The development of damage-resistant structural materials that can withstand harsh environments is a major issue in materials science and engineering. Bioinspired brick-and-mortar designs have recently demonstrated a range of interesting mechanical properties in proof-of-concept studies. However, reproducibility and scalability issues associated with the actual processing routes have impeded further developments and industrialization of such materials. Here we demonstrate a simple approach based on uniaxial pressing and field assisted sintering of commercially available raw materials to process bioinspired ceramic/ceramic composites of larger thickness than previous approaches, with a sample thickness up to 1 cm. The ceramic composite retains the strength typical of dense alumina ($430~\pm 30MPa$) while keeping the excellent damage resistance demonstrated previously at the millimeter scale with a crack initiation toughness of $6.6MPa.m^{1/2}$ and fracture toughness up to $17.6 MPa.m^{1/2}$. These results validate the potential of these all-ceramic composites, previously demonstrated at lab scale only, and could enable their optimization, scale-up, and industrialization.
This is a reply to the correspondence of Prof. Robert Ritchie: "On the fracture toughness of bioinspired ceramic materials", submitted to Nature Materials, which discusses the fracture toughness values of the following papers: Bouville, F., Maire, E., Meille, S., Van de Moortèle, B., Stevenson, A. J., & Deville, S. (2014). Strong, tough and stiff bioinspired ceramics from brittle constituents. Nature Materials, 13(5), 508-514 and Le Ferrand, H., Bouville, F., Niebel, T. P., & Studart, A. R. (2015). Magnetically assisted slip casting of bioinspired heterogeneous composites. Nature Materials, 14…
Glasses have numerous applications due to their exceptional transparency, however, poor fracture and impact resistance limit their applications as an engineering material. One relatively recent approach to improve the mechanical properties of materials is through bio-inspiration. Structural biological composites such as nacre, the protective inner layer of mollusk shells, offer far superior mechanical properties relative to their constituents. This has motivated researchers to mimic the design principles in natural composites to create tough transparent materials. However, current bio-inspired…
High strength and high toughness are usually mutually exclusive in engineering materials. Improving the toughness of strong but brittle materials like ceramics thus relies on the introduction of a metallic or polymeric ductile phase to dissipate energy, which conversely decreases the strength, stiffness, and the ability to operate at high temperature. In many natural materials, toughness is achieved through a combination of multiple mechanisms operating at different length scales but such structures have been extremely difficult to replicate. Building upon such biological structures, we demons…
Zirconia ceramics have been known as a structural material with high fracture toughness and strength since Garvie et al. discovered phase transformation toughening in 1975 [1]. Although these mechanical properties are the most excellent among the advanced ceramics, the toughness has not yet reached the level of metallic materials. Here, we demonstrate for the first time that 2.9 mass% Y2O3-stabilized ZrO2s doped with Al2O3 greatly exceed the toughness of conventional zirconia ceramics which is comparable to those of metallic materials, even with slightly higher strength. The excellent mechanic…
To respond to the increasing need for bone repair strategies, various types of biomaterials have been developed. Among those, calcium phosphate ceramics (CPCs) are promising since they possess a chemical composition similar to that of bones. To be suitable for implants, CPCs need to fulfill a number of biological and mechanical requirements. Fatigue resistance and toughness are two key mechanical properties that are still challenging to obtain in CPCs. This paper thus reviews and discusses current progress in the processing of CPCs with bioinspired microstructures for load-bearing applications…
Superlattice (SL) thin films composed of refractory ceramics unite extremely high hardness and enhanced fracture toughness; a material combination often being mutually exclusive. While the hardness enhancement obtained whentwo materials form a superlattice is well described by existing models based on dislocation mobility, the underlying mechanisms behind the increase in fracture toughness are yet to be unraveled. Here we provide a model based on linear elasticity theory to predict the fracture toughness enhancement in (semi-)epitaxial nanolayers due to coherency stresses and formation of misf…
Changes in crystalline phases resulting from low-temperature ageing of different yttria doped and non-doped zirconia-toughened alumina composites and nanocomposites were investigated under controlled humidity and temperature conditions in autoclave. A classical powder mixing processing route and a new modified colloidal processing route were used to process the composites. Different compositions ranging from 2.5 wt.% zirconia in a matrix of alumina to pure zirconia (3Y-TZP) were studied. It was observed that Al2O3+yttria stabilised ZrO2 composites exhibited significant ageing. However, ageing …
High hardness and toughness are generally considered mutually exclusive properties for single-crystal ceramics. Combining experiments and ab initio molecular dynamics (AIMD) atomistic simulations at room temperature, we demonstrate that both the hardness and toughness of single-crystal NaCl-structure VNx/MgO(001) thin films are simultaneously enhanced through the incorporation of anion vacancies. Nanoindentation results show that VN0.8, here considered as representative understoichiometric VNx system, is ~20% harder, as well as more resistant to fracture than stoichiometric VN samples. AIMD mo…
