Sintering behavior, microstructural evolution, and mechanical properties of ultra-fine grained alumina synthesized via in-situ spark plasma sintering

Ultra-fine grained Al2O3 was fabricated by in-situ spark plasma sintering (SPS) process directly from amorphous powders. During in-situ sintering, phase transformation from amorphous to stable α-phase was completed by 1100 °C. High relative density over 99% of in-situ sintered Al2O3 was obtained in the sintering condition of 1400 °C under 65 MPa pressure without holding time. The grain size of in-situ sintered Al2O3 body was much finer (~400 nm) than that of Al2O3 sintered from the crystalline α-Al2O3 powders. For in-situ sintered Al2O3 from amorphous powders, we observed a characteristic microstructural feature of highly elongated grains in the ultra-fine grained matrix due to abnormal grain growth. Moreover, the properties of abnormally grown grains were controllable. Fracture toughness of in-situ sintered Al2O3 with the elongated grains was significantly enhanced due to the self-reinforcing effect via the crack deflection and bridging phenomena.