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

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...

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...

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...

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...

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...

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...

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...

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),...

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...

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....

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...

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...

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...

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...

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...

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...

High entropy alloys (HEA) [1] are alloys containing at least five elements in equiatomic or near-equiatomic concentration. They adopt simple crystallographic structures such as bcc, fcc and hcp structure solid solution phases. Identified rapidly for their outstanding mechanical properties, HEA have also been considered as potential coatings for thermal and diffusion barriers, and for oxidation...

The single-phase microstructure of high entropy alloys (HEA) makes them perfectly suited to address fundamental scientific issues related to concentrated solid solutions. For this purpose, fcc and bcc HEA CrMnFeCoNi, TiZrNbHfTa and TiZrNbHfV were characterized as single-crystal (SX) and polycrystal regarding tensile and creep properties at higher temperatures, as well as dislocation...

Refractory multi-principal element alloys (MPEA) with single-phase body-centered cubic (bcc) structure, such as the NbMoCrTiAl system and TaNbHfZrTi, are promising candidates for high-temperature applications. NbMoCrTiAl, like other refractory HEAs, are typically brittle at ambient temperature and fail in a catastrophic manner during conventional mechanical testing. However, TaNbHfZrTi shows...

To apply high-entropy alloys (HEA) of the CrMnFeCoNi family in challenging atmospheres, their degradation behavior under harsh environments needs to be investigated. Oxidation studies to HEAs have not been extensively investigated and most of them are concentrated on environments like synthetic air, laboratory air, CO/CO, O2 and H2O atmospheres [1]. Main corrosion products which were...

High entropy alloys (HEAs) show interesting mechanical properties and deformation behavior due to their unique structural characteristics, such as high configuration entropy and large local chemical fluctuations. In this talk, our research efforts on strengthening mechanisms in this special family of metallic materials will be summarized. Specifically, focuses will be placed on the following...

Body-centered-cubic (BCC) high entropy alloys show exceptional strengths up to 1900K [1]. Few such alloys have been tested. Fundamental understanding of the mechanisms that control strengthening is necessary to formulate theories that enable screening over the immense compositional HEA space.

Supported by the recent experimental findings in NbTaTiV and CrMoNbV alloys [2], we show with...

Contrary to the conventional alloys with one principal element, multicomponent alloys (MCAs), e.g. high-entropy alloys (HEAs) and compositional complex alloys (CCAs), contain many elements in near-equimolar ratios. We investigated whether the structural and functional properties like superconductivity would vary from three- to five-component alloys. For that purpose, we chose six alloys: a...

High and medium entropy alloys gained increasing academic and industrial interest as novel materials for engineering applications. This project is aiming to clarify and compare the general and local corrosion properties of high entropy alloy CrMnFeCoNi and medium entropy alloy CrCoNi in different aqueous environments. The focus lies on the local corrosion processes that result either from...

The CoCrFeMnNi high-entropy alloy (HEA) is a magnetically concentrated crystalline system with all lattice sites magnetic, containing randomness (five different types of spins are randomly positioned on the lattice) and frustration (a consequence of mixed ferromagnetic and antiferromagnetic interactions). We have studied experimentally the nature of the magnetic ground state and found out that...

Eutectic high-entropy alloys (EHEAs), with mixed microstructures of HEA matrix and intermetallics, have advantages on flexible adjustment of microstructures. Recently, we developed a novel non-equiatomic eutectic high-entropy alloys (FeCoCrNiTaAl) with appreciable high-temperature strength. However, the intrinsically brittle Laves phase in the lamellar structure causes limited ductility at...

A particular need to increase the efficiency of gas turbine engines induces the searching for new materials with higher performance than currently used commercial alloys. One of the prospective candidates for high-temperature applications is the so-called refractory high entropy alloys (RHEAs). RHEAs are often based on body-centered cubic (bcc) or ordered B2 solid solution and can contain...

