Effect of Heat Treatment on Fracture Toughness of Alumina Ceramics and Its Process Optimization

The influences of the heating rate, heat treatment temperature and holding time on the fracture toughness and microstructures of Al2O3 ceramics were studied by the response surface method and the optimum heat treatment process was determined. The properties and microstructure of the ceramic after heat treatment with the optimum process were analyzed. The results show that with the increase of the heat treatment temperature and holding time, the fracture toughness of Al2O3 ceramics first increased then decreased. The factors, in order of effect significance, were ranked as follows: heat treatment temperature, holding time and heating rate. The effect of interaction between temperature and holding time on the fracture toughness was the biggest, followed by the interaction between heating rate and temperature and that between heating rate and holding time had the smallest influence. The optimum heat treatment parameters were found as follows: heating rate of 4 ℃·min-1, temperature of 1 150 ℃ and holding time of 230 min. After heat treated under this condition, the fracture toughness of the Al2O3 ceramic improved from 3.25 MPa·m1/2 before heat treatment to 5.1 MPa·m1/2. The grain sizes were uniform and internal defects and pore amounts were decreased.