped understand why. They highlighted that both up- and downstream QHECs coexist along the same device edge and that impurities, located between these counterpropagating QHECs, couple them and allow backscattering of charge carriers, normally prohibited. Nevertheless, the origin of counterpropagating QHECs remains largely debated and it is unclear whether they exist both for holes and electrons.

To answer these open questions, we performed scanning gate microscopy (SGM) in the quantum Hall regime on a graphene constriction. SGM, consisting in scanning a biased AFM tip, used as a local top gate, while recording the device resistance, gives access to the locations where backscattering occurs.

Our results suggest different mechanisms of topological breakdown for holes and electrons. While backscattering occurs along the edges for holes, in line with previous studies, it takes place in the vicinity of the constriction for electrons.

Supported by simulation results, we find that counterpropagating QHECs exist for both types of carriers but the metallic contacts cause the observed contrasting behaviour. By inducing a local doping in their vicinity, contacts lead to a decoupling between counterpropagating holes QHECs while they cause a perfect equilibration of electrons QHECs. Our results highlight the importance of contacts when designing a QHECs-based device and apply to other two-dimensionnal materials, especially for those presenting topological properties.

Studying local variations in the Peltier [1] or Seebeck coefficient of materials is important to optimise their thermoelectric properties and to enable applications like single-material thermocouples [2]. Yet most global experiments overlook spatial divergences in the signal and the role of local variation and the internal structure. Here, we developed Scanning Thermal Gate Microscopy (STGM), a non-invasive method to obtain high-resolution 2-dimensional maps of the thermovoltage [3]. We investigate junctions formed between single- and bi-layer graphene, identify the impact of internal strain and reduction of channel width on the local Seebeck. These findings and the newly developed STGM method will help to further understand and improve the thermoelectric properties of 2D devices.

References
[1] Harzheim et al. Nano Letters, 18, 7719-7725 (2018).

[2] Harzheim et al. Advanced Functional Materials 30, 2000574(2020).

[3] Harzheim et al. 2D Materials 7, 041004 (2020).

Highly filled particulate metal-dielectric nanocomposites films have unique functional properties with hosts of applications. To explore collective interactions between the particles, we control the particle separation on the nm scale by employing vapor phase deposition, which is a scalable approach permitting, inter alia, excellent control of the filling factor. For polymer films, we have recently used initiated chemical vapor deposition (iCVD) to avoid decomposition of the functional groups, e.g. in highly stable electrets for electret microphones and magnetoelectric sensors, 3D superhydrophobic coatings, and nanoscale gradient copolymers. The nanoparticles can form during co-deposition via self-organization or by means of high-rate gas aggregation cluster sources, which provide independent control of filling factor and size. Formation of plasmonic nanoparticles can be monitored in situ via UV-vis spectroscopy. We also demonstrated in situ control of the composition of alloy nanoparticles and the ability to fabricate multiple core-shell particles. Recent examples of nanocomposites range from plasmonic meta-materials through photoswitchable devices to memristors and memsensors for neuromorphic electronics. We also developed a new process for photocatalytic growth of needle-like metallic nanostructures. Research on layered magnetoelectric sensors will be touched only briefly.

Initiated Chemical Vapor deposition (iCVD) is an original technique for the fabrication of polymeric thin films. This method relies on the radical polymerization under vacuum, which takes place on a cooled substrate. The main advantages that render iCVD a very promising method for polymer thin films deposition are the low substrate temperature, the absence of solvent, the large range of monomers that can be used and the possibility to preserve “delicate” functional groups of the monomer structure. In this work, an organosilicate polymer, the p(V3D3), formed from the precursor trivinyltrimethylcyclotrisiloxane was deposited and studied as a low-k dielectric material for use in microelectronics for the realization of capacitors. More precisely, the thickness of the films has been varied from few nm to several microns and the physicochemical along with the mechanical properties were investigated. This study shows that the p(V3D3) is polymerized in uniform thin films on all the surface of a 200 mm Si wafer, for both thinner and thicker films. The polymer has also been conformably deposited on substrates with 3D structures for the evaluation in integrated capacitors. The deposition rate which depends on the process conditions, is constant for all deposition times. AFM, FTIR and ellipsometry results confirm that the obtained polymer is amorphous, cross-linked, and composed of siloxane rings and polyethylene chains. Moreover, the polymer composition remains similar and relatively independent of the film thickness. Electrical tests that were made in order to evaluate the dielectric properties of the material reveal a low dielectric constant (<3), low leakage currents (few nA/cm2 at 1 MV/cm) and high breakdown voltage (higher than 7 MV/cm). These characteristics are maintained over the whole range of thickness studied, which positions this material as a state of the art dielectric polymer for high-voltage applications.

Oxidative chemical vapor deposition (oCVD) is a solvent-free technique, enabling growth of network polymers with stoichiometric compositions in a single processing step. Deposition proceeds via vapor-phase eliminating limitations of insufficient monomer solubilities of conjugated polymers (CPs) faced by conventional methods. Further, unlike traditional methods, oCVD accommodates mild operation conditions providing additional advantages such as the ability to conformally coat sensitive substrates or 3D porous microstructures. In this work, we use oCVD to engineer hybrid conductive polymer hydrogels (CPHs). CPHs are excellent candidates for a plethora of biomedical applications that rely on electrical conductivity, including wearable and flexible resistive strain sensors for healthcare monitoring.

We have developed hybrid CPHs which combine strong mechanical and electrical properties. Ultrathin hydrogel films with gradient microstructure and tunable porosity have been synthesized using two different techniques: (1) salinity-triggered phase-separation of polyelectrolyte complexes, and, (2) electrospinning. Porous interconnected hydrogels serve as a molecular template, guiding in-situ vapor-phase polymerization of a CP backbone into the matrix by oCVD. The growth mechanism of oCVD CP network alongside physicochemical properties of CPHs have been investigated. CPHs are synthesized by oCVD of polypyrrole (PPy) on free-standing hydrogels. FTIR spectroscopy confirms formation of PPy and SEM imaging shows conformal coating of oCVD PPy on the pore-walls within the microstructure. Current work includes mapping dispersion of PPy network inside the hydrogel matrix. Effect of different parameters such as reactant flowrate, substrate temperature, and pressure on the growth rate will be presented. A good control over the deposition parameters enable tunable mechanical and electrical properties of the resulting material. Synergistic interpenetrating CP chains throughout the hydrogel matrix can be used to reversibly manipulate mechanical and electrical properties of the designed CPH.

By applying ion irradiation it is possible to produce materials at room temperature for which generally high temperatures are needed. If we irradiate a layer structure at the interfaces atomic mixing, or ion mixing happens and compound formation might occur as well. Previously we have shown that this method can be applied to produce SiC-rich protective nano-coatings which are applied in harsh environments. The produced coatings exhibited excellent corrosion resistant properties and reasonable good wear resistance as well [1,2]. Now we deal with the possible extension of the method. C/W multilayer structures - with individual thicknesses of 10-20 nm - are irradiated by xenon and argon atoms. The irradiation conditions are chosen with the help of simulation programs (TRIDYN, SRIM). The layer thickness and the in-depth distribution of the formed tungsten-carbide is investigated by Auger electron spectroscopy depth profiling. We show that the thickness of the carbide-rich region can be tailored by changing the ion irradiation conditions and the layer structure. The corrosion resistance of the layers is tested by potentiodynamic corrosion test. Process-property relationships are discussed.

Acknowledgements
RADIATE project, HZDR-Dresden and project funding of Centre for Energy Research is highly acknowledged.

References: [1] A.S. Racz, M. Menyhard, ACS Appl. Mater. Interfaces, 10 (2018) 22851.
[2] A.S.Racz, D.Dworschak, M.Valtiner, M.Menyhard, Surf. Coat. Technol., 386 (2020).

The search for more effective as well as novel functional materials, such as heterogeneous catalysts, would benefit when we could bridge the molecular world with the macroscopic world, which involves materials performance.

Such detailed information can be obtained if we would have access to a very powerful camera probing the dynamics of a functional material when it is at work. By shooting molecular movies of e.g., an active catalytic solid down to the level of single atoms and molecules we could start to understand how solid catalysts really work, but also how they evolve as a function of their lifetime. In other words, can we probe the birth, life and death of a solid catalyst under true reaction conditions, i.e, at elevated temperature and temperatures and in the presence of a gas and/or liquid. This is the field of operando spectroscopy and microscopy. Recent breakthroughs in chemical imaging techniques, based on optical, electron and X-ray methods, demonstrate that such molecular movie concept is within reach.

This keynote lecture discusses the recent advances in in-situ and operando spectroscopy and microscopy of heterogeneous solids at different length scales, starting from single molecules and single atoms up to the level of individual catalyst particles. We will discuss different methods, including scanning probe microscopy (i.e., PiFM and TERS),optical methods (e.g., fluorescence, Raman and UV-Vis spectroscopy) as well as X-ray methods (i.e., TXM, STXM and ptychography). These methods will be illustrated in the areas of thermal catalysis, photocatalysis and electrocatalysis.

Interfaces govern the behaviour of all electronic devices. Herbert Kroemer coined the famous phrase “the interface is the device” in his 2000 Nobel Prize lecture, and we are still applying tremendous effort to understand interfaces in new material generations, with wide-bandgap materials being no exception. If anything, wide bandgap materials are more vulnerable to defect states purely due to their larger bandgap. Understanding of the bulk behaviour of semiconductors can often not be extended to their behaviour in structured film stacks were interfaces play a vital role. SiC/SiO₂ is a prototypical wide-bandgap semiconductor/dielectric interface. A multitude of different defects leads to unacceptably large defect densities in the vicinity of the conduction band of 4H-SiC. The management of interfacial defects remains a topic of lively discussion and current interest.

Here, we present a systematic study of the 4H-SiC/SiO₂ interface in industrially manufactured samples with a particular focus on the effects of nitridation in N₂, NO, NH₃ and NO+NH₃ atmospheres. High temperature nitridation has been shown to compensate interface defects leading to an increase in device performance, however, information on the local chemistry at the interface after such processes is scarce, limiting the understanding of the interface and consequently the targeted improvement of device characteristics. The present work uses energy-dependent hard X-ray photoelectron spectroscopy (HAXPES) to systematically study the elemental distributions and chemical environments across the 4H-SiC/SiO₂ interface. We combine both laboratory- and synchrotron-based HAXPES results to obtain a complete picture of this important technological interface and to benchmark the capabilities of this spectroscopic technique for the exploration of buried interfaces in device heterostructures in general.

The interest in novel carbonaceous materials with large effective surface areas, as well as high conductivity and stability, is growing due to the downsizing of electrical devices and the demand for new low-cost materials. For those applications it is necessary to find materials with high electrical conductivity like it is the case for graphene and nitrogen doped graphene. These nanostructures are of interest for many applications, e.g. batteries, super capacitors, electrodes in electrocatalysis to name a few. Plasma methods provide suitable pathways to obtain high nitrogen doping rates in such materials often in a one step synthesis or by a plasma post-treatment. As there are many possible sites for nitrogen incorporation often a combination of several analytical techniques are needed to relate the incorporation at the different nitrogen sites to the used precursors and processing conditions. Here, it will be shown how a combination of synchrotron x-ray photoelectron spectroscopy (XPS) and near edge x-ray absorption fine structure (NEXAFS) can be used to identify and quantify the different nitrogen species in different plasma grown N-graphene based functional materials including carbon nanowalls and composites with different metal oxides.

The authors acknowledge the support of the PEGASUS (Plasma Enabled and Graphene Allowed Synthesis of Unique Nanostructures) project, funded by the European Union’s Horizon research and innovation program under grant agreement No. 766894. We further thank Helmholtz Zentrum Berlin for the allocation of synchrotron radiation beamtime at BESSY II. Experiments at BESSY have been also supported with H2020 Calypso Plus project, grant Nr. 18207084-ST, 182¬07393-ST and 192-08646-ST.

The progressive miniaturisation of feature sizes in microelectronic devices has increased the probability of higher local power densities and consequently temperatures. Complex multi-layered metallisation schemes, often implemented in devices, can suffer from detrimental interdiffusion phenomena between adjacent layers, compromising device reliability, when subjected to such severe local conditions.

The challenge of interdiffusion is particularly persistent in power semiconductor devices due to the high-power loads. Copper metallisation schemes in combination with titanium-tungsten (TiW) diffusion barriers are used, where the TiW barrier is required to isolate Cu from the silicon substructure, but local high temperature events can induce the diffusion of titanium out of the barrier and into the top Cu metallisation layer. This loss of Ti can ultimately lead to the degradation and failure of the diffusion barrier. Additionally, oxygen accumulation at the TiW/Cu interface can occur, adding an additional reliability challenge as this can promote delamination at the interface.

Here, device-relevant Si/SiO2/TiW and Si/SiO2/TiW/Cu thin film stacks were characterised using a combination of soft and hard X-ray photoelectron spectroscopy (SXPS/HAXPES). Combining the two techniques provides the opportunity to non-destructively study both the titanium diffusion mechanism and the oxidation behaviour of TiW at multiple sampling depths. Annealing for varying durations at 400°C under forming gas is used to simulate temperature stress on the device stacks and systematically follow occurring processes across the multi-layer structures. A clear dependence of the titanium surface enrichment and oxidation behaviour on the annealing duration is observed and can provide a detailed explanation of the degradation mechanisms associated with the TiW/Cu heterostructures. Overall the SXPS/HAXPES characterisation approach delivers an insight of the depth dependent behaviour of metallisation schemes under thermal stress and can be extended to other multi-metallic systems.

High Silicon Strengthened Ductile Irons (HSiSDI) with 3.5, 4.2 and 4.5 % wt. silicon contents were produced in Y-blocks with different geometries to investigate the effects of silicon and solidification rate on microstructure integrity and tensile mechanical properties. With increasing silicon the strength of the HSiSDs increased, while the ductility decreased progressively, with an abrupt reduction for silicon content higher than 4.2 % wt. With decreasing solidification rates the graphite degeneracy with the appearance of chunky graphite became more significant at the highest silicon contents, so chemical ordering and graphite degeneracy seemed to be qualitative explanations of tensile property degradation. However, a deeper analysis of the relationship between solidification rate, microstructure and tensile properties was realized through an innovative approach based on the Matrix Assessment Diagram (MAD) [1,2], where the parameters of Voce equation resulting from best-fitting the experimental tensile flow curves of a significant number of HSiSDI samples, were plotted. For 3.5 % wt. silicon content, the MAD analysis indicated that the microstructure was sound for any solidification rate, while for 4.5 % wt. the microstructure was sound only for the fastest solidification rates. For 4.2 % wt. silicon content the MAD analysis pointed out that the tensile plastic behaviour and the microstructure integrity was in between the 3.5 and 4.5 % wt. silicon contents, representing indeed a composition threshold where however the reliable microstructures were found with the fastest solidification rates, while for the slowest ones considerable variability was found. Support to MAD analysis results was given from microstructure observations.

1 - Angella G., Cova M., Bertuzzi G., Zanardi F. Int. J. of Metalcasting, 14 (3) 2020, pp 816-826.

2 - Angella G, Donnini R., Zanardi F. Int. J. Cast Metals Research 2020, Vol. 33, NOS. 2–3, pp. 89–102.

Fatigue properties of tool steels and ductile irons are a concern in many of its applications, and the two materials may in some applications be competitor selections. In many cases are long life endurance a requirement, and it may even be as high life lengths as ranging up in the Very High Cycle Fatigue (VHCF) regime, i.e. above 107 load cycles. Tool steels are mostly used with a martensitic microstructure in the hardened and tempered condition. Similarly for ductile irons where one class is a bainitic/martensitic structure but with the graphite nodules dispersed in it. For both materials, high static and fatigue strengths are often an engineering requirement.

In the present study, the fatigue strength has been tested in a wide life range for both tool steel and ductile irons. At lower life a servohydraulic machine was used for fatigue testing, while at higher life a 20 kHz ultrasound equipment was used to manage reasonable test times. Hour-glass specimens were loaded in uniaxial fatigue at R=0.1 load ratio, and the specimens were designed to operate in resonance at 20 kHz load frequency. SN-curves were obtained with fatigue lives from 105 to 109 load cycles. Microstructure was characterized and fractography by SEM was performed. The life limiting defect distributions were mapped. Fatigue strength and life was discussed using different model equations, and a comparative perspective of the materials was laid out involving strength, microstructure and defect distribution.

High-chromium cast irons are typically used in high demanding applications, where low production costs and wear performance are key factors. The excellent resistance of these alloys to both abrasion and erosion results from the overall microstructural features, i.e. type, morphology and distribution of hard primary and secondary carbides, along with the matrix constituents. More specifically, it has been suggested that erosive wear resistance is strongly affected by the behavior of the matrix. Hence, according to the specific chemical composition, the microstructure can be tuned, e.g. by increasing its hardness and toughness, to enhance the lifetime of such wear-resistant materials. Heat treatments performed to destabilize the austenite promote its transformation into martensite, the coalescence and thickening of secondary carbides thus increasing the overall hardness of the material.
The present study investigates the effects of different destabilization heat treatments performed on a hypereutectic white cast iron, with 21 % Cr and 4 % Nb, applied as an hardface coating to a low carbon steel substrate to improve its erosive wear resistance. The hardfacing plate was made by the open-arc welding of a flux-cored wire: high-chromium cast iron electrodes were deposited onto the substrate. The as-received and the heat-treated material was analyzed through optical and scanning electron microscopy, X-Ray diffraction and hardness tests to determine the relationship between microstructural variations and heat-treatment parameters. The erosive resistance was evaluated per the ASTM G76 standard in a purpose-built air blast test rig: experiments were performed with clinker powder (with a d90 of 9.73 µm) as erodent particles at an impingement angle of 90°. The tribological performance was assessed through weight loss measurements and analyses of the worn surfaces. The results suggest that erosion is dependent on carbide volume fraction and hardness along with the matrix microstructure: the hardest martensitic matrix gave the greatest erosion resistance.

The interaction between precipitation and deformation in aluminium alloys can profoundly affect microstructure and hence properties. Deformation is observed generally to have an accelerating effect on the precipitate evolution processes of nucleation, growth, and coarsening. This acceleration is due to the interaction of deformation induced defects, such as dislocations and vacancies, with solute atoms. A better understanding and ability to predict these interactions offers the possibility to exploit deformation to reduce process times or improve performance of age hardenable aluminium alloys.

This paper discusses the interactions between deformation and precipitation for AA7075, a widely used commercial aluminium alloy. The effect of important process parameters such and temperature, strain, and strain rate on the dynamic processes are explored using simple models. These predictions are compared with results from recent in-situ dynamic precipitation experiments.

The implications of this work on the warm forming and processing of AA7xxx for applications such as automotive sheet are discussed in light of the model and experimental results.

Precipitation hardening is the key of the mechanical properties for 6xxx series Aluminium alloys. The precipitation sequence is complex and dependent of the alloy composition, particularly on the Mg/Si ratio. A compositionally-graded alloy is obtained with high-temperature compaction using Spark Plasma Sintering on Al-Si and Al-Mg model alloys atomised powders. The different stages of the fabrication process include a sequence of interdiffusion heat treatment, homogenisation, and quenching. Energy dispersive X-ray spectroscopy (EDX) and wavelength dispersive X-ray spectroscopy (WDS) ensure a well-controlled gradient in a single direction. Small pores are formed during the interdiffusion treatment with a volume fraction below 1.5%. After ageing, the composition-dependent precipitation is evaluated by microhardness profiles and multiple differential scanning calorimetry (DSC) measurements, supported by transmission electron microscopy observations. Mechanical behaviour is also inspected through tensile tests on both homogeneous and graded specimens. In parallel, simulations of precipitation kinetics within the graded material are performed and optimised in order to match with the experimental results.

6XXX alloys (AlMgSi) are of great importance for the automotive industry and lightweight design. Currently, more than 100 different compositions (different levels of alloying elements, different magnesium:silicon ratios, trace elements) of the alloy 6082 are known. In this study, quench rates between 1 and 200 K/s were applied to study the effect on mechanical properties and microstructure. Dif-ferent magnesium and silicon levels were analyzed as a function of quench rate and aging parameters. It has been found, that in most cases a higher strength can be achieved with a hot quench medium, acting as a “pre-aging” treatment. TEM studies indicated that not only precipitation hardening, but also solid solution and cluster hardening are significantly contributing to the strength of artificial aged samples.

The Al-6XXX alloys are widely used in automotive applications for their high strength to weight ratio. The desired properties are achieved by precipitate hardening through the process of artificial aging at elevated temperatures. However, these alloys undergo natural aging at room temperature which is undesirable, and a mechanistic understanding of the early stages of precipitation in natural aging is still lacking. We perform off-lattice kinetic Monte Carlo simulations of vacancy migration using a near DFT-accurate machine-learning potential for Al-Mg-Si to study the dynamics of vacancy-solute interactions during natural aging. Early-stage clusters of Si and Mg atoms are found to trap vacancies, in agreement with indirect evidence for 'vacancy prisons'. The clusters and trapping times are studied qualitatively and quantitatively, and the implications of the early-stage kinetics on subsequent artificial aging is discussed.

Abhinav C. P. Jain, Daniel Marchand, Albert Glensk, Michele Ceriotti, W. A. Curtin

The equiatomic CrMnFeCoNi high-entropy alloy (HEA), also named Cantor alloy, was generally considered to be a stable disordered FCC solid solution. Indeed, this alloy was reported multiple times to solidify in this state and remains so after cold forming operations and recrystallization heat treatments. However, it was later discovered that secondary phases precipitate in the Cantor alloy when subjected to long-term anneals below ~800°C [1-3]. In this contribution, different factors affecting the phase stability of the Cantor alloy and the precipitation kinetics of secondary phases, namely, chemical composition and microstructure will be presented [4]. Through a systematic characterization of the temporal evolutions of the phase fractions, the morphologies and sizes of precipitates as well as the concentration profiles forming at matrix/precipitate interfaces, we were able to identify the mechanisms and elementary diffusion processes responsible for the precipitation kinetics [5]. Based on this knowledge, the influence of the precipitation of secondary phases on tensile properties is investigated with a focus on embrittling effects. This work sheds light on the long-term stability and precipitation kinetics in the Cr-Mn-Fe-Co-Ni system but also motivates the investigation of other HEAs and compositionally complex alloys that are considered for elevated-temperature applications.

[1] B. Schuh, F. Mendez-Martin, B. Völker, E.P. George, H. Clemens, R. Pippan, A. Hohenwarter, Acta Mater. 96, 258-268 (2015).
[2] E.J. Pickering, R. Munoz-Moreno, H.J. Stone, N.G. Jones, Scripta Mater. 113, 106-109 (2016).
[3] F. Otto, A. Dlouhý, K.G. Pradeep, M. Kubenova, D. Raabe, G. Eggeler, E.P. George, Acta Mater. 112, 40-52 (2016).
[4] G. Laplanche, S. Berglund, C. Reinhart, A. Kostka, F. Fox, E.P. George, Acta Mater. 161, 338-351 (2018).
[5] G. Laplanche, Acta Mater. 199, 193-208 (2020)

Studies on high-entropy alloys (HEAs) mainly set off to tune the substitutional elements in the single-, dual- or multi-phase matrix, yet, the resultant mechanical properties are often not substantially improved compared to that of the traditional “low-entropy” alloys such as high-strength steels or Ti alloys. In this work, we present how we further tune the phase stability and enhance the mechanical properties of HEAs of CoCrFeMnNi family via the doping of interstitials, e.g., carbon and nitrogen. Thermo-mechanical processing was also employed to refine the matrix grains as well as trigger precipitation of nano-sized particles. The approach enables the synthesis of alloys that show a combination of multiple mechanisms such as significant interstitial solid solution strengthening and twinning-induced plasticity upon deformation. Owing to the multiple strain hardening mechanisms that are jointly active, the combination of tensile strength and ductility of the interstitial HEAs can be significantly better than that of the interstitial-free counterpart, which is strongly related to the phase stabilities affected by interstitials.

Nano-lamellar materials with ultrahigh strengths and unusual physical properties are of technological importance for structural applications. However, these materials generally suffer from low tensile ductility, which severely limits their practical utility. In this talk, we show that markedly enhanced tensile ductility can be achieved in coherent nano-lamellar high-entropy alloys, which exhibit an unprecedented combination of over 2 GPa yield strength and 16% uniform tensile ductility. The ultrahigh strength originates mainly from the lamellar boundary strengthening, whereas the large ductility correlates to a progressive work-hardening mechanism regulated by the unique nano-lamellar architecture. The coherent lamellar boundaries facilitate the dislocation transmission, which eliminates the stress concentrations at the boundaries. Meanwhile, deformation-induced hierarchical stacking-fault networks and associated high-density Lomer-Cottrell locks enhance the work hardening response, leading to unusually large tensile ductilities. The coherent nano-lamellar strategy can potentially be applied to many other alloys and open new avenues for designing ultrastrong yet ductile materials for technological applications.

Recent experimental studies report that several body-centered cubic (bcc) refractory high-entropy alloys (HEAs) exhibit transition-induced plasticity (TRIP) by transforming to the hexagonal close-packed (hcp) structure, which would be beneficial for better ductility. On the other hand, there are also the reports of the ω phase precipitates in bcc HEAs, which would cause embrittlement. It is therefore crucial to better understand phase transitions of such HEAs to further improve their mechanical properties. We study thermodynamic and dynamic stability of bcc refractory HEAs based on ab initio simulations. We first demonstrate that, in atomistic simulations, careful analysis for relaxed structures of bcc HEAs is essential. With the developed proper analysis of structural relaxation, the bcc–hcp phase stability is found to be closely connected to the TRIP composition in Ti–Zr–Nb–Hf–Ta-based HEAs observed in experiments. The obtained bcc–hcp equilibrium composition of these HEAs also show a substantial correlation to the valence-electron concentration (VEC). We also show that thermodynamic integration in combination with machine-learning interatomic potentials enables us to accurately compute the vibrational free energies of HEAs even near the melting temperature.

A detailed study is presented comparing the deformation mechanisms operating at service temperatures in the Ni-based disc alloy RR1000 during monotonic tensile, high stress creep and fatigue conditions. By using bright field conventional and scanning transmission electron microscopy to observe tests interrupted at low strain, it was possible to follow the sequence of events and highlight the many features common to these different deformation modes. While coupled shear of full matrix dislocations forming slip bands is found to different degrees in all test conditions, it is predominantly a process favoured by the high strain rates of tensile and fatigue deformation. The occurrence of stacking fault deformation becomes increasingly prevalent at higher temperature and decreasing strain rate. In this alloy, intragranular carbides appear to act as prolific sources of dislocations which can combine to produce active stacking fault deformation, a feature common to tensile and creep deformation, but there also appears to be the direct emergence of stacking faults from the grain boundaries. While dislocation sources are initially comparable, stacking fault shear plays a negligible role in the analysed fatigue tests. The way in which these detailed observations from monotonic testing can inform the behaviour under complex creep and fatigue conditions is discussed.

Acknowledgements:
This work was supported by Rolls-Royce plc and the EPSRC under EP/H022309/1, EP/H500375/1 and EP/M005607/1.

High temperature and total strain controlled low cycle fatigue tests for smooth and notched specimen were carried out for the nickel base superalloy Rene80. Two different material batches were tested, where smooth specimen with a preferential grain orientation distribution showed distinct higher lifetimes compared to smooth specimen made of material with random grain orientation. However, for notched specimen no lifetime improvement could be determined for both batches.

Polycrystalline finite element simulation were conducted to understand the influence of different grain orientation distribution on the mechanical behaviour of the specimen in order to explain the observed lifetime behaviour. For smooth specimen the texture of the grains lead to lower Young’s moduli in loading direction and therefore to lower stresses during total strain testing, when compared to a random grain orientation distribution. Lower stresses in combination with also observed lower Schmid factors of the grains, delays the crack initiation and extends therefore the lifetime for smooth specimen with textured grain orientation.

For the notched specimen the simulations reveal an inverse behaviour. The texture of the grains leads to a slightly higher stiffness when compared to random grain orientation distribution. Whereas the bulk of the notched specimen, where a uniaxial stress state can be assumed, shows low stiffness (similar to the smooth specimen) the interaction of varying principal stress along the notch with constant grain texture leads to areas at the notch where the stiffness is significantly increased. It follows that high stresses occur within the notch, which are similar to the stresses in a specimen of the random orientation distribution. Also no differences in the Schmid factor for both orientations distributions could be found. Due to minor differences in mechanical behaviour the lifetimes of textured and random orientated are comparable under same test conditions.

The main aim if this study is to investigate influence of coarse grained microstructure of a nickel-based superalloy on TMF crack growth behaviour. For this purpose, single-edge U-shaped notched (SEN) and corner crack (CC) specimens were machined and tested under out-of-phase (OP) and in-phase (IP) TMF crack growth test conditions between 400 and 750 oC in laboratory air. The loading waveform was triangular with a load ratio of R=0 and no hold time. All tests were run on servo-hydraulic test machines with induction heating systems. The crack length was measured using the compliance method with the SEN specimens and a direct current potential drop (DCPD) technique on the CC specimens. Electron backscatter diffraction (EBSD) was used in order to relate the crack growth path to the microstructure on the micron scale. The EBSD characterisation was made by orientation mapping of metallographically prepared specimens in an advanced HITACHI SU-70 field emission gun scanning electron microscope (FEG-SEM) equipped with the Oxford Instruments ESBD detector. Micro-hardness was also measured to examine crack closure effects on the deformed material around the crack tip. It has been found, that in the coarse grained material TMF in-phase crack growth rates are highly sensitive to the material microstructure. TMF out-of-phase tests show no sensitivity to microstructural aspects.

This study has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 686600.

Aluminium castings often possess complex geometries with only selected surfaces machined. Thus, the overall fatigue assessment needs to cover the heterogeneously textured as-cast surfaces considering local casting process conditions as well.
Recent research activities of Pomberger and Oberreiter introduced an alternative sub-area based fatigue assessment methodology for as-cast and pore surface-layer afflicted specimens. The conducted research work focusses on flat sample geometries taken out of aluminium crankcases covering different manufacturing process conditions.
The new testing concept features the experimental fatigue assessment of as-cast surfaces on specimens taken out of the water-cooling-jacket volume crossways to the axial piston movement. The transverse arrangement of the specimen enables a testing load step which is most representative to the actual loading conditions of combustion engines. In addition, the transversal sampling position implies that the local casting process condition is nearly constant throughout the tested volume. A pronounced variation in microstructure and spatial roughness parameters was observed in previous studies for axial orientated samplings. Finally, the new transversal specimen arrangement features the study of local process conditions, as the highly-stressed volume is maintained within a specific height of the cylinder covering statistically coherent roughness parameters.
The tangential ring segments possess a circumferential as-cast surface, which is bend by applying an exterior compressive load at the sector ends. Thus, featuring a cyclic tension load with high stress ratio at the rough surface.
The experimental work covers two cast aluminium alloys, focussing on the effect of local casting conditions. Therefore, several specimens are additionally analysed with computed tomography to evaluate the distribution of casting inhomogeneities within the surface layer. The sub-area based fatigue assessment is statistically applied for the previously non-destructive scanned as-cast surfaces. The conducted experimental results show a sound correlation to the numerical fatigue assessment which enhances the current validation range of the method significantly.

Low alloyed steel slabs produced by the continuous casting process can present transverse corner cracks, which cannot be repaired afterwards due to the formation of an oxide layer within the crack. Because of that, the understanding of the formation of these cracks, as well as the reproducibility of the phenomenon through laboratory tests is of great value. The present work analyzed samples taken from the slab corners, where cracks were identified. The fracture surfaces were observed with the scanning electron microscope (SEM) and afterwards the samples were cut to have the microstructure analyzed with the light optical microscope (LOM). By using two different etching methods to reveal the microstructure, it was clearly seen that the cracks were initiated and propagated at the prior austenite grain boundaries. Furthermore, the SEM images from the corner samples were compared to the samples tested by physically simulating the continuous casting process, and the structure found was similar to the ones tested at the critical temperatures. The same was noted for the microstructure analysis, where cracks were also frequently seen at the former austenite grain boundaries. Therefore, it could be concluded that the steel behavior in the laboratory tests done with in-situ melted samples showed to be in good accordance with the reality of the continuous casting process.

Recent work indicates that HVOF thermal spraying WC-Co coatings have been used to enhance the wear resistance of various engineering components in a variety of industrial environments. In the present work WC-Co powder containing Cr particles in an amount of 10% was deposited on ductile cast iron with high velocity oxy-fuel (HVOF) thermal spray coating technique. An investigation was conducted to determine the role of Cr particles in the WC-Co coating produced with HVOF technique on microstructure, mechanical and wear properties in a system of type: WC-Co coating/ductile cast iron. The microstructure of the HVOF-sprayed WC-Co+Cr coating was characterized by light microscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS). The analysis of the microstructure showed the formation of coating with low porosity, compact structure, good adhesion to the substrate with typical lamellar structure composed of a fine molten Cr particles and finely fragmented WC grains embedded in a Co matrix, coming to the size of nanocrystalline. For analysis of the adhesion of coatings to the substrate, the scratch test was applied. An assessment of the erosive wear resistance of coatings was also carried out, confirming the significant impact of Cr particles as well as the microstructure and phase composition of the carbide coating on the wear resistance of the tested coating system. Moreover, the results were discussed in relation to the bending strength test, including cracks and delamination in the system of the WC-Co+Cr/ductile cast iron as microhardness and erosion resistance of the coating. It was found that the addition of Cr particles was significantly increase resistance to cracking and wear behaviour in the studied system.

Effective surface pretreatment is the key to long-term stable and durable bonds between different materials, e.g., used in structural bonding and coatings. Its purpose, besides a general cleaning of a joint surface, is to structure and functionalise the interface. Particularly attractive and fast, laser surface pretreatment enables simple, reproducible and waste-free processing of surfaces of different materials (e.g. metals, fibre-reinforced plastics). The laser pretreatment, the requirements for obtaining suitable surfaces as well as the optimisation for structural bonding and coating will be highlighted using different material combinations and application examples.

For structural applications, metal-polymer and -FRP joining is very common. Metals are pretreated with a pulsed Nd:YAG laser and bonded with thermoset or thermoplastic matrices. For the purpose of forming protective metallic coatings on FRP components, the laser can be employed similarly. Various microanalytical, surface and mechanical characterisation methods are used to study the joint interfaces.

Laser pretreatments of titanium, aluminium and steel resulted in nano- and microstructures that consist of solidified melt structures covered by oxidic films. Depending on the alloy, the morphology and chemistry of the surface structures varied. The optimal laser pretreatment leading to a stable interface depends strongly on the alloy itself, i.e., the reflectivity of the surface, the presence of contaminations, and the particular laser parameters. Generally, the formation of a stable, homogeneous nanostructure is a prerequisite for long-term stable adhesive bonding.
Laser pretreatment of FRP, in contrast, leads to structuring of the surface by ablation of the matrix, thus exposing the underlying fibres. The metallic coating on the fibres is substantially more reliable than a coating deposited purely on the polymer matrix.

Therefore, the laser pretreatment of metals and FRP for bonding and coating follow different concepts. The pretreated surfaces allow mechanical interlocking and chemical interactions leading to long-term stable bonds between different materials.

The development of carbon nanotubes (CNTs)-reinforced metal matrix composites (MMCs) is challenged by the production of a homogeneous distribution of CNTs in the metal matrix and the formation of a good interface between the CNTs and the matrix. Therefore, we propose that surface modification of CNTs with a coating material such as silicon carbide that is thermally stable and wettable by the matrix prior to composite processing is an effective solution to address these issues. In this work, a continuous coating on individual CNTs were successfully achieved via a novel coating technique. The tailoring of the coating characteristics such as thickness, geometry and chemical composition was performed by controlling the coating technique parameters to determine the most suitable coating characteristic on the CNTs to improve their dispersion and wettability by the metal matrix. It was discovered that the distribution of the coated CNTs in the matrix was improved meanwhile the grain size of the coated CNTs reinforced metal matrix composites was significantly reduced in comparison to the monolithic material and pristine CNTs reinforced metal matrix composite. Finally, the microstructure of the composites were also studied to characterise the interface and mechanical testing were performed to investigate the strengthening effect of the coated CNTs in the metal matrix.

One of the promising methods of microstructure modification in surface layers is a friction stir processing (FSP). This method is based on the basic principles of friction stir welding technology (FSW) however, the FSP method, unlike FSW, is used to modify the microstructure of the materials, and not to join metal elements. The process consists in heating and plasticizing the material as a result of the friction of a tool equipped with a shoulder and a pin plunged into the material and moving along the modified surface of the element. The movement of the tool causes heating, intense stirring, and densification of the deformed material.
In the study, the FSP method was used to modify the surface layer of a SnSbCu bearing alloy. The modification was aimed at extending the service life of bearings by improving their tribological properties.
The research carried out in this paper covered investigations of the microstructure using light and scanning electron microscopy along with analysis of the chemical composition in micro-areas, as well as Brinell hardness tests and uniaxial compression tests. Additionally, the phase composition was tested using X-ray diffractometer, the size of the precipitates present in the microstructure before and after the modification process was determined, as well as the tribological properties under technically dry friction conditions and lubrication with TU 32 oil.
It was proved that the use of friction stir processing for surface treatment of the SnSbCu bearing alloy causes significant changes in the morphology of the hard phases, including their refinement and improves the tribological properties of the analyzed alloy.

Copper and its alloys play an elementary role in industrial applications due to their excellent thermal and electrical conductivity. In the field of electromobility, plugs made of copper materials are used as connecting elements between the charging station and the vehicle. Another example is the application of precipitation-strengthened copper alloys, e.g., CuCr1Zr and CuNi2SiCr, for manufacturing of welding electrodes and tools. With the help of LPBF, the excellent thermal, electrical and mechanical properties of copper alloys can be combined with the greatest possible geometric freedom, thus enabling new types of application with a high degree of functional integration, like water-cooled plug connections. However, the complete remelting of copper powders with a high copper content (> 95%) by LPBF is associated with considerable difficulties due to the large beam reflection and the high thermal conductivity. In order to increase the absorbance, the usage of a green laser system is therefore recommended for copper alloys.
Within the scope of this study, various copper materials, for example, Cu-OFE, CuCr1Zr and CuNi2SiCr, were considered. By means of gas atomization, metal powder was produced, metallographically prepared, microscopically analyzed with respect to pore formation and spherodicity and eventually processed by LPBF using both, a 532nm green and a 1060nm red laser system. Different process parameters, such as laser power, feed speed, hatching strategy and focus diameter were used. The manufactured components were then prepared metallographically and characterized by means of light optical microscopy (incl. microhardness testing) and analytical scanning electron microscopy in combination with EDX, EBSD and FIB to obtain the microstructure parameters, pore size and distribution, precipitates, layer structure and texture effects.

With the growing industrial application of laser-based powder bed fusion (LB-PBF) there has been an increase in the amount of powder suppliers and powder grades. Despite similar atomizing technology, the quality of the powder feedstock can vary significantly between suppliers and batches in terms of powder flowability, impurities and powder surface chemistry. While high quality powder has its mandated uses, there are instances where high purity is not essential, allowing for lower cost powder to be considered. To date, the effects of powder properties, both physical and chemical, on the resulting mechanical properties of as-built components is still a topic that is not well understood. One of the contributing factors is the lack of relevant methods for evaluating powder spreadability rather than powder flowability. This study presents a review of different 316L powders that were produced using various atomization techniques. The physical powder properties were evaluated using powder metallurgical techniques, a powder rheometer and a revolving drum analyzer. Significant and correlative powder properties were highlighted, with a brief discussion on their applicability to powder spreading. Furthermore, the surface chemical state of the powder with regard to oxide composition was characterized and correlated to defects within the microstructure as well as to the mechanical properties of the as-built components. This review provides insight regarding the implication on potential changes in processability that different powder feedstocks can have and how different levels of e.g., oxygen can impact the final properties.

Given nearly ambient temperature conditions in laser powder bed fusion (LPBF), spatter accumulation is usually the main source of powder degradation. Spatter particles are normally molten/partially molten or overheated particles ejected from the melt pool and its vicinity, that are oxidized due to the presence of residual oxygen in the build chamber. Melt pool ejections are finer and have a higher temperature and hence get highly oxidized during the solidification and cooling process. In this study, spatter generated during the LPBF fabrication of Ti-6Al-4V parts under different atmospheric gas conditions (including Argon, Helium, and a mixture of both) were analyzed. Bulk oxygen analysis has shown a slight decrease in oxygen content of spatter particles with the introduction of He gas, and the decrease was highest in 100% He environment. Morphology analysis of these spatter particles by scanning electron microscopy (SEM) showed that the surface was covered with oxide particulates enriched in Al oxide alongside Ti-based oxides. Further surface analysis by X-ray photoelectron spectroscopy (XPS) confirmed the presence of Al- and Ti-based oxides. The depth profile analysis by XPS illustrated a decrease in oxide layer thickness with the introduction of He gas, in agreement with the trend in bulk oxygen content. The results indicate that introducing He as a processing atmosphere is a potential solution to increase both, productivity and powder reusability.

In the past decade, the industrial interest for Laser Powder Bed Fusion (LPBF) additive manufacturing (AM) process has significantly grown and the technology is on track for full scale production. Yet some key mechanisms of the process are not fully understood. To create a new layer, the powder is deposited on a previously solidified layer. This volume of powder defines the available amount of material for the next solidified layer. The particle size distribution of the powder is an important parameter as it influences not only the laser/material interaction but also the spreading behaviour of the powder. In this study we investigate the use of different particle size distribution of an AISI 420 martensitic stainless steel using powder characterization tools as a rotating drum, a tapped density analyser and an experimental bench for spreading behaviour. This bench allows controlled recoating speed and layer height. The effect of the particle size distribution on the spreading behaviour and the properties of the formed layer has been investigated. A finer powder has shown an aggravating cohesive behaviour resulting in inhomogeneous powder layers. Powder blends has been developed as a proposal for improved layer homogeneity, density and spreading behaviour. This powder blend results from the mixture of two powders with different particle size distribution. The sizes of constitutive powders have been varied in order to study the effect of size ratio. It is shown that, in the blend, the density increases with the weight percentage of fine powder until 40 wt%. Beyond this value, the increase of fine powder doesn’t further increase the density. By changing the weight percentage of fine powder in the blend, a transition has been found between cohesive and non-cohesive behaviour. The requirements for design of a powder blend are discussed according to a part manufacturing perspective.

Thermodynamic properties of phases and phase equilibria are the key to the analysis of pyrometallurgical processes and they enable to describe the limiting boundary conditions for metallurgical processes. The raw materials basis of non-ferrous metals needs an effective control of slag fluxing due to the unavoidable fact that the targeted metal values of, e.g., copper, nickel, lead and tin will be as minority components in the smelter feed compared to iron sulphides, gangue and hazardous elements. This means that the slag compositions will become more complex and the amount of produced slag is several times that of the metal production. This feature has also severe impact to the heat balance of the smelting where autogenous smelting becomes more and more difficult to maintain in industrial smelting vessels.

Thus, minimisation of the slag/metal ratio in smelting and effective fluxing strategies are the big challenges of the non-ferrous smelting and refining industry in the future which is additionally challenged by the massive use of secondaries required by the ethical use of natural resources and the Circular Economy. This is a specific need where computational thermodynamics helps us beyond the printed 3-component and constrained 4-component phase diagrams available in various compilations.
This paper will introduce the use of constrained phase equilibria in the process analysis where the boundary conditions are derived in a straightforward manner from the industrial processes and their characteristic features. The case studies have been taken from the copper and nickel smelting and refining industry.

In this contribution, selected key thermophysical and thermodynamical properties of Fe-C-Cr, Fe-C-Ni and Fe-C-Cr-Ni based alloys such as solidus and liquidus temperatures, peritectic transformation temperature and other phase transition temperatures, heats of fusion, specific heat capacities, enthalpies, densities, coefficient of thermal expansion, viscosity, surface tension, wettability expressed by the wetting angle on alumina substrate of liquid alloys were experimentally determined in a high-temperature area up to the temperature of 1600 °C. The effect of the temperature and chemical composition of alloys on these properties was investigated using 3D heat flux DSC, DTA, dilatometry, sessile drop and viscosity method. The interaction of the studied alloys with the alumina substrate was studied by SEM, EDX, and XRD methods. To assess the influence of the major elements (carbon, chromium, and nickel), the alloys with different carbon, chromium and nickel content varied in the range of 0-1.5 wt.%, 0 5 wt.% and 0–5 wt.%, were chosen.

In steelmaking processes, the presence of higher phosphorus concentrations in the liquid steel is generally undesired as P may affect the product quality during continuous casting, e.g. internal cracking and micro-/macrosegregation. In order to guarantee a successful process control and to precisely predict the solidification progress in the casting machine, thermodynamics of the ternary Fe-C-P system play a key role. The present study deals with the experimental methods of differential scanning calorimetry (DSC), high-temperature laser scanning confocal microscopy (HT-LSCM) and high-temperature X-ray diffraction (HT-XRD) to characterize melting equilibria and solid-state phase transformations in the Fe-C-P system. Based on the novel experimental results a thermodynamic database for the Fe-C-P system was developed using the modified Quasichemical model (MQM) for the liquid phase. Application of the database to continuous casting simulations will be shown in the final part of this work.

Today steelmaking is driven by specific demands regarding material properties for high-quality applications, often involving the precise adjustment of non-metallic inclusion populations in the surrounding steel matrix. On the one hand, fine dispersed inclusions below 1 µm in size can improve the final microstructure by e.g. grain boundary pinning or by acting as nucleation sites for phase transformations. On the other hand, to achieve requirements of super clean steels for high performance applications, the amount and size of undesirable particles needs to be as low as possible, even for small particle sizes. Thus, also analytics are constantly facing new challenges for a representative and comprehensive characterization of non-metallic inclusions.
Although automated SEM/EDS analyses are a well approved and state of the art method for inclusion characterization, the described developments also require an ongoing effort in the optimization of the measurement itself as well as in the subsequent data evaluation. The present paper outlines different improvement approaches in the application of automated SEM/EDS analyses covering the aspects matrix correction in dependence of inclusion size and composition, as well as the accurate representation of inclusion morphology. Using an adapted form for inclusion categorization based on so called morphology factors and next neighbor relations, stereological effects of cross-section preparation as well as different cluster situations can be evaluated. For three-dimensional particle investigation, different techniques for inclusion extraction from the steel matrix are applied. For all aspects, special focus is put on the characterization of multiphase inclusions.

Nanomaterials are important for a wide range of applications because of their unique properties, which are strongly connected to their three-dimensional (3D) structure. Electron tomography has therefore been used in an increasing number of studies. However, the increasing complexity of nanomaterials has driven the development of even more advanced 3D characterization techniques, which will be discussed in this contribution.

For example, 3D characterization of structural defects in nanoparticles by transmission electron microscopy is far from straightforward since the presence of diffraction contrast in a tilt series of images violates the projection requirement for tomography. However, being able to visualize defects is of great importance to understand e.g. the initial growth of metallic nanoparticles or the effect of pulsed laser irradiation on the crystal structure. By simultaneous acquisition of tilt series using different annular detectors, we were able to visualize both the morphology and the defect structure of several types of nanostructures [1,2]. Moreover, also a 3D characterization at the atomic scale could be performed.

In order to preserve the carefully designed morphologies and functionalities, understanding the stability of nanomaterials during application is of equal importance. It is hereby important to note that most electron tomography investigations have been performed under the conventional conditions of an electron microscope. An emerging challenge is therefore to fully understand the connection between the 3D structure and properties under realistic conditions, including high temperatures as well as in the presence of liquids and gases. Therefore, I will discuss novel methodologies to track the fast 3D changes of nanomaterials that occur under such conditions [3].

[1] N. Winckelmans et al., The Journal of Physical Chemistry C 122 (2018), p.13522
[2] J.D. Smith et al., Angewandte Chemie 59 (2020), p.943
[3] W. Albrecht et al. Accounts of Chemical Research, doi.org/10.1021/acs.accounts.0c00711

Even trace amounts of impurity atoms can greatly influence the structural and functional properties of Materials. Applications of this effect range from doping of semiconductors to strengthening of alloys. One important research topic for these applications is the temperature dependent bulk diffusion of impurity atoms in their host lattice. While this has been studied in great detail using computational approaches and experiments on larger scales, atomic-scale observations of the diffusion of impurity atoms are surprisingly lacking.

In this work, we show the diffusion dynamics of individual tungsten atoms in an aluminium matrix using in situ High Resolution Scanning Transmission Electron Microscopy (HRSTEM). The temperature dependence of diffusion is elucidated using a MEMS-based in situ heating holder. We deposit the material using a unique combination of magnetron sputtering (for Al) in conjunction with a nanoparticle gun (for W). With this technique, we are able to get finely dispersed tungsten atoms in a crystalline aluminium thin film, ideally suited for TEM investigations.

We observe that diffusion is largely facilitated by vacancies, which cause random walk patterns of substitutional impurities. In some instances, substitutional impurities may also diffuse to an octahedral interstitial site, which is then followed by diffusion from one interstitial site to another. Looking at different grain orientations, we see preferential diffusion along certain crystallographic planes. Finally, we investigate the effect of defects such as grain boundaries and twins on diffusion. While the movement of the impurity atoms is greatly enhanced by arbitrary grain boundaries, we see very little influence of twin boundaries on the overall speed of diffusion. With this work, we expect to deepen the general understanding of diffusion mechanisms at the atomic scale, benefiting future material developments.

