TimeMan Seminar - Hiroshi MASUDA

Small-scale plasticity of oxide ceramics: impacts of orientations and grain boundaries

Hiroshi Masuda
Department of Materials Engineering, The University of Tokyo, Japan

In engineering applications, ceramics with ionic and/or covalent crystals exhibit excellent robustness to environments including temperatures, pressures, chemicals, and radiations. However, the brittle nature typically with stochastic fractures at low temperatures, approximately <1000°C, have been the thick barrier against many potential applications of ceramics. The brittleness is mostly attributed to the limited plasticity, which is associated with poor mobility of lattice defects such as dislocations and interfaces. Therefore, defect engineering is of importance to enhance the plasticity and finally to overcome the brittleness, but conventionally with limited methodology to evaluate plastic behaviors of ceramics below their ductile-to-brittle transition temperatures. In recent years, researchers have been attracted to micromechanical testing extended from nanoindentation technologies, where macroscopically brittle ceramics exhibit considerable plasticity even at room temperature [1]. Our group has also characterized small-scale plasticity of oxide ceramics such as Y2O3-stabilized ZrO2, Al2O3, and SrTiO3 to evaluate the impacts of orientations and grain boundaries on their strength and ductility through nanoindentation [2,3] and micropillar compression [4]. In these works, plastic behaviors of oxide ceramics exhibited strong anisotropy due to dislocation activities, whereas grain boundaries insignificantly affected the local hardness as compared with metallic materials. This seminar would discuss their physical mechanisms based on the metallurgical frameworks.

1. [1]  S. Korte-Kerzel, Microcompression of brittle and anisotropic crystals: recent advances and current challenges in studying plasticity in hard materials, MRS Commun. 7 (2017) 109–120.

2. [2]  H. Masuda, K. Morita, T. Ohmura, Nanoindentation-induced plasticity in cubic zirconia up to 500 °C, Acta Mater. 184 (2020) 59–68.

3. [3]  R. Nakamura, H. Masuda, H. Yoshida, Nanoindentation responses near single grain boundaries in oxide ceramics, J. Am. Ceram. Soc. 106 (2023) 2061–2072.

4. [4]  H. Masuda, K. Morita, M. Watanabe, T. Hara, H. Yoshida, T. Ohmura, Ferroelastic and plastic behaviors in pseudo-single crystal micropillars of nontransformable tetragonal zirconia, Acta Mater. 203 (2021) 116471.