Fabrication and microstructure of sialon-bonded silicon carbide

The sintering behaviour of ceramic-matrix composites consisting of a sialon matrix and silicon carbide particulate reinforcement has been studied in o rder to elucidate the densification behaviour and the formation of the micr ostructure. The materials are produced from a mixture of clay, silicon nitr ide and yttria sintering additive mixed with 60% of silicon carbide grit. T he results lead to a description of the mechanism of phase formation which consists of the following steps. 1. Decomposition of china clay and formation of mullite and silica on heati ng. 2. Formation of liquid phase from these reaction products, together with ex cess silica from silicon carbide and yttria sintering additive. 3. Dissolution of silicon nitride in the liquid and precipitation of sialon X and O' phases. 4. Formation of a high-yttrium, nitrogen glass on cooling. Composites of this kind with porosity of about 14% and zero linear shrinkag e on Jiving, due to the rigid skeleton of carbide particles, ave promising candidate materials for high-temperature applications where the microstruct ure offers the prospect of superior high-temperature strength through the c ontinuous interlocking texture of the X-phase and O'-silicon oxynitride cry stalline phases, the carbide skeleton and the high viscosity yttrium-nitrog en glass matrix. (C) 1999 Elsevier Science Limited. All rights reserved.