High-entropy alloys (HEAs) are a new class of materials exhibiting a superior combination of magnetic, mechanical and electrical properties. FeNiCoAlMn is a promising candidate for a soft magnet, important for applications in electrical systems such as power generation and electromagnets. However, the high entropy effect is partially true, since other thermodynamic properties can also play a role in phase stability, making the alloys vulnerable to phase separation that could affect their magnetic behavior. Here, we report on the first nanoscale investigation of FeNiCo(AlMn)x processed by Laser Metal Deposition, by applying (Scanning) Transmission Electron Microscopy ((S)TEM) combined with Energy-Dispersive X-ray spectroscopy (EDX) and Electron Energy-Loss Spectroscopy (EELS). Experiments were performed on an FEI Titan G2 60-300 kV equipped with a CEOS DCOR probe-corrector, monochromator and Super-X EDX detectors.
A gradual change of the FCC phase towards BCC by increasing x was observed. A thorough analysis employing STEM-EELS revealed a coexistence of L21 and B2 ordered structures in the BCC phase, and ordered nano-percipitates were detected in the FCC phase. Low-loss EELS revealed a plasmon-peak splitting in FCC indicative of two valence electron densities. This finding in combination with intense Moiré fringes and high-defect density indicate that FCC exhibits intense phase separation tendency. However, ordering and phase separation trends did not have a severe impact on the magnetic properties. All samples exhibited good soft-magnetic behavior since they were easily magnetized to the saturated state with coercivity values of <1000 A/m. This finding indicates that the magnetic properties of ordered B2 or Heusler alloys with similar compositions to HEAs, are more associated with the specific chemical environment of the segregated atoms. Finally, in-situ experiments in STEM revealed that ordering is suppressed with increasing temperature.

Nanomaterials with well-controllable structure are of particular interest in many fields of research, and knowledge on their formation mechanism and structural evolution is essential for developing precise chemical synthesis routes. Complementing the capabilities of liquid-cell transmission electron microscopy (TEM), we can use X-ray ptychography, a scanning coherent diffraction imaging (CXDI) technique, to record micrographs inside an extended and heated chemical reactor. This can enable us to follow the evolution of size and morphology of nanoparticles in a solution-based synthesis in real time. With state-of-the-art nanofocused synchrotron beams, a spatial resolution of a few tens of nanometers can be achieved even when imaging weakly scattering objects in an extended liquid environment [1,2].
I will briefly introduce the Ptychographic Nanoanalytical Microscope (PtyNAMi) [3] at the nanofocus endstation of beamline P06 at PETRA III, and present a sample environment for running chemical syntheses in the X-ray beam, featuring a heatable pressure cell with nanoscale position stability. This setup enables long-term observations of chemical processes.
We synthesize cuprous oxide nanocubes in a solvothermal approach from a metal-organic precursor, that exhibit a dynamic morphological evolution at later reaction stages, when a solid-state reduction to the metallic state takes place [4]. This nanomaterial with sizes in the range of a few hundreds of nanometers is well suited to demonstrate the advantages of our X-ray microscopy approach. Such rare visual insights into structural changes in solution are important to deepen our understanding of the origins of nanomaterial morphology.

References
[1] M. Kahnt et al. Scientific Reports 11, 1500 (2021)
[2] J. Reinhardt et al., Ultramicroscopy 173, 52 (2017)
[3] A. Schropp et al., J. Appl. Cryst. 53, 957-971 (2020)
[4] N. Kränzlin et al. Adv. Mater. Interfaces 2, 1500094 (2015)

Efficient joining materials and characterization techniques are of critical importance for the integration of ceramics in high performance structures.
This talk will overview several issues occurring when measuring the shear strength of joined ceramics and ways to overcome them.
An important topic relevant to the use of joined ceramics and composites to themselves or to other materials is the assessment of the shear strength in a reliable manner.
As it is well known, most lap tests give only an apparent shear strength useful for comparative purposes but unfit to quantify the shear strength of the joint.
The situation can be even more complicated in case of joined ceramics, and the lack of reliable, easy to perform, shear tests may pose limitations in fabricating the desired joined component.
Innovation in joining and their characterization developed within our research group (www.composites.polito.it) will be summarized, together with a brief overview on J-TECH@PoliTO, Advanced Joining Technology research center at Politecnico di Torino (http://www.j-tech.polito.it/).

The influence of the various content of the multilayered graphene (MLG) on the structural and mechanical properties of the final bulk porous silicon nitride-zirconia (Si3N4-ZrO2) based ceramics was investigated. The ceramic composites were prepared in the form of the laminated structure with different (5-30-5 wt% and 30-5-30 wt%) MLG content by hot isostatic pressing. ZrO2 particles were incorporated into the Si3N4 matrix by attrition milling to improve the mechanical properties of the final composite. Homogeneous distribution of the MLGs, a completed phase transition from α to β-Si3N4 in case of 5 wt% MLG have been observed. The structural examinations revealed that the multilayered graphene and zirconia particles owing to their different sizes and shapes influenced the porous microstructure evolution and the related mechanical properties of the composites. The sandwich structures enhanced the mechanical properties compared to reference ceramic with 30 wt% MLG. The position of the layer with higher graphene content, high ratio of α / β phase of Si3N4 and higher porosity had crucial effect on the final mechanical properties.

Keywords: sandwich structure; porous ceramic; Si3N4-ZrO2 / MLG; hot isostatic pressing; multilayered graphene

The authors thank to the support to the FLAG-ERA project „Multifunctional Ceramic/Graphene Thick Coatings for New Emerging Applications”.

This study reports the first experimental evidence of the violation of the classical law for grain growth in twinned boron carbide ceramics. Grain-growth kinetics is drastically dependent on the presence of twin steps at the grain boundaries in B4C ceramics sintered by spark plasma sintering. The conjunction of high temperature gradients with large compressive stress when a pulse electric current passes through the ceramic powders gives rise to an intense twinning–detwinning formation. These forming steps at the grain boundaries change the grain mobility drastically. Therefore, a new ‘exotic’ law for grain-growth kinetics is found and validated at different temperatures and dwell times. The time dependence of the grain size is proved to follow one law which has the same functional form as the Bose-Einstein distribution law.

This study is shown as an example of the potential of synchrotron X-ray refraction technique to determine the evolution of damage in brittle (microcracked) materials. The strength of X-ray refraction resides in its high detectability of features (e.g., cracks, pores) within large volumes, enabling a macroscopic characterization of the microstructure. The case study is a Zirconia-based cast refractory, which is aimed to function at high temperatures (even in excess of 1700°C) in industrial furnaces to enable the production of special glasses. Therefore, this material must withstand severe in-service conditions (both thermomechanical and chemical). X-ray refraction technique is used to monitor the microcracking evolution of the material, which was previously subjected to thermal cycles (crossing the martensitic phase transformation around 1000°C) at two different stress levels.

The range of materials used for additively manufactured products is currently still very limited, as the materials often cannot be transferred to this new production technology or cannot compete with conventionally manufactured products in terms of properties. On the other hand, however, additive manufacturing such as laser powder-bed fusion (LPBF) offers completely new degrees of freedom for the development of novel alloys whose material properties lie far beyond those of conventionally manufactured products. In terms of this, each new alloy composition requires holistic development that consideres the entire process chain - from powder production to the additively manufactured and heat-treated component. The properties of the newly developed alloy can be adjusted either by in-situ heat treatment during LPBF or by a subsequent so called direct aging and can be varied over a wide range. In addition, the potential of specific in-situ technologies enabling a local modification of the microstructure will be discussed as promising methods further improvements of the overall properties.
The presented contribution focuses on selected developments along the process chain, which essentially support the realization of novel alloys with advanced properties.
Due to the high solidification rates of the melt pool in the LPBF process, extreme non-equilibrium states such as highly supersaturated solid solutions can be achieved, which allow exceptional properties. Using the example of the newly developed alloy Custalloy®, which is based on the cost-effective Al-Mg-Si system and, thus, suitable for automotive applications, it can be shown that strength and ductility values can be achieved, which are above of conventional high-strength 7xxx aerospace wrought alloys and close to the most performing, but highly cost and ressource intensive AM Alloy Scalmalloy®. As an outlook, locally acting in-situ technologies are shown, which allow promising local modification of the microstructure.

In search of lower emissions in the transportation sector, the focus shifts to alternative energy storage systems. By switching from fossil fuels with a high gravimetric and volumetric energy density and easy storability to battery systems or hydrogen tanks, a new demand for lightweight and multifunctional designs arises. Fiber reinforced materials help to fulfill these requirements, due to low restrictions on shape and a high specific strength. Load bearing structurally integrated battery casings or hydrogen tanks could benefit from composite materials. In both applications, feedthroughs are necessary either for sensors and cables or for operating fluids. In case of hydrogen tanks, it is obvious that a leak proof design is mandatory. However, for battery casings it is also essential to keep water or any kind of pollution away from sensitive equipment. However, the usefulness of metallic feedthroughs in composite structures offers the best compatibility to piping and wiring demands. Therefore, a hybrid solution of a composite tank or casing in combination with a metallic insert is needed.
The aim of the presented research is the formulation of general design guidelines for metallic feedthroughs fully integrated in fiber-reinforced laminates. Typical solutions to achieve a leak proof feedthrough make use of sealings, threaded fittings or bonding. From injection molded electrical housings the concept of in-mold integration of the feedthrough in the final part is common practice. This is also true for load introduction points in continuous fiber reinforced thermoset laminates. However, the mechanisms for optimal load transfer are different to those leading to leakage at the metallic interface. A newly developed testing procedure is presented as well as the findings for different insert alloys, reinforcement types and measures to enhance the durability with respect to media tightness.

Hybrid laminates are used as a lightweight material system with high specific strength in e.g. the aerospace or wind-energy industry, where fatigue loads occur over decades of service lifetime accompanied by numerous numbers of cycles, in the very high cycle fatigue (VHCF) range. Especially for safety-relevant components a thorough understanding of the fatigue behavior up to VHCF regime is necessary to estimate lifetime expectancy correctly. Hybrid laminates based on metal and fiber-reinforced polymers exhibit complex damage behavior, which affects the integrity of the entire composite structure and the mechanical properties significantly, leading to steady material degradation with progressive numbers of cycles. For thermoplastic-based hybrid laminates, which offer the possibilities of formability, recyclability and mass production due to short consolidation cycle times, the VHCF behavior is fairly unknown.

Thermoplastic-based hybrid laminates containing AA6082 aluminum alloy sheets and unidirectional glass and carbon fiber-reinforced polyamide 6 were investigated. Fatigue tests up to the VHCF regime of max. 10E8 cycles were conducted on an innovative resonant fatigue testing system offering a frequency of 1,000 Hz. A sinusoidal stress amplitude was used with a stress ratio of R = 0.1. Fatigue progress and accompanying damage evolution were monitored through combined stress-strain hysteresis analysis and temperature monitoring. To conclude onto microstructural changes, microscopic analysis of damage states after defined stiffness decreases and numbers of cycles were conducted.

The test results show the necessity of improved air cooling for maintaining thermoplastic matrix properties despite self-heating. During VHCF load the mechanical properties are influenced mostly by changes in microstructure and damage development within the aluminum alloy sheets. Compared to HCF regime the interface damage changes in terms of crack and delamination rate.

Layered material compounds of thin metal sheets and fibre-reinforced plastics (FRP) combine the advantages of the individual components. A decisive advantage is the tailor-made design by combining different compositions, material fractions and fibre orientations depending on the application and load direction. In this work the thermoplastic based hybrid laminate CAPAAL 2/1 composed of a 1.25 mm graded glass- and carbon fibre-reinforced polyamide 6 layer between two 0.5 mm thin sheets of the aluminium alloy AA6082-T4 is used to study the directional properties of this hybrid material utilizing three different configurations of the FRP-layers. The first design is the unidirectional (UD) orientation of all FRP-tapes in the rolling direction of the aluminium sheets. The hybrid laminates with bidirectional (BD) design are composed of 0 and 90° oriented FRP-tapes and the quasi-isotropic (QI) design has a composition of 0, +45, 45 and 90° FRP-tapes in a symmetrical arrangement. The various arranged thermoplastic tapes between aluminium sheets are consolidated by pressing under the pressure of 1.5 MPa and temperature of 295 °C in a dipping edge tool. The microstructure and thickness of the FRP-layer was examined by light microscopy. Tensile tests were performed on water jet cut samples in 0, 45 und 90° direction to the rolling direction of the aluminium. The quasi-isotropic design leads to balanced mechanical properties of the hybrid laminate. It was found that the tensile strength of the hybrid laminate is influenced by the orientation of the fibres. Maximum tensile strength can be reported by a UD design in fibre direction. Across the fibre direction, the tensile strength decreases strongly. Nearly isotropic properties can be reached by the quasi-isotropic design of the FRP.

Chronic bone infection is considered one of the most problematic biofilm-related infections with high morbidity and mortality rates, prolonged hospitalization and costly health care expenses [1]. Nanomedicine has entered into this scenario by bringing new approaches to develop new therapies to enhance the standards used today [2,3]. The scientific efforts are mainly focused on the design of new nanostructured materials with anti-infective properties for both prevention and treatment or the infections [4]. The characteristics of these materials must be tailored to achieve improved antimicrobial performance and good integration with the surrounding tissue [5,6]. Herein we will focus primarily on three areas: (i) new technological advances in the surface modification of biomaterials for the design of antimicrobial coatings; (ii) multifunctional scaffolds with antimicrobial properties and the ability to regenerate damaged tissue; and (iii) nanomaterials based on mesoporous silica nanoparticles with the capability to carry different families of antimicrobial agents to target the bacteria and/or biofilm, and release them in response to certain stimuli.

[1] C. R. Arciola, D. Campoccia, L. Montanaro, Nat. Rev. Microbiol. 2018, 16, 397.
[2] M. Gisbert-Garzarán, M. Manzano, M. Vallet-Regí, Pharmaceutics 2020, 12, 83.
[3] M.Vallet-Regí, D. Lozano, B. González, and I. Izquierdo-Barba. Adv. Healthcare Mater. 2020, 2000310
[4] R. Alvarez, S. Muñoz-Piña, M. U. González, I. Izquierdo-Barba, I. Fernández-Martínez, V. Rico, D. Arcos, A. García-Valenzuela, A. Palmero, M. Vallet-Regi, A. R. González-Elipe, J. M. García-Martín, Nanomaterials 2019, 9, 1217.
[5] M. Colilla, I. Izquierdo-Barba, M. Vallet-Regí, Medicines 2018, 5, 125
[6] M. Vallet-Regi, B. Gonzalez, I. Izquierdo-Barba, Int. J. Mol. Sci. 2019,
20, 3806

In the last few years there has been an expanding concern about osteoporosis due to its constantly growing prevalence and its enormous socio-economic impact.1 As an alternative to conventional treatments, combination therapies, including gene therapy, have emerged with promising results. However, the transport and delivery of those molecules still remains a challenge.2
In this work, we propose a new system based on mesoporous silica nanoparticles (MSNs) able to co-deliver nucleic acids and osteogenic peptides through systemic injection to bone tissue. The nanoparticle administration produced an increased expression of certain osteogenic related genes, improving the bone microarchitecture and achieving osteoporosis remission. In particular, the importance of this work relies on the achievement of delivering both molecules with remarkable results. The treated osteoporotic mice recovered values of healthy animals. The osteoporosis remission in these animals was achieved by using a MSNs-based system designed for co-delivering small interfering RNAs and an osteogenic peptide such as osteostatin.3 The designed system was able to protect and deliver both biomolecules to the target tissue by systemic administration modifying gene expression and improving bone microarchitecture. To the best of our knowledge, this is the first time that MSNs have been employed in a combination therapy for the treatment of osteoporosis, which has leaded to promising results of bone recovery in osteoporotic animals.

References
1. J.E. Compston, M.R. McClung, W.D. Leslie. LANCET, 2019, 393, 364.
2. M. Manzano, M. Vallet-Regí. Adv. Funct. Mater., 2020, 30, 1902634
3. P. Mora-Raimundo, D. Lozano, M. Manzano, M. Vallet-Regí. ACS Nano, 2019, 13, 5451

In recent years, antimicrobial resistance has become one of the main threats to global health. This drawback lies mainly in the formation of biofilms, which are a defense mechanism of microorganisms against external aggressions, including antibiotics [1]. In addition, it has been shown in previous studies that severe infection leads to changes in factors such as vascular endothelial growth factor (VEGF) [2] which plays a key role in initiating the process of angiogenesis [3].
Herein we have developed a multicomponent nanocarrier based on mesoporous silica nanoparticles (MSN) to combat bacterial biofilm and also help angiogenesis during bone tissue regeneration process. The nanosystem has been designed bearing polycationic dendrimers in the external surface (MSN-G3) to favor internalization in bacteria [1]. Cu2+ cations with both bactericidal and angiogenic effect have been anchored to the dendritic branches by complexation with the amino groups of the dendrimer (MSN-G3-Cu2+), and a broad-spectrum antibiotic such as levofloxacin has been incorporated into the mesopores.
In vitro antimicrobial assays performed with E. coli and S. aureus bacteria in planktonic and biofilm state have shown that MSN-G3-Cu2+ exhibit antibacterial behavior in Gram negative and positive bacterial models. In addition, a combined effect was found when the nanosystem incorporates the antibiotic. Biocompatibility has been evaluated in vitro in the preosteoblastic cell line MC3T3-E1, showing adequate cell viability In addition, the effect of Cu2+ on VEGF expression on HUVEC cell line shows an increase in cell proliferation and a higher expression of VEGFR2
[1] González, B., Colilla, M., Díez, J., Pedraza, D., Guembe, M., Izquierdo-Barba, I., & Vallet-Regí, M. (2018). Acta Biomaterialia, 68, 26. [2] Mankhambo, L. A., Banda, D. L., Jeffers, G., White, S. A., Balmer, P., Nkhoma, S., Carrol, E. D. (2010). Critical Care, 14(3), 1. [3] Xie, H., & Kang, Y. J. (2009). Current Medicinal Chemistry, 16(10), 1304.

Mesoporous bioactive glass nanoparticles (MBGNs) are multifunctional materials for various biomedical applications [1]. MBGNs are usually synthesized using sol-gel based strategies. Their composition and morphology (e.g., particle size, pore structure) can be conveniently tailored by tuning sol-gel processing parameters, e.g., the concentration of pore-forming templates [2]. Incorporating biologically active ions into MBGNs can extend and boost the therapeutic effects (osteogenic, angiogenic, antibacterial, immunomodulatory properties. We have developed a series of ion-doped MBGNs for chronic wound healing and infected bone defect repair. Key results will be presented. Specifically, Ag-doped MBGNs exhibited enhanced antibacterial activity as indicated in a 3D infected skin model [3], while B and Ce doped MBGNs showed anti-inflammatory and pro-angiogenic activities. MBGNs could also act as delivery carriers of BMP-2, exhibiting a sustained release of BMP-2 and enhancing bone healing through synergistic effects of released ions and growth factors. In addition, the incorporation of MBGNs as fillers into hydrogels can improve the mechanical performance and osteogenic activities of matrices. Given their unique compositional and morphological characteristics, ion-doped MBGNs exhibit great potential in various applications ranging from (hard/soft) tissue regeneration to drug delivery.

[1] K. Zheng, B. Sui, K. Ilyas, A.R. Boccaccini, Porous bioactive glass micro- and nanospheres with controlled morphology: developments, properties and emerging biomedical applications, Mater. Horizons. 8 (2021) 300–335.
[2] K. Zheng, A.R. Boccaccini, Sol-gel processing of bioactive glass nanoparticles: A review, Adv. Colloid Interface Sci. 249 (2017) 363–373.
[3] K. Zheng, P. Balasubramanian, T.E. Paterson, R. Stein, S. Macneil, S. Fiorilli, C. Vitale-brovarone, J. Shepherd, A.R. Boccaccini, Ag modified mesoporous bioactive glass nanoparticles for enhanced antibacterial activity in 3D infected skin model, Mater. Sci. Eng. C. 103 (2019) 109764.

Biodegradable implants constitute a new generation of biomedical materials that are being developed to assist the tissue healing processes and gradually corrode and degrade in-vivo after their function is being fulfilled. Among others, Fe-based alloys show promising mechanical properties such as ductility and high ultimate strength. However, the corrosion rate of those implants is relatively slow, therefore alloying with other elements such as Mn, is studied to accelerate the biodegradation rate.

In this work, porous Fe-Mn austenitic equiatomic alloy with additions of antibacterial elements such as Zn and Ag has been fabricated through powder metallurgy using two approaches, namely simple pressing of ball-milled powders and vacuum sintering at 1173K and polymeric sponge impregnation with slurry, followed by heat treating the foam/slurry mixtures at 1273K under a flow of Ar+H2. Antibacterial Zn and Ag, aimed at limiting the infection rates of implants, are added to the Fe50Mn50 base alloy using different approaches such as mechanical alloying of metallic powders or incorporation as nanoparticles through electrodeposition. As a result, materials with varying degrees of porosity and Zn/Ag distribution are obtained to assess their influence on the degradation rates. The microstructure of fabricated materials is studied using scanning electron microscopy and X-ray diffraction. Mechanical properties are examined through nanoindentation while biodegradability is investigated by immersing the specimens in simulated body fluid (Hank’s solution).

Our results reveal that porous, non-cytotoxic, metallic FeMn-based biomaterials with higher degradation rates can be fabricated by the powder metallurgy route. The addition of Zn/Ag is believed not only to accelerate the corrosion rate but also to limit the biofilm formation on the surface of implants.

Magnesium alloys exhibit promising properties as bone implant materials due to their biodegradability, non-toxicity and mechanical properties. Compared to steel and Ti, Mg implants can be fully re-absorbed by the human body and the mechanical properties are similar to that of the bones and do not lead to stress shielding. Porous scaffolds are ideal structures for bone regeneration as they allow tissue growth, prevent implant loosening and permit body fluid transportation. However, such structures are difficult to obtain by conventional manufacturing methods, but can obtained by additive manufacturing strategies. Lattice structures of Mg-RE alloys with different strut sizes were manufactured by Laser Powder Bed Fusion (LPBF) process and modified by thermal treatments. The relationship between processing conditions and the microstructure was carefully analysed by means of X-ray µtomography, scanning electron microscopy and electron-backscatter diffraction as well as transmission electron microscopy. The mechanical properties and the fracture mechanisms were ascertained by means of in situ compression tests within an X-ray µtomography system in lattices that have been immersed in simulated body fluid for different time periods. Additionally, in-vitro biocompatibility studies were also conducted. These results were used to ascertain the influence of processing parameters, lattice dimensions and heat treatments on the mechanical and degradation behavior of lattice structures of Mg-RE alloys manufactured by LPBF.

Twinning-induced plasticity (TWIP) steels have been recently proposed for manufacturing biodegradable stents. Thanks to their exceptional mechanical properties, closely resembling those of the commonly used L605 Co-Cr alloy, thinner structures can finally be targeted. However, in vivo studies on Fe-based alloys reported that a compact layer of phosphates formed on the surface during implantation, thus decreasing the degradation rate. In an attempt to reverse this tendence, galvanic coupling was investigated, and the addition of Ag forming noble second phases was studied. Therefore, this work aimed at assessing whether such a strategy could successfully prevent passivation over medium-long degradation time in vitro while preserving excellent mechanical and processing properties. Results showed that the addition of 0.4% wt. Ag did not change the tensile strength nor the yield strength of a Fe-16Mn-0.7C steel, but elongation at failure was reduced by 13%. This was attributed to preferential formation of {111} grains during thermal treatments in the Ag-containing alloy, thus promoting the formation of mechanical twins, limiting dislocation gliding. Furthermore, the presence of Ag promoted galvanic coupling in the first 7 days of immersion. Mn carbonates started depositing at the surface after 7 days, for then forming a nearly compact layer after 28 days, on top of which Fe hydroxide islands were detected. After 60 days, part of this compact layer detached, replaced by Fe phosphates. After 120 days, a new layer of Mn carbonates and Fe hydroxides formed on top of the phosphates attached to the surface. The superposing nature of the degradation layers was further confirmed by impedance spectroscopy. Although the addition of Ag did not prove to effectively prevent phosphate formation, the acquired knowledge on the evolution of the degradation mechanism in TWIP steels can foster the development of new strategies for accelerating their degradation rate when implanted in humans.

Metallic biodegradable alloys constitute a new class of biomaterials for temporary applications. Fe-Mn-C steels are particularly attractive for the production of very thin implants, including stents, mainly due to their outstanding mechanical properties. To cut the complex geometry of stents, laser processing is considered the gold standard, even if it results in debris and slag materials on the surface that need to be removed. Electro polishing constitute the envisaged technique for removing debris and slag, and achieving the appropriate surface finishing of the device made of corrosion-resistant metals. However, for degradable metals, electro polishing may initiate the degradation process, and mechanical polishing is often privileged, although its homogeneity is not comparable with electro polishing. This work aimed to investigate the influence of different electrolytes for electro polishing, and compare with mechanical polishing.
Samples were mechanically polished with 80-240 grit Si-C papers prior to subsequent treatments: a mirror finish mechanical polished (MP) and electropolished samples (EP). Three distinct electrolytes EP1 (ethanol, perchloric acid and glycerol), EP2 (perchloric acid, acetic acid and glycerol) and EP3 (choline chloride and ethylene glycol) were selected. Morphology, chemical composition, topography and wettability were assessed by scanning electron microscope (SEM), X-Ray Photoelectron spectroscopy (XPS), Atomic Force Microscope (AFM), and by water contact angle (CA). Electrochemical tests as potentiodynamic polarization (PDP) and impedance spectroscopy (EIS) measurements were carried out for treated samples in modified Hanks’ solution (MH) and M199 medium.
EP samples showed the typical morphology and wavily structure, mainly due to the dissolution mechanisms governed by electrolyte composition, temperature and duration. Briefly, EP2 samples presented a smoother surface if compared to mechanical polished ones or to other conditions attaining the same cell viability behaviour. Results demonstrate that electro polishing under controlled conditions constitute the choice for surface finishing of Fe-based biodegradable metals.

Networks formed of natural nano-fibrils are an appealing approach to integrate the advantages of nano-scale fibers with sustainable raw materials. Whereas cellulose nanofibrils are already widely applied, nanofibrillated chitin is lagging behind this development. Chitin is commonly derived from crustaceans, necessitating harsh and prolonged chemical and mechanical processes for the isolation of nanofibrils. Opposed to that, fungal chitin, coming in a natural complex with glucan, is easily accessible by mild extraction methods. The structural component of fungal cell walls comprises of chitin nanofibrils covalently bond to glucan thus constituting a native nano-fibrous composite material (chitin-glucan, CG) combining the strength of chitin and the toughness of glucan. Isolation of such fungal chitin nanofibrils (FChNF) does not require energy-intensive extraction methods as necessary for the extraction of cellulose nanofibrils or chitin nanofibrils of crustacean origin. FChNF can also be derived from mycelium, the vegetative part of fungi. Thus, fungal growth can be utilized as low-cost source for on-demand generation of natural nanofibrils that are subsequently utilized in the formation of nanostructured networks.

Here, we extracted natural polymers from white button mushrooms (Agaricus bisporus), tree-bracket fungi (Daedaleopsis confragosa) and mycelium grown on sugarcane by-product molasses. A mild alkaline extraction process was applied and isolated polymer fibrils processed into nanopaper networks. Extracted polymers and nanopapers were characterized regarding their surface characteristics and mechanical properties.

Fungal extracts were readily disintegrated into nanofiber dimensions by low-energy mechanical blending, preserving the native quality of the CG complex. Mechanical properties of CG nanopapers were determined by the nanostructure of the network with glucan playing a crucial role. Furthermore, hydrophobic surface properties originated from the composition of the nanopapers. Biopolymers prepared from these resources are applicable in a wide range of applications from packaging over filtration membranes to composites.

Bacterial cellulose (BC) is an ultrapure form of cellulose nanofibres with mechanical properties exceeding those of both Kevlar and E-glass fibres. A single BC nanofibre has an estimated Young’s modulus of 160 GPa, which makes it a promising reinforcement for biocomposites. In this work, the focus lies on reinforcing impact modified (IM) acrylic to increase its impact strength while maintaining high transparency. The aim is to create a more lightweight alternative to glass-based composites, which are currently used in impact-resistant, protective applications like windshields or bulletproof casings. The challenge here is to obtain a highly transparent composite while using BC nanopaper which is opaque in its untreated form.
In this study composites with alternating sheets of IM-acrylic and layers of BC nanopaper were prepared, using one, three and five layers of nanopaper. The dried BC nanopapers were vacuum impregnated with a ductile, UV-curable matrix, sandwiched in between plates of IM-acrylic and polymerized. As a reference, samples without the BC were prepared by sandwiching plates of the IM-acrylic with the UV curable matrix. All samples with BC showed high transparency with a transmittance of up to 84 % at 550 nm compared to 90 % of pure IM-acrylic at a sample thickness of 3 mm. The impact strength, measured by the Charpy impact test, was increased by 48 % upon the use of one layer of BC and by 130 % to 26.7 KJ/m2 when using five layers of cellulose compared to the neat IM-acrylic. The reference samples exhibit a 2 – 10 % higher transmittance compared to the corresponding samples with BC, however, their impact strength is around 50 % lower, respectively. This study shows that using BC as reinforcement in IM-acrylic based composites results in increased impact properties at a minimal loss of transparency.

Cotton is a predominant raw material in the textile industry. One of the most demanding procedures for the textile industry is dyeing of cotton fabrics with reactive dyes, since traditional dyeing processing leads to substantial environmental impacts, through the discharge of a highly colored and saline dyebath. This can be attributed to the high electrolyte concentrations, such as sodium chloride, needed to overcome the repulsive forces between the negative charges of cellulose fibers surface with the ionic species of dyes.
The most important contemporary challenges is the eco-friendly modification of cotton textiles to achieve a greener dyeing approach. To this end, the present study focuses on the water-based modification of cotton fabrics with cationic polymers, in order to achieve the charge inversion of cotton fabrics’ surface, allowing for a greener dyeing process, bypassing the use of electrolytes. The modification of cotton and the dyeing of the thus-modified cotton fabrics through water-based procedures at ambient temperature and salt-free conditions were followed by a variety of techniques, including UV-Vis spectrometry for the polymer or dye exhaustion and ζ-potential measurements of the net charge of cotton surface. In addition, characterization of the modified fabrics at molecular level by application of Raman as well as XPS spectroscopy revealed the physicochemical processes associated with the modification and the related modification kinetics.
This effective salt-free dyeing procedure, well-comparable to the traditional dyeing process, is an eco-friendlier way to overcome significant environmental problems, providing considerable benefits in industrial application such as elimination of electrolyte and significant savings in process costs.
Acknowledgement: This research has been co-financed by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH–CREATE–INNOVATE (project code: T1EDK- 03073)».

Antimicrobial coatings that prevent the growth of biofilms are an alternative and effective way to inhibit the spread of microbial infections. The sustainable use of these polymers for the development and application of novel green methodologies remains a challenge. This work demonstrates a facile and scalable fabrication approach for the development of new water-based, stable materials bearing biocidal groups, as potential antimicrobial and antifouling coatings for diverse applications such as paints for aquaculture nets, clean surfaces etc. The new polymeric coatings were constructed by blending water-soluble copolymers with complementary reactive groups such as acrylic acid (AA) and glycidyl methacrylate (GMA). An eco-friendly method was developed for the combination of the copolymers poly (4-vinyl benzyl trimethylammonium chloride-co-acrylic acid) P(VBCTMAM-co-AAx) and poly (cetyltrimethylammonium 4-styrenesulfonate-co-glycidyl methacrylate) P(SSAmC16-co-GMAx) to obtain crosslinked polymers bearing both covalently and electrostatically bound biocidal species. Moreover, a water-based approach was also used for the synthesis of the P(VBCTMAM-co-AAx) copolymer. All these polymers had strong antimicrobial activity against Staphylococcus aureus and Escherihia coli in standard bacterial media. Additionally, these stable materials were used for coating aquaculture nets and were evaluated in respect to their release rate using Total Organic Carbon (TOC) and Total Nitrogen (TN) measurements. Selected combinations were tested under real conditions in aquaculture farms in seawater.

We have recently shown that proximity with a high-temperature superconductor induces unconventional superconducting correlations in graphene[1]. We will here talk about recent experiments demonstrating [2] that those correlations propagate hundreds of nanometers, allowing for the unique observation of d-wave Andreev-pair interferences in YBCO-graphene devices that behave as a Fabry-Perot cavity. The interferences show as a series of pronounced conductance oscillations. We are able to separate from these conductance oscillations the part stemming from the superconducting normal interface and the part stemming from Fabry Perot like oscillations. The present demonstration is pivotal to the study of exotic directional effects expected for nodal superconductivity in Dirac materials.

[1] Perconte, D., Cuellar, F. A., et. al. (2018). Tunable Klein-like tunnelling of high-temperature superconducting pairs into graphene. Nature Physics, 14(1), 25-29.
[2] Perconte, D. and Seurre, K. et. Al. (2020). Long-Range Propagation and Interference of d-Wave Superconducting Pairs in Graphene. Physical Review Letters 125 (08). 087002

We report recent work in DNA translocation in 2D nanoslit. 2D nanoslit devices, where two crystals with atomically flat surfaces are separated by only a few nanometers, have attracted considerable attention because their tunable control over the confinement allows for the discovery of unusual transport behavior of gas, water, and ions. Here, the passage of double-stranded DNA molecules is studied through nanoslits fabricated from exfoliated 2D materials, such as graphene or hexagonal boron nitride, and the DNA polymer behavior is examined in this tight confinement. We observe two types of events in the ionic current:1) long current blockades that signal DNA translocation and ) short spikes where DNA enters the slits but withdraws. We use coarse-grained molecular dynamics simulation in order to explain and identify the different polymer configurations in our measured ionic current signal. DNA molecules, including folds and knots in their polymer structure, are observed to slide through the slits with near-uniform velocity without noticeable frictional interactions of DNA with the confining graphene surfaces. We anticipate a new class of 2D-nanoslit devices that will provide unique ways to study polymer physics and enable lab-on-a-chip biotechnology.

Electron-transfer reactions are ubiquitous in chemistry, however, there are still gaps in the fundamental understanding of electron transfer at the molecular level, particularly the degree to which the nuclear dynamics that accompany the process straddle the quantum-classical boundary. We use graphene-based single-molecule transistors [1] to study the mechanism of electron transfer over a wide range of temperatures – from 3 K to 77 K – at the level of an individual molecule. Charge transport through molecular junctions is often described either as a purely coherent or a purely classical phenomenon, and described using the Landauer formalism or Marcus theory, respectively. In our experiments, however, observe a simultaneous breakdown of quantum coherent Landauer and semi-classical Marcus theory. We propose a theoretical model based on generalised quantum master equation [2], where we derive an expression for current through a molecular junction modelled as a single electronic level coupled to a collection of thermalised vibrational modes, and demonstrate that it quantitatively describes the experimental data. We show that nuclear tunnelling enhances the rates of low-energy electron transfer, and demonstrate that the rates are sensitive to both the outer and inner-sphere environmental interactions. We find that the nuclear dynamics accompanying electron transfer must be treated quantum mechanically as the quantitative validity of Marcus theory is expected to occur at temperatures exceeding 298 K [3].

[1] Limburg et al., Adv. Funct. Mater. 1803629 (2018)
[2] Sowa et al., J. Chem. Phys. 149, 154112 (2018)
[3] Thomas et al., Nat. Commun. 10, 4628 (2019)

Significant advances in the synthesis of low-dimensional materials with unique and tuneable electrical, optical and magnetic properties have led to discoveries ranging from single-photon sources to the observation of Majorana states. However, the lack of ability to precisely integrate individual nanomaterials into devices at scale limits their technological application. In this talk we will examine how graphene nanogaps can be used to directly capture single nanoparticles from solution at predefined locations by exploiting the large electric field gradients generated around their point-like, atomically sharp electrodes. First, we will demonstrate the technique by showing how gold nanoparticles can be trapped to form graphene-gold-graphene devices which behave as single-electron transistors at low temperatures. Then, we will go on to discuss and show how other nanomaterials can be trapped and integrated into nanoscale devices. This platform offers a route to the creation of novel low-dimensional devices, nano- and opto-electronic applications and the study of fundamental quantum transport phenomena.

Graphene is a monolayer of sp2-bonded carbon atoms tightly packed into a two-dimensional honeycomb lattice. This material is very intensively studied nowadays due to its extraordinary properties. While graphene is nonmagnetic in itself, experimental observations show that magnetism can be induced by introduction of impurities, boundaries or defects. The properties of graphene can also be modified by doping, chemical functionalization or decoration by NPs. Magnetic nanoparticles (NPs) have interesting properties, which are dependent on their size. In this work, we are interested in chemical functionalization in order to decorate graphene with magnetic NPs, and in particular with magnetite (Fe3O4). The electronic and transport properties of modified graphene are evaluated thanks to local measurements using AFM-derived techniques. In this context, the chosen functionalization is a very attractive method because it offers the possibility to decorate graphene without disturbing its crystalline network.
The magnetite NPs were synthesized by thermal decomposition of iron acetylacetonate, Fe(acac)3. The adsorption of oleylamine at the surface of the iron oxide leads to the formation of well-formed and separated NPs of 7-10 nm of diameter. The particles are dispersed in hexane and characterized by HR-TEM, EDX and SEM. In parallel, single-layer graphene was prepared and transferred on SiO2/Si chips. The CVD graphene devices are then functionalized by drop casting of the suspension of NPs. The device is rinsed with isopropanol and acetone to remove the excess of NPs. SEM and XPS analyses allowed us to confirm the presence of magnetite on the surface of graphene and to evaluate its coverage. The transport measurements are performed to investigate the influence of the particles on the properties of graphene. The Dirac point and the mobility are compared between pristine and functionalized graphene.

In this work, we study the advantages of two advanced sputtering techniques for the preparation of a nanostructured thin-film conductometric gas sensor. We combined tungsten oxide (WO3) thin films with other materials to achieve enhanced sensory behavior towards hydrogen. Thin films of WO3 were prepared by the HiPIMS technique and annealed in air at moderate temperature (350 °C). By tuning the deposition parameters of reactive high-power impulse magnetron sputtering, specifically the pulse length, we were able to prepare WO3−x films with various stoichiometry and structure. To characterize the sensory behavior of the films, the tungsten oxide films were decorated by Pd nanoparticles before annealing and were assembled as a gas sensor. We demonstrate that the stoichiometry of the as-deposited films influences considerably the type of crystalline phase formed in the annealed films. The appropriate sub-stoichiometry of the films (approx. WO2.76) enabled crystallization of the monoclinic phase during the annealing

The specimens were tested for the response to a time-varied hydrogen concentration in synthetic air at various temperatures. The sensitivity and response time were evaluated. The performance of individual films is presented as well as the details of the synthesis. The sensory response of the films that crystallized in the monoclinic structure was proven to be superior to that of the films containing other phases.

Operando characterization of working catalysts, requiring the simultaneous measurement of catalytic performance, is crucial to identify the relevant catalyst structure/composition and how molecules interact with surfaces/interfaces. The two examples, covering nanoparticles, thin films and meso-scale aggregates, bridge the "materials and pressure gaps".
i) Area-averaging operando spectroscopy: CO oxidation on Pt/ZrO2 prepared by atomic layer deposition (ALD) was examined by sum frequency generation (SFG) spectroscopy and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), combined with mass spectrometry (MS) [1]. Combining experimental data with ab initio Density Functional Theory (DFT), we show that the reaction onset is determined by a delicate balance between CO disproportionation (Boudouard reaction) and oxidation. Disproportionation occurs on low-coordinated Pt sites at high CO coverages, when the remaining C-atom is stabilized by a favorable coordination. At variance with the general expectation, rough Pt nanoparticles are seemingly less active than smoother Pt films.
ii) Spatially-resolved operando microscopy: H2 oxidation on polycrystalline Rh was studied by scanning photoelectron microscopy (SPEM) and photoemission electron microscopy (PEEM), which allow local surface analysis and visualising the heterogeneity of ongoing reactions on a µm-scale [2]. This revealed an anisotropy of surface oxidation (depending on the local step/edge density, yielding an oxidation map), as well as its effect on catalytic activity. In situ PEEM imaging of ongoing H2 oxidation directly compares the local reactivity of metallic and oxidised Rh, demonstrating the effect of surface oxides. Employing the velocity of propagating reaction fronts as indicator of reactivity, a high transient activity of Rh surface oxide was observed. The corresponding velocity map reveals the structure-dependence of such activity, representing a direct imaging of a structure-activity relation for plenty well-defined surface structures within one sample.
[1] V. Pramhaas et. al, ACS Catalysis, 11 (2021) 208.
[2] P. Winkler et al, Nature Communications, 12 (2021) 69.

The increasing global energy demand has fuelled considerable effort into improving upon current energy storage technologies to keep in step with this demand. Improving current energy storage technologies, such as lithium ion batteries (LIBs), requires insight and understanding of the fundamentals of their operation. A key component of LIBs is the solid-electrolyte interphase (SEI), which develops at the interface between the electrode and the electrolyte as a result of reaction with, and degradation of, the battery electrolyte [1]. This passivating layer is vital to the operation and performance of batteries, but little is known of its exact structure since these electrode/electrolyte interfaces are buried deep within the battery, and so are difficult to “look” at using standard characterisation techniques [2]. So-called “post-mortem” studies, which involve taking batteries apart inside a glove box, are methodologically simple, but may alter the SEI surface chemistry through exposing highly reactive materials to glove box contaminants.
Here we introduce a platform for in situ characterisation of electrode/electrolyte interfaces, capable of operation and disassembly of LIB components (anode, cathode and electrolyte) completely in situ without the need to transfer materials to a glove box prior to characterisation. We demonstrate the capabilities of the platform using interface sensitive techniques, including data from one of the first lab-based hard X-ray photoelectron spectrometers, which is based at the Henry Royce Institute at the University of Manchester. Electrochemical data is also presented, demonstrating the electrochemical characterisation abilities of the platform, and shows potential for extending beyond studies of LIB technology.

References
[1] Peled and Menkin, J. Electrochem. Soc., 164, 7 (2017).
[2] Wu et al. Phys. Chem. Chem. Phys. 17, 30229, (2015).

Deposition of thin protective films on the cathode surface is an efficient approach to overcome interfacial degradation processes and control ionic mobility across the interface. An essential requirement of a good coating layer is that in addition to surface passivation, it will enable unimpeded ion transport between the electrode and electrolyte. To date, the rational design of such protective layers is limited, mostly due to the lack of sensitive characterization tools that can provide atomic-molecular level insight into both the structure and function of thin amorphous layers.
Here I will present a new approach to examine thin interphases and gain atomic level insight into their composition, 3D structure and lithium ion transport properties by using solid state nuclear magnetic resonance (ssNMR) spectroscopy. The approach is based on (i) 10-10^4 fold increase in ssNMR sensitivity provided by Dynamic nuclear polarization (DNP), a process in which the high electron spin polarization is transferred to surface nuclei in the sample, enabling the detection of otherwise invisible nanometer-thick layers, and (ii) tracking 6Li-7Li isotope exchange processes across the electrode-electrolyte interface.
I will describe the application of this approach to a novel surface treatment for high energy cathodes, here lithium rich LiNixMnyCozO2 (NMC), which leads to substantial improvements in rate performance and capacity retention. Specifically, I will show how the combination of DNP and ssNMR provides a detailed chemical map of the surface composition and structure of this lithium-silicate protection layer. The permeability of the coating and the role of lithiated interphases was assessed by 6,7Li exchange experiments on coated and uncoated NMC and further compared to Electrochemical Impedance Spectroscopy (EIS) results.
The combination of structural insight from high sensitivity ssNMR and lithium exchange brings us closer to understanding the functionality of electrode surface layers.

From single-crystal model catalysts to nanoparticle catalysts deposited on a substrate: Operando characterization of catalytic materials has become an important research field to unravel the complexity of catalytic reactions on the atomic level at the gas-surface interface. To bridge the pressure gap between industrial applications and surface science research , an interest in photon-in-photon-out techniques, which can be applied within a broad pressure range, has evolved.

We combine different optical techniques to simultaneously study the surface and gas properties during catalytic reactions, such as CO oxidation. Thereby, we can capture a maximum of information about the complexity of the reaction by measuring the surface and the gas phase at the same time at ambient pressures.

Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) probes the vibrational bonds of the adsorbed molecules, such as CO adsorption on Pd(100), while Surface Optical Reflectance (SOR) images the surface morphology over the entire sample providing us with information about surface oxide formation. Simultaneously, we measure the gas formation, e.g. CO2, above the sample using Planar Laser Induced Fluorescence (PLIF).

All techniques are incorporated in a unique compact setup that provides measurements that complement synchrotron-based measurements, and can also be combined with such techniques. We will describe the technical setup and present its capabilities by showing simultaneous data from all techniques in an operando study of CO oxidation over Pd(100).

Understanding the mechanisms behind chemical transformations is key to developing improved catalytic systems. In this context, operando spectroscopy has contributed significantly to advance our molecular view of many reactions at heart of the chemical industry. Here we show the application of complementary spectroscopic techniques to elucidate the mechanism of a reaction that has always occupied a central role in emission control research – the selective catalytic reduction (SCR) of NOx over vanadia-based catalysts.

IR spectroscopy revealed that NH3 could adsorb on Lewis and Brønsted-Lowry acid sites as NH3 and NH4+, respectively. Upon NO addition, the SCR reaction started and adsorbed Lewis-bound NH3 molecules were consumed preferentially over NH4+ species, thereby suggesting that the Lewis sites are the active sites for SCR. The catalyst also reduced simultaneously as indicated by UV-Vis spectroscopy. Under reaction conditions, vanadyl species (VOx) adopt various states of coordination, as demonstrated by the width of the VOx peak in the time-resolved Raman spectra. However, only the coordinatively unsaturated species (i.e., Lewis sites) were found to be responsible for the SCR activity as their response to repeated NH3 pulses caused their characteristic signal to appear in the phase-resolved spectra.

The synergy between complementary operando techniques, demonstrated here in the particular case of SCR, opens up new possibilities in deciphering the structure-performance relationship of catalysts. Ultimately, this would enable the rational design of enhanced catalytic materials.

Nitriding of cast iron can improve mechanical surface properties. The non-nitridable graphite, however, causes heterogeneities in the nitride layer which limit improvements in corrosion resistance usually achievable upon nitriding of other Fe-based alloys. A strategy to overcome this problem for cast iron is surface remelting to form a white-solidified surface layer and subsequent nitriding.
This contribution reports the fundamental insights gained by microstructure investigations on nitrided Fe-Si-C alloys but also C-free variants and variants containing Cu and/or Mn. In case of C-containing alloys, ledeburitic cementite is Si-free, whereas the remaining pearlite is enriched in Si. Occasionally also Fe-Si carbide Fe23Si5C4 is formed. Since Si diffusion is only very short-range at the nitriding temperatures of 540°C, the heterogeneity in the Si distribution present after remelting is retained during nitriding. Whereas Si-free regions basically behave like Fe-C alloys upon nitriding, the behavior of the Si-enriched regions is much more complicated. Si in Fe is regarded as a “weak nitride former”, leading to nanoscopic precipitates of an amorphous nitride of composition classically believed to be Si3N4. In the course of our studies, it was made likely that the amorphous nitride referred to as X has a composition (Fe3N2)x(Si3N4)1-x with the Fe content increasing with the chemical potential of N, implying metastable local equilibrium between matrix and the amorphous nitride.
The slow formation of the amorphous nitrides also affects type and morphology of the Fe nitride, into which the Si-depleted Fe matrix transforms. Remaining Si appears to promote formation of the epsilon iron nitride at the cost of the gamma' iron nitride, an effect which is enhanced by remaining carbon. Presence of Cu, Mn or Cu+Mn change the situation characteristically which can be rationalized in terms of stabilization of epsilon or gamma' or due to acceleration of the precipitation of the amorphous nitride X.

The complex metallurgical interrelationships in the production of ductile cast iron can lead to enormous differences in graphite formation and the local microstructure by small variations during production. Artificial intelligence algorithms were used to describe graphite formation, which is influenced by a variety of parameters. By predicting the local graphite formation, measures to stabilize production were defined and thereby the accuracy of structure simulations improved.

The aim of this paper is to elucidate the controlling factors of graphite formation during manufacture of nodular cast iron. The complex physical relationships in the formation of graphite morphology are also controlled by boundary conditions, which effect can hardly be assessed in everyday foundry operations. The influence of various factors can be predetermined using artificial intelligence based on conditions and patterns that occur simultaneously. In course of this work, the most important dominating variables, from initial charging to final casting, were detected and analysed with the help of statistical tools. A model for the prediction of graphite formation in spheroidal graphite cast iron was created and validated. By prior thermal modelling with common software packages used in the foundry industry, the cooling rates in the castings were calculated and used as additional input variables for the prediction algorithm.

Initial programme designs using machine learning algorithms based on neural networks achieved encouraging results. To improve the degree of accuracy, this algorithm was subsequently adapted and refined. The algorithm is supposed to learn and improve itself with every further attempt due to the increasing amount of data.

