Nonequiaxial grain growth and polytype transformation of sintered a-silicon carbide and b-silicon carbide

*a(6H)- and *b(3C)-SiC powders were sintered with the addition of AlB2 and carbon. *a-SiC powder could be densified to #~98% of the theoretical density over a wide range of temperatures from 1900DG to 2150DGC and with the additives of 0.67-2.7 mass% of AlB2 and 2.0 mass% of carbon. Sintering of the *b-SiC powder required a temperature of > 2000DGC for densification with these additives. Grains in the a-SiC specimens grew gradually from spherical-shaped to plate-shaped grains at 2000DGC; the 6H polytype transformed mainly to 4H. On the other hand, grains in the *b-SiC largely grew at > 2000DGC; the 3C polytype transformed to 4H, 6H, and 15R. The stacking faults introduced in grains were denser in *b-SiC than in a-SiC. The rapid grain growth in the *b-SiC specimen was attributed to polytype transformation from the unstable 3C polytype at the sintering temperature.