Effect of Heat-Treatment on Thermal and Mechanical Properties of Silicon Nitride Ceramic at Room and High Temperatures

摘要

Alpha-silicon nitride powder with the SiO_2-MgO-Y_2O_3 system as sintering additives was pressurelessly sintered at 1650°C for 2 h in atmospheric N_2. Subsequently, these specimens were heat-treated at 1950°C for 8 h under N_2 gas pressure of 1.0 MPa to eliminate grain boundary phase. The oxygen content in these specimens was reduced by reactions of Si_3N_4 and the sintering additives during the heat-treatment. Thermal conductivity in 3mass%SiO_2-3mass%MgO-6mass%Y_2O_3-added Si_3N_4 specimen was improved from 36.6 W/m · K to 90.4 W/m · K by decreasing the amount of grain boundary phase after the heat-treatment. Bending strength of the sintered bodies both before and after the heat-treatment was sustained more than 550 MPa up to 1200°C.