Cracks in components are subjected to crack-closure-mechanisms that affect the build-up of the relevant stress intensity range threshold during cyclic loading. These mechanisms are essential for crack propagation under service loads in mechanical engineering applications. Such varying load ratios enforce an appropriate change of the long crack threshold value, thus leading to stress ratio depended resistance curves incorporating the build-up of crack-closure-mechanisms. It should be noted that an extensive number of crack propagation experiments is required to gain statistically evaluable fracture mechanical parameters for a specific material.
In the present work a generalized dataset to describe the formation of crack-closure-mechanisms is developed for the cast steel G21Mn5+N. Numerous crack propagation experiments covering a stress range from alternate to tumescent are conducted and a generalized resistance curve is derived statistically, which allows the description of the build-up of effects on the crack propagation rate uniformly for varying load ratios. The effect of initial pre-cracking by compressive loading on the fracture parameters is also studied.
Furthermore, the approach according to Newman is implemented to derive the respective long crack threshold value for arbitrary load ratios. Thus, a generalized dataset for crack-propagation studies considering closure-effects for G21Mn5+N is maintained by statistical evaluation.
To validate the aforementioned dataset, analytical fracture mechanical calculations invoking a modified NASGRO equation are conducted for the utilized SENB-sample geometries. A sound correlation of analytical and experimental crack propagation rates is observed.
The analytically derived fatigue life calculations show slightly conservative predictions of the experimental fatigue life of the considered specimens and validate the established generalized dataset for G21Mn5+N. Hence the implementation of the derived master resistance curve in numerical crack propagation calculations is featured and finally demonstrated for respective SENB-samples. This facilitates the calculation of the fatigue life of crack-affected cast steel components subjected to arbitrary load stress ratios.

Reheating of steel slabs for further processing such as hot rolling usually takes place in gas-fired pusher furnaces. Temperatures well above 1000 °C, combined with an atmosphere containing H₂O, CO₂, and O₂, lead to substantial oxidation of most steel grades. Newly developed advanced steels often contain significant amounts of Si. This element plays a dominant role in the scaling behaviour near the steel-scale-interface, since fayalite (Fe₂SiO₄) forms a eutectic with wustite (Fe_1-xO) that melts as low as 1177 °C.

To better understand the high temperature oxidation behaviour, lab-scale trials were performed with different steel grades containing up to 3 wt% Si. Possible interactions of Si with other alloying elements present in the samples such as Cr, Mn and Al were also of interest. The atmosphere contained 20 % H₂O, 7 % CO₂, and 3 % O₂ and temperatures ranged from 1100 to 1240 °C. For metallographic investigation, the oxidised samples were cold mounted under vacuum using taper section angles. After preparation, the sections were examined through light microscopy, SEM/EDS, XRD, and TEM. The local distribution of the alloying elements could be mapped efficiently, and phase identification was successful in most parts. Under the applied experimental conditions, the elements of interest were present in their oxidic form either as pure or as mixed oxides. Higher Si-contents led to an increased build-up of eutectic melting phase at the steel-scale-interface at temperatures above 1177 °C, which in turn further accelerated the oxidation.

Composition graded AlMgSi wires were achieved with a to a two-step process. A composite made of 1370AA inserted in a 6201AA tube was first cold drawn to obtain appropriate mechanical bounding and then annealed at 500°C to achieve a composition gradient along the wire diameter. These diffusion gradients were estimated by nano-hardness profiles and a good agreement with theoretical prediction was found. The same approach was used to evaluate the evolution of the property gradient resulting from precipitation treatments. Precipitates that nucleated and grew in the composition gradient were characterized by TEM, and the solute content was measured using APT. These microstructural data were finally correlated to the macroscopic properties of the wires that were evaluated thanks to tensile tests and electrical conductivity measurements. This work shows that a full range of properties combination can be achieved thanks to composition graded structures.

Heat-treatable aluminium (Al) alloys obtain their strength from the nucleation of precipitates during artificial aging. The thermomechanical history of the alloy determine the type of precipitate phase that nucleate, their interface plane and their distribution. If the alloy is stored at room temperature after solution heat treatment, the hardness increases in time due to the formation of nano-sized clusters. The clusters that form are known to affect the subsequent precipitation process during artificial ageing by either promoting or impeding the nucleation of hardening precipitates. Hence, for design of better alloys it is important to understand the crystal structure and to quantify the distribution of these clusters. The main cluster type in the Al-Zn-Mg alloy system is the GPI zones and their crystal structure has been a subject for debate for decades. One of the most powerful tools to determine the crystal structure of precipitates in Al alloys is transmission electron microscopy (TEM). The GPI zones however are small compared to the thickness of a typical TEM specimen, making it challenging to detect them. In this work, we elucidate the structure of the GPI zones [1]. Based on atomically resolved high-angle annular dark-field scanning TEM images, we found a unique fundamental building block for the clusters. The unit is described by partial substitution of Mg and Zn on the fcc Al matrix positions and its surrounding truncated cube octahedral (TCO) shell with a possible interstitial position at the centre of the TCO. A simple set of principles describes how these units arrange to form larger clusters. Density functional theory calculations, scanning precession electron diffraction and simulated diffraction patterns support the proposed atomic models. The newfound undestanding is believed to play a major role in the future development of age-hardenable Al alloys.

[1] A. Lervik et al. Acta Materialia (2021). DOI: 10.1016/j.actamat.2020.116574

The talk brings together two areas of research: the mechanical behavior of nano-structured materials with a grain-size gradient and the plastic instability in metal alloys, known as the Portevin-Le Chatelier (PLC) effect. The treatment of the surface by hyper-deformation processes locally increasing the dislocation density and/or forming a fine-grained layer has proven its effectiveness in the development of metallic materials with high mechanical properties. However, the influence of gradient microstructure on the PLC instability is very little studied, probably due to the complex multi-scale nature of the instability phenomenon. Moreover, most works aim at establishing the relationships between the microstructure and the macroscopic behavior of the material and remain within the framework of the continuous plasticity approach, i.e., are based on the hypothesis of a homogeneous plastic flow, where random fluctuations of the distribution and mobility of dislocations compensate each other statistically. However, the interaction between dislocations results in their self-organization and generates collective effects characterized by mesoscopic-scale internal lengths, which bring into play an intrinsically heterogeneous and intermittent plastic flow. Considering these aspects is crucial when the size of the grains is comparable to the intrinsic lengths controlled by the collective processes.
The talk will present first results of experimental and numerical study of the effect of SMAT (Surface Mechanical Attrition Treatment) on both the mechanical properties and spatiotemporal complexity associated with the unstable plastic flow of an AlMg alloy. The influence of SMAT on the correlations of deformation processes will be revealed through statistical analysis of stress serrations, acoustic emission, and local strain-rate fields provided by the digital image correlation technique. Modeling of the PLC effect will be implemented based on an elasto-visco-plastic model regularized by virtue of the second strain gradient approach.

Natural aging of Al–Mg–Si alloys is a complex process, which is not fully understood yet. Nonetheless, it is widely known that for the EN AW6082 alloy natural aging has a negative effect. For the alloy EN AW6060, however, natural aging was assumed to have a beneficial influence on the hardening potential. Contradicting these assumptions, our studies showed that not only the type of alloy but also the alloy composition influences the impact of natural aging. Within the same alloy positive and negative effects were observed, which led to the determination of a threshold. This has great importance for industrial applications since allegedly same alloys processed with the same thermomechanical parameters possess different mechanical properties.

In further experiments it was evaluated if the effect of natural aging in low alloyed 6xxx also maintains when adding contributions of 0.05 wt% Sc. Long term analyzes of hardness were performed, where
• the material was stored at room temperature after solution heat treatment (T4 process)
• the material was artificially aged with varying aging times after being solution heat treated (T6 process)

The Portevin-Le Chatelier (PLC) effect describing unstable plastic flow in alloys is an exceptional example of self-organization phenomena in plasticity. Its dynamics stems from the mechanism associated with nonmonotonous behavior of the strain-rate sensitivity of stress, negative in a strain-rate interval allowing for dynamic strain ageing of dislocations by solutes. If the motion of all dislocations were identical, this nonlinearity would give rise to periodic relaxation oscillations. The intrinsic heterogeneity of plastic deformation leads to complex behaviors of real materials. Investigations of the PLC effect using acoustic emission (AE) revealed that the microscopic dynamics of dislocations is characterized by scale invariance reflected in power-law statistics of acoustic events. Moreover, such AE statistics were found to be a ubiquitous feature of plastic deformation in the absence of macroscopic instability. These observations led to a conclusion on the avalanche nature of the dislocation dynamics at fine scales. In contrast, the analysis of stress serrations caused by the PLC effect revealed a wealth of dynamics on the macroscopic scale, including avalanche behavior, deterministic chaos, or relaxation oscillations. To shed light on the distinction between different scales, the present study involves analyses with intermediate resolutions. The work will present statistics of local strain-rate maps built for an AlMg alloy exhibiting the PLC effect. The data testify to a coexistence of large characteristic events and power laws for smaller events. The scale separation is interpreted in terms of phenomena of self-organized criticality and synchronization in complex systems. Furthermore, it is observed that bursts in the local strain rate are organized in wavy patterns. This duality, little studied so far, is of great interest for understanding the correlations between temporal instabilities and spatial heterogeneities in the dynamics of crystal defects.

High-entropy alloys (HEAs) open up a new horizon for discovering un-explored mechanical properties and deformation mechanisms. Local chemical fluctuations (LCFs) in HEAs were found to have significant influences on their mechanical performance. In this letter, we briefly discuss experimental findings of formation and characterization of LCFs, as well as their effects on the deformation behavior especially of BCC HEAs. We show that existence of LCFs is a common yet key structural feature of HEAs. The observed change of deformation model caused by the LCFs is beneficial for both strengthening and ductilization in typical BCC HEAs. It was found that tuning the degree of LCFs can be an effective way for optimizing mechanical properties of HEAs.

High-entropy alloys (HEAs) push the boundaries of high-stiffness lightweight alloy design through their exceptional chemical diversity. Specifically, refractory HEA compositions have shown great promise as their specific stiffness surpasses that of even the more advanced high-modulus steels. A common occurrence in BCC refractory HEAs is their limited ductility due to the complete or partial transformation of the high-temperature BCC solid solution to the BCC_B2 ordered phase at lower temperatures. As this transformation is associated with the presence of generally beneficial alloying elements in terms of the elastic properties and the density of said alloys it is critical that it is suppressed without altering the chemical composition. In the literature, a series of heat treatments have been suggested to control the formation of the ordered phase and achieve a proper balance between strength and ductility. In this work we investigate this processing pathway to tackle such problems evident in the equiatomic AlTiVCr and AlTiVCr-7.2Si alloys. Furthermore, we apply this processing route on two novel high-modulus HEA compositions. The associated experimental work involved manufacturing four HEAs based on the AlTiVCr system through Vacuum Arc Melting (VAM). The alloys were heat treated at $1200\unicode{xb0}$C for 8h followed by quenching to room temperature and subsequently aged at $700\unicode{xb0}$C for 24h. The samples were characterised through means of Optical, Scanning and Transmission Electron Microscopy (OM, SEM, TEM), X-Ray Diffraction Analysis (XRD), together with elastic properties measurements through Microindentation testing.

The influence of solutes and stacking fault energy on sazuration grain size after severe plastic deformation was studied recently for binary alloys, whereby the saturation grain size (ds) correlates with the solid solution strengthening contribution and not with the stacking fault energy. In this context we investigate the microstructural evolution of a series of Nickel diluted compositions from pure Nickel to the chemically complex equiatomic CrMnFeCoNi Cantor alloy ((CrMnFeCo)xNi1-x) with x=0.8, 0.4 and 0.08 after high pressure torsion. The solid solution strengthening was determined using the conventional Labusch model and the more recent Varvenne model, which was specially developed for chemically complex alloys. A correlation between the solid solution strengthening contribution and the saturation grain size can be found, whereby higher Δτ cause smaller ds. Isochronal heat treatments were performed in order to reveal the microstructural instability i.e. the decomposition tendencies and grain growth. Significant changes in hardness as well as Young´s modulus were observed for Ni20 and Ni60 for different annealing temperatures between 450 and 600 °C, which indicate the formation of second phases. Nanoindentation strain rate jump tests on the deformed samples show similar low strain rate sensitivities of the deformed states without any pronounced transient regimes. Additionally, all compositions exhibit a history dependent softening, which indicates an unstable microstructure.

The equiatomic hexagonal closest-packed (hcp) high entropy alloy (HEA) YGdTbDyHo consists of rare earth elements with very similar chemical properties. Therefore, it is a suitable candidate for the investigation of the Gibbs paradox and of a possible entropy effect on mechanical behavior of alloys. To evaluate the influence of the configurational entropy, different medium entropy alloys (MEA), low entropy alloys (LEA) and pure constituent elements are considered as well.
All samples were prepared via suction casting in an electric arc furnace. Different manufacturing influences on the suction casting of YGdTbDyHo are discussed. The microstructure and chemical composition of YGdTbDyHo is analyzed via Scanning electron microscopy (SEM), Electron backscatter diffraction (EBSD) and X-ray fluorescence analysis (µ-XRF). To evaluate the strength and ductility of the materials, tensile tests are conducted. Additionally, the Vickers hardness HV 0,3 of all materials is determined.
The results show no direct correlation between Vickers hardness or tensile strength and the configurational entropy of the tested materials. This work contributes to the understanding of mechanical properties and the influence of configurational entropy on the hcp HEA YGdTbDyHo.

Power electronic modules are integral for energy conversion in applications like renewable energy generation and transport. Sintered nanosilver die-attachments have been proposed as a more reliable and environmentally friendly alternative to solder alloy joints for emerging power electronics module designs. However, their degradation mechanisms are not as well understood. This talk is about how three-dimensional (3D) X-ray tomography is used to carry out cradle-to-grave studies of these attachments under operation. 3D tomography provides perspectives otherwise infeasible, such as virtual cross-sections in the lateral plane of the attachment. These perspectives have been key in pointing towards the degradation mechanisms at play. They demonstrate, for example, how the structure of the sintered attachment continues to densify under operation, and a consequence of this is the formation of shrinkage cracks which resemble mud-cracks in the most porous regions.

Focused ion beam (FIB) and electron backscatter diffraction (EBSD) imaging have also been used in correlation with 3D renderings of these cracks to analyse their propagation and reveal their relationship both with the internal structure of the sintered attachment itself, and the structure of the substrate to which it is joined. As-sintered and cycled sintered Ag layers both exhibit heterogenous porous structures consisting of randomly oriented equiaxed grains whose size vary depending on the local density of the region sampled. Power cycling brings about grain growth and the loss of twin boundaries, and these are more pronounced within more dense regions of the Ag attachment. The copper substrate undergoes some grain refinement. Cracks, which appear to initiate within the Ag layer, propagate across the Ag-Cu boundary and transgranularly through fine grained regions within the copper with little tortuosity.

This work was supported by Mentor Graphics and the UK Engineering and Physical Sciences Research Council projects EP/K035304/1 & EP/R004366/1 through the Centre for Power Electronics.

Monitoring pressurized water reactors casted duplex stainless steel parts is of interest in long-term operation of nuclear power plants. It has been shown that these components are subjected to ageing when held at their operating temperature. In the long run, thermal ageing results in embrittlement due to a microstructural evolution of one of the two phases constituting duplex steels. Kinetics and impact of ageing on fracture mechanics have been studied to a great extent. However, deformation and damage mechanisms leading to fracture are not yet fully understood owing to the complexity of duplex steels microstructure. Resorting to traditionally used global energy balance methods (J-Δa curves) is not sufficient to understand the primordial role of microstructure in the evolution of mechanical properties with thermal ageing. In this context, a microstructure characterization is performed jointly to in-situ mechanical characterization to build a consistent micromechanical model taking the multi scale aspect of the microstructure into account. Eventually, the model must provide a fine description of the material mechanical behaviour taking into account the aged state
In order to relate crystal plasticity finite element computations to experimental observations, digital images correlation (DIC) is used to provide full-field measurements. They must be consistent with the deformation mechanisms of the studied steels and be accurate enough to capture small deformation mechanisms occurring in each phase (at a micrometre scale) and the resulting displacements at the larger scale of the microstructure (several millimetres). Duplex steels natural texture is not sufficient to carry out digital images correlation. Thus, an adequate speckle pattern was designed and deposited through electron beam lithography.

Titanium alloys oxidation leads to the simultaneous formation of an oxide layer and an oxygen-enriched layer below the oxide scale due to high solubility of oxygen in titanium. A few tenths of atomic percent of dissolved oxygen is sufficient to weaken the mechanical properties of titanium alloys. It is thus necessary to take into account the impact of this oxygen-enriched layer to predict mechanical behaviour of oxidized thin components. The mechanical properties of samples with various oxygen-enriched layers are studied with room-temperature and high-temperature tensile tests on ultra-thin Ti6242S samples more or less pre-oxidized paired with digital image correlation techniques. Ultra-thin samples were prepared with different thicknesses ranging from 100 μm to 1 mm and then exposed at 650°C for durations between 40h to 120h. The purpose was to explore different ratios between the thickness of the oxygen-enriched layer and sample thickness (5% to 50%). The thickness of the oxygen-enriched layer was characterised with microhardness tests and electron probe micro analyser (EPMA) profiles.
Fracture surfaces have been investigated with scanning electron microscopy to identify the brittle and ductile areas and to quantify their proportion in the different pre-oxidation conditions.The measured thicknesses of brittle areas were in good agreement with the thickness of the oxygen-enriched layer characterised by EPMA and microhardness techniques.
Tensile tests revealed that the oxygen-enriched layer in Ti6242S induced a decrease in yield strength and ductility. Mechanical properties have been studied as a function of sample thickness and proportion of oxygen-enriched section. At room temperature, the decrease of these mechanical properties seems proportional to the proportion of oxygen-enriched section. A good correlation has been found between the losses of ductility, the oxygen gradient and analyses of fracture surface.

Many applications of glass fibres reinforced laminates (GFRP) require stable properties along many years of use, thus studies on how they will behave under the influence of weather conditions are necessary. Satisfactory would be no changes or a slight decrease in the microstructure and mechanical properties that may indicate degradation resistance of the composite material.
The aim of the study was to evaluate the effect of aging conditions on the strength and microstructure of fabricated GFRP laminates. The laminates were fabricated by the vacuum bag method using epoxy or epoxy vinyl ester resins reinforced by glass unidirectional fabrics. The epoxy resin has a higher viscosity than the epoxy vinyl ester resin and its curing is conducted at a higher temperature. The aging tests were conducted under the following conditions: temperature 80 °C, 80% humidity with test duration of two weeks.
In order to verify material properties tensile, bending, and impact strength tests, as well as microstructural observations, were carried out before and after aging. The glass transition temperature was determined by DMA analysis. In the end, Tg temperature was assessed whether it changed after aging.
Based on the test results, it can be concluded that the strength properties decrease by no more than 20% as the result of aging tests. Moreover, laminates fabricated using epoxy resin exhibited higher mechanical properties before as well as after aging in comparison to laminate based on epoxy vinyl ester resin. However, few material defects, such as air bubbles, were observed in the SEM images of the laminate microstructure. In addition, from the industrial point of view, the advantage of the application of epoxy resin is the styrene-free fabrication process.
The work was supported by National Center for Research and Development as a grant no. MAZOWSZE/0141/19-00.

Magnesium silicide and titanium suboxides (TiOx) are considered promising thermoelectric materials to generate electricity from waste-heat thanks to their thermoelectric performance, low-cost, low-toxicity and light-weight. Nevertheless, the stability and oxidation resistance over time at temperatures higher than 500° C for Mg-silicide and 400°C for TiOx respectively, are critical issues. Therefore, the development of protective coatings for TE legs is fundamental in order to prevent the degradation of their thermoelectrical properties at high temperature. Glass-based materials, with low electrical and thermal conductivity, are good candidates as protective coatings against oxidising atmospheres.
In this work, a Sb doped Mg2Si-Mg2Sn based thermoelectric, densified by spark plasma sintering (SPS), was successfully coated with a new silica-based glass, which was specifically designed as an oxidation protective coating for mid-temperature range (up to 500° C) applications. Despite the high coefficient of thermal expansion of Sb doped Mg2(Si,Sn) based materials (17-17.5·10-6 K-1), very good thermo-mechanical compatibility between the substrate and the coating was obtained. Oxidation tests, performed at 500° C for 120 hrs in air, established the effectiveness of the glass coating for the protection of Sb doped Mg2(Si,Sn) thermoelectrics.
Moreover, a new Y2Ti2O7 containing glass-ceramic was specifically produced as a protective coating for the titanium suboxide (TiOx) up to 600 °C. Excellent thermo-mechanical compatibility between the substrate and the coating was obtained. Oxidation tests, performed at 600 °C for 120 hrs in air, demonstrated the effectiveness of the glass-ceramic coating for the protection of TiOx.

To improve the performance and efficiency of combustion engines, higher operating temperatures are required. Commonly used high temperature structural materials (e.g. Ni-base) reach their limitations beyond 1100 °C.

Refractory metals are promising substitutes due to their high melting point and their good mechanical properties at high temperatures. One major drawback of most of these metals is their low oxidation resistance, so further processing, such as coating or alloying, is necessary for their use as high-temperature materials. Among the class of refractory metals, Cr has an outstanding resistance in oxidizing and hot corrosion environments while Mo-Si-based or Nb-Si-based alloys exhibit outstanding mechanical properties.

Using in situ chemical vapor deposition (CVD), Cr-coatings with layer thicknesses below 10 m were successfully applied on the refractory bulk materials Mo, Nb, Ta and W. In addition, such coatings were manufactured on recently developed Mo-Si-Ti alloys (eutectic and eutectoid) [1]. Thermogravimetric analysis (TGA) was used during exposure for 100 h in synthetic air at three different temperatures (700 °C, 900 °C, 1300 °C) to record the oxidation kinetics. The applied layers, the formed intermetallic phases and the formed oxide scales were analyzed before and after exposure to the oxidizing atmospheres using optical microscopy, XRD, SEM, EDX and EPMA. The coated materials show an improved oxidation behavior due to the formation of a protective Cr2O3-scale. This results in a substantially decreased oxide growth rate in comparison to uncoated substrates.

[1] Schliephake, Daniel, et al. "Constitution, oxidation and creep of eutectic and eutectoid Mo-Si-Ti alloys." Intermetallics 104 (2019): 133-142.

Since their first mentioning in the early 2000s, the interest in high entropy alloys (HEA) as a new material class has been ever increasing. Starting with bulk materials, also thin films gained attention in the past years due to the wider flexibility in the available synthesis methods and attainable growth conditions. Among the different HEAs, alloys mainly comprising refractory metals, so-called refractory HEAs, showed a good thermal stability after annealing in vacuum which makes them a potential thin film material for high temperature applications. Within this study a series of refractory HEAs were deposited using high power impulse magnetron sputtering keeping the base alloy MoNbTaW constant and adding a fifth element: Ti, V, Cr, Mn, Zr and Hf. The targets used for the synthesis of each alloy contained all five elements in an equimolar concentration. As analysed by X-ray diffraction (XRD) and transmission electron microscopy (TEM), all films showed a bcc solid solution phase structure in as-deposited state. Subsequently, the thermal stability of the films was investigated using high temperature XRD up to 1200 °C in vacuum. While alloys like MoNbTaW+V and MoNbTaW+Cr showed minimum structural changes up to the maximum annealing temperature, others like MoNbTaW+Ti and MoNbTaW+Zr revealed several phase changes. The obtained high temperature XRD results are complemented by differential scanning calorimetry, temperature-stress measurements as well as by TEM analysis of selected annealed refractory HEA films. The performed work is intended to contribute to a comprehensive understanding about the thermal stability of refractory HEA thin films which in turn can enable their use for industrial high-temperature applications.

The nowadays requirements for high-performance materials in aerospace industry pose a challenge in terms of their tooling and machining. A promising way to reduce the wear of cutting tools, thereby extending their lifetimes, is represented by the application of self-lubricating nanocomposite coatings. It has been recently shown that Ag nanoparticles dispersed in a superhard TiSiN matrix are very promising.
In these systems Ag diffuses to the surface within and along the matrix free surfaces and grain boundaries (GB), and the control of the diffusion rate is fundamental to design the coating and optimize its performance. Here, we employed ab-initio calculations and molecular dynamics (MD) simulations to understand the diffusion mechanism of Ag within the nanocomposite coating.

Firstly, the formation energy of Ag-related point defects such as Ag interstitials and substitutions has been calculated using density functional theory (DFT). Potential energy landscapes were obtained for Ag diffusion over TiN and SiN surfaces, as well as for diffusion along grain boundaries.
MD simulations of TiN/Ag systems have been performed, using a hybrid MEAM-Mie forcefield obtained by merging pre-existing ones and adding a Mie term for the Ag-N interaction, with the help of DFT data. Ag diffusion in presence of GBs and surfaces was characterized under different temperature and pressure conditions.

Our results indicate that the diffusion along TiN surfaces is the fastest diffusion mechanism. Diffusion along grain boundaries is slower and directly related to the size of GB. Conversely, bulk diffusion appears extremely slow due to the high interstitial and defect formation energies. Surface defects might act as diffusion traps for Ag.

Our study provides a clear understanding of the Ag transport in TiSiN/Ag nanocomposite coatings, indicating that the correct strategy to control Ag diffusion is to act on the surface diffusion process.

Spark Plasma Sintering (SPS) is a powder metallurgy technique used for the elaboration of dense materials with a fine-grained microstructure [1]. In this process, a pulsed electric current and a uniaxial pressure are applied simultaneously, leading to high heating and cooling rates, thus limiting the grain growth [2]. The powder is placed into a graphite die and the pressure is applied by two graphite punches. A graphite foil is inserted between the punches and the powder and between the die and the powder to ensure a good electrical, physical and thermal contact [3]. In the case of the SPS sintering of metallic powders, one of the major drawbacks is the carburization of the powder in contact with the graphite tooling. This phenomenon is particularly pronounced in the case of Fe-based powders. The length of the carburized area could reach some hundred microns, depending on the powder composition, then affecting the integrity of the sintered material. In this study, a PVD coating of a carbide element (Ti) was applied on the graphite foils in contact with the metallic powder (pure iron), in order to limit the carburization phenomenon. Several coatings’ thicknesses were tested ranging from few hundreds of nanometers to more than one micron. The contact zones between the coated graphite foils and the metallic powder were analysed by optical microscopy and scanning electron microscopy coupled with EDX. The results showed that a Ti PVD coating is effective to prevent carburization of the metallic sintered sample. The effect of the PVD layer thickness on the diffusion mechanisms is also compared and discussed.

[1] Y. Zhang et al., Mater. Trans., 46 (9) (2005) 2015-2019.

[2] Z.A. Munir et al., J. Mater. Sci. 41 (3) (2006) 763-777.

[3] K. Vanmeensel et al., Acta Mater. 53 (2005) 4379–4388.

The powder as raw material, either for powder bed or blown powder technologies, constitutes an important strategy in metal additive manufacturing (AM). Metal powder used for powder bed fusion AM is characterized by high surface reactivity due to the large surface area of the powder that is about 10 000 times larger than the surface if the bulk material of the same mass. This results in the powder surface chemistry, determined initially determined by powder manufacturing method and alloy composition. This initial chemical composition is, however, not stable and progressively changes with time in dependence on powder handling procedures and especially processing by metal additive manufacturing. Changes in powder surface chemistry during powder reuse and hence its processability are determined by alloy composition and AM technology in general as well as hardware design and processing conditions in particular.
Paper summarizes recent experimental observations and theoretical simulations of the changes in powder surface chemistry during the whole life-cycle of metal powder: from its manufacturing using different powder manufacturing technologies through powder handling and AM processing by variety of powder manufacturing methods. Results of the qualitative and quantitative analysis of the powder surface chemistry by surface-sensitive chemical analyses using XPS, AES, HR SEM+EDX, etc. are presented and combined with thermodynamic and kinetic simulation. Results indicate significant enrichment in the thermodynamically stable surface oxides in case of high-alloyed powders during both, Electron Beam Melting (EBM) and Laser Powder Bed Fusion (LPBF). However, powder degradation processes differ significantly in dependence on AM technology/hardware and alloy composition. Generic model of the powder degradation, depending on the alloy composition, during different AM processes, is elaborated. Effect of the reused powder on the defect formation during AM processing is discussed as well.

In Laser Powder Bed Fusion (LPBF), a significant amount of metallic powder is not melted by the laser beam. Costs and material yield strongly depend on the ability to reuse metal powder efficiently. However, some of the unfused powder is exposed to high temperatures during the manufacturing process in an imperfectly controlled atmosphere. Therefore, there is a need to study and understand powder degradation during the process and its direct effects on the printed parts. One batch of gas-atomized 316L stainless steel powder was used, recovered, sieved and reused to produce 12 successive LPBF prints without adding any virgin powder. Both recycled powders and elaborated parts were characterized throughout each iteration. Particles analysis was carried out using laser granulometry, scanning electron microscopy, flowmeter funnels, inert gas fusion, and X-ray diffraction. Solidified specimens features were investigated by means of optical microscopy, scanning electron microscopy, electron backscattered diffraction, microhardness and uniaxial tensile testing. Powders morphology, rheology, microstructure and oxygen content display slight changes with recycling, along with parts density and mechanical properties. The effects of processing conditions, especially the chamber oxygen content were also studied, and strongly influence the kinetics of degradation.

The development and utilization of metal powder for additive manufacturing processes requires deep comprehension about the complete process chain including atomization, processing and recycling of powder material. Using laser powder-bed fusion, a huge amount of the powder feedstock is left after the process. To increase the efficiency of such processes, it is essential to reuse excess material. Therefore it is from high importance to obtain information about the influence of powder recycling.

In this work, the influence of recycling on properties of AISI 904L powder and on printed parts was investigated. The chemical composition as well as morphology and flowability of virgin and recycled powder was analysed. Furthermore printed parts from virgin and recycled powder were investigated. Besides cubic samples for determining porosity and microstructure also samples for tensile tests and notched bar impact test were produced. To obtain best results, the process parameters were initially adjusted in an optimal range to build parts with relative density higher than 99 %.

Particle size distribution and morphology were determined by optical and scanning electron microscopy. The chemical composition of both powder and built samples was analysed with energy-dispersive X-ray spectroscopy and inert gas fusion for carbon, sulphur, nitrogen and oxygen. Flowability of the different powder grades was measured with Revolution Powder Analyser. The microstructure of parts including porosity and grain size was analysed using optical microscope as well as a scanning electron microscope with electron backscatter diffraction.

In powder bed additive manufacturing technique, the powder characteristics can determine the success or the failure of the job. In the Electron Beam Melting (EBM) process is generally used spherical powder with a particular size distribution of 40-150µm. During the EBM process the powder is spread onto the platform by the rake, therefore is essential to use powders with optimal rheometric properties and powder quality is a key aspect that strongly affects the processability.
In this work, different γ-TiAl powders coming from different suppliers as well as different lots of the same suppliers were characterized in terms of flowability by Hall flow, apparent density, tap density, grain size distribution by granulometer, morphology properties of the particles as well as characterization of the internal defects to correlate the result with processability in the EBM A2X machine.

The thermophysical properties, including viscosity, density and surface tension of some industrial blast furnace slags, industrial basic oxygen furnace slags, ladle slags and mold powders with varying compositions were measured and discussed at a temperature range between 1400 and 1700 °C using the rotating bob and maximum bubble pressure methods. The experimental investigations were supported by thermochemical modelling (FactSage 7.2).

A Gibbs energy minimization algorithm [1] has been developed and is used for calculating phase equilibria in the quinary slag system CaO-SiO2-FeO-MgO-MnO. Assuming local equilibrium at the solid-liquid interface, the kinetics of lime dissolution in this system is simulated by means of a finite-difference diffusion model. Different initial lime particle geometries such as plates, cylinders and spheres can be considered. Experimental observations [2] indicate that the first, comparably fast dissolution stage of the lime particle is competed by the formation of a boundary phase retarding the dissolution kinetics of the particle. The intermediate dissolution process characterized by the formation and dissolution of the boundary phase is considered by a reduced effective diffusion coefficient. Comparison of the simulated results with dissolution kinetics deduced from experimental data suggests that diffusion-convection processes are the rate-controlling dissipative processes for the dissolution of the particle.

[1] M.H.A. Piro, S. Simunovic, T.M. Besmann, B.J. Lewis, W.T. Thompson: “The thermochemistry library Thermochimica”, Comp. Mater. Sci. 67 (2013) 266-272

[2] X. Guo, Z.H.I. Sun, J. Van Dyck, M. Guo, B. Blanpain: “In Situ Observation on Lime Dissolution in Molten Metallurgical Slags − Kinetic Aspects”, Ind. Eng. Chem. Res. 53 (2014) 6325−6333
Key Words: Gibbs energy minimization, metallurgical processes, thermodynamics, kinetics of metallurgical reactions

In the present work, the state of steelmaking slags and their dephosphorization potential is re-evaluated using a computational thermodynamics approach. The thermodynamic simulations are carried out by coupling a newly developed thermodynamic database BOFdePhos to the software package FactSage TM. The non-ideal associate solution model is used for the description of the Gibbs energy of the liquid phase and the Compound Energy Formalism (CEF) for the description of the Gibbs energy of the solid solution phases, while the solid stoichiometric compounds are treated with simple temperature-dependent Gibbs energy functions.

The results indicate that steelmaking slags are heterogeneous for a large part of the blowing process, and are mostly saturated with silicates and/or with monoxide phases. The type and amount of solid phases is a strong function of the temperature, the oxidation state of FeOx, as well as the content of minor oxides such as MgO-, MnO- and Al2O3-content. The overall phosphorus distribution ratio Lp, between the heterogeneous slag and the liquid Fe solution, increased considerably when the solid phase 2CaO.SiO2-3CaO.P2O5 (C2S_C3P) was present while other phases such as 3CaO.SiO2, CaO-ss, and MgO-ss had a negative effect. Based on those findings, a new slag target region for achieving optimal dephosphorization results is suggested for the industrial process.

Typical commercial calcium silicate based mould powders (CaO-SiO₂-Al₂O₃-CaF₂) are used in casting high aluminium (Al) steels. The dissolved Al in liquid steel reacts with the mould slag during casting. In high Al alloyed steels, SiO₂ of the slag is partially reduced and high amount of alumina (Al₂O₃) up to 30 % is formed. The resulting change in mould slag composition causes modified physico-chemical properties. Especially viscosity and solidification behavior are affected. Also, lubrication and heat transfer conditions in the mould deteriorate due to the changing SiO₂/Al₂O₃ ratio. This are the reasons why various kinds of casting problems such as increased number of breakout alarms, longitudinal cracks and depressions. Therefore, a calcium aluminate based mould powder (CaO-Al₂O₃-CaF₂-Li₂O) has been developed by thyssenkrupp Steel Europe AG and Imerys Metalcasting GmbH. A comparison with a commercial calcium silicate based mould powder was performed. The new calcium aluminate based mould powder reaches the operating point much faster than the calcium silicate based mould powder. Operational tests show that slag composition, viscosity, crystallization temperature and heat transfer rate reach a steady state within about 20 min. Mineralogical phases and fabric of formed slag films were characterized and compared on polished cross sections from both mould slags. Measurements of crystallization temperatures and viscosities of mould slags were performed in laboratory trials. Further optimization of physico-chemical properties was achieved by tuning the chemical and mineralogical composition of the new calcium aluminate mould powder. This optimization procedure was supported by thermodynamic calculations of viscosity and melting behavior for different compositions. The operating tests carried out with the new calcium aluminate mould powder showed an improved surface quality of the slabs with decreased number of longitudinal cracks. It is planned to establish the new mould flux in series production.

Electrometallurgical extraction of metals is becoming increasingly important in the course of higher availability of renewable electricity. Submerged Arc Furnaces use the electrical resistance of the slag produced during the reduction process as their heating medium. The higher the output, which normally goes up to 100 MW today, as more complex is the control technology as more important it is to know the specific electrical resistances of the slag at operating temperatures. Extensive studies of electrical conductivity, the inverse value of the resistance, over a wide temperature range were carried out and evaluated for slags of the type FeO-CaO-SiO2, which are particularly generated in ferronickel extraction, but also in other processes. The results of this work and the relevance for the electromechanical dimensioning of electric furnaces are presented.

CuNiFe alloys have shown to be promising materials in terms of manipulating magnetic properties by controlling their microstructure. Despite extensive research activities for several decades now, the relationship between the evolution of the microstructure and its magnetic properties still remains to be fully explored. In this study, we investigate a spinodally decomposed CuNiFe alloy, using modern (S)TEM methods, particularly EDX spectroscopy and differential phase contrast (DPC) imaging. The specimen under investigation was solution treated and a subsequent heat treatment at 625°C for 10 hours leads to a spinodal decomposition of the alloy. EDX elemental maps reveal the characteristic stripe/plate like Ni-rich phase embedded in a Cu-rich matrix. Those plates are growing along the [100] directions of the crystal which is shown in figure 1 a). The EDX analysis reveals a chemical composition of 54 at% Ni, 27 at% Fe and 19 at% Cu for the Ni-rich phase and 15 at% Ni, 4 at% Fe and 81 at% Cu for the Cu-rich matrix. To investigate the magnetic structure, LM-STEM DPC with a switched off objective lens was performed to ensure a nearly field-free environment. A magnetic field map is shown in figure 1 b) in which the colour represents a certain direction of the magnetic field. The DPC map shows a direct relationship between the magnetic field structure and the nanostructure along the [100] directions. Interestingly, the DPC map displays field vectors that point along the diagonals of the image, suggesting a [111] direction of the magnetic easy axis.

Micromechanical behavior of the dual phase silicon stainless steel alloys during tensile testing has been studied using in-situ electron backscattered diffraction (EBSD). The texture development alongwith the effect of strain on the grain orientation has been studied individually for both the phases. The changes in the grain orientation have been characterized by the inverse pole figure. In the undeformed state γ-austenite grains were found to oriented in the line link <001>-<111> plane-normal. With increasing strain, grains gradually rotated towards their stable end orientation <111> while intensity for the δ-ferrite grains increased in <102> direction. Deformation twins with 60° rotation along the <111> axis was observed in the γ-austenite grains. No deformation twins were observed in the δ-ferrite grains which elucidates that deformation is primarily caused by slip only. However, both slip and twinning are the predominant deformation mechanism in γ-austenite grains. The EBSD phase maps indicate the presence of transformation-induced plasticity where the phase fraction of δ-ferrite increases with the deformation. The present investigation explores the strain accommodation mechanisms in these alloys.
Keywords: Grain rotation, Misorientation, Electron backscattered diffraction (EBSD), Deformation behavior

Mechanical properties of metallic material can be predicted as a function of their microstructure by constitutive laws [1]. One of the key microstructural parameters, which is often difficult to precisely characterize, is the dislocation density.

For the metallurgical community, there is a need for more representative measurements in order to better describe the mechanical behavior of such materials.
Dislocations can be observed in a SEM using ECCI (Electron Channeling Contrast Imaging), when the sample is correctly oriented in a condition to generate a contrast between the matrix and the dislocations. However, the precise orientation of the sample is difficult due to the SEM set-up.
R-ECCI (Rotational-ECCI) method [2-3], consists in acquiring a series of rotating back scattered electron images. From this image serie, an intensity profile of the different dislocations and of the matrix can be extracted. The dislocation density can then be automatically determined by applying a clustering algorithm on the intensity profiles.
The lowest and highest dislocation density measurable with this method was determined by analyzing a duplex steel sample presenting a deformation gradient. Moreover, a quantitative comparison between the results obtained using this method and traditional measurement techniques such as TEM, XRD and EBSD was achieved.

References:

[1] J. Blaizot et al. / International Journal of Plasticity xxx (2015).

[2] L’hôte, G. et al. Rotational-Electron Channeling Contrast Imaging analysis of dislocation structure in fatigued copper single crystal. Scripta Materialia162, 103–107 (2019).

[3] Cazottes Rotational-Electron Channeling Contrast Imaging analysis of dislocation structure in fatigued copper single crystal. Scripta Materialia162, 103–107 (2019).

Keywords: SEM, R-ECCI, dislocation, deformation, clustering

Understanding the relationship between microstructure and properties is a necessary step for the improvement of existing materials or the development of new materials. The microstructure can be characterised using orientations maps, from which information like grain size distribution and deformation state can be extracted.

Apart from EBSD (Electron Backscattered Diffraction), a promising approach to obtain orientation maps with the SEM (Scanning Electron Microscope) is the eCHORD method [1], which is based on electron channelling contrast. This method has the advantage that the sample tilt is only about 10°, and that the accelerating voltage can be lowered to a few kV, resulting in an improved spatial resolution. A series of BSE images is recorded during the rotation of the sample around its tilted normal direction, from which the intensity profiles of each pixel can be extracted as a function of the rotation angle. By comparing the obtained intensity profiles with the one calculated from ECP (Electron Channelling Patterns) simulations, the orientation of each pixel can be determined. The angular resolution achieved on Aluminium alloys is about 0.1°.

In addition to orientation maps, we present here an original method to characterize the local disorientation by comparing the distances between profiles of adjacent pixels, without the need to compute pixels orientation. The results are compared with EBSD Kernel maps obtained on Duplex steels with different levels of strain.

REF:

[1] C.Lafond, T.Douillard, S.Cazottes, P.Steyer, and C.Langlois. Electron CHanneling Orientation Determination (eCHORD): An original approach to crystalline orientation mapping. Ultramicroscopy,
186 :146–149, March 2018.

During laser Additive Manufacturing (AM), a just deposited material undergoes melt-pool dynamics and rapid solidification within a few milliseconds. Then, for the rest of the process, it undergoes cyclic re-heating and cooling in the solid-state i.e., Solid-State Thermal Cycling (SSTC), until the end of the AM process. These non-equilibrium processes result in the formation of metastable hierarchical microstructure with physical and chemical heterogeneities at multiple length scales. Amongst all the microstructural features, precipitates are one of the most important ones due to their direct impact on the mechanical properties of the material.

Microstructure characterization is typically performed via electron and x-ray microscopy/diffraction techniques. However, it is impractical to probe microstructure evolution due to SSTC during the building of an AM part via these techniques. As an alternative, instead of probing microstructure evolution during an AM process, we propose to subject pre-built AM samples to SSTC under controlled conditions.

Recently, we performed a series of novel in-situ rapid/gradual SSTC experiments on Laser Metal Deposited (LMD) 316L Stainless Steel (316LSS) lamellae inside a transmission electron microscope. We evidenced significant changes to the precipitate structure and composition at high resolution.

In order to obtain complementary and statistical information from “bulk” samples, we then performed a series of ex-situ SSTC experiments on micropillars extracted, via focused ion beam, from LMD 316LSS and studied them via Transmission X-ray Microscopy (TXM), also known as 3D nanotomography. These novel experiments provide unprecedented insight on precipitate evolution in the bulk LMD 316LSS during SSTC. Mechanisms such as dissolution, coalescence and formation of new precipitation were observed to govern the evolution of precipitates. In this talk, we present and discuss the results of these ex-situ TXM SSTC experiments.

With the continuous miniaturization and increasingly performance requirements of microelectronic devices, new materials have been integrated as the low-k SiOC:H dielectric, introduced in the interconnections. This low dielectric constant material was developed by introducing porosities, which reversely have negatively affected its mechanical properties. Thus, product reliability becomes a challenge for microelectronic industry. To understand the crack initiation and propagation in these materials, a microbending machine was designed to perform fracture tests under optical or scanning electron microscopy.

Double-torsion tests were performed on 775 µm-thick silicon wafers. Results confirmed that silicon is highly brittle and with no measurable subcritical crack growth. Even at $K_I$ approaching 98% of $K_{IC}$, crack rates were at least lower than $10^{-11}$ m/s. It was even possible to obtain relevant measurements of $K_{IC}$ on thinned substrate (200 µm), for loads lower than the newton. These results agreed with the literature and showed the potential of the method to accurately monitor crack propagation in very thin samples on which films can be deposited.

The same tests were done on a 0.7 µm-thick SiOC:H film deposited on the substrate. The crack initiates in the substrate rather than in the layer. Indeed, the low thickness of the coating, associated to its low stiffness compared to the silicon, lead to a crack propagation from the substrate. The same observations were done with a four-point bending configuration. Therefore, various sample preparations and pre-defect initiations are currently evaluated to contain the crack within the dielectric material.

This work brings insights on the double-torsion tool capability but also on the silicon fracture behavior at low thickness, which may be useful for microelectronics. It also highlights the difficulty to address the crack propagation in SiOC:H dielectric at submicron thicknesses.

Porous anodizing has recently attracted great interest as a simple and inexpensive method to produce nanostructured materials. By varying the anodizing conditions, the structure of the formed porous anodic Al oxide can be tuned and subsequently functionalized, making it highly attractive for various industrial applications from nanoscale electronics and optoelectronics to template, catalysts and sensors surfaces.
During the growth of anodic Al oxide layers mostly performed in aqueous electrolytes, water incorporates in the film and therefore influences the intrinsic properties of the oxide formed. In this study [1], high-resolution neutron imaging was performed using the neutron microscope at POLDI beamline (SINQ, PSI) to visualize and quantify the water content in porous Al oxides as a function of anodizing conditions. While single crystal Al2O3 is almost neutron transparent, we confirm that, as expected, porous anodic Al oxides contain water incorporated directly in the oxide structure (structural) in addition to the one present in the pores (morphological). The differences in water content of porous anodic Al oxide layers are strongly related to the oxide growth parameters but interestingly cannot be directly correlated to a specific change in the amorphous oxide structure or in the pore morphology.
Investigations on reference Al oxides – C-sapphire, sintered Al oxide, plasma sprayed Al oxide, a commercial Al oxide membrane – and Al hydroxide further prove that neutron imaging is highly sensitive to crystalline structure and disorder, allowing differentiating crystalline Al oxides based on their phases and defect content. Lateral resolution permitting, high-resolution neutron imaging can become the ideal technique to study the changes occurring in porous ceramics, in particular with regards to the formation and thermal stability of hydroxides, which can be highly detrimental to surface protection and template applications.

[1] Ott N., Cancellieri C., Trtik P., Schmutz P., Materials Today Advances, 8 (2020) 100121

One of the research tasks for piezoresistive sensing and applications (e.g. healthcare monitoring, electronic skin, human–machine interfaces, and soft robotics) is the realization of efficient processing methods that allow both sensitivity at low and high strains [1]. Here we present such a processing method relying on extrusion involving thermoplastic polyurethane (TPU) and/or olefin block copolymer (OBC) as polymer matrix and carbon black (CB) as filler. By blend design we can access the challenging region of high sensitivity and high strain [2],[3], including a minimization of hysteresis. This is particularly true for ternary blends although basic sensing binary blends can be utilized, provided that a sufficiently high CB amount is employed. The findings are supported by dedicated SEM and TEM analysis as well as mechanical analysis.

[1] L. Duan, D.R. D’hooge, L. Cardon Prog. Mater. Sci. 2020, 114, 100617
[2] L. Duan, D.R. D’hooge, M. Spoerk, P. Cornillie, L. Cardon ACS Appl. Mater. Interfaces 2018, 10, 22678
[3] L. Duan, M. Spoerk, T. Wieme, P. Cornillie, H. Xia, J. Zhang, L. Cardon, D.R. D’hooge Compos. Sci. Technol. 2019 , 171, 78

The behavior of ceramics at the nanometer scale strongly differs from the one of the corresponding bulk material. For instance, strong plastic deformation has recently been reported in isolated nanometer-sized alumina nanoparticles or MgO nanocubes, when tested in situ in a transmission electron microscope (TEM). This plastic behavior may also occur in a powder during the compaction process, even at room temperature. An effect of nanoparticle surfaces may also have to be considered in the plastic behavior of nanoparticle during compression since it can affect the deformation mechanism or induce phase transformation. Controlling plastic deformation of nanoparticles during the ceramics processing might be a way to enhance their properties or to improve the processing route (compaction and sintering steps, for instance). We present here a comprehensive study of the mechanical behavior of transition alumina in the compacted powder.

Transition alumina nanoparticles, stored in different atmospheres to modify the nanoparticle surfaces, have been compacted at room temperature under 15 GPa in a Paris-Edimbourg press. XRD analysis have been performed on the compacted powder to monitor a possible phase transformation of alumina.

Thin foils of these compacted powders have been prepared by Focused Ion Beam machining (FIB) and analysed by TEM. In situ nanocompression tests have then been performed on the different thin foils to compare the behavior of the compacted powder depending on the nanoparticle surfaces of the initial powder. Several imaging conditions have been investigated to follow the nanoparticle movement and/or their deformation during the compression. The results obtained on the compression of thin foils will be presented and discussed in function of the sample microstructure.

The usage of multi material design in modern vehicles and particular in the body in white (BIW) production is steadily rising to fulfil demands of emission laws and conservation of resources. Besides the conservative joining methods for a multi material design (e.g. screws and rivets) the well-known hybrid casting with steel inserts and aluminium can be used with the advantage of reducing the additional joining operations and therefore to reduce the costs and cycle times in the production itself.

The process of hybrid casting is normally applied on non-structural parts where a force or form locking is enough for the life cycle of the component and the desired properties. In order to achieve a high performance material based bonding between the steel inserts and the aluminium cast components for body or chassis structures, a novel physical vapour deposition (PVD) Al-Si coating was developed and applied.

The applied Al-Si PVD coating on the steel insert inhibits the growth of brittle Al-Fe intermetallic phases in-between the components. Several casting trials (low pressure sand casting and high pressure die casting) were done with different casting parameters. Shear tensile strengths of 10 to 13 MPa were measured on simple overlap geometries.

Combined SEM and EBSD analysis showed, that the PVD coating is acting like a bonding agent in-between the steel insert and the aluminium cast. Cross-section analyses predict a fracture of the interfacial area of the coating and the aluminium cast. Nonetheless, a ductile mechanical behaviour can be observed due to the honeycomb like structures on the fracture surfaces. Additional EDX analyses of the surfaces are showing only aluminium and silicon signals, which are contributing to the failure mechanism, that the bonding is breaking in-between the coating and the aluminium cast.

