Evaluation of Microstructure of High-Strength Reaction-Sintered Silicon Carbide

A newly developed high-strength reaction-sintered silicon carbide (SiC), which has two or three times higher strength than the normal sintered SiC, is one of the most promising candidates such as the lightweight substrate of optical mirror, because of fully dense, small sintering shrinkage ( 1%), good shape capability and low sintering temperature. In this paper, in order to improve the performance of newly developed reaction-sintered SiC, the microstructure was investigated by paying attention to the crystal structures using the observation of transmission electron microscope and X-ray diffraction analysis. As a result, it made clear that the finer-scale microstructure could be observed as consisting of large particles (similar to 1 mu m in diameter) of starting powder beta-SiC and small particles (similar to 1 mu m in diameter) of beta-SiC formed during the reaction (Si+C=SiC) with the residual silicon filling the remaining porosity. Also, it was identified that the beta-SiC formed during the reaction referred to the cubic (3C) polytype and the alpha-SiC of starting powder referred to the hexagonal (6H) polytype.