Grain boundary crystallization during furnace cooling of α-SiC sintered with Y2O3–Al2O3–CaO

For the SiC specimens prepared with Al2O3, Y2O3, and CaO (AYC-SiC), it was observed that the intergranular films and triple-junction phases were completely crystallized without subsequent heat-treatment after sintering. The intergranular films were determined to have hetero-epitaxially grown (Al,Si)2OC of a 2H-type wurtzite structure, with partial substitution of Al by Si. Segregation of Ca and Y at the grain boundaries was also detected by energy-dispersive X-ray spectroscopy (EDS). On the other hand, the composition and structure of the triple junction phases were different from those of intergranular films. It showed hexagonal structure and topotactic relationships with SiC grains (aSiC//ajunction, cSiC//cjunction, and aSiC = 2ajunction).