Influence of different BN grades on sintering behaviour, microstructure and properties of machinable Si3N4-MoSi2-BN Composites

The effects of the addition of 20 vol% of BN particles to a Si3N4-5 vol% MoSi2 ceramic composite have been studied. Three BN powders, differing for the grain size and impurities content, were used. An higher amount of oxygen in the starting BN powders leads to densification curves similar to that of the matrix, while the use of sub-micrometric BN powder leads to less anisotropic materials than those developed by micrometric powders. Due to a residual porosity and inhomogeneities, mechanical properties were lowered by BN addition. Oxidation resistance at 1500°C was excellent due to the simultaneous presence of BN and MoSi2