Pressureless sintering and mechanical properties of alumina-sialon composites

Compositions of Al₂O₃, Si₃N₄ and AlN were sintered to produce six different alumina-sialon composites. The composites reached the highest density at 1700 °C in a nitrogen atmosphere. Sialon acted as a binder, promoting the densification and suppressing the grain growth of alumina. The composites had a bending strength of 450 MPa at room temperature and maintained high strength over 300 MPa at 1400 °C. The composite with 30 wt % sialon had the maximum fracture toughness of 4.3 MPa·m^1/2 and exhibited good oxidation resistance even at 1400 °C. Mullite was formed in the oxidation layer and little degradation in strength was observed after oxidation.