Aluminium alloys have a wide range of applications, especially in the fields of aviation and aerospace. However, the complexity of the manufactured parts is sometimes limited when produced with conventional manufacturing processes. With the use of additive manufacturing techniques, near net-shape parts with a great structural complexity can be produced. When it comes to manufacturing aluminium alloys with laser beam powder bed fusion (LB-PBF), many issues can emerge. These are mainly due to the intrinsic material properties of aluminium – e.g. a high reflectance of the laser beam by the surface of the powder – which make these alloys difficult to process. This study concentrates on the printing of AlSi10Mg, a commercially available alloy widely used in AM, and AA5024, a promising Al-Mg alloy which was modified with Scandium and Zirconium to enhance its mechanical properties. The effects of different process parameters, as well as the influence of heat-treatments on the mechanical properties are discussed. For this purpose, the properties density, hardness, tensile strength and impact energy were investigated on both as-built and heat-treated samples. Microstructural analysis was performed with light optical microscopy and SEM-EBSD in order to understand the process-related phenomena and changes in material properties taking place during LB-PBF. Furthermore, new artificial intelligence models will be addressed to support the understanding and prediction of additively manufactured material properties (i.e. density and hardness) and their correlations with process parameters (e.g. laser power, scanning speed, layer height and hatching distance) .

In laser powder bed fusion (L-PBF), the mechanical performance of fabricated parts are significantly improved by hot isostatic pressing (HIP) as the density increases (pores are closed) and the microstructure improves. HIP ensures consistent and defect-free material, and consequently, this high-temperature and high-pressure process is often a requirement for safety-critical aerospace applications. The use of HIP to directly consolidate intentionally-unmelted interior powder in a L-PBF part was recently demonstrated. By confining the laser melting to only the outer shell (contour) of the structure, L-PBF production times can be dramatically reduced. A subsequent HIP cycle, which may be mandatory for reliability reasons, and therefore does not add additional costs, can then be used to densify the entire structure. Production rates and energy efficiencies can therefore be improved in this way. This presetnation describes the exploration of the effect of relying on the HIP process to consolidate interior sections of test coupons, for which micro computed tomography (microCT), process simulation and tensile tests were conducted. MicroCT of coupons with varying shell thicknesses identify the minimum shell thickness required; and provide indications of the shrinkage ratio as a function of powder content relative to shell thickness. Preliminary results are presented in which any shrinkage has been shown to be compensated for during design with deformation simulations. The simulations allow for accomodatin the 50-60% metal powder density and the consequent collapse as the powders are consolidated with HIP.

In recent years advanced high-strength steels (AHSS) including dual phase (DP) and complex phase (CP) steels have been increasingly used in automotive lightweight design, as these steel grades may improve the crashworthiness without increasing the weight of car bodies. The good formability of AHSS makes them particularly suitable for deep-drawing applications. Hence, the present work investigates the influence of the drawing velocity and of the blankholder force on the formability of different AHSS grades with sheet thicknesses of 1-2 mm. Five typical drawing velocities in the range of 10-120 mm/s and five blankholder forces in the range of 0-1200 kN were considered. Deep-drawing experiments at semi-industrial scale were performed using a standard cross tool consisting of the punch, the die and the blankholder. The cross tool was equipped with a load cell, a distance sensor and an accelerometer for measuring the forming force and the die displacement as well as for detecting the crack initiation at the deep-drawn component during the process. The maximum drawing depth achieved without cracking of the component was considered as characteristic parameter that quantifies the formability. Thinning and strain distributions of crack-free components were determined using optical 3D scanning and forming analysis systems. The results of the experimental investigations were utilized for validating a numerical model of the deep-drawing process, which was built using the AutoForm R8 finite element (FE) software. This model included the actual elastoplastic properties of the investigated AHSS grades. In general, the maximum drawing depth was observed to decrease with increasing tensile strength, drawing velocity or blankholder force, respectively, but with decreasing sheet thickness. For drawing velocities below 60 mm/s, however, the investigated DP steels did not show any significant velocity influence.

In recent years aluminum alloy sheets have been increasingly used in the automotive industry for producing lightweight vehicles. However, the complex tribological system and the occurrence of adhesive wear makes forming of aluminum alloys challenging. In particular temperature-induced friction during deep drawing may remarkably alter the tribological system. Therefore, tribological investigations are required at different testing conditions to determine the coefficient of friction (COF) between the aluminum sheets and the forming tools. In this research pin-on-plate tests were performed using pins of steel 1.3505 and plates of aluminum alloys EN AW-6016-T4 and EN AW-5182. The surface of the plates was either electric discharge-textured (EDT) or mill-finished (MF). The tests were performed under both dry and lubricated conditions and at different nominal contact pressures and surface temperatures. The surface topography of the aluminum plates was investigated by means of an optical 3D profiler before and after pin-on-plate testing. The results showed that the COF depends significantly on the testing conditions. For both, EN AW-6016-T4 and EN AW-5182, the COF mostly increased with decreasing contact pressure or with increasing surface temperature. Investigation of the surface topography after pin-on-plate testing revealed remarkable plastic deformation of the surface asperities of the plates. Plastic deformation and wear of the plates increased at higher contact pressures or at elevated temperatures, respectively.

Borate glasses have gained attention in soft tissue applications, and especially in wound healing due to their lower chemical durability compared with the silicate glasses. The high ion release profile is expected to have a positive effect on the healing process. Boron enhances vascularization during the proliferation phase, and calcium improves hemostasis at the very beginning of the healing process. In this study, 1393-B3 borate glasses doped with up to 6 mol % Ga3+ and Zn2+ therapeutic ions were prepared by the melt-quenching. The effect of the therapeutic ions on thermal, degradation, bioactivity, anti-bacterial, and cytotoxicity properties was investigated. The compositions of prepared glasses were verified by ICP-OES. The real (measured) compositions of all prepared glasses are close to their nominal compositions. Differential thermal analysis was conducted to determine the effect of therapeutic ions addition on glass transition temperature. The ion release profile from doped borate bioactive glass was investigated in PBS and DMEM media. In vitro bioactivity tests were carried out in SBF solution. The antibacterial activity of doped borate glasses was separately tested with S. aureus as Gram-positive and E. coli as Gram-negative bacteria using the broth dilution method for 4h, 8h, 1 day, and 2 days and agar disk diffusion method up to 3 days. The produced glasses showed significant inhibition effect for both S. aureus and E. coli from already the first hours of the test. The E. coli was more susceptible to the presence of Zn and Ga than S. aureus. Preliminary cytocompatibility tests of studied glasses in the cell culture with MG-63 cells were also carried out. The incorporation of Zn and Ga enhanced the cell viability compared to parent glass. The presented study shows the potential of Zn and Ga doped borate glasses in tissue engineering applications.

Mesoporous bioactive glass nanoparticles generated significant attention in recent years as suitable materials for biomedical application. In this study, cerium was incorporated into mesoporous bioactive glass nanoparticles (MBGNPs) using two different approaches. In the first approach, cerium was added to the glass system directly during the synthesis, while in the second approach cerium was added to the as-synthesized MBGNPs ex-post, via post-modification method. The influence of the method of synthesis method on physicochemical properties of nanoparticles was examined by SEM, TEM, XRD, FTIR, and N2 adsorption-desorption method. The MBGNPs have spheroidal and pineal shaped morphology and disordered mesoporous structure. XRD analysis confirmed the amorphous nature of the nanoparticles. The chemical composition was determined by the acid digestion method using ICP-OES. The influence of the synthesis method on the specific surface area, mesoporosity, and solubility of synthesized nanoparticles in Tris and Acetate buffer has been also studied. MC3T3-E1 cells viability after direct exposure to MBGNPs up to 500 ug/mL were evaluated over time using WST-8 assay. MBGNPs did not show any cytotoxicity towards the MC3T3-E1 cells up to 100 ug/mL. To investigate the cell viability further, the cells were stained with calcein-AM and propidium iodide which selectively stained live or dead cells. Additionally, Ce doped MBGNPs also showed antibacterial activity against S. aureus and E. coli. The mentioned features of the obtained cerium containing MBGNPs particles makes them useful for multifunctional applications as drug delivery carriers or bioactive fillers for bone tissue engineering applications with enhanced antibacterial effect.

Mesoporous glass nanoparticles (MGNs) on the SiO2-P2O5-CaO system are receiving great research interest for bone regeneration applications. The good biological capabilities of MGNs can still be improved by doping with inorganic ions and loading with biologically active molecules. In this communication, two MGNs compositions: 79.5SiO2-2.5P2O5-18CaO (MGN-79.5) and 60SiO2-4P2O5-36CaO (MGN-60) were synthesized and doped with 2.5 or 4 mol-% of ZnO, because of the osteogenic and bactericidal properties of Zn2+ ions, and loaded with Curcumin as a bactericidal substance. The osteogenic and antibacterial capabilities of MGNs were evaluated in vitro. Transmission Electron Microscopy showed that both ZnO-containing and ZnO-free MGNs exhibited radial mesoporous and a diameter close to 100 nm. MGNs exhibited good properties for their intended biomedical applications including negative Z-potential (- 18 mV) at physiological pH, due to the presence of silanol groups on the surface, and very high BET surfaces, in the range of 700 ± 100 m2/g. On the other hand, MGNs were successfully internalized by MC3T3-E1 pre-osteoblastic cells that showed proliferation with time without significant differences for ZnO-containing samples. However, MGNs doped with 2.5% or 4% of ZnO exhibited lower cytotoxicity than Zn-free ones. Antibacterial assays showed a decrease in S. aureus population for MGNs doped with zinc and loaded with Curcumin. Thus, after 24 h, S. aureus proliferation decreased to 99% and 97% in Zn-MGN-60 and Zn-MGN-79.5 compared with control. Moreover, a synergistic effect was observed when ZnO and Curcumin were simultaneously present. Therefore, Zn-MGNs loaded with Curcumin exhibited higher osteogenic activity and enhanced the antibacterial effect against S. aureus. These results suggest that the system MGNs + ZnO + Curcumin is a promising candidate for bone regeneration therapies with capabilities to fight infection.

Some bone diseases require the use of biomaterials that facilitate the natural bone regeneration processes. In this context, the use of 3D scaffolds based on mesoporous bioactive glasses (MBGs) improved with therapeutic ions, biologically active molecules and mesenchymal cells (MSCs) is a remarkable strategy to improve bone repair. In this study, the osteogenic ability of ZnO-enriched MBG scaffolds loaded or not with osteostatin (OST) and autologous MSCs was evaluated after implantation in New Zealand osteoporotic rabbits. Cylindrical meso-macroporous scaffolds with composition 76SiO2-15CaO-5P2O5-4ZnO (mol-%) (4ZN) were obtained by rapid prototyping and then coated with a gelatin layer for easy handling and to favor the release to medium of ions and biomolecules in the scaffolds. Then, 4ZN was loaded with OST, by soaking in a 100 nM peptide solution and seeded at 15.104cells/scaffold with autologous MSCs obtained from bone marrow of donor femur rabbits. Bone defects 7.5 mm diameter, 12 mm depth, were drilled in distal femoral epiphysis and filled with 4ZN or 4ZN + MSC + OST. Rabbits were sacrificed at 6 and 12 weeks extracting the distal third of bone specimens for microtomography (µCT) and histological analyses. 4ZN + MSC + OST scaffolds exhibited improved bone repair ability compared to 4ZN scaffolds in histological sections stained with Von Kossa and Goldner's trichrome. These positive results were confirmed by µCT determinations in both trabecular and cortical bone at 6 and 12 weeks. Trabecular bone volume density (BV/TV), trabecular number and cortical thickness parameters were significantly improved by 4ZN + MSC + OST scaffolds compared with 4ZN scaffolds. In this regard, trabecular separation was also decreased in presence of 4ZN + MSC + OST materials. Our in vivo findings suggest the interest of these MBGs-based systems loaded with OST and decorated with autologous MSCs to improve bone repair in the clinical practice.

Bioactive glasses (BGs) are well-recognized multifunctional biomaterials for bone regeneration and wound healing applications. Protein adsorption on BG surfaces plays an essential role in determining biocompatibility, cell adhesion and proliferation as well as influencing a series of cellular pathways after cell-BG contact. Understanding protein adsorption on BGs is thus necessary for accelerating the development and applications of next-generation BG-based healthcare materials and devices. However, the influence of BG characteristics on protein adsorption has not been fully understood.
In this work, we investigated the influence of BG composition on protein adsorption. Specifically, two types of BGs, i.e., bulky 45S5 BG and BG nanoparticles (BGNs), were used to understand how glass composition could affect protein adsorption. A series of techniques including FTIR, XPS, ToF-SIMS and the BCA assay were used to characterize the amount and structure of adsorbed proteins. The results revealed that 45S5 BGs could adsorb a larger amount of bovine serum albumin (BSA) than bioinert glasses at different pHs. BSA adsorption on 45S5 BG surfaces was pH-dependent. Apatite formation on 45S5 BGs could enhance the amount of adsorbed BSA but it attenuated the trend of pH-dependent protein adsorption. For SiO2-CaO BGNs, the incorporated Ca did not significantly affect the particle size, specific surface area, and structure. The amount of adsorbed proteins increased over time at the early stage of adsorption (<2 h), regardless of glass composition and protein type (BSA and lysozyme). Further incubation of BGNs with proteins seemed to induce a reduced amount of adsorbed proteins, which was more significant in BGNs with higher Ca content. The results revealed that the composition of BGs indeed affected protein adsorption behavior. However, the influence is complicated and also depends on the types of BG, medium and protein.

Magnesium (Mg) is investigated as a powerful alternative to state-of-the-art titanium implants for temporary bone support, due to its biodegradability, biocompatibility and mechanical properties. However, certain processes occurring during Mg degradation are still unclear, in particular the relative importance of transport phenomena vs. micro-galvanic corrosion. Mechanistic and computational models consider the degradation as a diffusion-limited transport problem, yet the diffusivity of the medium in the degradation layer is mostly unknown.

We will present a multi-scale imaging approach using micro computed tomography (µCT) and transmission X-ray microscopy (TXM) that enables studying the degradation of Mg at resolutions down to 40 nm. We have degraded pure Mg (>99.92%) discs in simulated body fluid (SBF) or Dulbecco’s modified Eagle’s medium (DMEM) with 10% fetal bovine serum (FBS) for one to four weeks. The immersion tests were conducted under physiological conditions (37°C, 5% CO2). The discs were then imaged using µCT to determine the degradation rate of the material. Subsequently, focused-ion-beam milling was used to extract small cylindrical samples (Ø25µm) for imaging with TXM. Following tomographic reconstruction, we can observe the interconnected pore network within the degradation layer, as well as remnants of micro-galvanic cells, and quantify the network morphology. Additional scanning electron microscopy and energy-dispersive X-ray spectroscopy, as well as X-ray diffraction measurements of the bulk samples were performed to enrich the observed degradation layer morphology with information on its composition. Based on the obtained results, we are able to infer the importance of the nanoporosity of the degradation layer on the overall degradation process of pure Mg in the immersion media. The results can be used directly to inform a computational model of Mg implant degradation, as will be presented in the outlook.

Metallic programmable mechanical metamaterials implement the bioinspired functionalities, for example, adaptability enabled by logical calculations and memory, in hierarchical structured metallic materials, and create huge design space for mechanically robust and functionally smart materials for biomedical, environmental, energy-related applications. The programmability of these materials systems arises primarily from their mesoscopic design (e.g. auxetic structures of hundreds of microns) among the design hierarchies from the atomic to the macroscopic shape levels. The unit cells of these metamaterial systems require the capability of producing large macroscopic or accumulative elastic deformation, compared to typical metallic metamaterials, to achieve the desired functions. The elements in the unit cells can also be loaded under rather complex conditions. In addition, these material systems are constructed hierarchically, which is made possible by minimizing the dimension of the elements in the unit cell, i.e., 100-200 microns in cross-section diameter. The intricate hierarchical structures are usually manufactured by selective laser melting. Structural defects are inevitable and critical for a better understanding and prediction of the micromechanical properties of unit cells. However, the systematic structure-property correlations with the focus on the surface roughness are still missing for metallic cylindrical beam elements, e.g., Ti64, 316L stainless steel, and MS1 steel. Presented here is firstly the quantification of the roughness of the printed beams from the computed x-ray microtomography scans. The comprehensive micromechanical characterization (e.g. tension, compression, bending, and torsion) of the elements are then performed with a micromechanical tester, and the strain distributions are calculated with digital image correlation. Finite element simulation approaches with beam elements are then optimized by the correlation obtained to represent the manufactured elements more accurately. Thus an improved prediction of the mechanical behavior of the unit cell and the cell arrays constructed upon these elements are possible.

Fetuin is a high abundant serum glycoprotein and a major non-collagenous protein, essential for biomineralization. The inductive effect on bone formation, thus mineralization, is one of the major benefits of magnesium (Mg)-based biomaterials for orthopaedic applications. Due to the high affinity of fetuin to calcium (Ca)-salts, fetuin might have a synergistic effect with Mg-based biomaterial on mineralization. Furthermore, as Ca-phosphate precipitates on passive layer, fetuin may also have an impact on Mg degradation behaviour. Therefore, the potential interaction of fetuin with Mg was investigated under in vitro conditions in the presence of Ca. Extruded pure Mg samples were immersed under cell culture conditions in Hank’s balanced salt solution (HBSS) with defined Ca (2-8 mM) and fetuin (1-3 mg/mL) concentrations.
The results showed a significant decreased degradation rate when both fetuin and Ca were present in immersion medium (compared to media without fetuin and Ca). The decrease of the Mg content released in the immersion media supported the reduced degradation of Mg under synergistic impact of fetuin and Ca. Microscopic images combined with elemental imaging showed a dense layer containing Ca and P at the surface, which probably act as degradation protection.
In vitro studies will be performed to show whether this protective layer is improving adhesion, proliferation, and function of osteoblast progenitor cells.

Multifunctional materials based on a combination of permanent and degradable metals open new perspectives for medical implants combining osseo-conductivity and drug-delivery functions, which can significantly decrease the number of implants´ revision. In this work, the hybrid magnesium-titanium materials were produced via sintering and the properties of the permanent titanium component before and after the degradation of the temporary magnesium part were evaluated. The changes of chemical composition and mechanical parameters were determined. Loading of hydrogen into the titanium part at room temperature was observed, which deteriorates the mechanical characteristics, but could also simultaneously improve the biocompatibility of the permanent titanium implant. The control of degradation of the magnesium part and the modification of the titanium part is required for the development of partly degradable hybrid implants.

Wool aerogel created from wool waste fibers is a potentially viable eco-friendly solution to oil spill clean-ups and thermal insulating material primarily due to is naturally oleophilic nature and insulating properties. Repurposing wool waste also allow us to tackle another issue this waste poses: decreasing landfill spaces. This study aims to develop wool aerogels using wool waste fibers and polyvinyl alcohol (PVA) as a cross-linking binder. The synthesized aerogels exhibit high porosity (97.73 – 99.63 %) and low densities (0.004 – 0.023 g/cm3). After being coated with methyltriethyloxysilane (MTEOS), the aerogels exhibit great hydrophobicity with contact angles up to 138°. Using pseudo-first and pseudo-second order models to study the kinetics of the aerogels’ oil absorption performance, it is found that the oil absorption kinetics is better modelled after the pseudo-second order model. The best performing wool-based aerogel recorded an oil absorption capacity of 136.2 g/g, an estimated 9.1 and 15.3 times better than commercial counterparts, polypropylene mat and nonwoven polypropylene respectively. Additionally, a low thermal conductivity (0.0333 w/m.K) can be achieved, making it a good thermal insulating material. The promising results obtained demonstrate that the wool fiber as a great waste material capable of generating high engineering value and provides a novel alternative in solving environmental impacts plagued by oil spills and landfill-demanding wool waste.

The increasing consumption of animal-based food, caused by a growing human population, resulted in the inevitable problem of higher waste generation, in particular faeces produced by the high number of animals bred. Although manure does not have a high commercial value in itself, it causes a high environmental impact by being one of the main contributors to emission of greenhouse gases in the agricultural sector and potentially threatening the safety of drinking water by leakage of nitrates and pathogens. Even though its use in the production of biogas by anaerobic digestion is one way to mitigate this environmental burden, this process is incomplete and wastes valuable resources. Biogas residues contain a significant amount of undigested lignocellulosic fibres and are therefore highly suitable as raw material for the extraction of cellulose, in particular nanocellulose (NFC). Due to elephant’s poor digestion capability and high biomass intake their manure was proposed as model system to study quantity and quality of NFC available from manure-biogas residues. Lignocellulosic fibres were isolated from biogas residues that were fermented for various digestion times and elephant manure directly, respectively. Resulting fibres were characterized with regards to their chemical and physical properties and NFC produced by defibrillation of those. To investigate the influence of anaerobic digestion, NFC papers from both reference and anaerobically pre-treated materials, respectively, were fabricated and their mechanical properties evaluated. NFC papers produced from agricultural waste streams required a lower number of grinding cycles to provide the same tensile strengths compared to NFC papers produced from high grade biomass, in addition to biogas having been produced prior to paper manufacturing. This demonstrates that agricultural waste is much more than an environmental burden but a raw material with high potential.

The cryopreservation of biological material has been consolidating its importance in biomedical research for decades now. Its biggest end goal has been to achieve timeless whole-body preservation but current methodologies still struggle with something as simple as cryoprotectant cytotoxicity. A bio-based approach then shows the most promise in tackling a cytotoxicity problem. Thus, we studied the adequacy of FucoPol, a fucose-rich bacterial biopolysaccharide, as a supplement in cryoprotective formulations.

After several years of studying FucoPol, we have unveiled its biocompatible, cryoprotective, antioxidant and photoprotective properties. FucoPol has demonstrated to be non-cytotoxic to animal and human cell lines, its inherent viscosity does not hinder nutrient diffusion, and is able to preserve the integrity of cells by extracellularly protecting them against cryoinjury. Its strong antifreeze activity is due to a non-colligative increase of the freezing point of water with concomitant reduction of mean ice crystal size. In vitro, this property appears to be independent of ionic composition or cell line studied, demonstrating its high versatility. Ionic multivariate cluster analysis shows that FucoPol can compete with textbook hypothermic formulations and CryoStorTM, showing similar cell viability post-storage whilst reducing formula complexity and production cost. Recently, we have discovered the photoprotective effect of FucoPol against UV radiation. Arctic frost flowers host psychrophilic bacteria that produce cryoprotective polysaccharides, but due to a thinner ozone layer, they are more prone to damaging irradiation. By adaptation, these molecules show good defenses against damaging UV radiation. Turns out FucoPol does not photodegrade under intense UV exposure and can protect human cells against all UV types.

This continuous multifunctional research focusing on FucoPol has raised questions regarding the truthfulness behind the affirmation that structure-function relationships are solely a cause of environmental adaptation when FucoPol derives from a mesophilic bacteria but shows traits of halophilic buffer capacity and psychrophilic antifreeze properties.

The need for a circular economy, given the ever-expanding plastics industry, cannot be contested. Their impact on the environment is one of the biggest challenges of the Millennium. This situation birthed the EU funded H2020 MSCA project C-PlaNeT (Circular Plastics Network for Training). By partnership with eight universities 15 Early Stage Researchers (ESRs) are being trained to be a part of a new generation of scientists, engineers and policymakers who challenge and rethink the design, processing, use and reuse of plastics for the EU’s circular economy vision. C-PlaNeT has five core objectives with one of them being - ‘To decouple plastics from fossil resources’. As part of this objective comes the research topic – ‘Biobased plastics for a circular economy’.
Packaging is one of the biggest applications of plastics. Conventional plastics such as PE, PP, PET, etc., which dominate this sector, are straining the crude oil resources, resulting in a high carbon footprint. Product packaging is indispensable as it protects the product, achieves the product utility, and displays information. In this scenario, biobased plastics come into the picture.
Polyhydroxyalkanoates (PHAs) are a family of bioplastics which are both biobased and biodegradable. They are already making inroads into the packaging and the medical industry (drug delivery, stents etc.) Polyhydroxybutyrates are the first discovered and widely studied in the family of PHAs. Nevertheless, the aspect of mechanical recycling has not been fully realised due to their complex properties. Other known bioplastics like PLA, PBS, etc. can act as reference systems with which several key properties can be compared.
The same processing principles as conventional plastics apply to biobased plastics. The mechanical recyclability of bioplastics has to be checked quantitatively and fine-tuned. Our research aims to achieve this objective. Other applications of the recycled material like food packaging are envisaged.

Concrete is responsible for generating up to 10% of the world’s CO2 emissions and due to its significant mineral resource consumption, has a dramatic effect on our natural infrastructure. There is an urgent need to increase the diversity of feedstock materials suitable for the manufacture of cementitious products, which are environmentally sustainable and have longevity in supply.

The aim of the present work was to investigate whether Redcar Mudstone mineral wastes, blended with recovered steel slags could be reused as an alternative active component for geopolymer production. Geopolymers are inorganic synthetic materials produced through the alkali-activation of aluminosilicates. Hardened geopolymers exhibit ceramic-like high-strength properties, whose production generates up to 60% less CO2 emissions compared with Portland cement manufacture.
The mechanical properties of various hardened geopolymer mixtures were tested by standard unconfined compressive strength (UCS) testing. The microstructure, chemical composition, and mineralogy of the materials were studied by direct physical methods including X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX). The maximum UCS recorded across all geopolymer mixtures was 70.6MPa, mechanical performance is shown to be based on the ratio between slag addition and the mineral waste silica and alumina composition.

These novel geopolymers have demonstrated great potential for numerous applications in the construction industry, including screeds and paving slabs. The potential for these new geopolymers to replace traditional Portland cement-based products while reducing the number of mineral wastes going to landfills has numerous commercial and environmental advantages – particularly in contributing towards an improved Circular Economy and in reducing global CO2 emissions.

KEYWORDS: Waste, Circular Economy, Geopolymer, Soil, Slag, Compressive strength

This presentation will summarise our recent works on the synthesis of functional nanocomposites thin films based on metal atom clusters by a chemical solution deposition (CSD) process namely electrophoretic deposition (EPD) [1-10]. CSD processing of inorganic nanocolloidal solutions is generally acknowledged to be highly flexible in terms of precursor composition, targeted substrate and procedures (dip-spin coating, spray coating, EPD…) in ambient pressures, and thus can be faster and less expensive than physical-based deposition routes while providing materials with matching or even superior properties. In this study, several octahedral atom clusters were characterised and used to prepare highly transparent thin films in the visible. Various coloured and transparent films were successfully fabricated on ITO glass substrates. In addition, transparent films with prominent photoactive or antibacterial properties were obtained by using specific Mo6 clusters whereas UV and NIR filters were realised by using Ta6 and Nb6 clusters. The EPD process appears a performant CSD strategy to fabricate highly transparent and coloured nanocomposite thin films for optical, biological and energy applications.

[1]B. Dierre et al., Sci.Technol.Adv.Mater., 2017,18,459
[2]T.K.N. Nguyen et al., ECS J.Solid State Sci. Technol., 2016,10,R178
[3]T.K.N. Nguyen et al., J.Electrochem.Soc. 2017,164,412
[4]T.K.N. Nguyen et al., J.Mater.Chem.C, 2017,5,10477
[5]T.K.N. Nguyen et al., Bull.Soc.Chem.Jpn., 2018,91,1763
[6]T.K.N. Nguyen et al., Royal Soc.Open Sci., 2019,6,181647
[7]A. Renaud et al., Electrochim.Acta, 2019,317,737
[8]W. Chen et al., Nanoscale Adv., 2019,1,3693
[9]T.K.N. Nguyen et al., ACS Appl.Mater.Interfaces 2020,12,40495
[10]K. Kirakci et al., ACS Appl.Mater.Interfaces 2020,12,52492

Metal Organic Frameworks (MOF), hybrid microporous crystalline materials are attractive for a large panel of applications due in part to their high specific surface area and physico-chemical stability. Recently, vapor phase-based routes were reported for the synthesis of MOF thin films. Vapour-phase process are usually preferred to obtain conformal coatings and they present a good compatibility with the Si technology. These breakthroughs have paved the way for the use of MOF in micro- and nanotechnologies but much remains to be done to control the growth and understand the potential and limits of these growth methods.
Here we developed a process to grow conformal ZIF-8 coatings with thicknesses up to 200 nm. This growth method is based on the deposition of ZnO layers by atomic layer deposition (ALD) on a substrate followed by ZIF-8 formation using cyclic exposure to water vapour and organic ligand in the gas phase. It was observed that this approach allowed formation of thin films with tunable thickness between 5 and 200 nm, independently of the initial ZnO thickness. The deposition was performed on several devices that can be used for gas analysis such as Quartz Crystal Microbalance and Si micro-pillars arrays.
Continuous ZIF-8 films were obtained and the composition, roughness and structure of the films were studied by FTIR, XRD and AFM experiments. Moreover, the growth mechanism was investigated by XPS and Tof-SIMS. Finally, the porosity was assessed using ellipsometric-porosimetry and the adsorption capacity and behaviour of the films towards several gases (methanol, acetone, water) were also established using gravimetric gas sensors in order to determine the benefit of ZIF-8 thin films for sensors.

Metal-organic-frameworks (MOFs) are an emerging porous materials class with many applications ranging from catalysis, chemical species separation to electronics. To date, the key synthesis routes for MOFs are predominantly wet chemistry based, resulting in either isolated MOF micro- and nanocrystals or in so-called surface-coordinated MOFs via layer-by-layer assembly. For conformal coating of complex three-dimensional nanostructures and also controlled core-shell structuring, the use of vapour-phase based synthesis routes for MOFs has promising advantages but has in comparison to wet synthesis to date only been little investigated. We here employ a state-of-the-art atomic-layer-deposition (ALD) system to grow ultra-thin MOF films. We screen the deposition parameter space in terms of precursor feeding protocols, growth temperatures and post-deposition-treatments with respect to structural and chemical properties of the resulting MOF films.

In the last years 2D materials have attracted a huge attention for spintronics thanks to the amazing properties that arise when thickness approaches the single layer level and thanks to the large number of functionalities that they offer. The recent introduction of 2D materials in magnetic tunnel junctions (2D-MTJs) offers very promising properties such as atomically defined interfaces, spin filtering, perpendicular anisotropy and spin-orbit torques modulation. Nevertheless, the difficult integration of exfoliated 2D materials in spintronic devices has limited so far their exploration and performances, maintaining experimental results still far from theoretical expectations [1]. Here, we will show successful fabrication of NiFe/MoS2/Co MTJs thanks to an in-situ fabrication process leading to the highest results reported so far for MTJs based on TMDCs 2D family [2]. Moreover, we will further discuss a path to alleviate fundamental technological and physics issues encountered for the integration of 2D-MTJs [2,3].

[1] (a) W. Wang et al, Nano Lett., 15, 5261, (2015); (b) A. Dankert et al., ACS Nano, 11, 6389, (2017). (c) W.C. Wong et al., IEEE Trans. Magn., 53, 1600205 (2017), K. Dolui et al., Phys. Rev. B, 90, 041401(R), (2014)
[2] M. Galbiati et al., Phys. Rev. Appl. 12, 044022, (2019).
[3] M. Galbiati et al., ACS Appl. Mater. Interfaces, 10, 30017 (2018).

Spintronics has opened a new paradigm through the use of the spin variable as the vector of information and has been largely applied from hard drives read-heads to the STT-MRAMs. While very recent, the introduction of 2D materials in Magnetic Tunnel Junctions (MTJs) has already shown some promising properties (atomic thickness control, diffusion barrier, spin filtering…)[1]. Graphene and the 2D insulator h-BN have been the first 2D materials to show strong impact on spin transport in MTJs. It was shown that strong spin filtering occurred with the creation of an insulating spin channel in metallic graphene and metallic channel in insulating h-BN[1][2]. The recent advent of the wide TMDC family of 2D semiconductors (MoS2, WS2…) opened new opportunities for further tailoring of spintronics properties.
Here, we will detail a protocol to fabricate spin valves based on CVD grown WS2, with step by step characterizations in support (Raman spectroscopy, photoluminescence, AFM measurements…) which aims at preserving interfaces spin properties by avoiding oxidations and degradations. The fabrication process is further validated by the measurements of magnetoresistance spin signals above state of the art for 2D semiconductors based MTJs. We then present experimental results on WS2 spin-filtering tunability with thickness that we discuss in light of its peculiar thickness band-structure evolution, with Density Functional Theory calculations in support. Our work opens the way to the integration of different members of the very large TMDCs family, in order to reveal their spin transport properties in MTJs[3][4].

[1] Review: Piquemal-Banci et al. J. Phys. D: Appl. Phys. 50, 203002 (2017).

[2] Piquemal-Banci et al. ACS Nano 12, 4712 (2018).

[3] Zatko et al. ACS Nano 12, 14468 (2019)

[4] Godel, Zatko et al. ACS Appl. Nano Mater. 3, 8, 7908 (2020)

Graphene's potential for spintronic applications has gained a lot of attention due to its gate tunability, high mobility and low intrinsic spin orbit coupling (SOC) strength. In recent works, researchers exploited these properties to propagate the electron spin up to 30 µm [1]. However, long communication distance is only one aspect in the search for spintronic related phenomena. Manipulating spin currents is essential to encode and process information in the spin degree of freedom. An interesting method to induce such a SOC in graphene is the controlled deposition of ad-particles [2].

Few atom clusters provide the ultimate control on the atomic scale. Gas phase clusters showcased a distinct atom-by-atom size dependence, dominated by quantum confinement effects in the electronic and structural properties. This leads to unique physico-chemical properties, such as magnetism made of atoms that form non-magnetic bulk metals [3] and metal-dielectric transitions that occur when adding a single atom [4].

Here we present the spin transport properties of cluster decorated graphene. It is found that Au$_3$ and Au$_6$ clusters deposited on graphene both reduce the spin lifetime compared to pristine graphene. However, at the same densities of deposited Au$_6$ and Au$_3$ clusters, the spin scattering rate due to the Au$_6$ cluster is significantly larger compared to Au$_3$, indicating the size-specific character of the cluster-graphene hybrid material.

[1] Z. M. Gebeyehu et al 2019 2D Mater. 6 034003

[2] K. Premasiri et al 2019 J. Phys.: Condens. Matter 31 193001

[3] A. J. Cox et al Phys. Rev. Lett. 1993 71 923–926

[4] B. Von Issendorff et al Annu. 2005 Rev. Phys. Chem. 56 549–580

Molecular spintronics involving spin-state switching in first-row transition-metal organic complexes has seen rapid progress in recent decades. In particular, molecular complexes hosting Fe, Co, Ni, or Mn ions can exhibit multiple spin-states depending on a subtle balance between molecular ligand field and Coulomb interaction. However, integration of such molecules into a spin-switch device remains a major challenge, mainly due to the poor reliability and reproducibility of how the molecule is contacted with metallic electrodes. Here, we propose a molecular-switch device with pure organic embedding, where iron-porphyrin bridges graphene nanoribbon electrodes that can potentially overcome these issues. Using density functional theory (DFT) and realistic many-body techniques combined with the Landauer-Büttiker formalism for transport properties, we explore the device under applied mechanical strain. We demonstrate a spin-crossover between low-spin (S=1) and high-spin (S=2) states, triggered at the experimentally feasible mechanical strain. We predict the change of the molecular spin state to toggle the current through the device by an order of magnitude.

We acknowledge financial support from the Science Foundation Ireland [19/EPSRC/3605] and the Engineering and Physical Sciences Research Council EP/S030263/1, European Research Council (Consolidator Grant No. 617196 CORRELMAT), SFI-EPSRC, Austrian Science Fund (FWF) through project ’LinReTraCe’ P 30213-N36 (JMT, AV) and project P 31631 (AV).

Atmospheric pressure plasma allows for the easy modification of materials surfaces for a wide range of technological applications. Coupling the aerosol injection of precursors with atmospheric pressure plasma largely extends the versatility of this kind of process; in fact solid and , in general, scarcely volatile precursors can be delivered to the plasma, extending the variety of chemical pathways to surface modification. Furthermore, labile bioactive molecule, that can be easily damaged in the reactive environment of plasma , when injected with aerosol are protected by a solvent shell. In this conditions, the deposition of drug containing coatings can be easily achieved, with application in the biomedical field as drug delivering systems, biosensing device and alike. Gentamicin, vancomycin and lysozyme containing films have been deposited preserving the antimicrobic activity. Such coatings show a release kinetic when immersed in water. Furthermore, it will be demonstrated that with a proper choice of aerosol solution and addition of ethylene as a source of the embedding matrix, unique core–shell nanocapsules can be obtained.

The macroscopic properties of the polymer are closely related to the morphology of the material. On the other hand, this morphology depends on the conditions used in the synthesis step. In our work, we present the results of morphological tests of polypyrrole deposited on the surface of a steel electrode and determine their influence on the properties of the obtained materials.

Industrial oil-containing wastewaters, derived from the petrochemical, pharmaceutical industries, etc., have become one of the wide-reaching environmental problems. Commonly conventional methods, such as in situ burning, etc., are used for the separation of oil from water. But high cost and low efficiency discourage the use of such conventional methods, especially for large-scale applications. Alternatively, hydrophobic/oleophilic absorbent materials have been developed for oil/water separation due to their low cost and ease of use. However, these materials mostly suffer from lack of good selectivity and recoverability. Therefore, there is a strong demand for oil/water-separation materials that can selectively absorb the oil whereas repel the water. One needs to combine surface topography and surface chemistry to achieve an extreme non-wetting regime. Recently, we have shown that metal and metal oxide micro/nanostructured surfaces can be used to tune wetting properties.[1,2]
In this current study, Ag microstructures were deposited on TiO2 thin film via photocatalytic reduction to create a unique surface topography composed of flower-like structures. These structures showed extremely superhydrophilic behaviour (Contact Angle CA ~0) due to the hydrophilic nature of TiO2. However, following the surface modification [ Polytetrafluoroethylene (PTFE), poly(1,3,5-Trivinyl-1,3,5-Trimethylcyclotrisiloxane) (p-V3D3)] via initiative chemical vapor deposition (iCVD), a superhydrophobic surface (CA > 155°) was achieved. Results showed that not only the iCVD layer, but also unique surface topography of Ag structures promoted the superhydrophobic behaviour. Furthermore, prepared surface exhibited high selectivity for the adsorption of the oil from the oil-water mixture. Especially p-V3D3 coated Ag-TiO2 surface may find application in self-cleaning, oil-water separation, etc., due to its high selectivity and stability under ultra-violet radiation.

[1] Appl. Surf. Sci. 2021, 537, 147795.

[2] Adv. Mater. Interfaces 2019, 6, 1801967.

Initiated chemical vapor deposition (iCVD) is a solvent-free, cost efficient technique to synthesize highly conformal organic thin films from the vapor phase. The underlying free radical polymerization happens directly on the material to be coated, without additional solvents or post-reactional treatment. In our work we present the highly controllable deposition of photoswitchable copolymers via iCVD, using a novel device for transportation of the solid chromophore inside the reactor chamber. Based on the underlying principle of iCVD, we were able to chemically modify the composition of the polymers which had a significant effect on the photoswitchability of the incorporated chromophore. Patterned polymer coatings, deposition on flexible substrates and writable surfaces were achieved, benefitting from the fact that the photoswitch used by us is excited by blue instead of UV-light. This advantage minimizes photodegradation of both substrate and functional coating.
Due to high controllability of the uniform film-formation, topography-preservation and manifold choice of potential substrates it is possible to equip surfaces with photoswitchable properties in the nano-range without losing the characteristic properties of the material.

Polarization-dependent sum-frequency generation (SFG) spectroscopy was applied to study the adsorption of carbon monoxide (CO) on the annealed and sputtered Ir(111) single crystal surfaces at various CO coverages [1]. Coverage was adjusted by varying the substrate temperature (300−575 K) and/or gas pressure (10−7 to 1.0 mbar). The cleanliness of Ir(111) was confirmed by Auger electron spectroscopy, and its long-range order and CO overlayer structures were characterized by low energy electron diffraction (LEED). With increasing coverage (gas pressure), molecularly adsorbed CO exhibited three overlayer structures: (√3×√3)𝑅30° →(2√3×2√3)𝑅30° →(3√3×3√3)𝑅30°. Under all conditions, only linearly bonded (on-top) CO was observed by SFG. Using different polarizations, PPP and SSP spectra were acquired with a high signal-to-noise ratio, whereby tilt angles of CO on Ir(111) could be determined for the first time by SFG. It was found that not only the vibrational frequency of on-top CO, but also the tilt angle was strongly coverage-dependent for CO on the annealed surface. The higher the coverage was, the larger the vibrational frequency and the tilt angle were. At about 0.7 ML coverage, a CO tilt angle of at least 20° was observed, in good agreement with density functional theory (DFT) calculations. In addition, the molecular hyperpolarizability ratio (R) of CO (at 0.13 ML in UHV) was determined to be 0.08. Based on the combined SFG/DFT results, it may change to 0.29 at 0.77 ML coverage. However, on the sputtered surface, CO preferred to stand upright with little coverage dependence. After heating to ~600 K in mbar CO pressure, LEED indicated disordered CO adsorption, but SFG showed red-shifted CO both on the annealed and sputtered surface, with reduced intensity. The irreversibility of SFG spectra may point to CO dissociation around 600 K.
[1] X. Li, G. Rupprechter, Catalysis Science & Technology, 11 (2021) 12.

Methanol has the potential to become an important energy vector. The so-called "methanol economy" is essentially a carbon-neutral cycle consisting of two groups of reactions: Methanol synthesis from a mixture of CO, CO2, and H2, and methanol-to-hydrogen conversion reaction. Latter includes methanol decomposition (or dry dehydrogenation), partial oxidation, steam reforming, and autothermal reforming. Cu-based materials are currently our best option as catalysts, and they are already used industrially in some of the above-mentioned reactions. This makes the interface between Cu and methanol vapor exceedingly important. Yet, only a handful of experimental mechanistic studies (at the molecular level), under realistic reaction conditions, are available in the literature. Herein, the interaction and decomposition of methanol on different copper surface orientations, Cu(111), Cu(100) and Cu(110), have been studied by means of PM-IRRAS and AP-XPS under 1 mbar methanol pressure in the temperature range of 25-100 °C. Our results reveal that methanol is dissociatively adsorbed on the clean Cu surfaces to form methoxy (CH3O*) and hydrogen at ambient conditions. The temporal evolution of infrared spectra with time indicates that a transient state of high-coverage methoxy layer forms immediately after methanol exposure. For achieving an equilibrium coverage, the methoxy excess is eliminated via a further dehydrogenation to CO and its desorption to the gas phase. The kinetics of this process, which involves the activation of C-H bonds, displays a significant structure sensitivity with a much faster kinetics on the corrugated Cu(110) compared to the close-packed surfaces of Cu(111) and Cu(100). We also propose a model that explains the origin of the initial metastable methoxy coverage by considering the previous step of molecular adsorption in the form of H-bonded assemblies.

Organic semiconductors are highly relevant materials concerning future electronic devices due to their advantageous properties like high charge injection ability. Thin layers of acenes on metals like copper or silver are discussed to induce complex electronic characteristics, depending on factors like substrate metal workfunction and molecule adsorbate electron affinity. In this study the growth and energy level alignment of the rod-like, long chain acene heptacene on a Cu(110) surface is evaluated. The impact on the charge transfer to this electron-acceptor molecule on the metal substrate is crucial. Our results show that the orientation of the 7A molecules can be controlled by the preparation conditions. This has also strong influence on the electronic properties. Photoemission tomography is used to investigate molecular geometries and assign specific emissions to molecule orbitals [1]. The findings are supported by other surface science techniques such as STM and LEED. Thermal cycloreversion of diheptacene isomers during evaporation produces highly oriented and epitaxial monolayers of heptacene on the metal surface. The molecules are oriented either along or perpendicular to the close-packed metal rows of Cu(110). Our combined experimental and computational results show that for heptacene oriented along the Cu rows, the lowest unoccupied molecular orbital (LUMO) and the LUMO+1 are occupied. The LUMO+1 receives no charge for molecules aligned perpendicular to the Cu rows. The possibility to tune the energy level alignment and charge transfer at organic-metal interfaces by means of adjustable molecular alignment is fully corroborated by our experiments and density functional calculations.

Acknowledgment
Financial support through FWF (FWF project number I 4145)

References
1. Hurdax, Philipp, et al. “Controlling the Electronic and Physical Coupling on Dielectric Thin Films.” Beilstein Journal of Nanotechnology, vol. 11, no. 1, 2020, pp. 1492–1503.

The ability to study the solid/liquid interface in situ is essential to gain fundamental understanding of electrochemical processes. A poor understanding of surface chemical processes at electrodes is a key bottleneck in the development of many energy technologies -e.g. alternative battery technologies or water splitting catalysts. X-Ray Photoelectron Spectroscopy (XPS) is one of the most powerful probes of surface chemistry available but addressing the electrode/electrolyte interface with XPS is a major technical challenge as it is buried by the electrode on one side and the electrolyte on the other - making detection of photoelectrons from this interface very difficult. There has been intense efforts to overcome these challenges by either establishing (electron-transparent) ultrathin wetting layers on sample surfaces (known as the “dip and pull” method) or by making ultrathin graphene electrodes through which the interface can be addressed.
I will present an alternative approach to establishing an ultrathin wetting layer on the sample surface, through which we can directly probe the electrode/electrolyte interface in-situ. We do this by introducing a droplet of electrolyte onto the sample, offset from the analysis area by a few millimetres. This “offset droplet” approach has the advantages of being applicable to virtually any sample, the capability to alter the solution composition dynamically and a short diffusion length from analysis area to the “bulk” droplet.
I will outline the capabilities and the challenges of this technique and present some results applying it to the study of model electrocatalysts and battery materials.

Tempering of nanostructured bainite has proven to be an excellent choice for components where requirements for enhance service properties at elevated temperatures are needed. Supporting secondary hardening by alloying Mo and V enables the possibilities to combine both effects: nanostructured matrix and secondary precipitation. Detailed characterization by dilatometry and phase analysis using XRD and in-situ XRD reveals and identifies the different tempering events occurring on these specially designed alloys, allowing for the identification of suitable temperatures regimes, where the nanostructured character of the ferritic matrix is maintained and V and/or Mo precipitates takes place, leading to better service properties at elevated temperatures.

This work will present on overview of the most relevant results obtained in a devoted Research Fund for Coal and Steel (RFCS) project, STEELSECO, where this concept has been explored and exploited. Covering from the steel and process design, the general secondary tempering behavior and a detailed discussion on the attained mechanical properties, with especial emphasis in fatigue properties (static and cyclic loading conditions). An attempt in establishing the correlation between the mentioned properties and the austenite stability will be also presented.

This research is funded by the Research Fund for Coal and Steel (RFCS) project, STEELSECO.

In this study, the thermal stability of bainitic ferrite and carbon-enriched retained austenite has been studied in in two steels containing 0.6 C (wt %) and microallowed with V and Mo. For this goal, a nanobaintic microstructure was developed in both steels by a thermal treatment consisting of austinitization at 1150°C for 180 s and a bainitic transformation at 250°C for 14h. High resolution temperature dilatometric studies consisting on heating cycles up to the Ac1 temperature or tempering treatments for 1h at temperatures ranging from 450 to 650°C showed a sequence of different decomposition events, that were characterized by both, X-ray diffraction and microstructural observations with the scanning electron microscope. The first event observed was associated to the precipitation of very fine cementite particles in the austenite thin films. For tempering temperatures higher than 500°C, it was identified another decomposition step in both steels, that was accompanied by a decrease on both, the austenite mass fraction and its lattice parameter. As the carbon content in this phase decreased, this transformation was associated to the precipitation of carbide particles in the retained austenite blocks. This process give raise to the formation of fresh martensite from this lower carbon austenite during cooling to room temperature after the tempering treatment. In the last tempering stages, the remaining austenite decomposes into ferrite and cementite, and due to carbide precipitation the bainitic ferrite loses its tetragonality, its dislocation density is reduced and the bainitic laths coarsen.
This research was funded by Research Fund for Coal and Steel, grant number RFCS-754070.

Tempering of martensitic steels is commonly employed to improve their ductility and increase their strength by secondary precipitation. The different phenomena which occur during tempering were intensively studied and are well established in such steels. Nano-bainitic steels represent a new class of alloys, whose microstructure consists of nano-structured bainite formed at low temperature with a high amount of austenite. This imparts simultaneously high ductility and high tensile strength to the steel. Recently it has been shown that adding secondary carbide forming elements such as V, Mo increases the resistance to softening and hence the properties at higher temperature. Investigating the secondary carbide precipitation inside a nano-bainitic structure is thus necessary to optimize the microstructure and the thermal treatments for this promising new class of steels.
The study aims to combine the mechanical properties resulting from the nano-bainite microstructure with secondary hardening precipitation as observed in martensite steels. One steel grade was chosen whose composition is based on previously investigated nano-bainitic steel (0.67C-1.5Si-1.7Cr-1.3Mn wt.%). Mo and V elements are added to further secondary carbide precipitation. In addition to the nano-bainite microstructure, two martensitic microstructures are also investigated.
The tempering of both martensites and nano-bainite microstructures are investigated in situ during the tempering by dilatometry, synchrotron XRD and ex situ by high resolution TEM. The global kinetics, the sequence of precipitation are established quantitatively, as well as the evolution of ferrite/martensite and austenite phase fractions and cell parameters. A nucleation and growth model with physical basis was used to predict the kinetics of precipitation as well as the particle densities, radii and matrix and carbides composition evolutions considering their interactions during the tempering treatments and give satisfactory results. The model allowed to interpret further the microstructure evolutions.

