Phase Evolution and Mechanical Performance of Zirconia Ceramics Synthesized Under High Temperature and High Pressure

Achieving simultaneous enhancement of Vickers hardness and fracture toughness remains a critical challenge in designing oxide ceramic materials due to their partially antagonistic nature. In this study, we address this trade-off by tailoring the microstructure of zirconia (ZrO₂) ceramics through Y₂O₃ doping and high-pressure high-temperature (HPHT) sintering. Nanostructured composites were synthesized using 50 nm monoclinic ZrO₂ and varying Y₂O₃ contents (3, 5, and 7 mol%) under 5 GPa at temperatures ranging from 400 to 2000 °C. Among them, 3 mol% Y₂O₃-doped zirconia (3Y-PSZ) sintered at 1200 °C achieved a well-balanced mechanical performance, with a Vickers hardness of 11.6 GPa and a fracture toughness of 9.26 MPa·m^1/2. These results demonstrate that it is feasible to retain a high hardness while significantly enhancing toughness by controlling phase composition and grain refinement under HPHT conditions. This work offers valuable insights into microstructural optimization strategies for zirconia-based ceramics aiming to overcome the conventional hardness-toughness trade-off.