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

Nacre-like aluminas are a new class of bioinspired ceramic composites developed over the last few years. These brick-and-mortar composites are obtained by aligning and concentrating alumina platelets and distributing a secondary phase (polymer, ceramic, glass, metal) at the platelets interfaces. The main interest so far of these materials is their damage resistance, resulting mostly from the...

Unlike synthetic ceramics which are brittle and thus prone to catastrophic failures, biological materials have found ways to combine both stiffness and toughness. Nacre, for example, is composed of 95 vol.% brittle calcium carbonate, yet exhibits a fracture energy 3 orders of magnitude higher than its principal component. This toughness amplification finds its root in nacre’s brick-and-mortar...

Texturing the microstructure may enhance the structural and/or functional properties of polycrystalline ceramics. For instance, nacre-like textured alumina obtained through tape casting using Templated Grain Growth (TGG) has been established as a strategy to obtain high degree “morphological” and “crystallographic” texture. However, a limitation of these methods is the rather simple geometries...

Bio-inspired material are designed by mimicking natural features. Indeed, billion years
of evolution under pressure from their environment have tuned natural structures into
outstanding components. Exemples of such appropriation are common in our everyday
life, from swimming suits inspired by shark skin to Velcro inspired by a particular sort
of seed.

Bio-inspiration can also benefit to...

Additive manufacturing or 3D printing has emerged as a viable alternative for the mould-less fabrication of monolithic ceramics. However, the practical printing of ceramic-based composites combining different materials still presents a difficult challenge. In particular, printing composites with long or continuous fibre while engineering the fibre-matrix interfaces has proven difficult. Here...

Embedded 3D printing is an emerging technique that allows the fabrication of complex structures inside a soft self-healing matrix and has been applied on polymers and organics. Multi-material composites with targeted structures can be obtained in a single embedded 3D printing step. Here we introduce the application of this technique to the printing of complex structures inside ceramic...

The Lithography-based Ceramic Manufacturing (LCM) technology has been established as promising technique for fabricating complex-shaped ceramics based on a layer-by-layer photo-polymerisation process. In recent times, much effort has been dedicated to investigate the mechanical response of 3D-printed bulk alumina.

In this work we employ the LCM technology to 3D-print alumina-based ceramics...

Objetive
The main goal of this study is the analysis of the mechanical enhancement of creep resistance in reduced graphene-oxide (rGO) reinforced alumina ceramic composites and compare the results with those found in the same ceramics without this secondary phase.
Materials and methods
The materials studied have been: Al2O3, Al2O3 + 2 vol.% rGO and Al2O3 + 6.7 vol.% rGO.
All the materials...

Transformation toughening, a stress induced martensitic phase transformation associated with volume expansion and shear is the main source of toughness and strength in zirconia structural ceramics. The commercially available portfolio of TZP (tetragonal zirconia polycrystal) materials is however very narrow and dominated by yttria and ceria stabilized zirconia materials which either lack...

In the last decade, the scientific community has tried to overcome the low strain failure of metastable tetragonal zirconia by introducing graphene-based nanomaterials (GBN). However, the difficulty in achieving a good dispersion of the reinforcement into the matrix still represents a brake on improving the mechanical properties. Moreover, owing to the nature of these composite ceramics, their...

Advanced structural ceramics play an important role in aerospace propulsion systems because of the increasing severity of conditions during operation. To this end, graphene-based nanostructures (GBN) have been demonstrated to be potential candidates to achieve an enhancement of mechanical and electrical properties in advanced structural ceramic matrix composites. Nevertheless, these properties...

The Ball-on-Three-Balls-Test (B3B) and the Ring-on-Ring-Test (RoR) were conducted on alumina discs and compared according to Weibull-Theory. Based on experimental results, the influence of various intermediate layers on strength measurement was evaluated. To support these findings, Finite-Element-Analysis was conducted to analyze the effects of deviations from ideal loading conditions for both...

In the last decade, there has been a growing interest on graphene-based nanomaterials (GBNs)/ceramic composites. It has been reported that the incorporation of these fillers into ceramic matrices enhances the mechanical, electrical and thermal properties of the resulting materials. Regarding the mechanical behavior of ceramic materials, direct crack measurement after Vickers indentation tests...

After two decades of research devoted to the reinforcement of ceramic composites with carbon allotropes such as graphene or nanotubes, the scientific community has developed different preparation routes and has achieved some significant milestones. Moreover, new reinforcing phenomena models based on the classic fiber reinforcement theory of ceramic materials have been developed. Nevertheless,...

