Mechanical Behavior of Cermaics
(1) Effects of electric field on microstructure evolution and defect formation in flash-sintered TiO2
Bo Yang, Zhongxia Shang, Jin Li, Xin Li Phuah, Jaehun Cho, Haiyan Wang, and Xinghang Zhang. "Effects of electric field on microstructure evolution and defect formation in flash-sintered TiO2." Journal of European Ceramic Society 42(13)(2022): 6040-6047.
Highlight: Various ceramic materials have been successfully flash sintered via mostly direct current (DC) and some by alternative current (AC). However, a direct comparison on the effects of different field types on the overall microstructure and atomistic defect distribution in flash-sintered ceramics is still very limited. In this work, rutile TiO2 was chosen as a model system to directly compare the effects of DC and AC fields on microstructure and defect distribution. DC flash-sintered TiO2 presents asymmetrical distributions of grain sizes and defects, while AC sintered TiO2 have more homogeneous microstructures. More interestingly, we demonstrated a reverse-polarity flash sintering technique can achieve dense TiO2 bulk samples with homogeneous microstructure and tunable defect gradient, which are previously not attainable from either DC or AC sintering alone. This study shows the importance of field on the microstructures of flash-sintered ceramics and the great potential in achieving dense and uniform microstructures via effective field control process.
(2) High temperature deformability of ductile flash-sintered ceramics
Jaehun Cho, Qiang Li, Han Wang, Zhe Fan, Jin Li, Sichuang Xue, K. S. N. Vikrant et al. "High temperature deformability of ductile flash-sintered ceramics via in-situ compression." Nature communications 9, no. 1 (2018): 1-9.
Highlight: This study highlights the first in-situ microcompression test done on flash sintered YSZ at elevated temperature up to 600 °C. At room temperature, YSZ micropillars sustain giant strain (~8%) comparing with its bulk counterpart (~2%) due to the stress-induced martensitic transformation toughening. However, the pillars fracture catastrophically after the nucleation of cracks. In comparison, a brittle-to-ductile transition of fracture mode is observed at 400 °C in flash-sintered YSZ, much lower than the ~800 °C reported in conventional bulk YSZ. The enhanced plasticity at elevated temperatures arises from the transition from phase transformation toughening to dislocation creep, as the dominant inelastic deformation mechanism due to the existence of a high density of dislocations in flash-sintered YSZ and/or to early initiation of grain boundary sliding of ultra-fine grains.
(3) Nanoscale stacking fault–assisted room temperature plasticity in flash-sintered TiO2
Jin Li, Jaehun Cho, Jie Ding, Harry Charalambous, Sichuang Xue, Han Wang, Xin Li Phuah et al. "Nanoscale stacking fault–assisted room temperature plasticity in flash-sintered TiO2." Science advances 5, no. 9 (2019): eaaw5519.
Highlight: In this study, in situ micropillar compression tests show that flash-sintered TiO2 exhibits unexpected substantial plasticity at RT, sustaining 10% strain without noticeable cracks. The high-density preexisting defects and O vacancies introduced during the nonequilibrium flash-sintering process facilitates the nucleation of dislocations. RT deformation is dominated by the formation of nanoscale stacking faults, followed by the creation of nanotwins when tested at 200° to 400°C. Dislocation glide takes over the deformation mechanism at 600°C. This study strongly suggests that the flash-sintering method presents great potential in promoting plasticity in a broad range of ceramic materials.