An important aspect of formability of Al sheet material in the automotive industry is the bendability without degradation of the surface quality. So far, microstructure, texture, the distribution of primary and secondary particles as well as these properties´ homogeneity over the sheet cross section are known as factors influencing the formability of Al-sheets. Recent studies for example evaluated bent EN-AW 6016 sheets and identified Copper and Brass as positive texture components which show a certain resistance against damage initiation via shear bands.
In the present study we include the analysis of microstructural features as primary- and secondary phases and the orientation- and position-dependent ability of the matrix to accommodate the external deformation. For this purpose, (partially interrupted) bending tests were performed on samples from the groups of 5xxx and 6xxx alloys after different processing parameters. Electron microscopic analyses including electron backscatter diffraction are utilized to identify the microstructural and texture changes during deformation. The analysis of deformation structure is comparatively straightforward, whereas the correct interpretation of a deformation-induced texture change is a more challenging aspect as the initial grain size is – especially in 6xxx alloys – large compared to the sheet thickness. Therefore, microstructure and texture can only together be correlated to the experimental bendability for identifying the most beneficial material properties.

The demands from industry and daily live have required the development of structural materials. For example, the heat-resistant Al alloys are expected for the improved performance at higher temperatures (≥300℃) due to their lower density and reasonable cost. However, the traditional heat-resistant Al alloys (i.e., Al-Si, Al-Cu) can only sustain at 250℃ currently, because the rapid diffusion of main reinforcement elements (Si, Cu) should cause the microstructure coarsening and related performance degrade. Therefore, the slowly diffused elements (i.e., Fe, Ni, etc.) are introduced to Al matrix to form eutectic Al alloys, which is considered to have higher potential for high temperature applications.
Typically, the Al-Fe-Ni eutectic alloy was characterized as Al matrix and Al9FeNi compound, and the Al matrix was strengthened by Al9FeNi eutectic frame by load transfer effect. Afterwards, the thermal exposure experiments exhibited that the alloy can maintain long-time stable at 400℃. Beside the load transfer provided by eutectic structure, the Al matrix was designed to be strengthened by thermally stable precipitates synergistically. Herein, the well-known thermal-stable precipitates (Al3Sc or Al3(Sc, Zr)) were introduced to eutectic matrix by the mirco-alloying strategy. Eventually, the alloy hardness was improved significantly by Al3Sc. Furthermore, the co-additions of Sc with Zr improved the alloy performance at 400℃, and the hardness can keep stable at 400℃.
Creep is the critical aspect to evaluate the high temperature mechanical performance of eutectic alloys. Experiments demonstrate that both threshold stress and load transfer effect can be induced by Al9FeNi to improve creep resistance. Furthermore, the Sc addition can improve both threshold stress and load transfer effect of the eutectic alloy, but the influence of Sc is varied with the temperature. Both analytical modeling and Finite Element Analysis methods are used to explain the underlying mechanisms.

The mechanical properties of commercial Al-Fe-Si alloys are influenced by the materials microstructure and microchemistry. In this work, the variation of alloying elements distribution, microstructure (e.g. grain size; dendritic arm spacing) and electrical conductivity across an AA 8079 DC-ingot were investigated. Furthermore, the effects of various experimental homogenization practices on the microchemistry of samples from edge and center of an ingot were analyzed. In particular, the evolution of phase volume fractions of constituents and dispersoids is discussed. This work shows, that a high-temperature, two-step homogenization practice results in larger dispersoids and decreased solute levels, which is expected to influence the materials later softening behavior.

Fragmentation of cube grains during rolling is of interest because their recrystallization advantage decreases when cube is misoriented at least 10 – 15° from its exact orientation. Thus, understanding evolution of cube in-grain microtexture and finding processing conditions promoting cube splitting into subdomains is of great importance.
The influence of crystallographic orientations of neighbor grains on the development of the in-grain microtexture of cube oriented crystals remains unresolved. Only one experimental study has been reported on plane strain compression (PSC) of cube aluminium single crystals “sandwiched” between two Brass-oriented or two Copper-oriented aluminium crystals. The purpose of this work is to assess the influence of different processing parameters (plane strain compression and shear loading conditions) and microstructure parameters (orientation of neighbor grains and of the initial cube misorientation) on in-grain microtexture evolution of cube.
Crystal plasticity simulations were performed using the freeware software package DAMASK considering different neighbor grain orientation sets (Brass, S, Copper and Goss) for cube grains and loading scenarios both in ideal plane strain compression (PSC) or with superimposed shear both, during cold and hot rolling. During hot-rolling, activity of non-octahedral slip systems was taken into account.
For hot-rolling, it was confirmed that non-octahedral slip systems stabilize cube orientation but this is affected by the orientations of the neighboring grains. More specific, when cube grains are surrounded by grains pertaining to the Brass component, they will undergo significant misorientation, while S oriented adjacent grains do not enhance the cube grain misorientation.
During cold rolling, the most effective orientations in misorienting cube grains turn out to be Brass and S. Superimposed shear loading is beneficial for cube splitting; however, for all neighboring orientations, the component F31 of deformation gradient has higher influence than F13 in promoting cube in-grain splitting.

Current state-of-the-art alloys that are used for turbine or high-temperature energy applications, are usually nickel-based (super)alloys. However, the use of these alloys has fundamental limitations such as their melting temperatures, their microstructure instability under irradiation or they limited corrosion resistance. Compositionally Complex Alloys (CCAs) represent a class of alloys that have shown promising properties in extreme environments, but their development is limited by the almost limitless compositional and phase space to explore. A comprehensive high-throughput platform has been developed to design CCAs resistant to extreme environment. Additive manufacturing via directed energy deposition was employed as a high-throughput technique to synthesize hundreds of CCAs. As an example, more than 100 compositions of FeCrMnNi system were synthesized in a week, exploring a vast portion of the composition space. Tight compositional control to within ±5 at% was achieved. Alloys are further heat treated in a high-throughput fashion (50 alloys at a time) which involved homogenization, followed by aging. At each temperature, the alloys were characterized by automated EDS and XRD, SEM imaging, and microhardness. These experiments were coupled with CALPHAD modeling to expand the thermodynamic databases. Novel high-temperature gas and molten salt corrosion, and ion irradiation high-throughput testing methods were designed to test corrosion and radiation resistance of CCAs. Examples of this high-throughput platform will be presented including development of NbMoTiTaAlCr CCAs for turbine applications, FeCrMnMoNi CCAs for structural materials in high-temperature molten salt energy systems, and FeCrMnNi and light/heavy refractory CCAs for advanced fast nuclear reactors applications.

The development of high entropy alloys (HEAs) and compositionally complex alloys (CCAs) have broadened the possibilities of alloy design by exploring wider regions of solid solubility. With an ever-increasing demand for high performance light weight alloys, the concepts developed within HEAs/CCAs is implemented into the design approach to alloys akin to the extensively used A357 alloy. Developing an alloy with an increase in the thermal stability or specific strength will give reductions in emissions within the transportation sectors, particularly within the aerospace industry. By utilising high throughput screening techniques, using the Al and HEA databases developed by Thermo-Calc, the solubility limit of elements currently used in Al-Si alloys is closely examined, as well as all available elements within the databases is further explored. Elements that were predicted to exhibit solid solubility with an Al-7Si (wt.%) alloy without precipitating additional phases was identified. A selection of alloys was designed and produced via conventional resistive heating, gravity casting and subsequent directional solidification containing varying additions of Mg, Zn, Ag, Li, Ga and Ti. The new alloys were microstructurally and mechanically characterised through SEM, EBSD, DSC, hardness and tensile testing at room and elevated (up to 200°C) temperatures. The newly developed alloys exhibited an increase in yield strength (up to 31%) over the base A357 at room temperature, and an improvement in ductility (up to 47%) at 200°C while still increasing the yield and tensile strength, without the introduction of new phases.

Stellite are Co-based alloys used as hardfacing materials of key moving-mechanisms in the primary circuit of pressurized water reactors. They exhibit a Co-Cr-rich matrix and W and Cr carbides that confer exceptional tribological properties under sliding wear conditions that no Ni- or Fe-based alloys have been able to replicate. Counterpart to Stellite efficiency is that 59Co fragments are generated under friction then activate under neutron irradiation in radioactive 60Co that increase workers exposure to radiative fluxes. Here, an alloy-design strategy based on a combination of Calphad calculations and hardness predictions and on experimental characterization was employed to find Complex Concentrated Alloys (CCA) to replace Stellite. Thermodynamic equilibrium calculations using Thermo-Calc and the TCHEA3 database were performed on the Cr-Fe-Mn-Ni alloy system to determine its single-phase solid-solutions at given temperatures. Then, five solid-solution strengthening models from the literature were represented in the “Cr20-Fe-Mn-Ni at 1100°C” pseudo-ternary system to identify elemental strengthening tendencies. Compositions were selected based on their predicted hardness, produced by arc-melting, cold-rolled and heat-treated to produce recrystallized microstructures. Grain growth, tensile and Vickers hardness tests were performed to determine the intrinsic yield strength by Hall-Petch equation. Microstructural characterizations such as X-ray diffraction, BSE and chemical analysis of main and minor elements were performed (resp. ICP and GDMS). The models accuracy was evaluated to assess a more precise and reliable solid-solution strengthening forecast in the single-phased region of the Cr-Fe-Mn-Ni alloy system. Most interesting compositions were selected as “matrix” for the second step of the alloy-design strategy where carbides precipitation was studied. Ternary diagrams were drawn out of solidification microstructures following Scheil calculations, which edges are the “matrix”, the substitutional (ex: W) and the interstitial (ex: C) elements. Therefore, the nature and fraction of carbides are estimated for further alloy synthesis, which should allow determining the prediction accuracy.

Material requirements in harsh nuclear environment are highly demanding. Structural materials in nuclear reactor fixtures require a good combination of high-strength, corrosion and irradiation resistance up to about 350°C. “High entropy matrix” alloys are suspected to bring an improved resistance to irradiation damage. In the purpose of identification of novel alloys from this group that address the demands, fast conception is set up using computational techniques, relying on combinatorial exploration and optimization, as well as on predictive models that co-relate composition, structure and properties. The models employed come from a mix of common approaches like computational thermodynamics using the CALculation of PHAse Diagrams (CALPHAD) method, simple regressions (physical/empirical), machine-learning/data-mining models or a combination of some/all of them. Some of the various combinatorial methods that are utilized are discussed.[1]
In conventional Ni alloys, γ + γ’ based microstructures are commonly found, therefore structure-property relationship can be based on them. Hence, a strategy of designing γ’ reinforced alloys was first framed. Multi-objective genetic algorithm optimisations were set up on Ni-Cr-Fe-Mn-Mo-Nb-W-Al-Ti system, using the predictive models developed. Several alloys were hand-picked for fabrication and experimental exploration, from a set of Pareto-optimal alloys. Their preliminary experimental characterisation is also presented.
However, the so-designed, Pareto-optimal alloys, present a moderate configurational entropy. A systematic CALPHAD exploration of γ + γ’ dual phase region of the alloy system Ni-Cr-Fe-Mn-Al-Ti indicates that the conception of CCAs in this phase region is thermodynamically restricted. An outlook into alternative strategies of different reinforcing phases and strengthening mechanisms to design Co-free CCAs is therefore also examined.
References: [1] D. Ram, A. Fraczkiewicz, and F. Tancret, ‘Development of predictive models for multi-objective optimization in the design of high-entropy super alloys’, presented at the Journées Annuelles du GDR HEA, 17 november.

An integrated framework for deformation modeling has been developed, which combines a physical state parameter-based formulation for microstructure evolution during plastic deformation processes with constitutive creep models of polycrystalline materials. The implementations of power law, Coble, Nabarro–Herring and Harper–Dorn creep and grain boundary sliding are described and their contributions to the entire stress response at a virtual applied strain rate are discussed. The effective diffusion coefficient is considered, which includes trapping of vacancies at solute atoms, excess vacancies, and dislocation pipe diffusion as inherent diffusion mechanisms. In contrast to constitutive correlations between stress and strain, physical effects, such as precipitation hardening, solid solution hardening and cross core diffusion effects can conveniently be included into these models by the mechanical threshold concept, to ensure a realistic reflection of the material behavior during even complex thermo-mechanical processing. The combination of thermally activated stress contributions and the athermal stress contribution from dislocation hardening allows simulating the stress-strain relations over a wide range of temperatures and strain rates. The present framework simultaneously allows calculating the plastic deformation under prescribed strain rate or constant stress, as well as stress relaxation after preceding stress or strain loading. In this presentation, the theoretical background of the underlying physical models of microstructure evolution are reviewed and exemplary stress calculations at a strain rate range of many orders of magnitude are presented.

The development of aeroengines with higher thermal efficiencies, has been facilitated by the advance in materials, notably the development of thermal barrier coatings and their testing techniques. The Small Punch Test (SPT) is a vastly used material test in industry, that is implemented to characterise mechanical behaviour of materials that are in a limited supply, such as thermal barrier coatings present on gas turbine blades.
However, after over 30 years of use in industry, the procedure still does not have a code of practice available and there remains dispute about the reliability of its results. This work therefore investigates the ability of the SPT to measure material mechanical properties. The material studied is CoNiCrAlY which is a bond coat in thermal barrier coatings. The work is undertaken by firstly conducting a sensitivity analysis of the Young’s Modulus (E) and Poisson Ratio (v) of CoNiCrAlY, to changes in the elastic properties of its β-NiAl phase. By creating a Representative Volume Element (RVE) of CoNiCrAlY, the impact of varying the elastic constant of its body-centred cubic β-NiAl phase on its E and v, is determined. Here the RVEs are used to model the polycrystalline microstructure of CoNiCrAlY whilst the elastic constants are responsible for defining the elasticity matrix of the cubic crystals present in the β-NiAl phase. Subsequently a finite element model of the SPT of CoNiCrAlY is constructed, using material properties obtained from the sensitivity analysis. The elastic and elastic-plastic results of the material are analysed based on the impact of several factors which are its yield stress, Young’s modulus and the friction between contacting surfaces in the SPT model. Finally, the results from the investigation are analysed to ascertain whether the SPT results are sensitive to changes in material properties of the material being tested or are more influenced by other factors such test parameters of the SPT.

This paper deals with ductile damage nonlocal modelling of semi-crystalline polyamides using state regularized formulation towards capturing ductile damage localization (softening) while overcoming spurious mesh sensitivity in the predictive numerical simulation. The mechanical behavior is simulated through a viscoelastic viscoplastic ductile damage model (VEVPD), from which the constitutive laws are derived within an extended thermodynamic framework combining both nonlocal viscoplastic and nonlocal damage internal variables. Typical local models often suffer from mesh dependency and non-physical solutions due to ill-posed differential equations in confronting with the model bifurcation limit. This research proposes a nonlocal gradient enhanced model aimed at capturing the material behavior at high damage levels, in which local models lead to instabilities. To this end, a gradient enhanced free energy is introduced into the thermodynamic framework, and the state variables are regularized through the interaction with their nonlocal counterpart. The model is developed as a UMAT subroutine based on a return-mapping algorithm, which updates stress, state variables, and the associated tangent moduli at each time step. The model is firstly investigated based on the nonlocal scalar damage variable and then is compared with the case that the nonlocal variable is derived from the plastic deformation. Finally, the capabilities of the developed numerical approach are examined via a set of representative examples under uniaxial monotonic strain-controlled tension. A parametric study is performed in order to evaluate the effectiveness of the method on the mesh objectivity and the regularization of the local variables in the softening zone. It is shown that the ductile damage localization and mesh insensitivity are evidenced more efficiently when the nonlocal variable is derived from the plastic strain rather than from the scalar damage variable. The current model is developed under small deformation assumption towards combining it with multiscale approaches for composites.

Electrodeposited chromium coatings exhibit high hardness, good wear resistance and corrosion resistance . Development of electrodeposited trivalent chromium coating Cr(III) baths becomes a new challenge for replacing the conventional Cr(VI) baths due to the hazardous character of hexavalent chromium salts. Several Cr(III) electrolytes were developed in the past , but the optimization of the electrodeposited coatings is required with a better understanding of their growth mechanisms and microstructure. This work is one of the objectives of the CRONOS 2024 project which focus on the optimization of the metallurgical state and properties of electrodeposited chromium produced from the trivalent chromium bath.
The organic species in the bath required for the electrodeposition and the co-deposition of hydroxides due to local pH variations near the cathode interface may induce high impurities concentrations in the deposits, mainly hydrogen, oxygen and carbon. Hot extraction analysis was carried out to evaluate the chemical composition of the deposits, confirm this contamination. In comparison with Cr(VI) deposits, the Cr(III) deposits are highly contaminated by H, O and C impurities. Several experimental analyses were performed in order to characterize the microstructure of Cr(III) deposits. XRD and TEM analysis revealed that the as-deposited Cr(III) is mostly amorphous. This amorphization is probably linked to the incorporation of high amounts of impurities during the electrodeposition. The origin and the localization of impurities incorporated in the coating are not well explained to date. In order to evaluate the individual contributions of impurities on the amorphization of the deposit, evolution of the impurities content and microstructure versus thermal treatments were studied by using different techniques namely DSC, in situ-TEM, micro-hardness and hot extraction analysis. This multi-scale approach can help to a better understanding of the amorphous structure of the as-deposited Cr(III) coating and it stability.

Alternative barrier layers have been considered to replace Ta/TaN, such as Ru and Co-based binary systems, e.g. Ru W, Ru-Mn, and Co W, in Cu interconnect metallization. The Co-W system is an interesting candidate to novel barrier materials due to its electrical and thermal properties. Co-W can function as both, the diffusion barrier and the seed layer whereon Cu can be directly electroplated, but this is a frankly unaddressed topic. This work consists of an introductory approach to the Cu electrocrystallization on top of Co W thin films using acidic electroplating baths, focusing on the initial stages of electrodeposit formation. Cu was directly electrodeposited (ED) on Co-W(PVD)/SiO2/Si substrates using a conventional acidic electrolyte, by direct and pulsed current. Co-W and Cu films were characterized by SEM/EDS, AFM, XPS and optical microscopy. The results show that the acidic nature of the solutions dissolves the Co-W substrate, but particularly Co is dissolved quicker than W. Through this mechanism, the nucleation of Cu decreases over time, rendering incomplete/discontinuous substrate coverage. A balance between Cu nucleation and substrate dissolution dictates the final soundness and compactness of the Cu films, which can be improved by decreasing substrate dissolution rate, using less aggressive/acidic solutions of pH 3.5.

The present work focuses on the fabrication and characterization of hard anodizing (HA) and plasma electrolytic oxidation (PEO) coatings on an Al10Si1Mg alloy manufactured via direct metal laser sintering (DMLS). The coatings were fabricated on both XY and XZ directions of the DMLS alloy. A A361 cast alloy was also treated for comparison. The hardness (H) and elastic modulus (E) of the coatings was measured by nanoindentation and the wear resistance was evaluated via reciprocating sliding tests.
The DMLS alloy presented microstructural anisotropy in the XY and XZ planes according to the direction of the Melt Pools (MP) formed along the laser path. The microstructure within the MP consisted on α-Al cells embedded in a fine 3D Si-network, which became coarser at the MPBs. HA and PEO coatings fabricated on both XY and XZ direction of the AM alloy were found to be more homogeneous in terms of morphology, thickness and composition than the coatings on the cast alloy. Crystalline SiO2 was formed in both HA and PEO coatings on the AM alloy probably due to the fine homogeneous distribution of Si. The estimated wear rates (Wr) were 1 and 2 orders of magnitude lower than the ones of the bare substrates for the HA and PEO coatings, respectively. On the other hand, AM-coated samples presented higher Wr than the A361-coated samples, as well as having certain mechanical anisotropy.
These results indicated that the fine 3D Si-network might compromise the mechanical response of the coatings fabricated via HA and PEO on the AM Al10Si1Mg alloy.

Motor neuron diseases like Parkinson’s can induce severe tremors in later stages, which seriously impair the daily life of elderly patients, particularly when drug-based treatments have ceased to work. A possible way to improve the patients’ quality of life is deep brain stimulation (DBS) treatments. Here, platinum neural electrodes are implanted into the brain, providing electric pulses to stimulate the subthalamic nucleus (STN) and in turn tune neuronal activity. Even though this treatment is routinely applied in clinical practice, difficulties such as low stimulation efficiency and reduced battery capacity of the pulse generator due to the increase of impedance over time between electrode tip and brain tissue occur.

Here we show that the impedance of neural electrodes can be significantly reduced in case their surface area is increased by sub-monolayer deposition of ligand-free laser-fabricated platinum nanoparticles (PtNPs). The coating of 3D electrode surfaces is done using electrophoretic deposition (EPD) in a custom-designed chamber with a field strength of 5 V/cm and a platinum mass concentration of 100 µg/ml. We compared the impact of DC (5 min) and pulsed-DC EPD (period of 1 µs and a duty cycle of 50%, 10 min) on stimulation conditions. Our findings reveal that the pulsed-DC coating procedure yields a more homogeneous surface coating and also the impedance is significantly reduced in contrast to the uncoated controls, an effect which could not be observed for DC-EPD in our previous works. In consecutive studies, the coated electrodes will undergo long term in vitro stimulations in saline solutions and in vivo stimulations in rat models and the influence of DC and pulsed DC electric fields on their functionality will be evaluated.

Additively manufactured (AM) porous metal and polymer materials were coated using thermal and plasma-enhanced (PE) Atomic Layer deposition (ALD). Structures were plates, lattice cells with a mesh size between 0.5 and 1.5 mm and random porous with a pore size between 1 and 2 mm. Applied AM methods were laser-beam powder-bed fusion (LB-PBF), material extrusion bonded by thermal reaction (MEX-TRB, fused deposition modelling, FDM) and material jet modelling with curing by ultraviolet light exposure (MJM-UV). The structures were printed from stainless steel 316L and titanium alloy Ti-6Al-7Nb powder, ULTEM 1010 biocompatible thermoplastic filament and MED610 acrylic resin (Stratasys Ltd.). Titanium oxide, zinc oxide and zirconium oxide coatings with a film thickness between 13 and 43 nm (measured on (100) silicon wafers) were applied on the structures by thermal and PE-ALD.
Film thickness, structure, chemical composition and homogeneity were characterized by numerous methods including stylus profilometry, atomic force microscopy (AFM), X-ray fluorescence (XRF), X-ray reflection and diffraction (XRR, XRD), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry, Raman spectroscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX).
The oxide coatings could be deposited on the surface and internal parts of 3D-printed substrates, on and in high aspect ratios and porous and mesh structures. However, delaminated coating fragments, and relatively high titanium and zinc concentration ranges suggests lower adhesion energies for coatings on the polymeric substrates. This could be explained by substrate dependent growth mechanisms, forming stronger chemical and weaker physical bonding and mixtures of both. Potential applications of these coatings are for example improvement of biological responses for implants or improved efficiency in fuel cells for power production.

Selective Laser Melting (SLM) has attracted major interest among the Additive Manufacturing methods (AM). SLM can deliver high manufacturing quality by adjusting production parameters on a given alloy which impacts on the grain structure, phase formation, microstructure, roughness, and porosity. AM aims to achieve superior or even comparable properties to the conventionally manufactured parts. Among the metallurgical features, surface integrity characteristics such as distorted subsurface microstructure and roughness primarily determine the functional life, especially in corrosive environments.
The present study involves the 18Ni-C300 Μaraging steel, an alloy with high strength and toughness and compares its behavior in fatigue resistance depending on the manufacturing method. Τhe comparison is made between conventionally manufactured specimens from a rolled bar and different post-treated SLM-fabricated specimens of the same geometry. The post-treatments refer to surface polishing, shot peening and heating. Experiments were performed in corrosion free and in 3.5% wt. NaCl aqueous solution. Metallography, microscopy (optical and electron), surface scanning, finite element analysis and hardness measurements were employed to help explain the results obtained. The rolled material show a both under pure fatigue and corrosion-fatigue, because of its dense and homogeneous microstructure, as well as its lower resulting surface roughness compared to the SLM. The “as received” SLM specimens, due to the distorted microstructure, but primarily to the higher roughness, showed an inferior fatigue and corrosion-fatigue performance which, however, improves with combination of shot peening and polishing in neutral environment. On the contrary, residual stresses imposed by shot peening have a negative impact on a corrosive environment. Heat treatment does not seem to have a positive effect in high stress fatigue life, however, increases the fatigue endurance limit.

Although laser based powder bed fusion (LB-PBF) is a prominent additive manufacturing technique, the number of alloys that have been approved for the process remains limited. This is especially true for iron-based alloys such as low-alloy steels, where the high carbon contents of said alloys can promote cold cracking defects. In other carbon-containing iron-based alloys, preheating of the build plate has proven to be an effective mitigation strategy. However, the understanding of how build plate preheating affects LB-PBF of low-alloy steels remains limited. This study details the influence of build plate preheating (at 25˚C, 100˚C & 180˚C) on the printability of 4140, 4340 and 8620 low-alloy steels. Said study was carried out using pre-alloyed, gas atomized powder that was subsequently LB-PBF processed using an EOS M290 machine. The influence of build plate preheating on crack formation was characterized. Results indicate that increasing the volumetric energy density (VED) and/or the build plate preheating could effectively mitigate crack formation in alloys with carbon contents ≥0.4 wt.%. Increasing the preheating temperature also increased the VED range of crack-free specimens, as it lowered the minimum VED that was required to avoid cold cracking defects. Based on the obtained data, robust processing windows for all studied alloys could be established that produced high-density (>99.8%), crack-free components.

Laser Powder bed fusion (L-PBF) has attracted a lot of interest in recent years, not only for its profound advantage of producing metallic components of complex geometries but also for the possibility of manipulating microstructures and crystallographic textures. Additionally, recent observations on wrought austenitic steels have revealed the strong dependence of the transformation induced plasticity (TRIP) effect in metastable stainless steels on the crystallographic texture. [1]–[3] Taking the aforementioned observations into consideration we employed a 304L steel, processed by L-PBF, in order to produce differently textured specimens. Uniaxial tension and compression tests, paired with in-situ neutron diffraction, enabled the monitoring of the microstructural evolution during deformation. The present study highlights how different microstructures, produced by L-PBF, lead to different deformation behavior in austenitic stainless steels and paves the way for tailored microstructures in different types of steels and for studies under different loading conditions.
Bibliography
[1] E. Polatidis et al., “The interplay between deformation mechanisms in austenitic 304 steel during uniaxial and equibiaxial loading,” 2019, doi: 10.1016/j.msea.2019.138222.
[2] E. Polatidis et al., “Suppressed martensitic transformation under biaxial loading in low stacking fault energy metastable austenitic steels,” Scr. Mater., vol. 147, pp. 27–32, Apr. 2018, doi: 10.1016/j.scriptamat.2017.12.026.
[3] E. Polatidis, J. Čapek, A. Arabi-Hashemi, C. Leinenbach, and M. Strobl, “High ductility and transformation-induced-plasticity in metastable stainless steel processed by selective laser melting with low power,” Scr. Mater., vol. 176, pp. 53–57, Feb. 2020, doi: 10.1016/j.scriptamat.2019.09.035.

Laser based powder bed fusion (PBF-LB) of metals enables the fabrication of geometrically complex structures, which are difficult or impossible to manufacture with conventional subtractive processing methods. Therefore, economic advantages in terms of enhanced cutting velocities can be facilitated by implementing internal cooling channels in drills or milling cutters made of tool steel. However, this microwelding process is restricted to small batch sizes for special applications as a consequence of low build-up rates. Additionally, severe cracking of these high-alloyed tool steels may occur due to a combination of process-related stresses and a susceptible material class.
The aim of this work is to illuminate the crack initiation and growth mechanism in a 0.85C-4.25Cr-2.46W-2.72Mo-2.01V-4.35Co (weight%) tool steel with extremely fine microstructure manufactured by the PBF-LB process. Primarily, multiscale correlations of process-related residual stresses and individual microstructural constituents, both formed as a result of rapid cooling during the fabrication process, were investigated using high-resolution techniques. Scanning and transmission electron microscopies were used to analyze the morphology of crack surfaces and their immediate proximity. These reveal dendritic structures on the surfaces and also crack branching according to a connected dendrite network, which was formed during rapid solidification. In order to investigate the chemical composition of microstructural features determining the crack formation, atom probe tomography measurements are performed. The spatial occurrence of particular cracks was correlated with residual stress concentrations and relaxations evaluated using synchrotron X-ray diffraction. The findings show accumulations of tensile stresses at the sample edges, which obviously promotes the crack initiation and growth.

In practice, the frequently used technique for removing dissolved hydrogen and solid impurities from aluminium melt is blowing of inert gas. The process of aluminium refining by blowing inert gas can be performed in ladle reactors. The efficiency of refining process can be influenced by relevant boundary parameters of the degassing process. The presented paper deals with the use of numerical and physical modelling of the degassing process of aluminium melt in ladle by blowing inert gas through a rotating impeller. The main aim of modelling was to achieve insight into the effect of relevant parameters, such as rotary impeller speeds/ flow rate of inert gas / impeller variant and distance of the impeller from the bottom of the refining ladle, on the removal of dissolved gas during refining. The numerical modelling was done in CFD programme ANSYS Fluent. For the purposes of physical modelling, a plexiglass model in a scale of 1:1 is used for the operating ladle. Based on the results obtained from modelling, the main findings and recommendation for optimal conditions of refining process were formulated.

Increasing interest in ICME for various steps of materials development has led to the development of various tools targeting different aspects of the Process-Structure-Property-Performance chain. When modelling Process-Structure relations of steel, the process-related details of steelmaking which influence the presence of impurities and cleanliness of the alloy are often neglected. Traditionally FEM and CFD based approaches have been utilized to understand the heat and mass transfer during steelmaking, but direct links to the underlying thermodynamics and reaction kinetics have been lacking. Recent advances in modelling capabilities, including CALPHAD-based thermodynamic and kinetic calculations within Thermo-Calc’s process metallurgy module allow for a streamlined integration of predictive calculations of typical steelmaking related challenges. Here, we provide an overview of the newly developed process metallurgy module and showcase how it can be utilized in an ICME framework to accelerate and reduce the up-front risks of development and up-scaling of new steels and steelmaking recipes.

Aluminum refining is a necessary technological stage of obtaining aluminum, both primary and secondary. Currently, refining is widely used by blowing liquid metal with an inert gas using a rotor terminated with a impeller that generates fine gas bubbles which, when introduced into the bath, bring up to the surface hydrogen and non-metallic inclusions. The paper presents the results of mathematical modeling with the use of the Engh and Sigworth equation. The optimal time of refining was calculated and it was found whether the process was determined by diffusion. The further stage of research includes tests of selected impellers on a physical model in order to select the optimal processing parameters. RTD curves were determined. The results of physical modeling were verified by numerical simulations conducted for the same process conditions: gas flow rate 5-25 l/min and rotor speed 200-600 rpm.

A comprehensive model of the steel tapping process addressing the reactions in the ladle is proposed. In the model, thermodynamic equilibrium calculations are performed using thermodynamic library—ChemApp. The effective equilibrium reaction zone (EERZ) method is applied to describe the steel/slag interfacial reaction. Most of the activities, such as the additions of ferroalloys and slag formers, carryover slag entrapment and air pick-up, are included. The model is calibrated by comparing the predicted compositions of the steel and slag with the measurements from a total of 10 heats from two plants. The composition developments of the steel, slag and inclusions can be tracked using the model. The influence of the amount of carryover slag is studied using the calibrated model.

The aim of the work is to get insight into the gas-metal-slag interactions in a bath smelting reactor, and in the settler of the flash smelting furnace (FSF). In both processes, it is important to find ways to enhance slag-metal reactions and separation by improving gas agitation and/or by finding ways to enhance droplet coalescence and, thus, settling and separation. Computational Fluid Dynamics (CFD) modelling towards a scaled down bottom blown copper smelting furnace (SKS furnace) with different tuyere arrangements have been conducted with the Multi-Fluid VOF model. Also, droplet settling through slag in the FSF settler was modelled with CFD-DEM (Discrete Element Method) coupling with a user-defined sub-model for including effects of coalescence and slag-matte reactions.

In the bottom blown copper smelting furnace (SKS furnace), tuyeres installed at each side of the furnace would help to strengthen the agitation. The distance between two line of tuyeres should be limited in a certain range to balance the requirement of better agitation efficiency and less impact on the refractory. It is also noticed that the impact on the side wall mainly comes from the surface wave. Based on the current work, modified SKS furnace structure with new tuyere arrangements can be constructed and simulated. The Multi-Fluid VOF model was found to have a good performance on the simulation of the macroscopic flow field in the submerged gas blowing system.

CFD-DEM gives ability to simulate individual droplets and their behaviour. Additional user-defined models increase accuracy of simulations and a new model can simulate constant changes of droplet properties, as slag and matte compositions would have some local variance in the slag layer. Also, due to high demand of computational resources, the CFD-DEM simulations had to be significantly scaled down and be more focused towards individual properties instead of simulating an industrial process.

During an alloy Additive Manufacturing (AM) process, just after the melting of feedstock, the molten material undergoes melt-pool dynamics and rapidly solidifies (typically, within a few milliseconds). Then, for the remaining build time, it undergoes multiple heating-cooling cycles in the solid-state, i.e. Solid-State Thermal Cycling (SSTC) or intrinsic heat treatment, at varying temperature amplitudes and rates. The thermo-mechanical driving forces during SSTC can trigger a plethora of mechanisms such as dislocation dynamics and defect interactions, precipitation, micro-segregation, solid-state phase transformation, recrystallization, grain growth, etc., which manifest as microstructural changes in the form of texture evolution, grain morphology, grain boundary evolution, low-angle grain boundary formation, etc.

A Scanning Electron Microscope (SEM) is well suited to probe polycrystalline microstructures and extract information on features such as texture, grain morphology, high and low grain boundaries, etc. However, it is impractical to probe microstructural evolution during an additive manufacturing process inside a scanning electron microscope. As an alternative, instead of probing microstructure evolution during an AM process, we propose to subject pre-built AM samples to SSTC under controlled conditions inside an SEM.

To that end, with support from the ERC Starting Grant project GAMMA (ID: 946959), a novel and (at the time of the writing of this abstract) unique coupling between a Continuous-Wave fiber Laser and an environmental-SEM (CWLaser-SEM coupling) has been implemented. In this talk, the details of the design of this CWLaser-SEM coupling and its operation will be presented first. Then, the results of a series of in-situ SSTC experiments performed on a stainless steel using this CWLaser-SEM coupling will be presented; the SSTC will be similar to that occur during an AM process.

Alloy Additive Manufacturing (AM) results in the formation of metastable hierarchical microstructures due to the highly non-equilibrium processes that occur during fabrication. Currently, most experimental/modeling efforts are aimed at studying the role of melt-pool dynamics and rapid solidification on the microstructure formation during AM. We are interested in studying the microstructure evolution occurring after solidification and until the end of the AM process, i.e. the long period during which the solid material is subjected to multiple heating-cooling cycles, called Solid-State Thermal Cycling (SSTC) or intrinsic heat treatment. During SSTC, a plethora of mechanisms could occur such as dislocation dynamics and defect interactions, precipitation, micro-segregation, solid-state phase transformation, recrystallization, grain growth, etc., which can result in a significant evolution of the microstructure, which can affect the mechanical properties of the AM parts.

Microstructure characterization is typically performed via techniques such as electron microscopy. However, it is impractical to probe microstructure evolution due to SSTC during AM via such conventional techniques. As an alternative, instead of probing microstructure evolution during AM, we propose to subject pre-built AM samples to SSTC under controlled conditions, in this case, inside a Transmission Electron Microscope (TEM).

In this work, an investigation of the precipitate microstructure in a 316L Stainless Steel (316L SS) manufactured via Laser Metal Deposition (LMD), a Directed Energy Deposition (DED)-type process, is reported. In situ high-resolution TEM SSTC experiments were conducted on thin film lamellae extracted from the LMD 316L SS. Results show that oxide and non-oxide precipitates can form due to the LMD process, where the material can be subjected to cooling rates as high as ~1e4 – 1e5 K/s. When the lamellae are subjected to SSTC inside TEM, both type of precipitates exhibit evolution in size, morphology and number.

Light alloys based on aluminum are an exceptionally versatile class of materials. They combine low weight and corrosion resistance with adjustable material properties, tunable by alloying with other materials or by subjecting them to accurately defined temperature treatments.
A popular approach is the strengthening of alloys formed from aluminum and copper by age- or precipitation hardening: Performing a careful series of temperature steps triggers the deliberate formation of a certain type of precipitate, yielding a material with defined hardness.
During this artificial ageing process, the supersaturated crystal starts to form small precipitates with a diameter of only several nanometers. When the procedure continues, they start to grow, forming different and larger types of precipitates, with massive impact on material properties.(1)

Commonly, investigations of precipitation processes rely on macroscopic mechanical testing and microscopic investigations of samples taken at various stages of the procedure. In situ TEM methods can be a valuable contribution for this field, since they provide immediate insight in the relevant processes on an atomic level while they are happening.(2)

In this study, we use in situ STEM for the investigation of nano- and microscale effects of temperature treatment on AlCu4. We directly capture growth and decay of the precipitates during various stages of the heating experiment, as illustrated in Figure1. Concomitant analytical investigation with EDS and EELS allows for in-depth “live” visualization of phase separation dynamics.
This high-resolution approach provides novel insights into precipitation processes in aluminum alloys, adding a new perspective for material development and optimization.

(1) Ashby et al, Engineering Materials, Vol2, 2nd Edition (1998) 100-112

(2) Lui et al, Scientific Reports, 7 (2017) 2184

The rise of in situ and in operando techniques for experiments in transmission electron microscopes has opened the door to powerful high-resolution analyses of dynamic processes at the nanoscale. To interpret the results, but also to be able to extrapolate and correlate them to macroscopic properties of a studied material, a precise knowledge of the experimental conditions is crucial. Temperature has a major influence on all dynamic processes, but even when defined by the in situ system, the actual value could vary at different locations of the sample. In experiments involving bias or mechanical loading, heat could be generated locally and critically affect the response of the sample. In addition, the temperature calibration of in situ instruments may deteriorate during sample preparation, potentially adding to measurement uncertainty. Consequently, there is an urgent need for approaches for both temperature measurement with high spatial resolution and system temperature verification. Ideally, these would be suitable for in operando performance testing during a TEM in situ experiment.

Methods for such reliability measurements, like electron diffraction [1], electron energy loss spectroscopy (EELS) [2] or Raman spectroscopy are well established and applicable for different classes of materials. However, previous work incorporates either high-end microscopes or special equipment. We therefore determined the accuracy of temperature measurements through the thermal expansion of Au and Ag nanoparticle “thermometers”, using a mainstream, two-condenser lens TEM with a LaB6 gun, a one-megapixel camera and a precise evaluation algorithm to translate the recorded diffraction images into temperature values. We present the challenges in verifying the system temperature during an everyday in situ TEM experiment and a way to accomplish it for most sample types nonetheless.

[1] F Niekiel et al., Ultramicroscopy, 176 (2017) 161–169

[2] BK Miller et al., Microscopy and Microanalysis, 24(S1) (2018) 1924–1925

95% of non-ferrous/ferrous metals and alloys are processed by strip rolling, arguably the most important metal forming process. Various models have been developed to optimize the multi-pass deformation process, yet further model advancement requires direct, accurate in-situ measurement of the full deformation and strain fields of the strip between the rolls. Standard (Local) DIC algorithms fail at this task, due to the harsh environment (oil, vibrations), high material velocity, challenging imaging conditions (obstructed viewing angle and field of view), unavoidable light reflections, and poor Digital Image Correlation (DIC) speckle pattern.

Therefore, building on our long-standing experience in developing advanced Global and Integrated DIC frameworks (e.g., Neggers et al. IJNME, 2016; Kleinendorst et al. CMAME, 2019), we derived (in a consistent mathematical setting) a novel Integrated DIC framework that fully exploits the knowledge of continuous, recurring material motion during strip rolling. High robustness against the above-mentioned challenges as well as high strain accuracy is achieved by simultaneous correlation of many (e.g. 200) image pairs, each correlated with the same average global displacement field but multiplied with a separate velocity multiplicator to account for (slight) differences in material velocity between image pairs.

The potential of the IDIC framework for recurring material motion is successfully demonstrated on two very different strip rolling experiments (operated at various settings), by unraveling subtle changes in the deformation and strain fields due to variations in pre-deformation, elastic recovery, and geometrical irregularities. Interestingly, these high-fidelity full-field results revealed that the residual stresses, which result from plastic bending on guiding rolls used to bring the strip to the pass line, cause asymmetric feeding of the strip into the mill, thereby altering the lubrication condition of the top/bottom strip surface.

Diamond foils are known to be exceptionally strong yet brittle. One approach to make ceramic foils less susceptible to brittle fracture is to introduce interfaces into the material that provide pathways for crack deflection. In this study, we were able to produce strong yet tough diamond/metal laminates (DMLs) with an outstanding performance from freestanding diamond foils using a brazing process with an active AgTi braze. The mechanic response was characterized via three-point bending (3PB) where the laminates exhibit a stepwise fracture behavior. Crack deflection at the interface induces toughening in the laminates. The diamond/metal laminates exhibit with approx. 3.0 MJ/m3 more than twice the fracture energy of a monolithic diamond foil by maintaining 90% the stiffness and about 70% the nominal strength. Classical laminate theory (CLT) supports to assess the deformation and step-like fracture behavior of the diamond/metal laminates. We find that the diamond-to-metal interface plays a critical role: it must be strong enough to enable the transfer of shear stress, while being weak enough to deflect a crack.

As new energy efficiency regulations tighten in the building sector, the required thickness for insulation with conventional materials (glass wool, polymeric foams...) may become prohibitive. This is a strong driving force for the development of a new class of products, the Super-Insulation at Atmospheric Pressure (SIAP) materials, based on the use of silica aerogel. Silica aerogels are characterized by a very high nanoporosity (~95%) responsible for their unprecedented low thermal conductivities but also for their very low mechanical properties. The materials studied here are composite panels produced using a bimodal distribution of silica aerogel grains, latex as binder and polypropylene fibers. The main objective in designing these composites is to improve their mechanical properties, mainly toughness, while preserving the silica aerogel thermal properties (thermal conductivity is approximately 15 mW/m/K). The composites and the aerogel particles used in their preparation were mechanically characterized: composites by using indentation, three point bending and Double Cleavage Drilled Compression (DCDC) tests and aerogel particles by uniaxial compression tests. Measurements of the thermal conductivity were carried out on composites using heat flux sensors. The data and mechanical properties collected experimentally were used to calibrate Discrete Element Method (DEM) simulations that successfully reproduce the fracture of aerogel particles. DEM simulations on composites were performed to determine potential optimisation paths for composite composition and preparation.

Bioactive-element doped hydroxyapatite bioceramic (dHAp) powders were successfully prepared from different calcium precursors, using wet chemical precipitation method. The bioactive ions were incorporated into the hydroxyapatite crystals by adding appropriate amount of chloride salts of Mg2+, Sr2+ and Zn2+ ions into the base solution and they were co-precipitated with the calcium phosphate particles. The phosphorous precursor was disodium hydrogen phosphate. The micro- and nanostructure of base HAp and dHAp powders from different sources were studied by scanning electron microscope (SEM) and transmission electron microscope (TEM). The measurements revealed that the structure and morphology of precipitated powders were highly dependent on the different precursors used, the precipitation parameters, pH of the suspension, the concentration of doping ions as well as the post treatment of precipitated powders after the chemical reaction. The smallest grain size with almost amorphous structure was obtained when calcium gluconate was used as Ca source, while in the case of nitrate and chloride salt of Ca, the crystallinity was higher and well defined, small, needle-like particles could be obtained. The post-treatment of suspensions with 1M Na2CO3 solution (for adjusting the pH to 11) caused phase transformation from monetite (CaHPO4) into a mixed phase of pure HAp and carbonated HAp with small, disoriented, needle-like particles in nanometre size, according to X-ray diffraction (XRD) measurement. The addition of different bioactive ions into the starting solution also changed the morphology of the precipitated powders. The doping ions were deposited in the form of low soluble phosphate precipitates along with different CaP phases. The elemental distribution of doping elements was homogeneous.

Acknowledgements: The authors are grateful for the SEM/EDX measurements to L. Illes (MTA-EK, Hungary) and thank for the financial support of National Research, Development and Innovation Office – NKFIH OTKA-PD 131934.

Novel eco-friendly method of preparation of Al2O3-AlN (AlON) composite ceramics was investigated using Hot isostatic pressing (HIP) technique. AlON ceramics are being investigated since 1980’s for their high strength and optical properties. Traditional synthesis of AlON ceramics include reactive sintering, carbothermal synthesis or spark plasma sintering. However, these technologies fail yielding a denser and transparent AlON ceramics. As an alternative pressing technology was employed and HIP technique was used in the present study to obtain better quality AlON ceramic. HIP requires shorter processing times and lower temperatures compared to sintering techniques and provides an exciting prospect. The precursor materials – AlN powder (0.80 – 1.8 µm diameter) was oxidized in ambient atmosphere for 3, 6 and 10 hours respectively. The oxidized powder was then subjected to HIP at 20 MPa, 1700 °C under N2 environment for 5 hours. The sintered samples were investigated using TEM and XRD for qualitative analysis. The phase transformation of AlN powder to Al2O3 during oxidation was observed proportional to the oxidation time. XRD analysis of the oxidized powders identified formation of α-Al2O3 and θ-Al2O3 phases. HIP Sintering has resulted in increasing the apparent density of the samples. Mechanical tests were also conducted on the sintered samples. Both 3-point and 4-point bending tests have shown an increase in the mechanical strength of the substrates with increasing oxidation time. Hardness of the substrates was also shown to be increased when compared to reference AlN with the highest hardness value obtained for the substrate with 10 hours oxidation time.

Polymer composites as high-performance materials are widely used and very specific for numerous applications. In building science, connecting and sealing joints with particle-filled thermoset polymers is a beneficial option due to its high mechanical properties and the ability to customize. It is therefore important to systematically predict the future performance depending on deviations between various composite systems.

Environmental exposure causes degradation in composites among which moisture uptake and hydrolysis can cause severe mechanical reduction. Chemical composition, degree of cure, void fraction, filler ratio, size, and material are determining diffusion and degradation rate.

To assess future behaviour of degrading composites, four different particle-filled polymers were stored in 9 in-house built climate chambers at various temperatures and humidities and characterized within defined storage periods. Two epoxy polymers with 18%vol. filler ratio with quartz or cement and two vinylester-based polymers with 45% or 58%vol. quartz filler ratio were the objects of study.

Applied characterization methods:
ˆ Electron Microscopy
ˆ Energy dispersive X-Ray Spectroscopy
ˆ IR Spectroscopy
ˆ X-Ray Diffractometry
ˆ Differential Scanning Calorimetry
ˆ Mechanical Tests

Moisture diffusion for all epoxy- and vinylester-composites follows a Fickian-type of diffusion. Water Saturation was highest for high humidities. A slight decrease in the saturation level with increasing temperature could be observed for composites with a higher void fraction. Mechanical properties declined proportionally with water absorption for all composites. Post-Curing effects could be observed for the epoxy composite with the smallest particle size distribution for higher temperature and low humidity. Spectroscopy revealed degradation effects due to oxidation.

The main reduction mechanism in mechanical properties for all composites
could be attributed to hydrolysis, scission of polymer chains caused by reaction with water. After 1 ½ year, tensile strength was reduced up to around 25% depending on the humidity level. Higher temperature acted positively on mechanical properties in general.

Injection molding of short fiber reinforced thermoplastics enables affordable production of complex geometries. Therefore, injection molded components conquer more and more the section of structural parts, especially in the automotive industry. The combination of lightweight material, efficient processing and design freedom is favorable. To increase mechanical performance and reliability deep knowledge of the material properties in the component is necessary.
Despite the short fiber length, a pronounced anisotropy characterizes the material behavior. Therefore, local fiber orientation needs to be considered in material characterization as well as component design and stress analysis. This paper presents the analytical chain from specimen preparation to consideration of local properties in component design depending on the microstructure. The nature of the injection molding process reveals a core-shell layered structure with changing fiber orientation and different degrees of anisotropy. This internal structure must be taken into account when resolving the measured engineering values from the specimen data. The proposed concept relates mechanical values to the local fiber orientation.
The availability of engineering values as a function of the microstructure of short fiber reinforced thermoplastics enables more precise and reliable design and stress analysis of structural components. Application of the analytical process will be presented by examples from practice.

Short fiber reinforced plastics are important materials in many fields of lightweight construction, especially in transport application. Their advantage is that they can be processed in a rather economic manner by the standard methods for processing of polymeric materials. Therefore, they are suitable for all kinds of industrial scale production. Nevertheless, a major challenge is the lack of validated precise material models for the numerical prediction of their mechanical response considering their complex fatigue damage and degradation behavior.

The present contribution is concerned with the definition of a continuum damage mechanics model for this class of materials. The model is based on the assumption of anisotropic linear elasticity in conjunction with a Tsai-Hill type failure approach. In contrast to the standard Tsai Hill approach assuming failure once the failure envelope is reached by the stress or strain state, a continuum damage formulation is proposed, using the distance of the respective stress point to the failure envelope as the damage driving quantity. Employing the concept of microplasticity, a damage evolution equation for fatigue damage development is derived. The model is implemented as a user-defined subroutine into a commercial finite element program.