The use of electrical-discharge machining (EDM) in ceramics is an emerging topic, due to the difficulties found by conventional machining techniques to obtain small or complex shaped parts from hard and brittle bulk ceramics. EDM is widely used in metals due to its high accuracy and the hardness-independent machining speed. However, most ceramics are electrical insulators and therefore not...

Oxide/oxide ceramic composites can be used for structural applications operating continuously at temperatures between 500°C and 900°C under oxidizing environment, such as in areas close to aircraft engines. In particular, composites based on a matrix combining alumina and silica are promising because this system has good mechanical properties up to 1000°C and allows to limit the grain...

WC-base cemented carbides, also referred to as hardmetals, have been the subject of intensive research and technological applications for past few decades, especially for metal cutting, mining and earth drilling industries. Several of these applications also include exposure to chemically aggressive media, such as lubricants, chemical products, petrochemical and mine slurries, and seawater....

Ultra-high temperature ceramics (UHTCs) are candidate materials for use in extreme environment owing to their melting point exceeding 3000°C and excellent ablation resistance. Despite the interesting combination of thermo-mechanical properties, they remain however failure sensitive materials. One route to mitigate the strength-ductility paradox is the creation of hierarchical structures, where...

Fully-dense ZrB₂ and HfB₂ samples were elaborated by SPS with three different additive compounds such as SiC, TaSi₂ or AlN (20 vol.%) to improve the oxidation resistance of the composite. To prevent grain growth during densification, sintering parameters were optimized following the process described by Piriou et al. [1].
Oxidation in air plasma from 1800 up...

MoSi2 as oxidation protective sintering aid in addition to reinforcing SiC fibers to increase fracture toughness are well known strategies to improve ZrB2-based UHTCs. However, the combination of MoSi2 with SiC fibers results in a detrimental reaction above a sintering temperature of 1700°C, jeopardizing the beneficial effect of the fibers. A buffer layer able to obstruct Mo-diffusion is hence...

The group of ultra-high temperature ceramics (UHTCs) are promising materials for extreme environmental conditions such as high temperatures (≥ 1300 °C). Among them, ZrB2 experienced extensive research due to its high melting point, low density and thermal shock resistance. However, ZrB2 shows rather low oxidation resistance, which is paramount for most applications in extreme environments. By...

Silicon nitride and SiAlONs are structural ceramics used in many wear parts, and recently have been indicated as promising materials for biomedical implants. The challenges for SiAlON densification can be overcome using additives and pressure assisted sintering. Traditionally, additives such as alumina and yttria are introduced using powders during powder processing. In this work, the use of...

MXene phases are bi-dimensional carbide or nitride phases generally synthesized by ablation of lamellar MAX phases. As a broad range of compositions is known, the properties of both the MAX and MXene phases can be tuned.
Syntheses of M(Ti, Zr or Hf)2AlC (e.g. 211) MAX phases by pressureless sintering and Spark Plasma Sintering (SPS) from metallic powders and a carbon source have been carried...

Multicomponent equiatomic oxides (MEOs), also named high entropy oxides (HEOs), have attracted great interest in recent years. Analogous to high entropy alloys (HEAs), they consist of five or more different cations on one or more cation sublattice in approximately same amount. , This leads to a big variety of compositions with adjustable material properties and promising versatile...

Combining high stiffness, strength and toughness is usually not obtained in engineering materials. This can however be achieved with bio-inspired ceramics mainly consisting for instance of alumina platelets [1]. The fracture behavior of such materials is mainly driven by their interfaces, which could possibly be tailored in order to improve the mechanical properties of the material. The design...

Structural ceramics are brittle materials with high strength. However, they often contain intrinsic flaws, such as pores, which may act as a stress concentrator during mechanical loading. Cracks usually initiate at such flaws and their unstable propagation follows, causing “catastrophic failure”.

One way of increasing the resistance to the propagation of cracks is combining ceramic...

One of the main issues about characterizing zirconia-based composites incorporating graphene-based nanomaterials (GBN) is the measurement of their fracture toughness. While indentation methods have been widely used to determine fracture toughness in ceramic materials, they are not of great value when ceramic-based composites, especially zirconia-based, need to be characterized. The Single Edge...

AlON transparent ceramics were fabricated by pressureless sintering starting from sub-micron AlON powders synthesized It was found that, for single phased synthetic AlON powders, there were special prisms, growth steps and pore structures on the surface and inside of the powder. Binary twin structure is ubiquitous in the synthesized powder particles. The EBSD results showed that the twin...