We first report the microstructure and mechanical properties of a non-equimolar eutectic high-entropy alloy (EHEA) CoCrFeNiTaAl fabricated by additive manufacture. The as-printed EHEA consists of a nanostructured network-like Laves phase (width ~ 30 nm) embedded in an fcc phase matrix (average grain size of 17μm). The alloy exhibits an excellent mechanical property (yield strength ~ 2.3 GPa,...

Two parallels of tensile tests at room temperature and at 650 °C were performed on the AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) in as-cast and aged conditions. The as-cast AlCoCrFeNi2.1 has a eutectic microstructure with B2-type NiAl lamellae inside the L12-type Ni3Al matrix in a ratio of 35% and 65%, respectively. Isothermal aging at 800 °C for 100 h was performed in order to induce...

Within the frame of a joint European project we developed a dual-phase medium entropy alloy Al8.5-Cr16.3-Fe35-Ni36.8-Mo3.5 (in wt.-%) which forms an ultrafine vermicular microstructure upon casting. The two phases (fcc) and (bcc) form a bi-continuous network with nearly equal phase fractions. We quantitatively describe the microstructure using scanning electron microscopy (SEM), energy-...

In this contribution the AlxTiyCoCrFeNi alloy system is explored thoroughly over a wide compositional range of x = 0 to 1. (0 to 17 at% Al) and of y = 0 to 0.7 (0 to 10 at% Ti). For this alloy system compositional gradient structures were produced by laser metal deposition of pre-alloyed CoCrFeNi and elemental Al and Ti powders using an in-house developed coaxial cladding system COAXpowerline....

Additive manufacturing has shown great potential for the development of high-performance high entropy alloys (HEAs), which is partially correlated to the fact that the rapid solidification within the melt pool could facilitate the formation of supersaturated metastable solid solutions. In this work, we introduce a metastable non-equiatomic FeMnCoCr HEA produced by selective laser melting (SLM)...

The main aim of this study is to understand the printability, phase stability, microstructure and resulting mechanical properties of the high entropy alloys using laser powder bed fusion (L-PBF). High entropy alloys (HEAs) are a novel class of alloys which contain multiple principal elements in near equiatomic proportions. The unprecedented compositional complexity has reportedly enabled HEAs...

Engineering alloys, such as steel, are often produced by the combination of several elements with one to be the base material, such as iron, with a mass contribution of about more than 70%. In the past couple of decades, a new group of alloys, known as high entropy alloys (HEAs), have been introduced that contain different elements with an equal mass contribution that could deliver...

High entropy alloys (HEA) are a new class of promising materials with very interesting properties. These alloys have particular and sometimes unstable microstructures. Using additive manufacturing (AM) processes for shaping these innovative alloys allows mastering their microstructures through the versatility and the flexibility of these processes. The AM processes like the laser powder bed...

With the partial dislocation assisted twinning and/or displacive transformation upon stress loading, metastable high-entropy alloys (HEAs) and their interstitial variants have shown excellent strength-plasticity synergy. However, the fundamental mechanisms of the dislocation nucleation and the onset of plasticity in these emerging materials remain unclear. The presentation is aimed to provide...

Nitrogen is a well-known gamma-stabiliser in austenitic steels, also responsible for significant improvement of mechanical resistance of these materials. Most of its interest is found when this interstitial element is dissolved in the matrix. Its impact in austenitic high-entropy alloys (HEAs) is already largely reported in the literature. However, nitrogen can also take the form of nitrides...

The best-known and widely-studied among high-entropy alloys is the so-called Cantor alloy (CoCrFeMnNi) with a face-centered cubic (fcc) structure. Cantor alloy and its derivatives have high ductility at room and cryogenic temperatures, , excellent fracture and impact toughness, etc., but mostly have quite low strength. It is known that doping with interstitial elements can lead to a...