The numerical development is complemented by an experimental study on fatigue of short fiber composites using an injection molded glass fiber reinforced PA66 as a reference material. The material is characterized in different directions throughout the relevant temperature range for automotive or similar transport applications. The experimental results are employed for both, material parameter identification and validation of the mathematical formulation of the material model.

New challenges related to the development of sustainable transportation solutions demand innovative high performance lightweight materials, as composites. Due to its recyclability, thermoplastic matrices are preferred. In addition to the recyclability advantage, thermoplastics have higher impact strength and ductility than thermosets [1].
Polyamide 6 (PA6) produced from anionic ring opening polymerization (AROP) of the low viscosity monomer ε-caprolactam (ε-CL) has been used for fabrication of lightweight composite parts [2]. One of the most suitable technologies for processing PA6 by AROP is thermoplastic resin transfer moulding (T-RTM). This process offers a significantly fast reaction rate, reducing the production cycle time. This technology is a natural evolution of the traditional low pressure resin transfer moulding [1]–[4].
This work focuses the synthesis of PA6 with different catalyst and activator dosage levels using a T-RTM prototype equipment. The properties of PA6 produced by T-RTM were analysed as function of catalyst and activator content. The results demonstrate the influence of catalyst and activator content in the final properties and highlight the importance of optimizing the dosage levels in order to maximize the physicochemical properties of PA6.

[1] O. V. Semperger and A. Suplicz, “The Effect of the Parameters of T-RTM on the Properties of Polyamide 6 Prepared by in Situ Polymerization,” Materials (Basel)., 13, p. 4, 2020.
[2] T. Ageyeva, I. Sibikin, and J. Karger-Kocsis, “Polymers and related composites via anionic ring-opening polymerization of lactams: Recent developments and future trends,” Polymers (Basel)., 10, p. 357, 2018.
[3] N. Zaldua et al., “Nucleation and crystallization of PA6 composites prepared by T-RTM: Effects of carbon and glass fiber loading,” Polymers (Basel)., 11, p. 1680, 2019.
[4] R. Boros, I. Sibikin, T. Ageyeva, and J. G. Kovács, “Development and Validation of a Test Mold for Thermoplastic Resin Transfer Molding of Reactive PA-6,” Polymers (Basel)., 12, p. 976, 2020.

Nowadays there is an increasing interest on the development of energy storage systems for electric mobility that could provide enough energy and reduce mass from vehicles. Structural supercapacitors based on composite materials are a potential alternative to satisfy both requirements. Transferring part of the energy storage responsibility towards structural elements will reduce weight from batteries currently used in electric vehicles.

Composite laminates are common structural elements due to their excellent mechanical properties and low weight. Electrical conductivity of carbon fiber also makes it a suitable material for energy storage applications. Supercapacitors storage capacitance rely heavily on the specific surface area of electrodes, which is the main weak point of the fibers.

Different structures with high specific surface have been studied to modify carbon fiber surface and increase their energy storage capacitance. Carbon nanoparticles, such as GNP, MWCNT and carbon black, with specific surface areas from 65 to 750 m2/g and excellent electrical conductivity have been deposited on the surface of carbon fibers. Synthesis of structures that can exceed 2000 m2/g of specific surface area, such as carbon aerogels and metal-organic frameworks, have also been studied.

Influence of particles and deposition technique on the multifunctional behavior of modified electrodes have been studied. Electrochemical characterization through cyclic voltammetry shows important improvements on the capacitance of the fibers. Modified carbon fibers mechanical properties have been evaluated with single filament tensile tests. Deposition of carbon nanoparticles show capacitance values up to 2 F/g keeping tensile strength close to 4000 MPa.

Structural supercapacitors were built with the modified carbon fibers and solid electrolyte developed. Both electrochemical and mechanical characterization were performed to evaluate their suitability for structural applications and study the effect of electrode-electrolyte interphase. These multifunctional composites store three times more energy than pristine carbon fiber with good mechanical properties.

High production rates and short cycle times are essential for an efficient manufacturing of high-performance components made of carbon fiber reinforced polymer composites (CFRPC). Within the framework of the project AIRPOXY, a new epoxy based vitrimer resin was developed, that is targeting at reducing costs in production and maintenance, as well as repair and operations (MRO) costs of CFRPC parts in aeronautics. Vitrimers are polymers, that provide similar specific properties as thermosets at room temperature, but can be processed like thermoplastics at higher temperatures. Due to dynamic-covalent bonds, vitrimers offer high stiffness, good chemical resistance and low tendency to creep together with the advantages of multi-reformability, weldability and recyclability. This unique material behavior allows the application of processes, which are commonly used within the production of thermoplastic CFRPC like continuous compression molding (CCM) and thermoforming.
In this study, the processability of carbon fiber reinforced vitrimer (CFRV) prepregs by hot pressing is investigated. Prepreg types with different resin formulations, curing rates, resin content and glass transition temperature were processed in order to determine the best possible material and processing parameters for the bonding of single layer prepregs to multi-layer laminates. The material layers were consolidated at temperatures between 180 °C and 240 °C, holding times between 5 minutes and 2 hours, as well as varying process pressures (2 – 4 MPa). The quality of the laminates was determined by microscopic examination of the pore content. Additionally, interlaminar shear strength tests (ILSS) were carried out in order to establish a correlation between microscopic properties and mechanical performance.
The results show that CFRV prepregs can be processed into high quality void-free laminates with an interlaminar shear strength of up to 50 MPa.

The regeneration of load-bearing bone segments is a critical need, still unmet due to the lack of bone scaffolds capable of inducing extensive osteogenesis and vascularization, and with appropriate mechanical performance. Indeed, conventional fabrication methods do not allow accurate control of compositional and structural changes, particularly during the consolidation of calcium phosphate bioceramics, where irreversible crystal growth and chemical stabilization occurs, reducing the scaffold bioactivity. The present work describes the unique properties of a large hydroxyapatite (HA) scaffold obtained by biomorphic transformation of natural wood structures, obtained thanks to the application of heterogeneous gas–solid reactions acting in the 3-D state. Thanks to this unpreceded approach, the scaffold shows enhanced bioactivity, induced by the synergistic effect of bone-like composition, lamellar nanostructure and hierarchical osteon-mimicking architecture exhibiting wide interconnected porosity from the nano to the macro scale. We found that these features enable continuous exchange of bioactive ions from and to the scaffold when soaked in physiological body fluids, as chemical signals supporting osteogenic cell differentiation. In this respect, bioreactor studies show overexpression of various osteogenic genes with the biomorphic scaffold in comparison with sintered hydroxyapatite scaffold with similar porosity extent. Moreover, the hierarchical, channel like porosity, closely resembling the osteon structure, was found to facilitate the crosstalk between mesenchymal and endothelial cells, very promising to promote vascularization in the whole scaffold volume. Furthermore, such a hierarchical architecture was found to induce damage-tolerant mechanical performance, unusual for a pure ceramic material, permitting the use of fixating screws during implantation in bone defects. We observe that such mechanical properties make biomorphic ceramics as unique materials laying between ceramics and woods, when depicted in Ashby maps. The biologic and mechanical performance so far observed are very promising for application as scaffolds to regenerate load-bearing segmental bone defects.

The polymer-derived ceramics (PDCs) route is a promising way for the production of silicate-based bio-ceramic/glass-ceramic materials: through suitable heat treatment, they yield materials with a distinctive control of phase purity and microstructures. Silicone-fillers mixture can yield bio-ceramics with a well-defined crystalline phase such as Biosilicate® glass-ceramics (Na2CaSi2O6). Commercially available silicone polymers ( such as H44, Silres® MK, H62C etc.) transform to pure SiO2 upon heating in ambient atmosphere, while their pyrolysis in the non-oxidizing atmosphere gives rise to the formation of amorphous residue composed of Si-O, Si-C and free carbon. In the present work, 3D-printed Biosilicate® glass-ceramic scaffolds with hierarchically porous struts were successfully manufactured by Direct Ink Writing (DIW) and subsequent thermal treatment of H44 silicone polymer filled with anhydrous CaO, Na2O and P2O5 precursors. Natural foaming ability of H44 silicone resin was utilized to obtain open-celled hierarchical micro-porosity. Additionally, green scaffolds were fired in the air and in the N2 atmosphere to compare the effect of residual free carbon on the mechanical properties of 3D-printed scaffolds. The hierarchical structure was created through foaming, which was to the result of crosslinking of the silicone resin at low temperature (ambient temperature, 60 °C and 75 °C) before its conversion to ceramics. Pure Biosilicate single crystalline phase (Na2CaSi2O6) was obtained both in air and N2 atmosphere with the help of anhydrous sodium phosphate filler (Na2HPO4) which provides a liquid phase (remained as a glass phase after cooling at room temperature) upon firing that promoted the ionic interdiffusion. The fabricated scaffolds exhibited compressive strength values up to 8 MPa and 13 MPa after pyrolysis in air and N2 atmosphere, with the open porosity 68% vol. and 66% vol. respectively.

One of the most important tissue engineering strategies is based on porous structures or scaffolds to provide a support for the growth and proliferation of cells in the damaged tissue. For bone regeneration, alumina is a suitable candidate thanks to its biocompatibility and its excellent and tunable mechanical properties. In this work, an original procedure is introduced, based on the combination of two techniques, namely, the spark plasma sintering (SPS), which allows fast sintering and maximizes the mechanical properties due to the control of microstructure, and the sacrificial template, which permits to generate a predesigned porous structures. Hence, we used different types of carbon particles as sacrificial agents which create different porous distributions and sizes with two-fold objective: mimic the porous distribution in human bone, and emulate its mechanical properties. Finally, in order to bioactivate the porous alumina scaffolds, we used the sol-gel method to create PDMS-SiO2 based coatings are employed.

Microstructural characteristics of the samples were studied by Hg porosimetry, nitrogen adsorption, CAT, and SEM and mechanical properties were assessed by uniaxial compression tests. EDX allowed to analyse the elements in the coating. Bioactivity was evaluated by immersion in SBF for identification of the precipitated apatite layer and analysis of ionic concentration in the fluid by ICP. The pore size distribution of the scaffolds as well as their Young’s modulus were compared to those of bone reference samples. First results showed satisfactory porous similarity between scaffolds and bone and suggested additional improvement in the mechanical properties.

In summary, these preliminary results showed an encouraging outcome and indicate that porous alumina scaffolds produced by this strategy are promising candidates for a new line of scaffolds for bone tissue regeneration.

Calcium phosphate scaffolds have been widely studied in the last decades as valuable solution for bone regeneration. However, the design and preparation of large bioceramic scaffolds for load-bearing applications, provided with tailored porosity, still represents a remarkable challenge. On the other hand, their porosity, pore size distribution and interconnection strongly reflect their bioactivity and osteoconductivity in vivo, that is the capacity of the scaffold to promote cell migration and proliferation.
Several methods are reported to produce porous scaffolds, including replica, sacrificial template and direct foaming [1]. In addition, the 3D Printing technology, which involves the extrusion of a bioceramic suspension as a filament following a three-dimensional project, has also shown itself short of preparing scaffolds with controlled porosity.
The issue comes around as all these techniques are based on the manipulation of slurries, that is highly concentrated powder suspensions with critical processing. In this context, a detailed rheological characterization of bioceramic suspensions is highly desired. For example, it was reported that the thermal calcination of the powder and the amount of dispersant agents significantly affect both the viscoelasticity of the slurry and the final properties of the scaffold.
In this work, concentrated hydroxyapatite (HA)-based slurries were prepared, while evaluating the effect of calcination treatment (800 and 1000°C), concentrations of powder (45, 60 and 75 wt%) and dispersing agent (3, 4 and 5 wt%) on the rheological properties of the suspensions. The stability of suspensions was monitored by pH and ζ-potential measurements, while both viscosity and viscoelasticity tests were performed.
The stability of the suspensions was mainly affected by the calcination temperature, while the effect of the dispersant becomes significant with increasing the powder concentration.

[1] Studart et al., Processing Routes to Macroporous Ceramics: A Review, J. Am. Ceram. Soc., 89 [6] 1771–1789 (2006)

Despite Ti alloys are biocompatible and non-allergenic, their use in blood contact applications including stent was rarely reported, mainly due to their low strength-ductility trade-off. In this work, two strengthening strategies were investigated to achieve Ti alloys with required mechanical properties for stent applications. The first tackled the increase of oxygen content in the TWIP (twinning induced-plasticity)/TRIP (transformation induced-plasticity) Ti-12Mo alloy. The second, aimed to design Ti-Mo-Fe alloys to combine TWIP/TRIP effects. Ti-12Mo-0.04O, Ti-12Mo-0.18O, Ti-8Mo-2Fe, Ti-9Mo-1Fe and Ti-10.5Mo-1Fe (wt.%) were produced by casting, swaging and solution treatment. Mechanical properties were assessed by tensile tests, while microstructures and deformation mechanisms by optical microscopy, X-Ray diffraction, transmission electron microscopy and electron backscatter diffraction. Hemocompatibility and direct cytotoxicity (endothelial and smooth muscle cells) were investigated. Results shown that the increase of O content in Ti-12Mo was responsible for an increase of nominal strength from 687 to 841 MPa, and for a decrease of uniform elongation from 39 to 28%. The increased strength of 0.18O alloy is associated to its superior work hardening rate (WHR) caused by the solid solution strengthening effect of oxygen. All the alloys showed plastic deformation by twinning and stress-induced martensitic (SIM) α" transformation. The twin density and area fraction of SIM α" were different for each alloy, affecting their WHR and mechanical properties. Concerning Fe, it resulted effective in strengthening Ti-Mo alloys. Ti-8Mo-2Fe and Ti-10.5Mo-1Fe exhibited high strength (986 and 823 MPa) and large uniform elongation (22 and 34%). The two strengthening strategies studied in this work leaded to Ni-free Ti alloys showing the high strength and high ductility required for stent applications. In particular, Ti-8Mo-2Fe appeared as potential candidate, showing strength comparable to L605 and elongation to failure up to 30%.

Ti6Al4V is the most widely used material for implant applications among titanium alloys that offer unique advantages over 316L stainless steels and Co-based alloys because of its low weight and high corrosion resistance. However, various interactions between implants and the biological environment can lead to the release of Al and V ions into the body fluid and raise long-term biocompatibility concerns.
With the fast development of new technologies and theories for exploring advanced materials, researchers have been attempted to discover a suitable alternative to conventional biomaterials. High entropy alloys (HEAs) with different compositional characteristics have attracted a lot of attention due to their potentially interesting properties for biomedical fields. Among different types of HEAs, the alloys consisting of non-toxic and non-allergenic refractory elements such as Ti, Ta, Hf, Nb, Zr, and Mo, known as refractory HEAs (RHEAs), could be potential candidates for biomedical applications.
This investigation was initiated to develop and study microstructure, mechanical properties, and corrosion behavior of non-equimolar Ti1.5ZrTa0.5Hf0.5Nb0.5 RHEA as bulk and coating in the simulated biological environment and to compare with those of the bare Ti6Al4V alloy. Bulk RHEAs were prepared by arc melting high purity elements on a water-cooled copper furnace in an Ar atmosphere. Ti1.5ZrTa0.5Hf0.5Nb0.5 RHEA thin films with a thickness of about 1.100 micron were deposited on Ti6Al4V substrate by RF magnetron sputtering. Phase and microstructural studies are carried out using XRD, SEM, and AFM. The hardness and elastic modulus of examines specimens were systematically investigated by nanoindentation with a Berkovich indenter. The corrosion behavior of the specimens was assessed using potentiodynamic polarization tests in the PBS electrolyte. The findings demonstrate that RHEAs, as a bulk and coating, could be prosperously used in biomedical applications.

The structural integrity of Nitinol stents is of great importance for the successful deployment and life-time service in the patients receiving stent implantation. Over years, problems caused by unknown reason keep being reported from industrial quality control and clinical operations, such as unexpected corrosion susceptibility, strut damage and incomplete self-expansion. In order to optimize the reliability and safety of industrial products, fundamental researches are carried out on non-metallic inclusions and hydrogen content in commercial Nitinol stents and materials. The presentation firstly reports on the recent findings about the dependence between the corrosion susceptibility and the inclusions contents The comparative microstructural characterization of the laboratory-made and commercial stents are presented before and after ASTM F2129 assessments to show the effects of inclusions on corrosion susceptibility for different area fractions. As the second part of the presentation, the recent findings about the effect of hydrogen is reported regarding the change of deformation mechanisms of Nitinol. The hydrogen concentration in the commercial stents is measured and used as studying targets. In-situ microstructural characterization, coupling EBSD with tensile loading, is performed on the samples charged to different hydrogen concentrations to investigate the hydrogen effect on the local operating deformation mechanisms of NiTi.

In the race towards the perfect implantable material, titanium and its alloys have been subjected to a great number of different surface treatments. A fundamental step in this way is to understand how biological fluids and proteins interact with biomaterials, since the layer of adsorbed proteins strongly influences the cell-surface interfacial region. In this work, c.p. Ti and Ti6Al4V alloy with different surface modifications are investigated to understand how the various surface characteristics, such as roughness, chemistry, zeta potential, hydroxylation degree, wettability and surface energy, affect protein adsorption. A set of conventional and innovative techniques is here proposed to characterize different aspects of protein adsorption on surfaces designed for implantation. Titanium samples were subjected to three different surface modifications for bioactivity enhancement: acid etching followed by controlled oxidation in hydrogen peroxide on Ti6Al4V: combined alkali-acid-heat treatment on Ti; alkali-heat treatment followed by Sr and Ag ionic exchange, for adding antibacterial properties, on Ti6Al4V;. Adsorption properties of these surfaces were evaluated using two proteins, albumin and fibronectin, which are relevant in the osseointegration and inflammatory pathway of implantable biomaterials. Quantification and assessment of adsorbed proteins was obtained by more conventional techniques such as bicinchoninic acid assay, XPS or fluorescent-labeled proteins and it was found that surface energy and micro- and/or nano-structuration play a major role in determining the amount of adsorbed proteins. An innovative approach to surface potential imaging, by means of Kelvin Probe Force Microscopy, allowed to visualize the layer of adsorbed proteins and to study its homogeneity, while proteins conformation and orientation upon adsorption was investigated thanks to novel Surface Enhanced Raman Spectroscopy method and to solid surface zeta potential titration measurements. As to get closer to the implantation environment, competitive and subsequent adsorption of albumin and fibronectin were also investigated.

Recycling of textiles is a major challenge because textiles, whether home or industrial, often consist of two or more materials that form an almost inseparable mixture during the manufacturing process. In the project Tex2Mat, two groups of textiles were investigated.
One group was a cotton-polyester blend for home textiles, the second group was a blend of polyamides (PA 6.6 and PA 6) of industrial textiles.
For the cotton-PET blend, a separation process based on an enzymatic process was developed. The resulting pure PET was to be prepared in such a way that it could be reused in the spinning process and recycled for its original purpose. To this end, the reprocessed PET fibers were systematically analyzed to determine the extent to which the material properties had changed as a result of processing and usage compared to virgin material. Based on these findings, the material was recondensed (solid state polymerization, SSP) to a level from which it can be spun and woven again. Tests on laboratory equipment confirmed that the material could be re-spun. The produced fibers were twisted into threads and the yarn were used to weave towels, the original product.
The polyamide mixture, which was originally used in industrial textiles, was tested for its suitability as material for technical injection molded components and analyzed for any signs of degradation. The material property requirements for spinning differ significantly from those for injection molding, but tests nevertheless demonstrated that the recycled material can be processed well.
In addition, tests were carried out with various impact modifiers in order to optimize the material for use in technical injection molded parts.
Subsequently, technical components with different recycled content were manufactured at project partners and tested according to the specifications. The components met the specifications in all respects.

Due to environmental, economic and regulatory aspects there is a strong need for novel strategies allowing environmentally friendly recycling of plastics and textiles. Enzymes have shown high potential especially for the step-wise recovery of building blocks from blended materials. We will show that enzymes can specifically hydrolyze and solubilize certain components of blended textiles or from packaging materials. Thereby, building blocks and/or polymers (e.g. fibres) can be recovered in pure form and reused for production of materials. Various examples for textiles and plastics will be presented. Despite the high potential of biocatalysts for this purpose, yet more efficient enzymes are required for economic industrial implementation. Hence, we will demonstrate how enzyme discovery, design and engineering can lead to more powerful tools for material recycling.

Polypropylene (PP) is the world’s second most widely used commodity polymer accounting for 13% of total usage by value (23% by volume) and is employed for a huge variety of purposes including packaging, textiles, furnishings, pipes, vehicle components, electrical equipment, ropes and even banknotes. As an oil-derived polymer the downside to PP is that it is a non-sustainable resource as well as an increasing pollution problem. At present only 1% of PP is recycled, for which mostly mechanical and/or thermal recycling methods are employed. These generally result in low quality products, and the rest ends up in either landfills or oceans.
Under the framework of the ISOPREP project funded by the European Commission, focus is put on an innovative, alternative approach for the recycling of PP from multicomponent waste carpet. A recycling process was developed using a proprietary solvent enabling the selective dissolution and recovery of PP. Starting from the pre-processes to increase the PP content in the waste carpet feedstock materials, the dissolution, dye removal, and precipitation processes were developed and optimized in order to obtain high purity recycled PP along with solvent recovery processes. Detailed analyses showed that the newly developed recycling process had no effect on the chemical structure of PP and all thermal transitions as well as thermal decomposition behaviour of the recycled PP polymer were identical to that of pure PP polymer. The process completely removes other polymers, dyes, metals and other contaminants, hence it represents a more environmentally friendly alternative end of life solution for the increasing amount of polypropylene carpet worldwide. Recycled PP was used in subsequent compounding and extrusion processes to produce multicomponent fibres and coatings for textile applications with enhanced fire-retardant, electrical conductivity or improved antimicrobial properties.

Mixed engineering plastic wastes (MPs) at the end-of-life vehicles (ELVs) have been overlooked for decades due to their low weight fraction in automobiles and complex characteristics. These resulted in landfilling 500 kilo tonnes of ELVs plastic waste in 2017. Generally, compounding these MPs, which are the residue after the sorting process, performs poor mechanical properties and devalued because of the immiscibility characteristic of polymer blends. In this study, mechanical recycling via a composite approach aims to revalue these MPs into secondary raw materials and structural application reducing the landfill rate and moving towards to a circular economy. After reinforcing these MPs with high stiffness and strength fibre; short carbon fibre (sCF) at 2.5, 5, 10 and 20%wt, both flexural and tensile properties improve linearly to the weight fraction of sCF. Flexural strength and modulus of sCF20%/MPs increased 2-folds and 5-folds, respectively compared to unreinforced MPs. Moreover, MPs reinforced composite outperforms virgin engineering plastic in both flexural modulus and strength. This leads to equivalent performance with 22% weight reduction. Finally, Life Cycle Assessment (LCA), which demonstrates the environmental effects with consideration of energy, raw materials and fuel consumption from cradle-to-grave was conducted to provide a sustainability overview of this upcycling process.

Plastic waste currently represents a very important environmental issue, with plastic global production being over 300 Mt and the EU recycled fraction under 40%. The non-recycled plastic undergoes energy recovery in the best case, but in the worst is dispersed or landfilled.
Plastic recycling into mortar/concrete is one of the possible solutions for immobilizing plastic for long times. The plastic lowers the density of the mortar/concrete and increases its thermal and acoustic insulation capability, but causes a reduction in mechanical performance.
Here we present three cases of plastic waste recycled into mortar: PVC from cables, where energy recovery is impossible due to the high chlorine content; mixed plastics from waste electric and electronic equipment (WEEE), that comprise several different plastic types; rubber from end-of-life tyres, half of which are still sent to energy recovery.
In all mortars the plastic wastes were partially substituted to the sand, and physical and mechanical testing was carried out. The main conclusions are:
- density of mortar decreases with increasing plastic content, while flexural and compressive strength decrease significantly;
- the adhesion between plastic and cement is scarce, and a weak interface is formed. Thus, cracks can form between plastic and cement, and plastic may behave almost as porosity, from the mechanical point of view;
- countermeasures can be taken to limit the mechanical performance loss. Physical and chemical treatments can be applied, or fibers can be added in small quantity, to counterbalance the strength reduction;
- plastic composition and homogeneity has a limited influence on strength;
- mechanical properties are still sufficient for non-structural applications.

Transparent electronics has gained special attention during the last decade and is today well established as one of the key technologies for a wide range of device applications and is one of the most promising technologies for new electronic products with high added value, away from the traditional silicon technology.

The key components are sustainable abundant and non-toxic materials based on metal oxides (like zinc oxide) of different origins and play an important role, not only as passive components but also as active components, similar to what is observed in conventional semiconductors like silicon. The viability of this technology depends to a large extent on the performance, reproducibility, reliability and cost of the metal oxide based thin film transistors (TFTs). Transistors are the key components in most modern electronic circuits, and are commonly used to amplify or to switch electronic analog and digital signals. The best known application of TFTs is in flat panel displays.

TFTs have been fabricated in a wide variety of materials, but hydrogenated amorphous silicon has been the enabling technology for the active matrix liquid crystal display (AMLCD), common place in portable and desktop computers, high resolution TVs, tablets and smartphones. However, due to low cost of production, low-temperature processing and high resolution, AMLCD technology is gradually shifting towards metal oxide based TFT. Beside higher resolution, one of the advantages of this technology is that it can use existing manufacturing infrastructure which was developed for amorphous-Si TFT. The metal oxide was already adopted by the industry and is based on IGZO (Indium-Galium-Zinc-Oxide) and it was a breakthrough in display technology since it delivers high-resolution, ultra-low power, and slim product profiles, plus exceptionally detailed touch panel capabilities (see Fig. 1). IGZO is a driving force behind new developments in a variety of fields, enabling LCDs, as well as OLED, and MEMS displays, with new levels of performance.

The first panels incorporating IGZO display technology first appeared in 2012 by Sharp. The following years saw the emergence of televisions and other consumer electronic products such as smartphones and laptops featuring the same innovative display technology. With industry trend and market asking for high definition and power-efficient display panels, IGZO is fast becoming a fitting display technology .

As it was projected by some forecast reports, transparent electronics market was valued at USD 1000 million in 2019 and is expected to reach USD 3800 million by 2025, at a CAGR of 25% over the forecast period 2020 – 2025. These numbers justify a real need as well as a scientific and social commitment in order to keep/increase the level of development but in a responsible way in terms of our planet in accordance with the green deal. We start it 10 years ago!. Besides that and by adding electronics to the rest of the 95% of objects surrounding us but do not have electronics yet, the market of electronics will growth at least 10 times.

Optical modulators are fundamental building blocks in a large variety of modern technological applications: phase, frequency, amplitude and polarization modulators such as electro-optic (EOM) and acousto-optic modulators (AOM) are widely used in fibre optic communication systems, ultrafast spectroscopy, metrology, active Q switching/mode locking of lasers and quantum information. The research and technological interest in optical modulators has further increased in concomitance with the progress in the field of integrated photonics with the ultimate goal to replace electrical interconnects with optical interconnects and provide faster response time, wider transmission bandwidth, and lower power consumption. In addition, novel functionalities for photonic circuits could be enabled by active modulation of nonlinear optical effects. Atomically thin two-dimensional (2D) materials could be ideal for such applications. Thanks to their high mechanical flexibility, ease of fabrication and robustness, 2D materials have already been successfully integrated on waveguides, microdisks, microrings and fibres and different kinds of electro-optic, thermo-optic and magneto-optic modulators have been realized. Moreover, 2D materials display strong nonlinear optical response and are thus ideal to enhance the performances and functionalities of standard photonic devices and to allow all-optical modulation of light. In this talk I will discuss our current efforts towards the realization of electro-optical and all-optical nonlinear modulation of third and second harmonic generation in graphene and related layered materials.

2D crystals like graphene and transition metal dichalcogenides are stable because of their fully saturated in-plane covalent bonds. Another way to stabilize crystals in a low-dimensional conformation is to restrict the inclusion of atoms at the crystal edges via kinetic barriers. Such systems that include for instance metal nanowires grown inside carbon nanotubes and molecular crystal in few-layer graphene encapsulation are intrinsically metastable but can continue to exist if the barriers remain unchanged.

Here we demonstrate two distinct crystals of the latter type that have been assembled within the van der Waals gap of two graphene monolayers that prevent the crystal expansion along the normal direction of their basal plane. Their structure is fully characterized via aberration corrected scanning transmission electron microscopy (STEM) and dynamics are observed at the atomic resolution. The first example is a hexagonally close packed monolayer of C$_{60}$ fullerene molecules grown by vacuum evaporation on free-suspended graphene and subsequent encapsulation in ambient conditions. The encapsulated C$_{60}$ molecules exhibit an anomalous, truncated intermolecular spacing of 9.6 Å but retain their rotational degree of freedom at room temperature. The second example is a more complex, trigonal 2D copper-iodine (CuI) crystal created via hydrogenation of Cu-intercalated graphene oxide by using hydrogen iodide. The experimental lattice parameters unexpectedly match well with the density functional theory model of a similar structure without graphene encapsulation. Finally, despite the occasional edge-reconstructions, rotational translations and the appearance of iodine vacancies, their basal plane retains integrity during the STEM experiments under a 60 keV electron beam.

Noble gas clusters trapped between two or more graphene layers form two-dimensional noble gas crystallites that are directly observable in an atomically resolved scanning transmission electron microscope (STEM). These otherwise inert atoms appear in both solid- and liquid-like phases, and in our experiments the clusters exhibit size-dependent, electron-beam driven dynamics that include, for instance, “jumps” over distances greater than the dimensions of the crystallites. Atomistic simulations confirm the stability of small clusters and shed light on the observed dynamics.

Ion irradiation is a widely adopted technique for electronic structure engineering in the context of silicon semiconductors. The implantation of hetero-atoms into bulk is thoroughly understood via existing experiments and semi-empirical modelling. However, applying this technique to 2D materials, which have a stopping power much lower than the samples of a greater thickness, necessitates the use of ion energies lower than what is available in most existing experimental setups. In contrast, in the present work we have used initially high-energy Xe$^+$ and Kr$^+$ ions that were decelerate by an electrostatic lens to kinetic energies ranging from a few tens to a few hundreds of eV to trap them in the van der Waals gap of graphene bilayers.

Understanding the mechanisms governing large scale defect and contaminants in CVD grown 2D materials on transition metal catalysts and their transfer to target substrates are of crucial importance when creating high performance devices. Contamination introduced during transfer and handling is one of the most common factors why devices underperform. The interface between 2D layers in a heterostructure is of great importance when comes to the device performance. A clear understanding of which contaminants affect the most the electrical characteristics of such devices is still overlooked. This research is focusing on understanding the types of contaminations introduced during transfer and fabrication of 2D heterostructures and how these relate to their electrical properties. Here, Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) has been used to monitor the interface composition of hBN/graphene/hBN, hBN/WS2/hBN and graphene/WS2 heterostructures. Comparison was done between exfoliated samples and CVD grown samples. Due to the gentle argon cluster sputtering we were able to obtain sub-monolayer sputtering resolution with reduced roughness. Lastly, we discuss ways to address these contaminants found at the interface.

Two-dimensional (2D) antimony (Sb, "antimonene") recently attracted interest due to peculiar electronic properties and suitability as anode material in batteries. Sb however exhibits a large polymorphic/allotropic structural diversity, which is also influenced by the Sb's support. Thus understanding Sb heterostructure formation is key in 2D Sb integration. Particularly 2D Sb/graphene interfaces are highly important in electronics and batteries. We thus study here few-layered 2D Sb/graphene heterostructures by atomic-resolution (scanning) transmission electron microscopy. We find the co-existence of two Sb morphologies: First is a 2D morphology of layered β-Sb with β-Sb(001) || graphene(001) texture. Second are one-dimensional (1D) Sb nanowires which can be matched to β-Sb with β-Sb[2-21] ⊥ graphene(001) and are also closely related to thermodynamically non-preferred cubic Sb(001) || graphene(001). Importantly, both Sb morphologies show rotational van-der-Waals epitaxy with graphene. Both Sb morphologies are resilient against environmental bulk oxidation, although superficial surface Sb-oxide formation merits consideration, including novel epitaxial Sb2O3(111)/β-Sb(001) heterostructures. Exact Sb growth behavior depends on processing and substrate properties including, notably, the support underneath the graphene. This introduces the substrate underneath a direct 2D support as a key parameter in 2D Sb heterostructure formation. Our work provides insights into the rich phase and epitaxy landscape in 2D Sb and 2D Sb/graphene heterostructures.

The use of polymeric nanostructures in bioapplications is gaining attention due to their large surface area and biocompatible nature. The response of these nanostructures to the external stimuli can be controlled by tuning the geometry and the chemical composition of these structures. Furthermore, additional functionalities can be introduced by coating the surfaces of these nanostructures with functional polymer thin films. However, coating of these nanostructures or tuning of their composition and sizes at these length scales prove to be challenging with many of the conventional synthesis methods. In this respect, vapor phase synthesis methods offer advantages by enabling the separate tuning of process parameters to achieve better control over nanostructure performance.

In this talk, I will present our studies on the design and synthesis of functional polymeric nanostructures via the templated chemical vapor deposition method. I will introduce different vapor phase deposition methods that we employ and discuss the effects of the deposition parameters on the formation and properties of the nanostructures. In the last part of my talk I will give examples to the bioapplications of these polymeric nanostructures, mainly in biosensors and controlled drug delivery.

Gradients of organic materials can be found in many structures that occur in nature. Polymers thus represent an excellent choice to artificially reproduce these gradient structures in form of gradient copolymers. In this talk, we report on the preparation of such gradient copolymers synthesized as thin films using initiated chemical vapor deposition (iCVD). The iCVD process is known for solvent-free, large-area deposition of high quality polymer thin films on complex geometries as well as temperature sensisitive substrates. In order to transfer the gradient film approach to the lower nanoscale, a detailed understanding and control of the vapor phase kinetics in the iCVD process is required. This is realized via a new in-situ quadrupole mass spectrometry (QMS) extension and supporting ab initio/density functional theory (DFT) calculations. It enables better understanding and control over the composition and processes in the vapor phase as well as insight into the underlying reaction kinetics that occur during the deposition. This paves the way for gradient copolymer films at the lower nanoscale below 30 nm that exhibit entirely new chemical and physical properties that cannot be achieved with current materials. These films provide new pathways for applications ranging from everyday uses to advanced optical devices and new electronic materials.

Exploring new 2D materials with semi-conductive nature has attracted researcher’s attention especially after the isolation of graphene, aiming to increase the performances in the fabrication of devices.
Transition Metal Dichalcogenides (TMDs) materials belong to a special class of semi-conductors materials with sizable bandgaps, which they found to be useful in the field of optoelectronics. Titanium disulfide(TiS2) is the lightest and cheapest member of the layered transition metal dichalcogenide family. TiS2 monolayer consisting of edge-sharing TiS6 octahedra with electrical properties ranging from semi-metallic to semiconductor makes TiS2 a good candidate as an electrode material for lithium batteries.
Tin disulfide (SnS2) is an emerging Layered Metal Dichalcogenides (LMD) having an indirect semiconducting nature. SnS2 has a cadmium iodide (CdI2)-type structure with outstanding properties useful for future electronic devices.
Atomic Layer Deposition (ALD) and Molecular Layer Deposition (MLD) are well known to be ideal techniques for depositing scalable, conformal, ultrathin inorganic, and organic layers. Most of the previous attempts to grow TiS2 and SnS2 by ALD have used H2S as the sulfide precursor, the use of which is very problematic because H2S is an inflammable and very toxic gas. Finding an alternative precursor sulfur source is a challenge.

For the purpose of obtaining our novel 2D thin films, the synthesis was divided into two stages. First, we grow an intermediate amorphous polymer film by MLD at low temperature on flat 100 nm thick thermal SiO2/silicon substrate, by alternating a metallic precursor (TDMAT, Tetrakis (dimethylamino) titanium) (Ti –thiolates), and (TDMASn, Tetrakis (dimethylamino)tin) (Sn –thiolates) (ALD) with an organic molecule containing sulfur (EDT, 1,2 -ethanedithiol) (MLD), the growth is monitored in situ by ellipsometry. Second, we anneal the thiolate under a controlled atmosphere for obtaining the desired crystalline materials

In this work, we have developed a multi-stimuli responsive sensor for artificial skin applications. The sensor can detect surrounding changes in pressure, temperature and humidity. The proposed design consists of a hydrogel core, responsive to temperature and humidity changes; and a piezoelectric shell for pressure sensing. Swelling of the hydrogel core upon stimuli results in a mechanical strain on the piezoelectric shell, which results in a measurable electric potential, detected by metal electrodes. The two materials are combined into core-shell nanorod structures, using novel vapor-based deposition techniques. Such deposition techniques provide control over material’s mechanical, optical and electrical properties as well as layer conformity and uniformity. Additionally, the core-shell nanorods are deposited into a nanostructured UV-curable resin, providing mechanical stability against structural collapse.

• Fabrication of hydrogel core: humidity and temperature responsive hydrogel, Poly-N-vinylcaprolactam (pNVCL), is synthesized using intitiated chemical vapor deposition (iCVD). The dry vapor-phase technique gives control over the lower critical solution temperature (LCST), amongst other material properties. (1) Tailoring the hydrogel’s LCST improves response over a wide temperature range.

• Fabrication of piezoelectric shell: piezoelectric zinc oxide shell is synthesized using plasma-enhanced atomic layer deposition (PE-ALD). In PE-ALD, substrate temperature defines the crystalline properties of the deposited material. An interchange between (100) and (002) crystallographic orientation gives control over zinc oxide’s piezoelectric properties. In this work, highly-resistive and piezoelectric zinc oxide layer with (100) preferential crystallographic orientation is deposited at room temperature. Using low substrate temperature is advantageous for the use of flexible substrates, such as PET. (2)

• Nanostructuring of UV-curable resin: The multi-stimuli responsive core-shell nanorods are deposited into a nanostructured UV-curable polyurethane acrylate (PUA) resin serving as a template layer for mechanical stability. Patterning the template material is realized using UV nanoimprint lithography (UV-NIL). For this purpose, a UV-transparent nanopatterned polymeric stamp is used.

1. F. Muralter, A. Perrotta, O. Werzer, A. M. Coclite, Macromolecules, 2019, 52, 6817-6824
2. Abu Ali et al., Phys. Status Solidi a, 2020, 2000319

The electrochemical deposition and growth of nanostructured platinum films was investigated in operando with Grazing Incidence Small Angle X-ray Scattering (GISAXS) - a non-destructive surface-sensitive technique for structure determination in the nm-regime. The deposition of the films was templated using hexagonal ($H_1$) lyotropic liquid crystalline phases of non-ionic surfactants, a ternary mixture of aqueous 0.2 M $H_2PtCl_6$ and $C_{16}EO_8$ (50:50 wt.%).

Previous studies$^{1,2}$ showed that the resulting $H_1$-e platinum films contain regular hexagonal arrays of cylindrical pores separated by platinum walls with a centre to centre distance of 5-6 nm. These films exhibit very high surface areas in the order of up to 91 m$^2$/g. In the present study, the cylindrical pores are preferentially aligned perpendicular to the electrode surface. The high surface area of the mesoporous films and the ability to control pore structure and orientation enable their successful application in fields such as catalysis, analysis separation technology, optical devices, and biomedical science.

The application of GISAXS in combination with the brilliant synchrotron radiation source at the ELETTRA-Sincrotrone Trieste enables in operando monitoring of the $H_1$-e deposited film regarding nanostructure and orientation of the mesopores. Time-resolved characterization of the structure evolution gives new insights into the kinetics of templated electrodeposition.

(1) Bartlett, P. N.; Gollas, B.; Guerin, S.; Marwan, J. The Preparation and Characterisation of H1-e Palladium Films with a Regular Hexagonal Nanostructure Formed by Electrochemical Deposition from Lyotropic Liquid Crystalline Phases. Phys. Chem. Chem. Phys. 2002, 4 (15), 3835–3842. https://doi.org/10.1039/b201845d.
(2) Attard, G. S.; Bartlett, P. N.; Coleman, N. R. B.; Elliott, J. M.; Owen, J. R.; Wang, J. H. Mesoporous Platinum Films from Lyotropic Liquid Crystalline Phases. Science (80-. ). 1997, 278 (5339), 838–840. https://doi.org/10.1126/science.278.5339.838.

Colloidal nanocrystals (NCs) offer the opportunity for realising novel solid state materials with tailored functionalities. By chemical synthesis, a large variety of semiconducting and metallic NCs can be realised [1] that can be used as efficient light emitters [1, 2] or in novel batteries designs [3].

Especially the inner structure and the shape of semiconducting core/shell NCs determine the photoluminescence (PL) output. We have revealed a relation between structure and functionality by combining different scattering techniques at lab and synchrotron sources with microscopy techniques [2]. In a study at the synchrotron ESRF, we have investigated CdSe/CdS core/shell NCs with different dimensions by recording ASAXS and WAXS spectra. We revealed an elliptical and strongly faceted NC-shape and could related this shape to specific crystallographic directions. This increased anisotropy is directly connected to a decreased PL.
The NC’s shape can also significantly influence the structure of colloidal supercrystals, where NCs act as building blocks to form 3D nanocrystal solids with designed properties [1]. We have probed such a self-assembly with in-situ synchrotron SAXS at ELETTRA using colloidal solutions of Bi NCs [4]. By combining synchrotron data with simulations, we are able to link the supercrystal structure via the NC-shape to the atomic Bi crystal structure: besides a positional ordering we found a parallel alignment of the large NC surface facets [4]. Such a global alignment of crystallographic directions within the superstructure is important for controlled electronic properties of the whole nanocrystal solid.

[1] M. V. Kovalenko, et al., & W. Heiss, ACS Nano 9, (2015) 1012–1057
[2] L. Ludescher, et al. & R.T. Lechner, Front. Chem. 6, (2019) 672
[3] K.V. Kravchyk, et al., & M. V. Kovalenko, ACS Nano 12, (2018) 8297-8307
[4] M.Burian, C. Karner, et al., & R.T. Lechner, Adv. Mater. 30, (2018) 1802078M

Recently the SMA and FeSMA field has attracted interest for solid state refrigeration applications. Among NiMnGa-based quaternary systems, NiMnGaCu exhibits an interesting giant magnetocaloric effect thanks to the temperature overlapping of magnetic transition and thermoelastic martensitic transformation (TMT), in particular for compositions with about 6at% Cu content. In the present work in polycrystalline alloy samples with Ni50Mn18.5Cu6.5Ga25 at% chemical composition, we investigate the contribution of TMT to the total deltaS change in the elastocaloric performances, to give a functional characterization of effect of microstructure on caloric properties and to give another term of comparison for the magnetocaloric properties. We present an extensive calorimetric and thermo-mechanical characterization to explore the correlation between microstructural properties induced by means of selected thermal treatments and elastocaloric response. Our results give important hints on how the efficiency of the martensitic transition and its modulation in temperature has a final effect on the total DeltaS measured.

For long steel products, the microstructure components have a major importance to guarantee good mechanical properties. This paper will discuss how the type of bainite microstructure can affect the impact energy. For this purpose, two bainitic steel grades with different impact energy were compared in term of microstructure. Both steel microstructures was investigated in terms of morphology, size and area fraction of martensite austenite islands and in terms of bainitic ferrite misorientation angle distribution by EBSD analysis combined with SEM and image analysis. The results obtained from the EBSD analysis show that the change in impact energy is related to the type of bainite identified in the microstructure according to the misorientation distribution.

In the aviation industry the commercial PH15-5 steel is predominantly applied in structural parts which are subjected to strict requirements for toughness properties. Its microstructure consists of a soft martensitic matrix exhibiting a hierarchical structure consisting of so-called laths, blocks and packets. Previous work of the authors suggested that a small martensitic block size increases the cleavage fracture toughness. The block size is strongly affected by the strength of the austenite, which is dependent on its grain size and chemistry, as well as temperature. Additionally, stress fields induced by martensite formed at early stages of transformation strengthen the adjacent austenite, thereby influencing the block size of martensite formed at later stages of transformation.

Consequently, this study aims to investigate the influence of local variations of austenite grain size, chemical segregations and elastic stress fields on the martensitic block size distribution.

To this end a comprehensive set of methods comprising in-situ secondary electron microscope recordings and high temperature electron backscatter diffraction during martensite transformation, as well as electron diffraction x-ray spectroscopy measurements of regions that transformed at different times has been conducted in this work. This facilitated the distinction between the influence of prior austenite grain size, chemical segregations of especially Ni and Cr, and elastic stress fields induced by the martensitic transformation on the block size distribution of the final martensitic microstructure.

Compared to other types of steels, maraging steels show an excellent combination of high strength and good toughness. This is achieved by precipitation of intermetallic compounds during ageing of a martensitic matrix. However, delta ferrite might be formed during processing due to non-equilibrium solidification. The present work investigates the influence of delta ferrite on the impact toughness of PH 13-8 Mo.

Computational modelling of the development of the phase fraction and chemical composition of delta ferrite during solidification was performed by applying the moving boundary model within the diffusion module (DICTRA) in Thermo-Calc for PH 13-8 Mo with varying chemical compositions. Furthermore, the chemical composition of delta ferrite was estimated by equilibrium calculations and the Scheil-Gulliver model. Results were validated by analysing the microstructure of PH 13-8 Mo in as-forged condition. Charpy V-notch impact testing was performed on specimens with different phase fractions of delta ferrite in order to evaluate its influence on the impact toughness. Since carbide precipitation was largely suppressed due to the low carbon content, it is assumed that solely the effect of delta ferrite on the impact properties was investigated.
The results show that a significant effect of the chemical composition on the phase fraction of delta ferrite was predicted by computational modelling and subsequently validated by means of metallographic examination and energy dispersive X-ray analysis.
Charpy V-notch testing revealed a clear trend, where the presence of delta ferrite led to lower impact toughness, which correlates with results from literature obtained for a low carbon 13Cr-4Ni martensitic stainless steel.

The present work outlines that even small variations within the chemical composition of PH 13-8 Mo might have significant influence on the phase fraction of delta ferrite and subsequently on the impact toughness.

Duplex stainless steels (SS) comprise of both ferrite and austenite phases. The combined properties of the individual phases in austenitic-ferritic stainless steel result in excellent combination of corrosion resistance and mechanical properties, and thus they are fast replacing the conventional single-phase austenitic or ferritic stainless steels. The strength of the duplex SS can be further increased by the addition of dispersoids. The most commonly used oxide (as dispersoids) in ODS steel is yttria (Y2O3). The addition of titanium to Y2O3 dispersed steel leads to the formation of Y-Ti-O clusters having a refined size of ~2-6 nm, also called nano-clusters. These nano-clusters act as obstacles to the movement of dislocations, and thus increase the strength of the alloys, especially creep resistance. Although extensive studies have been carried out with yittria as oxides in ODS steels, other rare earth oxides like lanthana (La2O3) have not been explored.
In the present study, both lanthana and yttria based ODS duplex SS have been fabricated using mechanical alloying followed by spark plasma sintering (SPS). Elemental powders with the composition of Fe-21Cr-8Ni-1Ti-0.5La2O3 (21LNT) and Fe-21Cr-8Ni-1Ti-0.5Y2O3 (21YNT) were mechanically alloyed for 35 h and then sintered at 900 oC and 1000 oC. The variation of the sintering temperatures on the density, microstructure and mechanical properties of the ODS duplex SS has also been reported. Microstructural characterization was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The quantification of mechanical properties was carried out using Vickers hardness, nano-indentation and compression testing, which indicated that 21LNT exhibit better mechanical properties than the conventional 21YNT alloy.

Keywords: ODS duplex SS, Spark plasma sintering, Nano-clusters, Mechanical alloying

Oxide Dispersion Strengthened (ODS) ferritic steels are promising candidates as cladding material for 4th Generation Sodium-cooled Fast nuclear Reactors. Conventional reinforcement is achieved by introducing titanium and yttrium oxide Y2O3 during mechanical milling with matrix steel powder. The strengthening particles are dissolved or reduced as sub-nanometric clusters during this step, before precipitating as complex oxides during heating and hot extrusion consolidation process. These ferritic ODS grades exhibit exceptionnal high-temperature strength and thermal creep lifetime. Nevertheless, they are difficult to cold form as tubes and are characterized by a low Charpy impact upper-shelf energy (USE) and brutal creep rupture. These halftone properties are mainly attributed to the uncontrolled precipitation : some nano-precipitates, such as small Y-Ti-O oxides, appear to be highly beneficial to the mechanical behaviour of the material, while coarser ones segregated at grain boundary – e.g. TiC, Y-Al-O, Y2O3 - embrittle it.

In order to avoid these detrimental phenoma, an innovative alloy-design approach is developed at CEA. Nanostructured Y2Ti2O7 pyrochlore phase oxides are elaborated by mechanochemical synthesis, followed by annealing under oxygen atmosphere. Microstructure and time-driven oxygen stoichiometry of pyrochlore oxides are studied through X-ray Diffraction Rietveld refinements.

Added instead of yttria, stoichiometric Y2Ti2O7 prevents from the presence of coarsed Y2O3 particles and reactive titanium excess. Results show that the introduction of these new strengthening nanoparticles reduces the micrometric precipitates volume fraction, and improves the ductility of ODS ferritic steels. Mechanical tests reveal a significant improvement in USE, while maintaining a good tensile strength up to 650°C. A 60% cold rolling rate has been achieved without any intermediate thermal processing, demonstrating the cold-forming possibilities of these new ferritic ODS grades.

