Microstructure and properties of submicron grained alumina ceramic tool material prepared by two-step microwave sintering

Abstract

Alumina ceramic with submicron grains was prepared by the two-step microwave sintering. Microstructure evolution and densification kinetics of alumina during microwave sintering were studied. The main densification mechanism of alumina ceramic is grain boundary diffusion at the temperature below 1100 °C, while the main densification mechanism is volume diffusion at the temperature from 1200 to 1300 °C. The mean activation energy of grain growth of alumina is 52.36 kJ/mol, and the minimum activation energy of grain growth (48.32 kJ/mol) appears at the holding time of 10 min. Submicron grained alumina ceramic was prepared by two-step microwave sintering (T1 = 1300 °C, T2 = 1100 °C with the holding time of 5 min). The grain size is 0.64 ± 0.16 µm, and its relative density, Vickers hardness and fracture toughness are 98.23%, 18.70 ± 1.01 GPa and 5.28 ± 0.26 MPa m1/2, respectively.