[SY-C5] Symposium C-5

[SY-C5] Plasticity and Fracture in Transition Metal Carbides

Invited

^○Giacomo Po¹, Suneel Kodambaka², Jeffrey M Wheeler³, Davide Sangiovanni⁴ (1.University of California Los Angeles, Mechanical Engineering Department, United States of America, 2.University of California Los Angeles, Materials Science and Engineering Department, United States of America, 3.Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Swaziland, 4.Department of Physics, Chemistry and Biology, Linköping University, Sweden)

Current and future applications in hypersonic flight, re-entry vehicles, propulsion, and power production create an insatiable demand for materials capable to perform in severe environments. Materials for these applications must possess a rare combination of properties, which include high specific strength, elevated melting temperature, high thermal conductivity, and low thermal expansion coefficient. Ultra-High Temperature Ceramics are being considered for applications in extreme environments, especially when oxidation is a major concern. Currently, the factor limiting the use of UHTCs as structural materials is their low-temperature brittleness. This talk focuses on the plasticity and fracture mechanisms of the transition metal carbide TaC, one of the highest melting temperature materials known to mankind. In-situ micro-pillar compression experiments carried out at different temperatures and orientations reveal unexpected intrinsic ductility of TaC, which contrasts its well-known bulk brittleness. These findings unveil new properties of the material, such as a pronounced non-Schmid behavior and a remarkable temperature/orientation dependence of the yield strength. A variety of multiscale modeling techniques ranging from ab-initio to discrete dislocation dynamics simulations are employed to understand the small-scale behavior of TaC. Computer simulations shed light on the room-temperature brittleness of TaC by explaining the link between plastic deformation and fracture.