Aviation's fossil fuel emissions contribute to global warming. The production and disposal of the materials used in aircrafts too. The current metallic alloys present in the hot section of engines pose constraints in terms of temperature, pressure and weight that restrain the performance of the aircrafts. Also, these alloys are produced using rare, depleting resources, and polluting processes. In this paper, we hypothesize the use of bioinspired nacre-like alumina (NLA), a ceramic material that exhibits unusual toughness, and evaluate its potential as a replacement for superalloys in aircraft'…
Dense ceramics are irreplaceable in applications requiring high mechanical stiffness, chemical and temperature resistance and low weight. To improve their toughness, ceramics can be reinforced with elongated inclusions. Recent manufacturing strategies have been developed to control the orientations of disc-like micro-particles in polymeric and ceramic matrices and to build periodic microstructures. Given the infinite number of possible microstructures available, modeling tools are required to select the potentially best design. Periodic microstructures can be involved in elastic wave scatterin…
Ceramic materials are ubiquitous in technologies operating under high mechanical, thermal or chemical constrains. Research in ceramic processing aims at creating ceramics with properties that are still challenging to obtain, such as toughness, transparency, conductivity, among others. Magnetic slip casting is a ceramic process where an external magnetic field is used to align the ceramic grains along preferential crystallographic directions, thereby creating controlled texture. Over the past 20 years of research on magnetic slip casting, ceramics of multiple chemistry were found to exhibit enh…
Composites are often made heterogeneous in nature to fulfill the functional demands imposed by the environment, but remain difficult to fabricate synthetically due to the lack of adequate and easily accessible processing tools. We report on an additive manufacturing platform to fabricate complex-shaped parts exhibiting bio-inspired heterogeneous microstructures with locally tunable texture, composition and properties and unprecedentedly high volume fractions of inorganic phase (up to 100%). The technology combines an aqueous-based slip casting process with magnetically-directed particle assemb…
Durable interfacing of hard and soft materials is a major design challenge caused by the ensuing stress concentrations. In nature, soft-hard interfaces exhibit remarkable mechanical performance, with failures rarely happening at the interface but in the hard or soft material. This superior performance is mechanistically linked to such design features as hierarchical structures, multiple types of interlocking, and functional gradients. Here, we mimic these strategies to design efficient soft-hard interfaces using voxel-based multi-material 3D printing. We designed several types of soft-hard int…
Soft materials capable of large inelastic deformation play an essential role in high-performance nacre-inspired architectured materials with a combination of stiffness, strength and toughness. The rigid "building blocks" made from glass or ceramic in these architectured materials lack inelastic deformation capabilities and thus rely on the soft interface material that bonds together these building blocks to achieve large deformation and high toughness. Here, we demonstrate the concept of achieving large inelastic deformation and high energy dissipation in soft materials by embedding microstruc…
Improved toughness is a central goal in the development of wear-resistant refractory ceramic coatings. Extensive theoretical and experimental research has revealed that NaCl structure VMoN alloys exhibit surprisingly high ductility combined with high hardness and toughness. However, during operation, protective coatings inevitably oxidize, a problem which may compromise material properties and performance. Here, we explore the role of oxidation in altering VMoN properties. Density functional theory and theoretical intrinsic hardness models are used to investigate the mechanical behavior of cub…
Nanocrystalline metals and ceramics with <100 nm grain sizes and superior properties (e.g., mechanical strength, hardness, fracture toughness and stored dielectric energy) are of great interest. Much has been discussed about achieving nano grains, but little is known about maintaining grain-size uniformity that is critical for material reliability. An especially intriguing question is whether it is possible to achieve a size distribution narrower than what Hillert[1] theoretically predicted for normal grain growth, a possibility suggested, for growth with a higher growth exponent, by the gener…
Materials that are strong, ultra-light weight and tough are in demand for a range of applications, requiring architectures and components carefully designed from the micrometer down to nanometer scales. Nacre-a structure found in many molluscan shells-and bone are frequently used as examples for how nature achieves this through hybrid organic-inorganic composites. Unfortunately, it has proven extremely difficult to transcribe nacre-like clever designs into synthetic materials, partly because their intricate structures need to be replicated at several length scales. We demonstrate how the physi…
