Fracture properties of SiC ceramics with oxynitride additives

Silicon carbide ceramics incorporating sintering additives from the system AlN–Y2O3 can be gas-pressure sintered to theoretical density. While commonly a combination of sesquioxides is used such as Al2O3–Y2O3, oxynitride additives offer the advantage that only a moderate nitrogen overpressure is required instead of a powder bed for thermochemical stabilization at the sintering temperature. In the present study aspects of the fracture behavior of these materials are addressed, namely the influence of anisotropic grain growth and processing flaws, additional toughening at high temperatures and thermal shock characteristics. They are correlated with microstructural data obtained by scanning electron microscopy.