SI3N4/SIC-PLATELET COMPOSITE WITHOUT SINTERING AIDS - A CANDIDATE FOR GAS-TURBINE ENGINES

A dense and isotropic Si3N4 composite body containing 25 vol% of alpha-SiC platelets, with average particle size of 24 mum and aspect ratio of 8 to 10, was fabricated by hot isostatic pressing without any addition of sintering aids. In this composite, desirable properties for structural ceramics to be used in long-term high-temperature applications are conveniently combined: a fracture resistance comparable with that of Si3N4 sintered with conspicuous amounts of additives, as well as a superior time-dependent strength and deformation behavior up to 1400-degrees-C, was found. The high-temperature reliability in the present composite was improved further than that of the additive-free Si3N4, mainly due to mechanisms operating in the wake of the crack. The key to the attainment of a valid synergism between nitride and carbide phase resides both in the presence of pure SiO2 glassy phase at the grain boundary and in the morphology of the reinforcement.