The low temperature hexagonal to orthorhombic transformation in Si₃N₄ reinforced BAS matrix composites

The amount of Si₃N₄ in a Si₃N₄-BaO · Al₂O₃ · 2SiO₂ (BAS) composite and the time of sintering was examined in the context of the low temperature hexagonal to orthorhombic transformation in BAS. It was found that with increasing amounts of Si₃N₄ in the composite, the temperature of the hexagonal to orthorhombic transformation was decreased. As the sintering time was increased for a given composite composition, a drop in the temperature of the hexagonal to orthorhombic transformation was observed. which was linked to an increase in the β-Si₃N₄ content in the composite. In addition, as the Si₃N₄ content in the composite was increased, a resultant drop in the coefficient of thermal expansion of the composite occurred. The extent of the linear dimensional change of the composite during the BAS hexagonal to orthorhombic transformation is reported.