Production and machining of titanium alloys are difficult as it involves a complex combination of high loading and rapid temperature evolution. In addition, due to the contact between the cutting tool and the material, the temperature can locally reach 800 °C and above. Consequently, understanding the phenomena behind the phase transformation during machining is scientifically crucial toward not only better machining efficiencies but also to improve the quality of the parts produced. Up to now, literature only provides phase transformation kinetics under thermodynamic equilibrium condition and relatively low heating rates, which are insufficient in describing the case of high heating rate.
These considerations motivate the current study to improve the understanding of phase transformation involved under rapid heating in the Ti-5553 titanium alloy. Phase transformation on heating was tracked in situ with high energy synchrotron diffraction (DESY). Rapid heating at 10, 50 and 100 °C/s from room temperature to 1050 °C were considered. Phase transformation during heating was studied by a combined analysis of the microstructural features that are: mass fractions, mean lattice parameters and full width at half maximum (FWHM) of the $\alpha$ and $\beta$ phases, which were determined by Rietveld refinement. The monitoring of mass fractions compared to equilibrium calculations (ThermoCalc) revealed a shift of the transformation domain toward high temperatures when the heating rate increased. Furthermore, a change in the transformation kinetics was evidenced whose origin was discussed in terms of differences between the nodular and lamellar morphologies of the $\alpha$ phase. The combined analysis of mean lattice parameters and FWHM suggested that the $\alpha$ phase dissolution on heating was controlled by the diffusion of molybdenum with the $\beta$ phase inheriting the solute content of the adjacent parent $\alpha$ phase, leading to chemical heterogeneities in the $\beta$ phase field regardless of the considered heating rate.

Recently, TRIP/TWIP effects causing high ductility due to martensitic transformation (TRIP) or twinning (TWIP) during loading were found to take place in finely tuned metastable β Ti alloys. These effects, well known from steels, are present in alloys that are in the proximity to β -> α” martensitic transformation after quenching. Typically, such alloys exhibit high ductility and very pronounced deformation strengthening, but their yield point is below 700 MPa. High levels of oxygen cause a substantial improvement of strength in β Ti alloys, therefore, oxygen addition was studied as a way to obtain TRIP/TWIP alloy with high yield strength.

Ti-Nb-Zr-O system has been selected for its potential applicability in medicine (all the elements are biocompatible). High throughput method, consisting of layering mixtures of elemental powders (and TiO2 for oxygen addition) and their compaction and homogenization via field assisted sintering technique (FAST), was utilized for preparation of such alloys. Concentrations of Zr and O were kept constant within each sample, while the Nb content was varied.

Individual layers were studied by scanning electron microscopy and microhardness mapping. Compression tests were performed on the layered samples with simultaneous in-situ measurement of acoustic emission and digital image correlation (DIC). The deformed microstructures were analyzed by electron back-scatter diffraction. Stress induced martensite and {332}<113> twinning was found in layers, containing from 26 wt% to 32 wt% Nb in sample with 0.5 wt% of oxygen and 7 wt% of Zr.

A physical-based model is developed to describe the microstructure transformations that occur during the processing of titanium alloys. The evolution of the microstructure during hot deformation is fully coupled with the phenomena of static recrystallisation and grain coarsening that occur during annealing. Static and dynamic recovery and continuous dynamic recrystallisation are considered as restoration mechanisms for β-phase. At the same time, α-phase deforms via crystal rotation, resulting in dynamic globularisation when the α-phase presents an initial lamellar structure. The microstructure evolves via static recovery or static recrystallisation by strain-induced boundary migration during annealing. The starting condition of the substructure plays a vital role in its evolution during deformation. Larger initial β-grain sizes lead to a fast evolution of the fraction of high angle grain boundaries for a given temperature and strain rate. Finer initial β-grains lead to faster annihilation of dislocations due to high angle grain boundary movement and a finer substructure formation. Thus, higher strains are required to achieve a steady-state condition. The microstructure evolves faster via continuous dynamic recrystallisation if the deformation occurs in a fully recrystallised microstructure considering the same initial grain size and the same initial mean boundary misorientation angle. Deformation at higher strain rates leads to higher stored energy, thus higher nucleation rate during static recrystallisation is achieved. A refined microstructure is not easily achieved because higher stored energy also leads to higher growth rates of the recrystallised grains. During heating and cooling, phase transformation is integrated into the model approach using a simple diffusion-based one-dimensional model. Small variations in the cooling rate or the size of primary α-phase lead to significant differences in the final fraction of the different α-morphologies. The integrated modelling tools enable a comprehensive understanding of the several thermomechanical processing steps of typical Ti alloys.

In the present study, the effect of cold rolling and subsequent annealing on the microstructure and mechanical properties of metastable β Ti-10V-2Fe-3Al (Ti-1023) and Ti-5Al-5Mo-5V-3Cr (Ti-5553) alloys have been investigated. Room temperature cold rolling have been conducted on the alloys (5 mm3 samples). A thickness reduction up to 43% and 45%, respectively for Ti-1023 and Ti-5553 have been achieved. Subsequent annealing treatment in single β phase regime have been considered to effectively control the grain size in both Ti-1023 and Ti-5553 alloys. The annealed microstructures have been analysed for their β grain size using a combination of optical microscopy and SEM tools along with ImageJ package. Grain sizes in the range of 45 to 125 µm and 58 to 130 µm, respectively for Ti-1023 and Ti-5553 have been achieved. The β grain orientations have been obtained using FESEM-EBSD tool. A nanoindentation study on the various grain size and grain orientations of the retained β phase was carried out. The alloys showed stress-induced martensitic (SIM) transformation. The triggering stress for this transformation have been measured at room temperature. A clear influence of β grain size and grain orientations on the SIM transformation have been obtained. As well an understanding on the favourable grain orientations for SIM have been obtained. (100), (101), and (111) orientations have been considered for the SIM study.

A physical-based model is implemented as a subroutine and used in FE simulations to predict the microstructure evolution during hot deformation and annealing of Ti alloys. During hot deformation, the material undergoes dynamic recovery of alpha and beta phases by forming new low angle grain boundaries, followed by continuous dynamic recrystallization. The microstructure evolves via static recovery or static recrystallization by strain strain-induced boundary migration during annealing. The model assumes a microstructure composed of three distinct populations of dislocations named mobile, immobile, and wall dislocations. Constitutive equations correlate the flow stress with the microstructure evolution and the flow softening in the α+β field is considered a result of the change in load partitioning. The grain sizes are related to the high angle grain boundary density. A subgrain is surrounded by low and high angle grain boundaries and is the representative microstructure entity. During deformation in the α+β domain, an initial α-lamellar structure suffers dynamic globularisation due to the formation of new boundaries within the α-platelet, and the model also predicts the evolution of this phenomena. During annealing, the static recrystallization kinetics is temperature and stored energy-dependent, and two phenomena of nucleation and growth describe the microstructure transformations. For validation of the model, the FE simulations were compared with EBSD maps measured after thermomechanical treatments. The results show that the mesoscale model predicts the non-linear microstructure evolution in complex-shaped objects during hot deformation up to large strains. Higher overall strain rates lead to higher wall dislocation production at the beginning of the deformation, smaller subgrain and grain sizes, and higher torque/stress values reached in the steady-state. The formation of subgrains, the progressive increase in boundary misorientation, and the transformation of LAGBs into new HAGBs via CDRX are well described in the proposed mesoscale model.

The two types of magnetic materials most important in applications are permanent magnets and soft magnetic materials, with the latter used in in transformers, electromotors, magnetic shielding, etc. This contribution will report on the discovery of an exceptionally magnetically-soft FeCoNiPdCu high-entropy alloy and investigation of the mechanism underlying its properties. Firstly, SQUID magnetometry was performed indicating interesting magnetic properties comparable to commercially used materials – a high relative permeability $μ_{r,max}\approx 3600$, a narrow and steep hysteresis curve with a coercivity of $H_{c}=115\,\mathrm{A/m}$. These properties were also accompanied by a favourably high electrical resistivity of $33.3$ μ$\mathrm{\Omega cm}$. Secondly, by HAADF STEM microscopy combined with EDS spectroscopy it was shown that during the short annealing of our FeCoNiPdCu at 1100 °C the attractive and repulsive interactions between the different atomic species cause the segregation of the elements in the alloy. The non-magnetic elements Pd and Cu form non-magnetic “spacers“ and the magnetic elements Fe, Co and Ni cluster together into magnetic domains. This particular nanocomposite structure of small magnetic domains and non-magnetic spacers of size just 2 – 5 nm is ideal as it means that the magnetic domains are magnetically single domain but still close enough to be exchange coupled. Thus, the prerequisites of the mechanism of exchange averaging of magnetic anisotropy are fulfilled in FeCoNiPdCu guaranteeing good soft-magnetic properties as long as proper heat treatment is performed.

P. Koželj, et. al. Adv. Eng. Mater 21, 1801055 (2019).

Until the early 20’s, metallic alloys were designed in a conventional way as far as their composition was concerned. At saturation level of their properties, the introduction of High Entropy Alloys (HEAs) challenge seemed to upgrade the commonly used alloy concept and transform the traditional view of metallic materials into an original breakthrough. HEAs have a broad range of structures and properties, and find use in multiple structural, magnetic, high-temperature, and oxidation-resistant applications. Due to their unique properties, these systems have attracted considerable attention both from academics and technologists.
In the present work, phase constitutions, either affected by alloying or structural changes, are explored as the key factors allowing to determine the mechanical and magnetic performance of the Additively Manufactured FeCoNi(AlMn)x systems. The microstructural features and crystal structures of the alloys were characterized, in both as received and heat-treated conditions. Hardness tests, under various indentation loads and dwelling times, were performed to assess the mechanical properties of the prepared samples. The work highlights a process-structure-property (PSP) relationship through creating hardness neural network profiles as a function of constituent elements concentration. Regarding the magnetic properties, the alloys exhibited good soft-magnetic behavior, being easily magnetized to the saturated state with coercivity values of <1000 A/m. Magnetic screening through Magneto-Optical Imaging (MOI), Magnetic Force Microscopy (MFM) and Vibration Sample Magnetometer (VSM) confirmed the importance of the structure evolution in defining the magnetic properties of the alloys. The trends in the magnetic behavior, as a function of the alloy composition are revealed.

We have investigated the nature of the magnetic state in a single-crystalline FeCoCrMnAl nanocomposite high-entropy alloy (HEA), composed of crystallographically oriented magnetic nanoplatelets embedded in a magnetic matrix of different magnetic order. The two-phase nanocomposite was formed by a bcc-B2 spinodal decomposition. Due to the single-crystalline nature of the material, there is no symmetry breaking of the surface atomic monolayer at the borders between the two phases and there are no interface regions between the nanoplatelets and the matrix. The material also does not exhibit grain structure, allowing the observation of a true intrinsic magnetism of a nanocomposite HEA. Upon cooling, the predominantly Fe-Cr-Mn chemically disordered bcc matrix orders first at T_C1≈ 425 K in an asperomagnetic-type magnetic state. Below T_C2≈ 370 K, the B2 nanoplatelets that are predominantly an Al30(Co,Mn)70 pseudo-binary intermetallic compound, start to order in a ferromagnetic (FM)-type manner. We have focused to the question whether the magnetic state of the nanocomposite below T_C2 is a collective state of the interacting nanoplatelets and the matrix or their coupling is weak enough that the magnetic ordering of each of them can be treated independently. Experimental results support the development of a single collective, disordered FM-type magnetic state upon cooling due to the exchange coupling between the nanoplatelets and the matrix. The nanocomposite is magnetically soft and the strong variation of the magnetization with the temperature in a large interval ΔT≈ 125 K just above room temperature due to two successive magnetic phase transitions make this material promising for the application in magnetocaloric refrigeration.

A good soft magnetic material that exhibit properties applicable for commercial soft magnets used in transformers, motors, generators and other electromagnetic machinery should show minimal magnetization hysteresis, low magnetostriction, high saturation magnetic polarization, the highest possible permeability and large electrical resistivity to reduce remanence and losses in static and AC application. Examples of widely used commercial alloys at frequencies from DC up to the audio range (100 Hz–100 kHz) are non-oriented and grainoriented silicon electrical steels, V-permendur, Hypernik, Mumetal, Supermalloy, Metglas 2628SC and Finmet, which possess negligible coercivities. For this presentations, the authors report on the discovery of a perfect magnetically soft high-entropy alloy of composition FeCoNiPdCu, which performs comparably to the best commercial soft magnets. Properly heat-treated FeCoNiPdCu develops nanostructure that can be viewed as a two-phase bulk nanocomposite of randomly intermixed FeCoNi magnetic domains and PdCu nonmagnetic “spacers”, both of 2–5 nm cross dimensions. Due to the nanometric size, the FeCoNi domains are magnetically single-domain particles, and since the particles are exchange-coupled across the boundaries, exchange averaging of magnetic anisotropy takes place, resulting in an almost vanishing coercive field and excellent magnetic softness. The formation of a two-phase nanostructure favourable for the exchange averaging of magnetic anisotropy is a consequence of specific values of the binary mixing enthalpies for the chosen elements. Though high-entropy alloys are generally considered to be random solid solutions of multiple elements on a topologically ordered crystal lattice, clustering of the atoms into preferential chemical environments on a nanoscale essentially determines their magnetic properties (P. Koželj et al., Advanced Engineering Materials 2019: 1801055).

Accurate simulation of finite-temperature properties of metallic alloys is often a challenge for computer-aided materials design, mostly performed with density-functional theory (DFT) calculations.
Not only it requires time-consuming molecular dynamics (MD) simulations to capture finite-temperature effects, but also questions like phase stability at different temperatures arise and become important, especially in the case of high-entropy alloys.
In addition, extensive study of a range of materials is often infeasible due to much time consumed by DFT calculations.

In the present work we tackle the challenge of investigating the relation between elastic properties and dynamical instability of bcc-phase in TiZrHfTa$_x$ alloys in a wide temperature range with varying Ta concentration.

We achieve a great performance boost while not sacrificing much accuracy (compared to DFT) by using both accurate interpolation of ab-initio data and intelligent learning principle (theo so-called active learning), allowing for extracting maximum information from the least possible number of DFT calculations.

For bcc-$\omega$ phases distinction we use recently proposed scheme based on analysis of atomic displacements along transformation directions during finite-temperature MD.
As a result a correlation between $C_{44}$ elastic constant and $\omega$-formation tendency has been revealed depending on the temperature and Ta concentration.

The research involves using such software as VASP (for ab-initio energies/forces), LAMMPS (for MD simulations) and MLIP (for interpolation of DFT data).
The framework proposed in the present work is essentially generic and can be used for different high-entropy alloys as well.

Abradable coatings such as AlSi-PES and AlSi-hBN enable small tip clearances in aeroengine axial compressors by reducing the severity of blade-casing interactions. However, as these abradables are typically plasma sprayed onto the internal surfaces of the casing, the precise makeup and properties of every spray batch are not well defined. This poses significant challenges regarding the simulation of blade-casing interactions and design of new systems, therefore a method for determining abradable properties is needed to better guide these processes.

An inverse analysis method utilizing both particle swarm optimisation and an Artificial Neural Network (ANN) has been created to predict the homogenised mechanical properties of an AlSi-PES abradable based on its Rockwell Hardness. Following this, the homogenised properties are set as target values in a second optimization process where the abradable constituent material properties and microstructural information such as PES content and void volume fraction are determined via a tensile test of an AlSi-PES RVE. The newly determined homogenised properties are to be used during blade-casing interaction simulations, allowing for the system behaviour following an interaction with a specific abradable to be investigated. Furthermore, the microstructural information can be used to better predict the specific abradable failure mechanisms.

This top-down-approach enables a target Rockwell Hardness to be used to determine the homogenised and constituent material properties as well as basic microstructural information of an AlSi-PES abradable. This information can then be used to better inform simulations of blade-casing interactions and the design process.

Tungsten and its alloys have emerged as the promising refractory materials to find applications in nuclear fusion reactors such as International Thermonuclear Experimental Reactor (ITER) and the Demonstration nuclear reactor (DEMO). Despite the attractive properties, limited ductility and high ductile to brittle transition temperature (DBTT) are observed in tungsten. Such behaviour is linked to the competition between bond-breaking and dislocation motion, that can be studied only using the powerful atomistic modelling methods like molecular statics/dynamics. However, these studies are significantly influenced by the quality of employed many-body interatomic potentials. Hence, the prediction capabilities of these potentials in fracture settings, along with the development of our own second nearest neighbour modified embedded atom method (2NN-MEAM) potential and the dependence of fracture toughness of single- and bicrystalline tungsten on different material properties, have been the focus of our present atomistic fracture analysis. The study has revealed (i) the existing embedded atom method (EAM) potentials underestimate the surface energies compared to the 2NN-MEAM potentials, as a result of which the reliability of their predictions of brittle fracture is questionable, (ii) the cracks along grain boundaries (GB, also called bicrystals) possess lower fracture toughness than the corresponding single crystalline cracks and (iii) the lattice (bond for GB cracks) trapping plays a vital role in deciding the fracture toughness and is directly proportional to the interatomic potential dependent ratio of peak cohesive stress, $\sigma_{coh,(klm)}$ (maximum in the traction-separation curve of a surface (klm)) and the maximum interaction distance, $\delta_{sep,max,(klm)}$ (the distance corresponding to zero stress in the traction-separation curve). Thereby, this study provides insights into fracture mechanisms and assists in the further development of potentials suitable for fracture studies.

It is vitally important to consider time dependent (or “viscous”) deformation behaviors when formulating material models, particularly when elevated temperature conditions are present in the intended application. In many macroscopic modelling attempts, time dependencies are limited to “plastic” regions of deformation. Under such modelling paradigms stresses will, under periods of strain hold (for example), relax back to the yield locus and no further. This is in direct conflict with experimental observations, wherein “sub-yield” stress relaxation is easily demonstrated. Limitations in how materials are typically tested in the laboratory, and thus how material model calibration data is interpreted, result in important macroscopic phenomena being neglected. The chromium steel P91 is considered in the present work and an an-isothermal elastic-viscoelastic-viscoplastic material model is developed over an industry relevant temperature range (400°C – 600°C). The developed model is grounded using the generalized standard materials and thermodynamics of irreversible processes formalisms. Calibration of material parameters is achieved through the application of targeted isothermal waveforms in uniaxial loading conditions. An-isothermal predictive capabilities are confirmed through application of the model to non-standard in-phase and out-of-phase thermo-mechanical waveform, in which strain and temperature rates are varied within a cycle itself. Strain rates between 0.1%/s and 0.001%/s are considered, with corresponding temperature rates ranging from 16.5°C/s to 0.17°C/s The additional effort of calibrating viscoelastic terms is justified by contrasting the model results with those generated by a simpler elastic-viscoplastic model. Many critical components are designed such that they experience extended periods of operation at modest load. Long term time dependencies excited by these conditions, as indicated by full multiaxial implementations of the two models in commercial FEA packages.

A recent study suggests about 20 % of the consumed energy worldwide is related to friction and 18 % of this energy can be saved. Carbon alloyed transition metal dichalcogenide coatings present a tremendous potential in domains where friction reduction is aimed. They possess exquisitely low friction coefficients in diverse environments and can self-adapt to a variety of sliding conditions. In this investigation, a DC magnetron sputtering device is utilized to deposit MoSeC coatings with carbon content from 6 to 60 at.%C. Then, with compositional, morphological, structural, mechanical and tribological characterization techniques, the influence of carbon content on the final MoSeC film performance is analyzed. A decrease in the chalcogenide over transition metal (Se/Mo) ratio with an increasing carbon content of the films was observed. SEM (scanning electron microscopy) allowed to detect a columnar cross-sectional growth with high porosity and roughness for the pure MoSe₂ films but less voids and continuously more compact development for medium and high carbon content coatings. The scratch test has shown the occurrence of the best adhesion strength for the 51 and 60 at. % C films. The stiffness and hardness of the coatings increase almost proportionally to the carbon content of the films, except for the two highest carbon content films, in which these properties almost stagnate. From POD (pin-on-disk) experiments performed in humid air, NBR (nitrile rubber) countersurfaces sliding against MoSeC demonstrate higher friction values than the steel countersurfaces rubbed on the coating, and that the CoF (coefficient of friction) is higher at 25°C than at 200°C. The lowest absolute specific wear rates were achieved for the 51 % of at. C, which combines increased hardness, stiffness and compactness. The study shows the potential of TMD-based coatings for friction and wear reduction sliding against rubber.

Owing to their advantageous properties such as a high hardness and good oxidation resistance, Ti(Al)SiN protective hard coatings can be used for metal cutting applications. Within this work, the microstructure of arc evaporated TiN, TiSiN and TiAlSiN coatings with low Al contents of 3 and 14 at.% was correlated with their mechanical properties. X-ray diffraction (XRD) as well as scanning electron micrographs of the cross-sections revealed a pronounced grain refinement upon addition of Si and Al to TiN. Furthermore, XRD pole-figures showed a change in texture of the coatings from a (111) preferred orientation for TiN to a (200) texture for Ti(Al)SiN coatings. A significant increase in hardness of more than 10 GPa when adding Si and Al to TiN was detected by nanoindentation. In order to gain a more detailed insight into the mechanical properties of the Ti(Al,Si)N coatings, micromechanical bending tests were conducted that showed an enhanced fracture stress and fracture toughness ($K_{IC}$) for Ti(Al)SiN compared to TiN. Hereby, the initially rather low $K_{IC}$ value of 2.4 ± 0.3 MPa√m for TiN could be increased to 3.3 ± 0.2 MPa√m for the TiAlSiN coating with an Al content of 14 at.%. The present findings provide a systematic overview of the microstructure and mechanical properties of arc evaporated Ti(Al,Si)N coatings, thus allowing to assess the suitability of these coatings for the cutting industry.

Keywords: hard coatings, arc evaporation, Ti(Al)SiN, micromechanical testing

Functional coatings (thin films and multilayers) are widely applied in technological applications due to the tunability of their mechanical, thermal, optical and electro-magnetical properties. An important factor which affects their reliability in applications, is the intrinsic stress generated during the deposition process, which can determine unwanted effects as cracking, peeling, and as well as a inferior thermal instability; contrariwise, in some cases stress can strengthen the mechanical properties. For these reasons, understanding stress generation and evolution mechanisms during thin films and multilayer fabrication and post high temperature processing, is paramount to achieve stress tailoring and engineer-ing for specific applications. This work focuses on Cu/W nanomultilayer (NML) systems; the high number of interfaces in such NML systems was found to govern their final stress state and thermal stability [1,2]. Cu/W NMLs with variable individual layer thicknesses are produced by DC magnetron sputtering, while in-situ monitoring the substrate curvature during growth by a multi-beam optical stress sensor (MOSS) technique. In-situ stress data are acquired at different deposition conditions (pressure, DC power, temperature): 1. to rationalize the stress development inside the NML systems, 2. to correlate it with the films microstructure and stability at high temperatures and 3. to control the desired final stress state. The curvature data will be compared to the ex-situ characterization performed by XRD.

[1] F. Moszner, C. Cancellieri, M. Chiodi, S. Yoon, D. Ariosa, J. Janczak-Rusch, L.P.H. Jeurgens, Thermal stability of Cu/W nano-multilayers, Acta Mater. 107 (2016) 345–353.
[2] A. V. Druzhinin, D. Ariosa, S. Siol, N. Ott, B. B. Straumal, J. Janczak-Rusch, L. P. H. Jeurgens, and C. Cancellieri, Effect of the individual layer thickness on the transformation of Cu/W nano-multilayers into nanocomposites, Materialia 7, 100400 (2019).

In the recent years, a shift from rigid to flexible electronics was observed where the latter enables new degrees of freedom in the design of consumer products like displays, wearable sensors, solar cells, among others. Unlike in rigid electronics, thin film materials used in flexible electronics are deposited on thin compliant polymer substrates and they have to withstand various static and dynamic mechanical loading conditions in order to ensure that the flexible electronic devices remain operational for a sufficiently long period of time. Among these loading conditions are also tribological exposures and, hence, suitable characterisation methods and strategies are needed to analyse friction and wear for a variety of tribological contact situations. In the present work, thin Mo films were deposited by high power impulse magnetron sputtering on polyimide substrates and tested in a ball-on-disk test configuration against a series of counterpart materials. The latter included polymers, steel, ceramics, rubber and glass to establish different tribological contact situations. The obtained results provided a basis for tests where the tribological exposure was combined with stretching. Here, pre-conditioned films were prepared by straining to different strain levels including the crack onset strain and strains within the crack saturation regime. Subsequently, these samples were tribologically tested using the same parameters. A comparison of the results from both experiments revealed information about how straining of the films and crack formation influence the tribological behaviour of the deposited Mo films. This knowledge is intended to aid establishing design rules for the synthesis of thin films on polymer substrates that can be used in flexible and wearable electronics.

Hydrogen-free amorphous carbon films gain increasing importance as wear resistant protective coatings in high-wear applications and are in industrial use on cutting tools and sliding components, especially in the automotive industry. Despite the broad use of these coatings in many applications due to their extremely high hardness, they reach their limits in applications with locally very high stress concentration.
Tailoring the (mechanical) properties often is an effective means for maximum performance in specific applications. Doping amorphous carbon coatings was found to be a promising approach to alter coating properties like hardness, residual stress, tribological interactions, surface energy, electrical resistance and others. The deposition of doped carbon coatings is easily realized with the LaserArc technique, because of its flexibility in the arc evaporation of manifold materials.
This presentation focuses on the effect of doping tetrahedral amorphous carbon coatings (ta C:X) deposited by LaserArc on the mechanical properties, especially fracture tolerance, for which an extensive investigation is given for the first time. For this purpose, ta C:X coatings doped with Boron, Molybdenum, Silicon, Copper and Iron were produced. The coatings were characterized by scratch testing, indentation fracture testing, high deformation bending on cylindrical mandrel and Raman spectroscopy.
The test evaluation was focused on the investigation of failure characteristics, especially crack appearance and the development of specific parameters for assessing the crack tolerance. Cross sections prepared by focused ion beam milling were utilized to investigate the indentation-induced cracks beneath the surface.

Wire arc additive manufacturing (WAAM) is a group of technologies suitable for producing large and/or thick parts due to high material deposition and building rates. Among many materials processed by WAAM, austenitic stainless steels, e.g. 316L, are of the most industrially relevant. The microstructure of WAAM 316L thin parts has extensively been studied, however, multiwalled WAAM 316L remains largely unexplored.

Hence, in this study, the microstructure over many beads, i.e. the repeating AM structure, of multiwalled 316L WAAM parts, produced with different building strategies, is characterized in detail, using optical microscopy with a specially designed automated stitching algorithm, scanning electron microscopy, electron back-scatter diffraction, energy dispersive X-ray analysis, and micro-indentation. The macrostructure of the part consists of large and highly-oriented columnar grains dominated by epitaxial and competitive growth. Long grains, crossing several layers, aligned with the building direction, were identified at the overlapping regions between adjacent weld beads. The long grains exhibited a strong <100> texture aligned with the building direction, demonstrating a strong influence of the building strategy on the microstructure. The microstructure consisted of two main phases, austenite matrix and ferrite with vermicular and lathy morphologies, with dispersed micron-sized silicon-rich oxide inclusions.

All this full-field microstructural information is mapped to an average bead shape to obtain maps of statistically averaged microstructure maps, by employing a novel micrographs mapping methodology for obtaining the representative repetitive microstructure cell of additively manufactured parts [1]. The statistically-averaged spatial variations across an additively manufactured part will be discussed and compared to thin-wall WAAM 316L literature.

[1] L. Palmeira Belotti, J.P.M. Hoefnagels, J.A.W. van Dommelen, M.G.D. Geers, A method for extracting average microstructure cells from micrographs of additively manufactured parts, submitted for publication (2021).

The use of additive manufacturing to fabricate metallic components following design optimization as well as the full Design for Additive Manufacturing (DfAM) paradigm, is now a consolidated reality. The ASTMF42 and ISOTC261 -defined powder bed fusion (PBF) and directed energy deposition (DED) processes are able to build metallic components using layer-upon-layer strategies, which are characterized by peculiar features. In the present study, two laser-based equipment from Prima Additive were used to fabricate samples starting from a micrometric pre-alloyed metal powder of 316L stainless steel. During the laser powder bed fusion (LPBF) process, powder particles in the range of 10-45 µm are spread on a building plate by a recoater blade and selectively fused by a laser source, while during the powder-DED process, particles with a diameter between 45 µm and 106 µm are injected through the path of a high-energy laser and deposited on the surface of interest as a molten metal. The main differences between the two process stand in the powder dimensions, energy input and overall speed of the process. These have a great influence on the final properties of the fabricated parts and on their microstructure, since LPBF has a resulting cooling rate which goes up to 106 K/s, while DED stand in the 103-105 K/s range. By using a wide range of characterization techniques, from optical and scanning electron microscopy (OM, SEM) to microhardness, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), the present study shows that it is possible to tailor the process parameters (overlap/hatch spacing, layer thickness, build rate, laser power) and post-process parameters (i.e. time and temperature during heat treatments) in order to reach a unique microstructural and metallurgical configuration, without changing the crystallography and the chemical composition of the starting 316L stainless steel alloy.

Additive manufacturing (AM) is one of the most rapidly developed fabricating techniques over last two decades. The microstructure feature or the residual stress distribution in AM components was widely investigated on its own. However, limited studies were attempted to reveal the correlations between the microstructure and residual stresses in AM components. In this study, high-energy synchrotron X-ray with the cross section of 0.5 mm × 0.5 mm was applied to determine the localized fluctuation in residual stress distribution for direct energy deposited 316L stainless steel thin plate with complementary microstructural investigation. The residual stress in macroscopic scale progressively varies with the changing bulk cooling rate, which was implied by the secondary dendrite arm lengths. The abrupt localized fluctuation of residual stress at meso-scale was revealed along with the corresponding variations in dendritic morphologies. Potential correlations between the meso-scale residual stresses and the microstructure morphologies were analyzed considering localized solidification conditions.

Low-alloy steels are one of the alloy systems missing in the materials portfolio of laser based powder bed fusion (LB-PBF). From a LB-PBF processing point of view, this primarily relates to their susceptibility to cold cracking that stems from their elevated carbon contents. There are number of recent works in the literature showing that in-situ annealing through build plate preheating can alleviate cold cracking issues, producing high-density (>99.8%) and defect-free low-alloy steel specimens. However, the effect of trace elements (e.g., B and P) on processability of low-alloy steels by LB-PBF remains unclear. This study details the influence of B and P on defect formation and mechanical properties of various 4140 low-alloy steel grades. Said study was carried out using gas atomized powder and printed with an EOS M290 machine using a build plate preheating of 180 ˚C. Results indicated that high specimen densities (>99.8%) could still be achieved. However, both B and P can cause micro-cracking within the as-built specimens. The influence of the observed micro-cracks on the mechanical properties were evaluated using Charpy and tensile testing. The B-containing specimens showed an improved material toughness when compared to the P-containing specimens. Furthermore, a fractography study on fractured specimens with scanning electron microscopy was used to identify the failure micro-mechanism and the characteristics of the formed cracks. From these results an improved understanding of how B and P affected the LB-PBF processing of 4140 low-alloy steel could be established.

Additive Manufacturing (AM) technologies can realize complex-shape structures, previously not feasible with subtractive manufacturing machines. From Computer-Aided Design (CAD) to a slicing software, which creates a G-code machine routine, it is possible to realize three-dimensional (3D) parts layer by layer. In the past, 3D printing was used only for rapid prototyping due to the required high tolerances and the low performance of the materials used. Nowadays, AM technologies are improved to the point that 3D printed parts can sometimes be used without tooling or post-processing. Directed Energy Deposition (DED) is a metal Additive Manufacturing (AM) process, where a 3 or more-axis arm moves an extruder with one or more nozzles and a laser beam that melts the powder particles. Parts realized with this technology are always near-net-shape. Due to high cooling rate of the DED process the melt pool is subjected to rapid solidification generating peculiar and thermally unstable microstructures. Therefore, the aim of this research is to characterize the microstructure of as-built DED samples and to understand the effects of a heat treatment. A set of the samples was indeed subjected to an annealing at 1150°C for 2h followed by cooling in air. Optical microscopy (OM) and scanning electron microscopy (SEM) were used together with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) to fully characterize the crystallography and the microstructural and metallurgical features of the as-build and heat-treated samples. Results showed a dendritic microstructure of the as-built 316L stainless steel which is highly influenced by the local cooling rate. Furthermore, preliminary results on the heat-treated samples highlight a peculiar evolution of the austenitic-ferritic microstructure linked to the temperature reached during the annealing phase, suggesting that tailoring the post-processing thermal treatment can be crucial to fully exploit the potential 316L processed by DED.

The SisAl Pilot project is an EC H2020 financed collaboration between 21 partners in the (silicon and aluminum) industry, universities and research institutes. It aims to develop the low carbon SisAl process as an alternative to the traditional carbothermic silicon production process.

The SisAl process encompasses the production of silicon alloy by reducing silica (SiO2) in CaO-SiO2 slag aluminothermically to produce the alloy along with a CaO-Al2O3 slag. Before the process can be implemented at a larger industrial scale, the aluminothermic process must be better understood, in particular the kinetics of approaching phase equilibrium.

Initial experiments were performed in a small-scale laboratory environment, where Al in the form of either pure Al-blocks or Al-dross at different amounts were mixed with pre-fused slag with a CaO/SiO2-ratio of 0.7, 1.0 and 1.2, heated to at 1650 °C and held from 20 to 180 minutes. Phases were subsequently separated and analysed. For some trials the effect of kinetics on Si yield was investigated with varying holding times and by upscaling by a factor of approximately 7.5 (in terms of mass) using a larger but similar induction furnace. The results show that (i) the Si alloy is produced rapidly due to liquid-liquid reactions and (ii) the Si yield mainly depend on the separation ability between Si-metal and the CaO-Al2O3 slag. Aluminium dross was found to be a suitable reductant for silica in slag, enabling a circular economy perspective on this secondary stream.

The climate crisis and the halting of climate change require the industry to detach itself from fossil fuels, both as an energy source and as an input material in processes. The steel industry in particular is called upon in this regard, as it is a significant contributor to the current situation, accounting for ~6-8% of the anthropogenic CO2 equivalent. The presentation will focus in addition to the fundamentals of hydrogen use in industry, on the most important economic points for the future hydrogen-based steel industry. Therefore the production, the future application, and the availability of hydrogen will be presented. Besides, the extent to which the use of hydrogen in metallurgy makes sense now and in the future will be shown. Additionally, the role of Hydrogen Plasma Smelting Reduction (HPSR) and Hydrogen Fineore Reduction (HYFOR) for the future steel industry are explained, and a concept for the industrial processes is presented. All of this should conclude, under which conditions the metallurgy of the future can largely disband from carbon as a reducing agent.

Abstract: The surface tension of liquid iron copper binary alloys containing 0.25 mass %, 0.75 mass %, 1.0 mass % and 2.5 mass % of copper has been investigated in the temperature range 1575 °C to 1650 °C in steps of 25 °C using the sessile drop method (SD). The sessile-drop experiments in a heating microscope have been conducted in Argon atmosphere at low oxygen partial pressure (up to 〖P_(O_2 )=10〗^(-22) bar). The sintered Al2O3 ceramic was applied as substrate. The results indicate that the surface tension of binary iron-copper increases with increasing of temperature. The kinetic of copper evaporation (1.0 mass % as an example) under the experimental pressure (1 bar) was discussed. In order to deeply study copper evaporation process, parameters such as vapor pressure of pure copper and the copper diffusion in the Ar atmosphere D_(Cu-Ar) at the present experimental conditions were calculated and those influence on the evaporation process was discussed.

Keywords: Fe-Cu System, Al2O3, Surface tension, Diffusion, Copper evaporation

A comprehensive experimental and theoretical study of the thermo-physical, thermodynamic, physico-chemical properties of steels and also the modeling of the processes of steelmaking it allow to achieve the top quality of the cast, semi-finished steel product, which is comparable or superior with the quality of world producers of these materials. The paper is focused on the study of phase transformations temperatures in different types of high-alloy steels during its solidification process. The field of the research reflects current world trends in the field of new steel grades, microstructure and mechanical properties of steel, subsurface and surface quality of final products, etc. The realization of highly specialized measurements of thermo-physical properties of steels, respectively the knowledge of phase transformation temperatures (liquidus and solidus temperatures) of steels, is the basic precondition for successfully understanding (manage) the process of cast of steels with the high internal homogeneity. Based on this information, important and significant parameters are specified in the whole technological flow of steelmaking production. Knowledge of those temperatures in combination with utilisation of the method of numerical modeling (setting of boundary condition of numerical simulation of steel solidification process) can then improve the quality of cast steel without any additional treatment.

Modern steel grades are subjected to constant development to perform weight reduction, energy-saving, and automobile safety performance. In the last decades, high strength and ductile steels were developed with increasing quantities of silicon and manganese. Three of these alloying concepts are Dual-Phase (DP), TRansformation Induced Plasticity (TRIP) and even TWinning Induced Plasticity (TWIP) steels. All these steel grades are based on the iron-carbon-manganese system with additions of ferrite former such as silicon and/or alumina, followed by micro-alloying elements. The main difference compared to previous steel grades are the significantly higher levels of ferrite formers.

Apart from the research on these new steels' material and product properties, the knowledge about the production process, particularly the continuous casting (CC) and the initial solidification in a water-cooled copper mold, is of significant importance. In this regard, the high-temperature phase transformation temperatures and the thermodynamic properties play a particular role.
An efficient pre-identification of hypo-peritectic steel grades by experiments or thermodynamics is relevant to ensure surface quality, productivity, and operational safety in the casting process. The potential of different laboratory experimental methods and thermodynamic approaches is critical evaluated in comparison with operational experience.
Since process data in the continuous casting process often overlap with different operating influences (e.g. casting speed changes, width adjustments…), a new approach is presented to identify the process behavior of peritectic steels without additional effects. For this purpose, operating data from the mold monitoring were processed statistically, and only data areas with a steady-state casting length of more than 100 m were used for further consideration. Using this data preparation method, the peritectic area in the continuous casting process can be clearly described. Statistically prepared process data and experimentally verified thermodynamic data are the basis for the development and validation of demanding process models.

Atomic-resolution imaging with a spherical aberration-corrected scanning transmission electron microscope (STEM) is now widely used for the study of interesting, complex material systems. This is owed both to the flexibility in detecting the electrons scattered off from matter, but also to the improved efficiency in collecting spectroscopic signals. Different variants of bright and dark-field imaging techniques provide unprecedented structural insights and electron energy-loss (EELS) or X-ray (EDXS) spectroscopy, have enabled elemental-specific imaging at that scale, while allowing for supplementary electronic and chemical information. The simultaneous collection of all these signals (“multi-modal STEM”) at various observation angles even, defining the technique of STEM-EELS/EDXS tomography, has given unprecedented insight into the 2D and 3D structural and physico-chemical material make-up.
Fundamental research in physics, chemistry and materials science is currently strongly empowered by electron microscopy - to name a few topics: Understanding transport properties (such as charge localization, band versus ballistic transport or the interplay between lattice strain, band structure and charge transport…). Fundamental aspects of spintronics (such as the interplay of structure, chemistry and defects and their role in complex oxides, doped semiconductor materials and other nanostructures,…). Understanding the physics fundamentals of photonic materials (such as excitonic or polaronic coupling, photonic density of states 3D reconstructions, …). In materials science: Improving and understanding defect-engineering (such as the role of dislocations, and remedies to improve mobilities in electro-active materials ,…) or the understanding of phase formations and transitions (like precipitation formation in metals and alloys, role of coatings and additives of precursor powders used in 3D printed materials…).
Overall, the STEM represents a quantitative instrument, which is capable of providing numerical data on some key properties of matter. The talk aims to give an overview to spectroscopic imaging in 2D and 3D, by showcasing some highly topical research questions on selected material systems.

Investigating and analyzing materials - especially comprising light elements - at both high spatial and spectral resolution has always been a challenge requiring sophisticated equipment such as UHV Auger microprobe systems or transmission electron microscopes equipped with an electron energy loss spectrometer. Moreover, these methods need advanced sample preparation techniques and are only suitable to analyze extremely thin layers.
In order to pave the way for easily accessible high-end spectroscopy of even bulk materials, JEOL has developed a new type of wavelength dispersive spectrometer (WDS) that can be mounted on common scanning electron microscopes or electron microprobes. It utilizes a variable grating, allowing the efficient and parallel collection of very low-energy X-rays (so called “soft” X-rays). This new Soft X-ray Emission Spectrometer (SXES) not only exhibits high spectral resolution (0.3eV) which allows, e.g., for the Nitrogen Kα and Titanium Lℓ line to be separated, but also ultra-high sensitivity to detect light elements down to Lithium to facilitate battery material research. Especially, those light elements like Beryllium or Boron can be detected at low 2-digit ppm concentrations.
Additionally, the spectrometer is suitable for chemical bonding state analysis. Differences between conduction band and valence band electrons can be observed as long as they emit X-rays allowing the distinction between bonding and crystal structure in samples containing the same elements. As proof, spectra shifts when observing hexagonal and cubic boron nitride are presented as well as mappings of Fe2B and FeB coatings.
Among other examples, we will also show results on Nitrogen trace element analysis in steel, differentiation of polymer species and characterization of doped amorphous carbon layers.

The focus of this talk is to present both the fundamental and practical limitations of the emerging technique of correlative Raman-SEM-EDX microscopy and to introduce the benefits of this technique using concrete project examples.
Recent years have seen the introduction of commercially available systems that integrate fully capable Raman microscopes with scanning electron microscopes (SEM). This opens up the exciting possibilities of combining high resolution SEM and elemental analysis by energy dispersive X-ray spectroscopy (EDX) with chemical mapping by Raman microscopy for a broad audience from fundamental research to industry. However, when it comes to correlative Raman-SEM, in addition to having the equipment it is also necessary to have experience with both measurement techniques. This is due to a multitude of issues including sample preparation, beam damage/sample contamination (both electron beam and laser), correlation of the Raman mappings and the SEM-EDX data, spectral interpretation especially of the Raman spectra and the inherent limitations that are put on Raman and SEM-EDX by requirements to combine both techniques. A lot needs to be considered in correlative Raman-SEM-EDX microscopy and some general best practices guidelines are very helpful for anybody venturing into this field of research.
Our first focus is to present advice how to deal with the inherent difficulties of correlating Raman and SEM-EDX data/ measuring Raman and SEM-EDX on the same sample. Our second focus is to demonstrate the advantages of this correlative approach using examples from ongoing research projects. Therefore, we are discussing fundamental considerations and limitations that arise for all involved microscopic techniques due to the correlation, best practices guidelines during sample preparation/measurements and the benefits that correlative Raman-EDX-SEM brings especially for complex composite samples.

MAX phases are a highly anisotropic material, giving rise to a large variation in their properties depending on orientation of the crystal lattice. Typically, orientation can be determined through Electron Backscatter Diffraction (EBSD), is a powerful technique with very high spatial resolution and the ability to determine strain in a crystal structure. However, it requires a high level of sample finish, long scan times and can be limited but sample size dependant on the machine used. Raman spectroscopy is highly sensitive to the anisotropic nature of the MAX phases, leading to significant changes to full width half maximums and intensities of peaks. Raman has a lower spatial resolution ( ~700 nm), but requires essentially no sample preparation and allows for rapid acquisition of data in comparison to EBSD. Therefore, we have been able to correlate orientations provided by EBSD to Raman spectra taken in those grains, allowing for rapid orientation analysis of samples.

As Raman is sensitive to changes in bond length, it can analyse strain at the bonding level, as any change in bond length will lead to a shift in the Raman peak. This makes it an incredibly powerful technique for MAX phases as peaks relating to the M-A and M-X are segregated into two different regions of the Raman spectra. This means it is possible to determine how strain is being accumulated in the different layers of the MAX phase. As each peak shows a specific shift, dependant on orientation and loading orientation, correlating to a specific strain. Therefore, we can determine the extent of the non-homogeneous deformation of the MAX phase lattice through Raman spectroscopy.

The fabrication of heterostructures consisting of one-dimensional (1D) and two-dimensional (2D) nanomaterials, based on top-down and bottom-up approaches, as well as their functionalization processes, have drawn much attention over the last decade. Carbon nanotubes (CNTs) and graphene are the most widely studied carbon allotropes that represent the 1D and 2D nanostructures, respectively. Structural characterization and characterization in nanoscale are of great importance to determine their remarkable properties, such as magnetism, piezoelectricity, thermal conduction and others. Because of their unique structural, electrical, mechanical, chemical and optical properties, 1D and 2D carbon nanostructures, hold promising opportunities for the development of new composite materials and have found their way to a wide range of potential applications in energy storage, optoelectronics, electro-chemical/mechanical systems and the environment (e.g. filters). The continuously increasing interest in engineered carbon-based nanomaterials both for research and commercialization purposes, resulted in public and private investments that focus on manufacturing and industrial uptake, with leading manufacturers investing approx. over 1€ Million/year in R&D.
According to the above, R-NanoLab’s research activities focus on the synthesis of CNT and graphene derivatives. CNTs have been applied in coatings providing anticorrosive and antifouling properties, and have been incorporated in polymer matrices to increase the thermal, electrical conductivity and mechanical properties. 1D nanostructures are tested also for the development of flexible supercapacitors, by using conductive carbon-based dispersions. Carbon-based inks for 3D printed biosensors have also been tested. CNTs are also investigated for their capability to sense the crack initiation and increase the mechanical properties when introduced in cement-based structures. Graphene derivatives are synthesized and used for the development of hybrid materials with advanced properties, as well as for their use in recycling activities.
For all the above, advanced characterisation techniques have been exploited, in order to study the properties and performance of the 1D and 2D nanomaterials.

Carbon-based hybrid materials are an important class of artificial materials with potential applications in various fields ranging from energy storage (e.g. harvesting) to recycling applications (e.g. smart debonding). For this reason, both their synthesis process and the assessment of their properties are of high interest. Herein, we present a brief summary of recent developments in the area of functional hybrid materials comprising one-dimensional (1D) carbon allotropes. One of the investigated hybrids are magnesium silicide thermoelectric carbon nanotubes (Mg2Si/CNT) for use as smart flexible n-type thermoelectric materials; these were successfully synthesized through a combined sol-gel and thermal reductive process.
Furthermore, the in-situ growth of CNT-hybrids through chemical vapour deposition process (CVD), was proved to be a facile way to create hybrid materials with unique and interesting properties. In this perspective, the synthesis of hybrid microwave and radiofrequency assisted materials has been investigated, based on metal and ceramic nanoparticles. Synthesis of CNTs on magnetic nanoparticles such as ZnFe2O4 and Fe3O4 was accomplished in a one-step CVD procedure. These hybrids can be used on recycling applications for thermoplastics including carbon fibres, by enabling local heating around the fibre and thus, smart debonding. Also, nanosized silicon carbide has been exploited by utilising the floating catalyst approach, in order to grow SiC/CNT hybrids. The aim for this microwave assisted material is to be incorporated into coatings in a concentration lower than 1 wt. %, in order to provide selective heating on the interphase between the coating and the plastic substrate. By this, smart debonding applications for effective polymers recycling can be achieved.
Acknowledgments:
This study was partially funded by the Horizon 2020 Projects "FAST-SMART", under G.A. 862289 and “DECOAT” under G.A. 814505.

Carbon-based nanomaterials have been proven to be cutting-edge filler materials with advanced thermal and electrical properties, while their nanodimensions facilitate the development of defect—free mechanically robust crystal structures. Their strong hexagonal sp2 lattice allows free electron mobility in plane as well as thermal transport. In particular, carbon nanotubes (CNTs) and graphene, are ideal to add multifunctionality to reinforced composites. In this work, two applications are investigated, i.e., a) functional thermoplastic materials with self-healing properties and application in leisure and every-day life, and b) functional thermoset materials with application on industrial heat management devices with complex architectures, such as heat sinks manufacturing.
The development of these composites covers the need for sustainable, cheap, and re-/up-cyclable composites with advanced thermal functionality. In the first case, Thermoplastic polyurethane (TPU) is reinforced with graphene nanoplatelets (GNPs) and CNTs and self-healing was demonstrated. Due to the high resistance of the polymer matrix, a high portion of electric energy is converted to thermal energy. Local temperature is monitored by using an infrared camera and can reach up to 160oC, and induces local melting and annealing of the TPU matrix. In the case study of a 3D-printed specimens with the TPU masterbatch formulations enriched in GNPs and CNTs, self-healing properties are demonstrated, both in the produced 3D filament and printed parts. Thus, any wear damage will be viable for the nanocomposite and consequently the life cycle will be extended. On the other hand, epoxy-based composites suitable for heat-sink application are also reinforced with GNPs and CNTs to fabricate complex and miniaturized structures. The successful demonstration of enhanced dissipation of heat is realized by achieving composite thermal conductivity equal to 1.4 W/m∙K exceeding many of the published state-of-the-art results.

Carbon nanostructures and specifically nanotubes (CNTs) are materials of significant importance in nanotechnology. They have a wide range of applications ranging from automotive to aeronautics, due to their exceptional mechanical properties such as strength and stiffness-to-density/weight ratio. The synthesis of CNTs includes a variety of methods amongst which the chemical vapor deposition (CVD) is the more attractive, since it can be used for their large-scale production with moderate cost. CVD is an extending technology used for growing thin films and coatings on surfaces, often complex-in-shape. In CNTs production, CVD provides the possibility of controlling the structure of the produced materials and as a consequence their properties. For this reason, it is necessary to control the complex chemistry reactions and transport mechanisms involved in a CVD process.

