Nonequiaxial Grain Growth and Polytype Transformation of Sintered α‐Silicon Carbide and β‐Silicon Carbide

α(6 H )‐ and β(3 C )‐SiC powders were sintered with the addition of AlB 2 and carbon. α‐SiC powder could be densified to ∼98% of the theoretical density over a wide range of temperatures from 1900° to 2150°C and with the additives of 0.67–2.7 mass% of AlB 2 and 2.0 mass% of carbon. Sintering of the β‐SiC powder required a temperature of >2000°C for densification with these additives. Grains in the α‐SiC specimens grew gradually from spherical‐shaped to plate‐shaped grains at 2000°C; the 6 H polytype transformed mainly to 4 H . On the other hand, grains in the β‐SiC largely grew at >2000°C; the 3 C polytype transformed to 4 H , 6 H , and 15 R . The stacking faults introduced in grains were denser in β‐SiC than in α‐SiC. The rapid grain growth in the β‐SiC specimen was attributed to polytype transformation from the unstable 3 C polytype at the sintering temperature.