THE DEVELOPMENT OF MICROSTRUCTURE IN SILICON NITRIDE-BONDED SILICON-CARBIDE

The microstructure of a commercial silicon nitride-bonded silicon carb ide ceramic composite, formed via the nitridation of silicon powder-Si C preforms, has been characterised using analytical transmission elect ron microscopy. It comprised coarse particles of SiC dispersed in a ma trix which was a mixture of crystalline phases based on Si2N2O and bet a-Si3N4, and an amorphous phase. Qualitative microanalysis of amorphou s matrix regions revealed the presence of significant concentrations o f aluminium, silicon, calcium and oxygen, while aluminium and oxygen w ere also readily detectable in both of the surrounding crystalline pha ses. Tt is thus suggested that the crystalline phases in the matrix ar e in fact O- and beta-sialons respectively. A mechanism, combining rea ction bonding and solution-precipitation in a (Ca,K)-aluminosilicate l iquid phase at the reaction temperature, is proposed to describe the d evelopment of the matrix microstructure.