Two-stage sintering inhibits abnormal grain growth during β to α transformation in SiC

Free sintering of SiC with Al, B, and C additions in two successive stages, first under nitrogen and then under argon, produced a near full-density ceramic with equiaxed grain structure. The β to α transformation proceeded to completion; however, the grain shape remained equiaxed due to the action of nitrogen present during the first stage of sintering. It is found that the β to α transformation is necessary but not sufficient for producing the microstructure of interlocking plates found in high-toughness SiC.