IN-SITU PROCESSED SI3N4 WHISKERS IN THE SYSTEM BARIUM ALUMINOSILICATE-SI3N4

The use of barium aluminosilicate (BAS) for transient liquid-phase sintering of Si3N4 is being explored as a low-cost processing route which can provide improved properties. The effect of processing conditions on sinterability, crystalline structure and microstructure was examined. It was demonstrated that Si3N4 could be pressureless sintered to high densities with BAS but that high volumes of BAS are required and hexacelsian preferentially forms as the intergranular phase. Even though hexacelsian is structurally unstable when acting alone, when present in a BAS-Si3N4 composite, the in situ reinforcement provided by Si3N4 serves to stabilize the composite sufficiently to permit its use in severe thermal environments.