Low temperature sintering of high performance Al₂O₃/ZrO₂ ceramics with ultra-fine nanoparticles strengthening

In this work, we propose a novel amorphous/solid solution Al2O3/ZrO2 powder with a low sintering temperature, capable of precipitating many ultra-fine nanoparticles in the ceramics. The powder was prepared by combustion synthesis assisted with rapid cooling in water, and then subjected to grinding for further refinement. The high preparation temperature and the rapid cooling process resulted in the formation of solid solutions and partially amorphous structures in the powder, which leads to a metastable state in the powder. The transformation of the metastable state and the presence of oxygen vacancies in the powder can accelerate mass transfer during sintering. Therefore, the powder can be densified through hot press at temperature as low as 1300 degrees C. During sintering, a large number of ultra-fine nanoparticles (similar to 5 nm) were precipitated from the solid solution and evenly dispersed throughout the matrix. The nanoparticles exhibit a high degree of coherence with the matrix due to the similarities in crystal structure between t-ZrO2 and alpha-Al2O3. The presence of nanoparticles shifts the fracture mode from intergranular to transgranular, and effectively improve the mechanical properties of the ceramics. Consequently, the bending strength, hardness and fracture toughness of the ceramic can reach up to 749 +/- 43 MPa, 16.2 +/- 0.24 GPa and 10.3 +/- 0.53 MPam(0.5), respectively. To compare the sintering capabilities and the performance of the ceramics, commercial powders were also sintered at the same temperature. This research may offer a new instruction for the low temperature fabrication of nanoparticles-strengthened ceramics.