Influence of the heat treatment on mechanical properties and oxidation resistance of SiC-Si3N4 composites

The basic mechanical properties and oxidation behaviour of liquid-phase-sintered SiC-Si3N4 composites were investigated as a function of the heat treatment at oxidising condition at 1350 °C/0-204 h. The results were compared to those obtained for a reference silicon carbide material, prepared by the same fabrication route. The heat treatment at higher temperature had a positive effect on fracture toughness values but no changes of hardness were observed. It was shown that the oxidation resistance increases with increasing temperature of heat treatment from 1650 °C to 1850 °C. Oxidation always followed parabolic rate law indicating diffusion as the rate limiting mechanisms. The addition of silicon nitride content had no significant influence on oxidation resistance of SiC-Si3N4 composites.