Effect of Sintering Atmosphere on Grain Shape and Grain Growth in Liquid‐Phase‐Sintered Silicon Carbide

We investigated the effects of the sintering atmosphere on the interface structure and grain‐growth behavior in 10‐vol%‐YAG‐added SiC. When α‐SiC was liquid‐phase‐sintered in an Ar atmosphere, the grain/matrix interface was faceted, and abnormal grain growth occurred, regardless of the presence of α‐seed grains. In contrast, when the same sample was sintered in N 2 , the grain interface was defaceted (rough), and no abnormal grain growth occurred, even with an addition of α‐seed grains. X‐ray diffraction analysis of this sample showed the formation of a 3C (β‐SiC) phase, together with a 6H (α‐SiC) phase. These results suggest that the nitrogen dissolved in the liquid matrix made the grain interface rough and induced normal grain growth by an α→β reverse phase transformation. Apparently, the growth behavior of SiC grains in a liquid matrix depends on the structure of the grain interface: abnormal growth for a faceted interface and normal growth for a rough interface.