In this work, a combined experimental and computational investigation is conducted for the growth of CNTs on silicon wafers and carbon fibers fabrics by CVD, with supported and floating catalyst, respectively. The phenomena occurring at the macroscopic level are governed by the conservation equations of mass, momentum and energy combined with the kinetics of the gas phase and surface chemical reactions. The analysis provides information for the flow field and the dominant reaction mechanisms and it reproduces the experimental data successfully in terms of the produced CNTs mass. It also provides valuable information for CNTs properties, such as the termination length and it illustrates their dependence on the process temperature and flow conditions. The presented computational investigation combined with targeted experiments provides an integrated tool for the understanding of the phenomena occurring at the macro-scale of a CVD reactor promoting the optimal design and the upscaling of the process.

Acknowledgements

This study was funded by the Horizon 2020 Project “SMARTFAN», under G.A. 760779.

The increase in the market share of electric vehicles is strongly linked to the increase in autonomy, to the reduction of costs and charging time of batteries, without forgetting to mention that the new generations of batteries will have to offer at least the same life span and safety than current batteries. Concerning the anodes of Li-ion batteries, graphite-integrated silicon composite is an alternative to any graphite which should make it possible to reach the evoked performance objectives. This composite is already integrated in some commercial batteries and is part of the roadmap of many industrials of the sector.
If Silicon is one of the most promising negative electrode (in combination with Carbone) for LIB and sodium-ion (NIB) batteries its practical application is hindered by a series of obstacles. For lithium (Li), the access to high lithiated phases causes extreme volume expansion (310%), resulting in a rapid capacity fade and for sodium (Na), the slow kinetics and the ionic radius restrict the sodiation of c-Si. We have used various strategies to address these issues by playing i) on the nanostructuration of Si in a carbon matrix, ii) on the alloying of Si with higher conductive element such as Ge or iii) by preparing a lamellar Si structure. The latter approach will be detailed and discussed.

Lithium-ion batteries have revolutionized the field of energy storage. World battery production has exploded in recent years, and demand will continue to grow in the future. However, there are fears of supply or cost problems for certain raw materials. Faced with this observation, it is therefore important to consider an alternative to the lithium-ion technology.
Among the so-called “post-lithium” systems, the Mg-ion batteries are interesting. Magnesium metal theoretically exhibits high capacities, and its low redox potential is compatible with the design of batteries with high energy densities. However, the difficult diffusion of Mg2+ ions in the classic host structures of positive electrode materials (layered or polyanionic compounds) is a challenge. The solution could be to consider positive sulfur-based electrodes, whose electrochemical conversion process also theoretically offers high theoritical capacities. The first electrolyte formulations proposed are in particular the Mg(HMDS)2-AlCl3 or MgCl2-AlC3 mixtures in ethereal solvents. The presence of chlorides increases the corrosive nature of the electrolyte, which is not suitable for industrial transfer. We proposed in 2019 the use of alloys to replace magnesium as the negative electrode and thus be able to use simpler electrolytes in particular based on Mg(TFSI)2. This follows from the good electrochemical behavior of certain elements of the p-block (bismuth, tin, etc.) with the magnesium ions. We will present here a first evaluation of the alloys Mg3Bi2, Mg2Sn and Mg2Pb prepared by mechanochemical synthesis, and the comparison of their electrochemical behavior in a system as standardized as possible. With the same objective, we will also present methods to create artificial layer of the same p-block elements on the magnesium surface.

French National Research Agency (ANR-19-CE05-0013 and ANR-10-LABX-76-01) are acknowledged for funding.

Future renewable energy integrated grid systems require rechargeable batteries with low cost, high safety and long cycle life. The much higher abundance and fair distribution of potassium compared to lithium in Earth crust indicates that rechargeable potassium batteries can represent an attractive replacement for lithium-ion counterparts. Rechargeable potassium batteries have gained tremendous attention during the past decade [1,2]. However, the development of rechargeable potassium batteries is still in its infancy.
Due to the large atomic radius of potassium, some electrode materials that are commonly used in Li‐ion systems are not suitable for potassium batteries. Thus, anode materials for these energy storage systems are mainly based on carbon materials, metal alloys and potassium metal. On the other hand, cathode materials can be divided into three categories: Prussian blue and its analogues, layered metal oxides and polyanion oxides.
In this emerging field, the main challenges are: i) achieving a strong structural stability of newly developed electrodes; ii) inhibit the formation of potassium dendrites and build a stable electrode/electrolyte interface; iii) trying to find an electrode to be considered as a reference/standard system when evaluating the performance of newly synthesized compounds for anodes and cathodes. In this contribution, a systematic study of a series of potential systems for anodes and cathodes in potassium batteries is presented, figuring out the most promising strategies to design lab-scale working devices.

References
1. W. Zhang et al., Nano Energy 2021, 83, 105792.
2. Y. Liu et al., Small 2020, 16, 2004096.

Politecnico di Torino is gratefully acknowledged by F.B. and L.F. for granting the fund named “Contributo ERC per chi ha superato il primo step di valutazione”.

In recent years, δ-MnO2 birnessite appeared as a promising positive electrode material for both hybrid supercapacitors and aqueous batteries due to its layered structure, which favors ionic diffusion, its low cost, high abundance and environmental friendly character. The δ-MnO2 phase possesses a high theoretical capacity (~300 mAh/g), however its low electronic conductivity strongly limits the electrochemical applications of the material [1]. In order to increase intrinsic conductivity of the birnessite, several works have been carried out to incorporate other transition metal like cobalt and nickel in the Mn network [2,3]. So as to use an abundant and eco-responsible element, we have chosen to incorporate iron by two different synthetic approaches, aiming at reducing the band gap and thus, improving the intrinsic electronic conductivity [4]. Iron was introduced either as a precursor during the high temperature synthesis of birnessite (HT-MnO2) or via ionic exchange by dispersing δ-MnO2 in rich iron medium during few days, involving different morphologies of initial δ-MnO2 (nano-platelets, nano-veils and micro-platelets (HT-MnO2)). Combining several characterization techniques (XRD, Raman, Mössbauer, XANES, EXAFS), we have shown that Fe3+ ions are incorporated in the structure. Depending on the various synthetic routes, iron is located in different sites in δ-MnO2 : i) only in the metal oxide layer when Fe is incorporated as a precursor during high temperature synthesis of birnessite, ii) only in the interlayer space when Fe is inserted by dispersing HT-MnO2 in Fe nitrate or iii) in both sites when MnO2 nano-veals and platelets are dispersed in Fe nitrate. In all cases, the incorporation of iron lead to a significant increase of the capacity especially due to new redox contributions involving Fe during the cycling. However, this capacity increase is counterbalanced by the limited stability upon cycling.

Solid-state batteries are intensively studied because they promise safer electrochemical storage with larger volumetric and gravimetric energy densities. One of the main scientific challenges in the cycling performance is the limited electrolyte stability, which leads to parasitic reactions that may lead to volumetric changes, contact loss, less conductive interphases and irreversible capacity loss. The electrochemical stability is usually evaluated by the formation energy of decomposition products using the grand potential phase diagram. However, this predicts a very limited electrochemical stability, inconsistent with experimental observations. We demonstrate a novel method calculating the intrinsic electrochemical window of solid electrolytes and apply this method on different classes of solid electrolytes. We show that the electrochemical window determined by (de)inserting Li in the solid electrolyte structure, often predicts the actual electrochemical window. Additionally, we find information about the structural stability and decomposition routes of solid electrolytes. We support our calculation with a full evaluation of an argyrodite solid electrolyte using ex-situ X-Ray Diffraction (XRD) and 6Li and 31P Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and provide an accurate measurement of the electrochemical stability of a NASICON and garnet solid electrolyte. Since the main scientific challenge is to improve the interfaces of solid electrolytes and solid-state batteries. Redox activity and decomposition of solid electrolytes are key aspects to take into account. The provided mechanistic insights provide guidelines for interface design of solid electrolytes.

The discovery of the lithium superionic conductor Li10GeP2S12 (LGPS) has led to significant research activity on solid electrolytes for high-performance and safe solid-state batteries. LGPS exhibits a remarkably high room-temperature Li-ion conductivity of 12 mS/cm, comparable to that of the liquid electrolytes used in current Li-ion batteries. Here, we predict that nanosizing of LGPS can be used to further enhance its already outstanding Li-ion conductivity. By utilising state-of-the-art nanoscale molecular dynamics techniques, we are able to simulate the Li-ion conductivities of nanocrystalline LGPS systems with average grain sizes from 10 to 2 nm. Our results reveal that the Li-ion conductivity of LGPS increases with decreasing grain volume. For the smallest nanometric grain size, the Li-ion conductivity at room temperature is three times higher that of the bulk system. These findings reveal that nanosizing LGPS and related solid electrolytes could be an effective approach for enhancing their Li-ion conductivity.

Lithium-ion conducting argyrodite materials, Li6PS5X (X=Cl/Br/I), are among the most well-studied inorganic solid electrolyte due to their large ionic conductivity. One of the major remaining concerns with the use of these materials in solid-state battery is limited information on their actual stability window. This work presents a systematic study to understand the influence of cationic / anionic substitution on the oxidative electrochemical stability limit of argyrodites, Li6PS5X using a combination of cyclic voltammetry, optical absorption spectra, hard X-ray photoelectron spectroscopy as well as density functional theory calculations. Even though bandgap changes from Li6PS5Cl to Ge/Si- substituted Li6PS5I due to changing cation-anion interaction, the onset of oxidative degradation doesn’t change significantly as the valence band edges are mostly populated by sulfide anion having similar energy. Understanding the underlying mechanism of electrochemical degradation in terms of thermodynamic electrochemical stability and electronic structure would further help design electrochemically stable solid electrolytes.

Design of Lithium ion conducting porous hybrid materials for the development of solid Li-battery electrolytes
Koceila MAOUACINE,Virginie HORNEBECQ,Chrystelle LEBOUIN,Luca PASQUINI
Aix-Marseille Université,France

Solid polymer electrolytes based on poly(ethylene oxid), and lithium-salt complexes are one of the promising materials for developing safe,and durable all-solid-state lithium batteries. However, the low ionic conductivity at ambient temperatur limit their practical application. The attempts to overcome the limitations of SPEs led to the generation of a new class of electrolytes in which ceramic fillers, are incorporated in PEO-Li matrix. In this context, the incorporation of mesoporous silica in the polymer matrix is attractive as its possesses interesting properties, such as its ordered structure and chemical properties.
In our work, we propose a novel approach that leads to the elaboration a porous organic-inorganic hybrid electrolyte containing a higher weight fraction of mesoporous silica than PEO. Here, the polymer-salt is entirely embedded inside the mesoporous silica matrix, offering the mechanical support to the electrolyte. Two morphologies of hybrid silica were tested, both powder and films. These were synthesized by classical (powders) and electro-assisted (films) self -assembly sol-gel method. In the first method, hybrid silica powder was synthesized and then calcined to liberate the porosity. After this, mesoporous silica was functionalized with PEO. Textural, and structural characterizations were performed by SEM,TEM,nitrogen sorption,XRD,FTIR and TGA. In the second method, hybrid silica films were deposited on glassy carbon substrates via electro-assisted self -assembly method. However, the resulting films were covered by silica particles thus reducing the pores accessibility. Several strategies were thus applied to address this problem. The convection of the sol using rotating
electrode was successful leading to particle free films. In this way, hexagonal and vertically oriented pores with a size of 3nm were obtained after template elimination. The permeability of these films was confirmed by electrochemical characterization.

Gelatin nanofibrous scaffolds fabricated using the electrospinning technique and stabilized using chemical cross-linking [1] are characterized using Field Emission Scanning Electron Microscopy (FE-SEM). Biomaterials like gelatin are commonly electron beam sensitive and non-conductive. Thus, high resolution SEM imaging of biomaterial samples is often challenged by charging and beam damage. Options to deal with these two issues are to use a low electron beam energy and low electron beam current which, however, lead to strongly reduced image resolution at low beam energy and very poor signal-to-noise ratio when using low beam current.

With the high-resolution capabilities of the ZEISS GeminiSEM 560 at low beam energies and low beam currents, beam sensitive and non-conductive samples like biopolymers can be pursued without encountering the challenges of charging and beam damage. The characterizations of uncoated crosslinked gelatin scaffolds are more time efficient and reveal even more structural details. A conductive coating on the surface of the non-conductive biomaterial sample is no longer necessary. The GeminiSEM 560 provides sub-nanometer resolution at low beam energy. The novel Gemini 3 column technology introduces the Nano-twin lens and a Smart Autopilot optical engine. Furthermore, the GeminiSEM 560 comes with significantly improved detection efficiency which allows to work with very low beam current and thus avoid sample damage. The low beam energy and low beam current approaches by means of the GeminiSEM 560 were successfully used to characterize the morphology of gelatin nanofibrous scaffolds and provide beneficial insights for the design and fabrication of novel fibrous materials.

[1] C.S. de Oliveira, A.T. González, T. Hedtke, T. Kürbitz, A. Heilmann, C.E.H. Schmelzer, J. Martins de S. e Silva, Materials Science and Engineering: C, Volume 115, October 2020, 111045

Bone is a biological nanocomposite, combining toughness and strength with a low weight. Similar to other complex composites, the hierarchical organization of mineralized tissues affects drastically their mechanical performance across different scales. The elementary building block of bone at the microscale consists of mineralized collagen fibril (MCF, each 10-300 nm in diameter) arrays embedded in an extrafibrillar matrix. Human cortical bone exhibits complex structural arrangement of MCF that may be affected by metabolic bone conditions like osteoporosis or Paget’s disease.
In this study, we explored the capabilities of scanning transmission electron microscopy tomography (STEM), nano X-ray computed tomography (nano-CT) and quantitative polarized Raman spectroscopy (qPRS) for the correlative structural and compositional analysis of bone. Freestanding bone micropillars (~25 µm diameter, ~55 µm height) were fabricated using femto-second laser ablation. The recently developed qPRS method (Kochetkova et al., 2020) allowed us to collect data on bone composition and MCF spatial orientation ~5 µm underneath the pillar surface with a spatial resolution of ~(0.3 µm)³. Laboratory phase contrast nano-CT tilt series were collected from selected volumes of interest up to 20 µm underneath the surface with an enhanced 3D resolution of ~(53 nm)³. Finally, sub-volumes were extracted by an established focused ion beam lift-out technique and imaged by STEM tomography. The quantitative local orientation of MCFs could be successfully estimated after 3D reconstruction and segmentation. The datasets were subsequently registered and correlated to each other to combine and cross validate the extracted information.
The combination of methods used in this study allows to resolve the ultrastructural organization of bone at the level of single MCF at a high resolution. The gained information may be used to identify novel biomarkers for bone quality, increasing the accuracy of bone fracture risk assessment in the future.

Chitin is the second most abundant polysaccharide in the world after cellulose. It is obtained from molluscs, shrimps, and insect shells. Chitin possesses a semicrystalline structure and has been identified in the literature as a piezoelectric system[1,2]. Nevertheless, chitin's low solubility makes it difficult to use in various applications leaving its derivative, chitosan (obtained by chitin deacetylation), as easier manipulating material with better mechanical characteristics for free-standing membranes. The electromechanical response of chitosan has been reported in the literature[3]. However, there is little knowledge about its piezoelectric properties, so a better understanding of this information is needed. The clear electromechanical characterization of chitosan will be useful for biomedical applications, considering the already known antibacterial, non-toxic and biocompatibility advantages.

In this work, we present a systematic characterization of chitosan films fabricated with different acids and amounts of plasticizer, intending to understand the influence of structural modifications on the mechanical performance and consequently on the electromechanical response. Structure modification on the chitosan films was analysed using XRD and FTIR. The thermal response was obtained by TGA and DSC, and the mechanical behaviour was analysed by the tensile until rupture test. The electromechanical response at low frequencies was measured by a vibration-setup and dielectric response was obtained from LCR meter measurements.
The structural characterization suggests that the addition of 50 wt% of glycerol increases the semicrystallinity of the films, the mechanical measurements show that the lactic acid increases elasticity and stretchability of pristine films by ~16%, and the addition of glycerol increases these properties by ~93%. Thermal stability improved with the presence of the plasticizer; electromechanical response increases by 50% with the higher glycerol concentration. The results suggest a high correlation between physical and mechanical properties with the electric performance of the films, highlighting the main variables to modify for further application development.

Poly(L-lactic) acid (PLLA) is a biodegradable and biocompatible thermoplastic polyester and an excellent candidate to replace traditional petroleum-based polymers in a wide spectrum of applications [1]. However, its poor mechanical and barrier properties, thermal stability and low crystallization rate render it slightly inferior to conventional thermoplastics. Tailoring the properties of PLLA through the targeted incorporation of nanofillers is a common approach to overcome these issues [2,3].
PLLA is semicrystalline with α crystal-form being the most common [1]. Upon industrial processing conditions the metastable and conformationally disordered α΄phase can be formed, which transforms to α phase upon heating [1].
Within this work, PLLA/TiO2 nanocomposites, were prepared in a twin-screw extruder in six different concentrations in TiO2. Samples of all concentrations were crystallized from the melt at 85°C and 130°C, where the formation of α΄ and α phase, is respectively favored. The melting behavior and crystallinity are investigated by Differential Scanning Calorimetry and the crystalline structure through X-ray Diffraction. Crystallization behavior and crystal morphology are investigated by means of Polarising Optical Microscopy. Raman scattering is employed to identify the chain packing and conformations of the crystalline forms, while Broadband Dielectric Spectroscopy is employed for the dielectric characterization of the bionanocomposites. Results are compared in terms of the effects of the added presence of the nanofiller and the crystallization temperature, on the properties of the bionanocomposites and are expected to give valuable feedback towards the development of new multifunctional biomaterials with superior properties.
[1] Di Lorenzo ML, Androsch R, Polym Int 68(3): 320-334, 2019.
[2] Kaseem M, Hamad K, Ur Rehman Z, Materials 12(22): 3659, 2019.
[3] Zavvou EE et al., Mod Concept Material Sci. 3(5), 2021. MCMS. MS.ID.000572.

Zeolites are hydrated aluminosilicate minerals with a three-dimensional open structure consisting of aluminium and silicon tetrahedra linked by shared oxygen atoms. Due to this structure, zeolites are characterized by high specific surface and cations exchange capacity making them very useful in environmental pollution remediation. Literature data have documented the synthesis of zeolite using many raw materials including wastes. In this work, fly ash, a waste product of coal combustion in thermoelectric power plants, red mud, a waste produced by the caustic leaching process to extract aluminum from bauxite, volcanic ash deposited on city ground and therefore classified as waste (European Waste Catalogue - EWC) were successful used to form zeolite. The pre-fused hydrothermal aging was compared with ultrasonic pre-treatment as well as short time ultrasonic process. The results indicated that the hydrothermal process determined the zeolite synthesis by a double steps mechanism characterized by geopolymers formation and following newly-minerals crystallization whereas ultrasonic pre-treatment improved zeolite formation at a lower aging temperature. The synthesis process through ultrasonic treatment alone for short time, showed instead the effectiveness of sonication energy in the formation of more stable zeolites over time by precipitation mechanism.
The synthetic products showed good efficiency in both organic and inorganic remediation of soil and water pollutants.

Keywords: wastes, zeolite, synthesis processes, environmental pollution

Circular Economy is a regenerative approach to reduce the waste generated and guarantee the eco-sustainability of post-use products. When a product reaches the end of its life, it is reused to generate high added-value materials, which reduces both the need for primary materials and waste production [1]. This explains the growing interest among the scientific community to develop and optimize different methods for recycling and reuse waste, especially hazardous waste which requires an adequate management.
Batteries are currently used in many electronic devices, including electric and hybrid vehicles. Spent batteries contain heavy metals which may seep out, negatively affecting the environment and human health. Leaching process has successfully been described as a method to dissolve metals present in the black mass, a commonly waste generated in the recycling of the batteries. Previous investigations showed that it is possible to obtain highly pure materials from black mass. However, after the leaching process a large amount of insoluble residues remain, mainly composed of carbon. This carbonaceous residue is an excellent precursor which can be turned into a high added-value material such as graphite, which is used in a great variety of electrochemical applications due to its electrical and thermal conductivity, inertness and resistance [2]. In this work, we report on an easy process to obtain good quality graphite from different black masses from Zn-C and Li-ion batteries, as well as a detailed characterization of its structure and morphology.

References:
[1] Bahar Moradi and Gerardine G. Botte, Recycling of graphite anodes for the next generation of lithium ion batteries, J. Appl. Electrochem. 46, (2016) 123-148.
[2] Mathis Wissler, Graphite and carbon powders for electrochemical applications, J. Power Sources 156 (2006) 142-150.

Funding from the European Union’s Horizon 2020 research and innovation program through Grant No. 776851 (Car-E Service) is acknowledged.

Rare earth elements (REEs) and their compounds are essential for quickly growing advanced technologies. These materials are essential in the area of green/sustainable energy. However, efficient separation and purification of REEs still remain challenging. Additionally, current extraction technologies frequently generate large amounts of wastes. In that perspective, the development of efficient and reusable sorbents is urgently needed. Among several ligands used in the liquid–liquid separation process, the diglycolamide-based (DGA) ligands play a prominent role. Although these ligands show good extraction behaviour in the liquid phase, their extractive behaviour is not broadly studied when these ligands are attached to a solid support. A detailed understanding of the relationship between chemical structure and extraction selectivity at the molecular level is still absent, although it is a main factor for the development of advanced sorbents. To answer this question, we synthetized and tested a series of functionalized mesoporous silica (KIT-6) materials as sorbents for the selective extraction of REEs (Scheme). We performed different spectroscopic studies (solid-state NMR, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy) to better understand the extraction performance of our materials. The obtained results provide valuable insights into the chemical environment and reactivity of the ligand tethered to the silica (KIT-6) support. From our results it can be suggested that depending on the extracted element, structure of the ligand and its attachment to KIT-6, different functional groups (i.e., C═O, N–H, or silanols) act as the main adsorption centres, which in turn can be linked with the different selectivity of the synthesized sorbents. Therefore, different extraction mechanisms or different complexation preferences may occur on the surface. By determining how metals interact with various functionalized silicas, we aim to better understand the solid-phase extraction process of hybrid (organo)silica sorbents and design better extraction materials.

One of the driving forces of the ongoing nanotechnology revolution is the ever-improving ability to understand and control the properties of quantum matter down to the atomic scale. Key drivers in this revolution are quantum materials, such as the two-dimensional (2D) materials of the transition metal dichalcogenide (TMD) family. The realization of novel TMD-based devices relies heavily on understanding the relation between structural and electrical properties at the nanoscale. The ultimate goal is that of crafting TMD nanostructures in a way that makes possible the tailored control of their properties. In this talk, recent studies illustrating novel fabrication approaches of TMD nanostructures based on combining top-down and bottom-up methods will be presented. These allow to control of the resulting geometries and material combinations, making possible the realization of novel functionalities such as metallic edge states arising in MoS$_2$ nanowalls and nanowires, enhanced nonlinear response in vertically-oriented MoS$_2$ nanostructures, and surface and edge plasmons in WS$_2$ nanoflowers. I will emphasize the crucial role that cutting-edge transmission electron microscopy techniques play in these studies, together with that of machine learning techniques which make possible extract a wealth of novel information that would be lost otherwise.

Topological semimetals are candidate hosts of interesting types of low-energy quasiparticles such as type-I and type-II Dirac and Weyl fermions. A type-III crossing point [1-3] emerges as a theoretical possibility exactly at the border between type-I and II, characterized by a line-like Fermi surface and a flat energy dispersion. We theoretically predict [4] that HfTe2 and ZrTe2 transition metal ditellurides are type-I and type-II Dirac semimetals, respectively. By alloying the two materials, a new HfxZr1-xTe2 alloy with type-III Dirac cone emerges at x=0.2 in combination with 1% in-plane compressive strain [4]. We also provide experimental evidence that by using molecular beam epitaxy, single and few layers of HfTe2 [5], ZrTe2 [6] and Hf0.2Zr0.8Te2 [4] can be grown on InAs(111) substrates, and by using in-situ angle-resolved photoemission spectroscopy, that the Dirac points lie at -or very close to- the Fermi level.

1. G. E. Volovik and K. Zhang, J. Low Temp. Phys. 189, 276 (2017).
2. H. Liu et al., Phys. Rev. Lett. 120, 237403 (2018).
3. L. Jin et al., Phys. Rev. B 101, 045130 (2020).
4. S. Fragkos et al., J. Appl. Phys. 129, 075104 (2021).
5. S. A. Giamini et al., 2D Mater. 4, 015001 (2017).
6. P. Tsipas et al., ACS Nano 12, 1696 (2018).

We acknowledge the financial support from the European Union H2020, Contract No. 824123 - SKYTOP and the Hellenic Foundation for Research and Innovation and the General Secretariat for Research and Technology, under Grant No. 435 (2D-TOP).

Doping is fundamental to tune the properties of 2D transition metal dichalcogenides for their future integration in the CMOS architecture, hence achieving substitutional doping during growth is of paramount importance. N-type monolayer WSe2 is often exfoliated from bulk crystals and a procedure to directly dope the material is yet to be established. Here, we demonstrate the synthesis of monolayer n-WSe2 via CVD starting from tungstic acid (H2WO4) and zinc selenide (ZnSe). We achieved large WSe2 triangular monolayer flakes, which exhibit n-type of transport which is attribute to donor states due to the incorporation of Zn ions in the lattice. The doping is very stable and the material exhibits good electron mobilities reaching the highest value at 50 cm2V-1s-1. The substitutional doping has been confirmed via secondary ion mass spectroscopy (SIMS), showing Zn inclusions into the individual WSe2 layers and throughout the layers. Our material is of high crystal quality characterized by a sharp room temperature photoluminescence (PL) assessed by the PL spectra evolution from 10 K to room temperature that shows the contribution of neutral and defect-bound excitons, a signal so far reported only in mechanically exfoliated material.

The controllable, reproducible and scalable growth of graphene and related 2D materials remains the foremost challenge for both research and any technologies exploiting their unique properties. While chemical vapour deposition (CVD) has become the most widespread method for 2D material film growth, even basic process parameters remain not well understood due to the manifold, complex parameter space. Here we focus on the catalyst as the key parameter, exploring a novel method of rapid epitaxial metal film deposition that can demonstrate the deposition of single crystal Cu films in any chosen orientation. By focusing on the catalyst, key problems such as contamination, roughness and polycrystallinity can be inherently solved within a single synthesis step to yield epitaxial graphene on single crystal Cu(111)[1]. Because of the simple in-situ nature of this approach there is no subsequent atmospheric exposure before the 2D material growth, removing the need for additional pre-treatments usually used to clean the catalyst[2].

[1] Burton, O. J. et al. ACS Nano 2020, 14, 13593–13601.

[2] Burton, O. J et al. J. Phys. Chem. C 2019, 123, 16257–16267.

Heavier group-IV element bismuth ultrathin films exhibit numerous interesting properties such as strong SOC, high carrier mobility at RT and large Fermi wavelength. These properties constitute Bi films as possible candidates for exploitation of dissipation-less spin channels for both electronics and spintronics applications.
Bi films on HfTe2/InAs(111) templates were grown by molecular beam epitaxy (MBE) and the atomic and electronic structures were studied by Reflection High Energy Electron Diffraction (RHEED), Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS), Angle-Resolved Photoemission Spectroscopy (ARPES) and Raman Spectroscopy.
At 6.5 Å of Bi deposition, atomically flat Bi islands with triangular and rectangular shapes are formed. Atomic resolution STM images on the rectangular islands show the presence of both BP-distorted α-Bi and BP α-Bi phases [1-3], while the triangular areas consist of hexagonal β-Bi phase. The mixed phases are confirmed by ARPES measurements [4].
At 12Å Bi deposition high-quality epitaxial growth of 3BLs β-Bi is achieved as verified by STM. The ARPES data of 3BLs shows the band structure of pure Bi(111) phase, while DFT calculated bands of 3BLs freestanding Bi(111) fit well will the experimental results. Thus, the 2D HfTe2 template [5] favors the formation of hexagonal Bi(111) for even the low thickness of 3 BLs.
3BLs Bi film was successfully capped by AlOx layer and ex-situ Raman measurements verified the presence of hexagonal Bi(111) phase. XPS after air exposure showed that 3BLs Bi film was protected by AlOx capping, which is crucial for future applications.

1. E. Akturk et al., Phys. Rev. B 94, 014115 (2016).
2. Y. Lu et al., Nano Lett. 15, 80 (2015).
3. P. J. Kowalczyk et al., Nano Lett. 13, 43 (2012).
4. G. Bian et al. Phys Rev. B 80, 245407 (2009).
5. S. A. Giamini et al., 2D Mater. 4, 015001 (2017).

Self-assembled monolayers (SAMs) of organic molecules have been used for a wide range of applications in medicine, surface protection as well as (bio)electronic devices. Extensive efforts have been dedicated to implement biomolecules in gold based diagnostic tools. The use of SAMs as an interface between metal surfaces and biological moieties allows the covalent attachment of receptors to gold, avoiding denaturation usually associated with physical adsorption approaches. In this context, thiol-SAMs containing ethylene glycol (PEG) subunits proved to be effective linkers to prevent nonspecific adsorption at the sensor surface. However, major drawbacks of thiol-SAMs such as limited thermal and long-term stability under ambient conditions as well as their sensitivity to oxidation of the sulfur headgroups hamper their application.

Recently, stable traceless single-source N-heterocyclic carbenes (NHC) have been introduced as anchor groups on gold. Their thermal and chemical stability render these compounds interesting for biosensing applications. In the present work, the synthesis and characterization of water-soluble PEG substituted NHC-SAMs will be presented. These new NHC-SAMs materials will be applied to functionalize gold nanoparticles as well as flat gold substrates. Furthermore, these functionalized gold materials will be used to immobilize biological moieties and tested toward their applicability in biosensors.

Phenothiazine (PTZ) as a heterocyclic compound contains electron-rich sulfur, and nitrogen atoms play a role of admirable electron-donating (D) moiety in donor-acceptor (D-A) systems. Phenothiazine and particularly its substituted derivatives can be applied in many versatile fields. The synthesis of new compounds based on the donor-acceptor (D-A) system has attracted significant interest and became an important target for scientists in recent years. The many ways to modify phenothiazine structure by adding a different type of substituents and/or elongation of π-conjugation with various linkers allow to get the dyes with desirable optoelectronic properties, significant photovoltaic performance, and be willingly applied in medicine and bio-imaging.

We present the synthesis and investigation of novel A-π-D-A and D-π-D-A systems based on phenothiazine framework with different electron-donating (D) and electron-withdrawing substituents (A). The phenothiazine derivatives were designed to study the relationship between the structure and their optoelectronic and thermal properties. The effect of π-conjugation enlargement by incorporating different heterocyclic substituents with various electron-donor affinity was systematically experimentally and theoretically examined. The novel compounds were obtained via multistep rection starting from phenothiazine and were fully characterized by spectroscopic methods (1H NMR, 13C NMR, HRMS).

The photophysical properties of phenothiazine derivatives were thoroughly investigated and confronted with DFT and TD/DFT calculations. The novel phenothiazine derivatives were applied as organic electronics materials as photovoltaic cells exhibiting PCE up to 6.22%, and emissive layers in organic light-emitting diodes (OLEDs), and additionally in bio-imaging.
The presented compounds' photophysical properties imply that they are very promising D-A materials for various applications.

This study is supported by the National Science Centre of Poland Grant No. 2016/23/B/ST8/02045 and PW-2004-105.

Despite more than a century of research to achieve oral delivery insulin, the current clinical reality remains unchanged in terms of therapeutic administration, due to the challenge of overcoming gastrointestinal barriers. It has been recently reported by our group that with the use of dendritic mesoporous silica nanoparticles (DMSNs) together with a protein-based excipient, succinylated $\beta$-lactoglobulin (BL), pH-responsive tablets could prevent the premature gastric release and degradation of encapsulated insulin. However, there are still open issues related to colloidal stability, control of release rate, permeation enhancement and mucoadhesion, which need to be addressed before reaching in vivo tests. To this aim, we focus our studies on the examination of the influence of surface chemistry/charge and colloidal stability of DMSNs on the loading efficiency and insulin release performances. For this, DMSNs (130 nm; pore size: 7.0 nm) were functionalized with polyethylene glycol (PEG, 2 kDa) and a phosphonate-silane, trihydroxysilylpropyl methylphosphonate (THMP), introduced through different post-grafting strategies. The functionalized DMSNs (DMSNs-PEG and DMSNs-PO$_3$) exhibited an enhanced colloidal stability in aqueous and saline media (PBS) over a wide pH range. Different formulations for oral administration were prepared by mixing BL with pure and functionalized DMSNs containing insulin (20 % w/w) and preliminary release tests were performed with simulated body fluids. Compared to a DMSNs-free formulation, encapsulated insulin was even more protected and the release was lowered down to acceptable threshold (less than 10 %) at pH 1.2, while at pH 7.4 controlled release could be reached for 24 h. The analysis of the released insulin confirmed that drug confinement into the pores of the hybrid DMSNs did not affect the peptide structure. The ability of DMSNs to be internalized by intestinal cells was tested using healthy human epithelial colon cells (HCEC) through live cell imaging, observing enhanced cell uptake of insulin.

The development of new biocompatible materials can lead to new ways to treat diseases in the human brain. By initiated Chemical Vapor Deposition (iCVD) polymeric thin films can be tailored to fulfill the needed specifications of drug release barriers. This way a local and time-specific drug-release can greatly reduce unwanted side-effects in these special surroundings. In combination with a Gas Aggregation Cluster Source, nanoparticles can be included in the polymeric matrix, that enable various stimuli-sensitivities of the polymeric coating. First results of nanocomposites created in this approach will be presented. Furthermore, we will show a new way to deposit 3D polymeric thin film structures via iCVD and present first applications.

The functional properties of materials are increasingly controlled and tuned through structural or chemical architectures whose engineering takes place at the nano or even atomic level. This enables emergent properties relying on the interplay between charge, spin or local atomic-scale chemistry. A particularly powerful means of characterization of these physico-chemical effects lies within a combination of high-resolution scanning transmission electron microscopy and energy-loss spectroscopy (STEM-EELS). Recent instrumentation advances have pushed the energy resolution of these instruments below 10meV while maintaining atomic-sized probes, thus truly realizing the promise of placing a ‘synchrotron in a microscope’ [1].
As a result, it is now possible to fingerprint the functional chemistry of materials as diverse as organic grains in chondrites or metal organic framework glass blends at the nano-scale while simultaneously correlating it with their vibrational response in the sub 100meV energy range. This enables a direct comparison with bulk optical characterization at unprecedented length scales [2]. Further methodological developments have demonstrated the ability to balance momentum and spatial resolution to either determine the electronic band structure of materials in momentum space from nanometre-sized volumes or carry out phonon spectroscopy at the atomic scale, culminating recently in the observation of a phonon signature localized at a single atom defect [3]. It is expected that building on these recent achievements, further improvements in energy resolution and the introduction of new direct/hybrid electron detectors will widen the range of chemistries that can be spectroscopically and spatially resolved, providing the ideal spectroscopic tool to understand the nanoscale organisation of organic and metal-organic bonding and complex interfacial structures in emerging hybrid composite materials.

[1] Q.M. Ramasse, Ultramicroscopy 180, 41-51 (2017).
[2] S. Collins et al., NanoLetters 20, 1272-1279 (2020).
[3] F.S. Hage et al., Science Advances 4, eaar7495 (2018); F.S. Hage et al., Science 367, 1124 (2020).

Indium Selenide (InSe) is a remarkable two-dimensional quantum material whose characteristic properties include a bandgap that increases with fewer layers and a high controllability of p- and n-type doping. Furthermore, its bandgap can lie in the near infrared region, depending on the specific crystalline phase adopted. Indium Selenide is known to crystallize in either the β(2H)-, γ(3R)- or the ε(2H)-phase. Of these three crystalline phases, only the β(2H) and γ(3R) ones exhibit a direct bandgap, which makes them particularly suitable for optoelectronic applications. However, while the β(2H)-phase can be easily disentangled from the other, the γ(3R)- and ε(2H)-phases are indistinguishable from the in-plane point of view and appear also very similar from the out-of-plane one. An attractive possibility to tailor the optoelectronic properties of InSe is based on the introduction of dopants, which leads to structural defects and can modify the crystalline structure and symmetry properties of the material. In this work, we investigate p- and n-doped (as well as undoped) Indium Selenide by means of Transmission Electron Microscopy and related techniques. We determine the crystalline phase present in these Indium Selenide specimens with High Resolution TEM by means of a systematic investigation of both in- and out-of-plane cross-sections, and compare the structural differences arising from different types and amounts of doping. We further assess the impact of dopants on the local electronic properties using Electron Energy-Loss Spectroscopy (EELS) by comparing how relevant features in the spectra (including surface- and edge-related properties) depend on the doping. Finally, we deploy Machine Learning techniques for a model-independent subtraction of the Zero Loss Peak, which makes possible identifying in an unbiased manner the impact of dopants in InSe in the ultra-low-loss region of the EELS spectra.

Within layered (two-dimensional) materials, the stacking sequences (polytypes) and physical properties of the materials are deeply intertwined. Tailoring specific stacking sequences thus provides a powerful handle in the design of nanostructures based on layered materials exhibiting novel physical properties. In this context, Transition-Metal Dichalcogenides (TMDs) based nanostructures crystallizing within in either the 2H or 3R phases have been extensively studied, but unfortunately our knowledge on TMD nanomaterials based on mixed polytypes is far more limited. In this work, we present an exhaustive characterization of CVD-grown free-standing flower-like WS2 nanostructures, displaying a mixed 2H/3R polytype, by means of state-of-the-art transmission electron microscopy. Their rich variety of shape-morphology configurations is correlated with relevant local electronic properties such as edge, surface, and bulk plasmons. Furthermore, machine learning techniques are deployed to determine that the band gap of the WS2 2H/3R polytype is indirect in nature and has a value of $E_{BG}$ = 1.6 eV. High resolution electron energy-loss spectroscopy reveals another striking property of the WS2 2H/3R polytype, namely the presence of energy-gain peaks exhibiting a gain-to-loss ratio greater than unity. This remarkable property could be exploited to design new cooling strategies for atomically-thin TMD nanostructures and devices built upon them. We investigate systematically the differences in the locations of the energy-gain-to-loss ratios, arising between the different shape-morphologies, including with measurements taken on exfoliated WS2 flakes and with theoretical calculations based on Density functional Theory methods. The latter provide unique insights on the underlying mechanism responsible for the appearance and properties of energy-gain features in WS2 2H/3R polytype. Our findings represent a stepping stone towards an improved understanding of TMD nanomaterials based on mixed crystalline phases.

Changes in the martensite structure of 0.1%C-2%Si-5% Mn steel with decrease in the prior austenite grain size have been investigated. While prior austenite grain size in the range of 150 to 24 micro-meter led to the formation of martensite with a multi-packet and multi-block structure, a single packet and multi-block martensite structure formed from the prior austenite grain size of about 7 mico-meter. Furthermore, prior austenite grain size of about 2 micro-meter led to the formation of a single variant (single block) martensite structure. This microstructural analysis indicates that the critical prior austenite grain size to form martensite with a single variant structure is about 2 micro-meter. The tensile strength (TS, 1490 MPa), uniform elongation (UEL, 7.1%), and total elongation (TEL, 14.2%) of the single-variant martensite was found to be higher than that of the multi-packet multi-block martensite (TS = 1270 MPa, UEL = 6.2% and TEL = 13.6%). The improvement in mechanical properties of single-variant martensite was attributed to enhancement in its strain hardening rate as a result of change in the structure from the multi-variant to single variant.

The cooling rate during the martensitic transformation has been shown to have a strong impact on the fatigue performance of case-hardened steels with differences of up to 20 % [1]. The mechanism for this increase is not fully understood. To clarify the underlying mechanism, the impact of cooling rates on the martensitic transformation in two high carbon steels (0.54 and 0.74 w% C) was studied. In-situ high energy x-ray diffraction (HEXRD) during dilatometer tests were conducted to study the transformation kinetics and the martensite tetragonality. A clear impact of the cooling rate on the tetragonality of martensite was found for both carbon contents. These results were supported by the analysis of the final microstructure by electron microscopy, focusing on the local tetragonality of martensite as determined by electron backscatter diffraction (EBSD) using the projective transformation approach by Winkelmann et al [2,3]. The combination of results from in-situ HEXRD with dilatometer tests and microstructure analysis will here be presented.

[1] Fahlkrans, Johan, et al. "Gas quench rate after low pressure carburizing and its influence on fatigue properties of gears." HTM Journal of Heat Treatment and Materials 68.6 (2013): 239-245.
[2] Winkelmann, Aimo, et al. "Mapping of local lattice parameter ratios by projective Kikuchi pattern matching." Physical Review Materials 2.12 (2018): 123803.
[3] Nolze, Gert, et al. "Tetragonality mapping of martensite in a high-carbon steel by EBSD." arXiv preprint arXiv:2011.10275 (2020).

Nanostructurization by bainitic phase transformation is a revolutionary method of improving mechanical properties of the wide range of steels. It can be applied as a single process or as a part of the innovative multistage heat treatment, named B-Q&P, which combines, in one route, two processes: Bainitization and Quenching & Partitioning. While implementing to high carbon low-alloy steels it allows obtaining a new type of complex microstructure consisting of very hard carbides in tough, nanocrystalline matrix. By changing the amount of particular components in the microstructure it is possible to change mechanical and service properties of steel.
In the present work, the kinetics of bainitic phase transformation was investigated in high carbon steel, containing enhanced concentration of silicon and carbide forming elements, by dilatometric tests. The phase composition and morphology of phase constituents were determined by observations with the scanning electron microscope (SEM) and transmission electron microscope (TEM), accompanied by the XRD and magnetic measurements. The study was completed with mechanical tests, including hardness measurements, uniaxial tensile test, impact and fracture toughness tests.
Content and distribution of precipitates in austenite influence the kinetics of bainite transformation, as well as the final microstructure morphology. It occurred that some of the particles can act as additional sites for nucleation of bainitic ferrite, which results in finer structure and larger misorientation. The investigation led to the hypothesis of the significant impact of the bainite morphology on the increase and deflection of crack propagation path.

Heat treatment with an electric current has gained interest in the last few years. However, the physical phenomena occurring in these type of treatments are not always fully understood. Thus, to study the influence of the electric current on the interstitial diffusion of carbon, an ARMCO iron sample is placed between the two graphite punches of a Spark Plasma Sintering facility. The current between the punches is used to regulate the temperature of the sample. The sample is heated in the intercritical domain (between 727 °C and 912 °C). The diffusion of carbon in ferrite induces its transformation into austenite. After cooling, the microstructure of the sample gives information on the transformation fronts positions and C concentration profiles. The transformation front velocity is higher in the direction of the electric current and lower in the opposite direction. To understand and predict this phenomenon, a model accounting for the allotropic phase change and the influence of the electric current on carbon mass transfer in iron is proposed. The simulation results are compared with the experimental observations allowing the identification of some model parameters.

Diverse pathways of {332}<113>β mechanical twinning and stress induced martensitic transformation (BCC-Orthorhombic) were studied in a metastable beta Ti-12Mo alloy, which presents Transformation Induced Plasticity (TRIP) / Twinning Induced Plasticity effect. This work aims to clarify the pathways involved in primary and secondary transformations under external tensile stress, such as the hierarchal transformations in {332}<113>β twin and the twinning-detwinning processes of stress-induced α″ martensite (SIMα″). The grain resolved transformations were traced by in-situ EBSD (Electron backscatter diffraction) mapping and in-situ TEM (Transmission electron microscope) observation under tensile loading and unloading conditions. Observations of unprecedented pathways between {332}<113>β twinning and SIMα″ are achieved by transformation partition mapping via in-situ EBSD statistic coupled with Schmid factor analysis. At finer length scales under in-situ TEM observations, the nucleation behaviors, growth kinetics and the reversible internal transformations are further investigated of both {332}<113>β twinning and SIMα″.

One of the most critical issues in titanium metallurgy has been and remains the impact of interstitial elements and specifically oxygen on mechanical properties of titanium alloys. In these materials, oxygen is indeed known to induce a strong hardening effect combined to a severe decrease of the elongation at fracture. This embrittlement has been interpreted, until now, as a consequence of the deformation localization initiated by the interaction between the dislocations and isolated oxygen atoms in solid solution. To prevent this ductility loss, many efforts have been made to inhibit oxygen diffusion during processing and thermal treatments of titanium alloys. On this basis, there is several key challenges in the development of new “oxygen-tolerant” titanium alloys, that could take advantage of oxygen hardening without suffering from embrittlement.
This work reports on the development of a series of ternary Ti-4.5Zr-xO α-alloys with oxygen contents up to 0.8 wt%. These materials are shown to present nano-precipitates with a Ti6O-structure resulting from local ordering of oxygen in octahedral interstitial sites. Although this structure existence had been predicted by ab initio calculations, these precipitates are here observed for the first time in structural alloys and with such low oxygen contents. This work highlights that the mechanical properties associated with this microstructure in Ti-Zr-O alloys, exhibit unprecedented combination of mechanical strength and ductility, reaching over 1000 MPa and 25% respectively.
During this talk, evidence of oxygen ordering in Ti-Zr-O alloys are exposed by means of several characterization techniques: Transmission Electron Microscopy (TEM) observations and X-Ray Diffraction (XRD) analyses. The influence of the oxygen content on the precipitates size and structure will then be investigated. The consequence of this microstructure on the mechanical properties will subsequently be showed and discussed. Finally, the different perspectives and questions raised by these findings will be considered.

Among the various significant questions affecting titanium metallurgy, the effect of interstitials, more specifically oxygen, on the (mechanical) properties of titanium alloys remains one of the most critical issues. For decades, oxygen has been considered as a detrimental element, leading to drastic embrittlement. However, there is still an important lack of knowledge on underlying mechanisms regarding this effect.

In this work, a series of Ti-O alloys displaying high oxygen concentration (between 0.4 and 1wt%) has been carefully investigated to address more specifically this question. A particular attention is paid to the process route, which is supposed to play a role. Two different aspects are of great interest: (1) the determination of the atomic scale structure of Ti-O alloys, as a function of the chemical composition, with special attention to possible local ordering or local oxygen-driven structural modification. (2) The impact of oxygen content on: (a) the macroscopical properties (resistance/ductility trade-off) and: (b) the operative deformation mechanisms, at room temperature.

Ti-O specimen with different controlled oxygen concentrations were fabricated by arc-melting and were investigated by DRX, EBSD and TEM analysis, at different stages of the process route but in particularly under their fully recrystallized microstructural state. The mechanical properties have been studied by tensile tests in quasi-static conditions. It was shown that this series of newly developped Ti-O alloys displayed a spectacular combination of tensile strength and ductility with a small drop of ductility with increasing oxygen content, in particular.

In this talk, the origin of these peculiar mechanical properties will be extensively discussed, based on new microstructural insights at the nano-scale, regarding more particularly local oxygen ordering in the alpha titanium matrix. The effect of the process leading to the strength-ductility trade-off will also be discussed. The larger perspectives opened by these new findings will then be described and discussed.

α+β-TiAl6V4 alloy is the most important titanium alloy for aerospace applications [1,2]. Depending on the thermo-mechanical processing route, a wide range of microstructures can be achieved which differ in proportion and arrangement of the α- and β-phase and the type of transformed β-phase. The microstructures in turn have a decisive effect on the resulting mechanical properties [3]. Since conventional processing is quite time-consuming for the majority of applications and further requires protective gas atmosphere, there is a general interest in shortening processing steps and avoiding the need of α-case protection measures.
In this work, the focus is set on studying the effects of short-time heat treatments on microstructure and mechanical properties of TiAl6V4 sheet metal. The effects of a) solution treatment temperature (below the β transus temperature) and time, b) cooling rate and c) annealing temperature and time are investigated. Samples were heat treated in ambient atmosphere to produce different STQ (solution treated and quenched) and STA (solution treated annealed) states. Microstructures were analyzed by means of scanning electron microscopy and Image J was used as image analysis tool to quantify the proportions of phases. Mechanical properties were determined by hardness and tensile testing at room temperature.
It turned out, that the deformation behavior in tensile testing of TiAl6V4 sheet metal is significantly influenced by the applied STQ or, respectively, STA processing parameters. In case of the most promising STA state, the strength can be significantly increased compared to the initial state while ductility remains in the same range. These observations are very promising for further studies and potential future applications.
The investigations are part of the BMWi-funded joint project TISTRQ. Within this project the Chair of General Materials Properties of the FAU Erlangen-Nürnberg cooperates with the partners Heggemann AG and Dynamore Materials Competence Center.

Metal-based additive manufacturing (AM) represents a paradigm change which will revolutionize the manufacturing across multiple industries such as the aerospace, biomedical and automotive sectors. However, today only a few alloys are compatible with AM. Most of those being used were developed for other manufacturing processes such as casting and forging processes where the mechanical properties can be controlled using thermal and thermo-mechanical processing, but not by the rapid solidification conditions of AM (steep heating and cooling rates between ~ 103-108 °C/s).
In this context, the control of phase transformations and deformation modes in AM alloys plays a key role to obtain microstructures leading to suitable properties directly in the as-built state. This work uses real-time characterization at synchrotron facilities to reveal the influence of phase transformations on microstructure formation and reveal the activation of deformation mechanisms improving the strength-ductility trade-off. Titanium alloys fabricated by the powder-bed AM technique laser powder bed fusion (LPBF) are investigated using in situ synchrotron tomography and in situ high energy synchrotron X-ray diffraction. They are developed to tackle the drawbacks occurring in titanium alloys fabricated by AM, namely the formation of microstructures with anisotropy and poor ductility.