MICROSTRUCTURAL CHARACTERIZATION OF SILICON-NITRIDE BONDED SILICON-CARBIDE

The microstructure of a commercial silicon nitride-bonded silicon carbide ceramic composite, formed via the nitridation of Si powder-SiC preforms, has been characterised by transmission electron microscopy. A mechanism combining reaction bonding and liquid-phase sintering is proposed to describe the development and observed morphology of the microstructure of the bonding matrix, which comprises predominantly phases based on Si2N2O and beta-Si3N4 and an amorphous phase. Qualitative microanalysis of amorphous matrix regions has revealed significant concentration of oxygen, aluminium and calcium, with Al also being detected in both of the surrounding crystalline phases. It is thus suggested that the principal constituents of the matrix are in fact O' and beta' sialons.