Alloy development efforts in the Al-Co-Cr-Fe-Ni and Al-Cr-Fe-Ni systems have shown that novel duplex materials composed of a mixture of FCC and BCC phases can be obtained. Among them, the Co-free alloys with a composition close to AlCrFe2Ni2 are interesting candidates for casting, forging and powder based additive manufacturing routes. This is due to their strength-ductility balance that can...

This study is focused on in-situ alloying of Al0,8FeNiCr composition
by melting commercially available powders using the LMD process. To obtain
an equivalent composition, commercially available powders of 316L, Inconel
718, pure Chromium and Al2024 were selected and provided in 45-105μm
powder diameter range. The final composition contain also Nb, Mo and Ti
from the alloys used in this...

The so-called refractory high entropy alloys (RHEAs) attract enormous interest from researchers worldwide due to their encouraging mechanical properties at elevated temperatures. However, most of the RHEAs are quite brittle at room temperature. RHEAs mostly have body-centered cubic (bcc) structure with the possible presence of B2, Laves, and other secondary phases. Here, we have systematically...

Refractory high entropy alloys (RHEAs) present a new class of metallic alloys with promising high-temperature properties. These alloys are mainly based on single-phase bcc or ordered B2 solid solution and can contain different secondary phases. However, secondary phases in RHEAs usually precipitate in an uncontrolled manner deteriorating room-temperature ductility abruptly. Thus, there is a...

High-entropy alloys (HEAs) constitute a new class of metallic materials attracting increased attention due to unusual combination of mechanical and functional characteristics. One of a strategy to design Ti-rich high entropy alloys with various active modes of deformation mechanisms (such as TRIP, TWIP or dislocation slip) is using the bond order (Bo) - mean d-orbital energy level (Md)...

High Entropy Alloys (HEAs) and the strongly related Compositionally Complex Alloys (CCAs) constantly draw much attention from both fundamental and applied research prospective. For special high temperature applications, γ’-precipitation strengthened CCAs have a high potential to replace some types of classical Ni based superalloys. This is because they partially show similar or even better...

During the last few years high entropy alloys (HEAs) have drawn a lot of attention mainly due to the vast range of designed compositions and properties. For many potential applications good corrosion resistance is among the principal requirements. In spite of numerous publications covering this topic, much information is still missing about the influence of individual components on the...

Cyclic loading leads to failure of the material in over 90% of cases. Therefore, it is important to develop materials with a high fatigue strength and to understand them in detail. High-entropy alloys (HEAs) have a great potential for application under cyclic loading, as they exhibit both high fatigue strength and fracture toughness. In addition to these positive characteristics, the fatigue...

The constitutive flow behavior of CoCrFeMnNi high entropy alloy (Cantor alloy) was investigated by means of isothermal compression testing in the temperature and strain rate ranges of 1023–1423 K and 10−3–10 s−1, respectively. Constitutive equations were developed based on hyperbolic-sinusoidal Arrhenius-type modeling. The influence of deformation parameters was further characterized in...

The present study attempted to understand the development of microstructure and texture in FCC equiatomic CoCrFeMnNi high entropy alloy during severe warm-rolling and compare the results vis-à-vis cold-rolling. The HEA was processed by warm-rolling up to 90% reduction in thickness at 600°C and at temperatures ranging from 700 °C to 1200 °C. The severely warm-rolled HEA showed a lamellar yet...

High entropy alloys or complex concentrated alloys have stretched the limits of mechanical properties like yield strength, ductility and fracture toughness over a wide range of temperature and strain rate for metallic materials in the recent past. Newly developed two phase Fe50Mn30Co10Cr10 alloy with FCC austenite (γ) phase and HCP martensite (ε) phase is characterized by γ to ε transformation...

The development of alloys with the necessary properties is one of the main objects of research in materials science. The phase structure of the material is the important characteristics of this process. The presence of secondary phases might change the mechanical properties of the materials. Therefore, the formation of ordered structures should be meticulously investigated for a safe and...