Effect of starting phase on microstructure and fracture toughness of hot-pressed silicon carbide

The effect of starting phase of raw material on the microstructure and the fracture toughness of silicon carbide was investigated. The starting phase was adjusted by varying the mixed ratio of α-SiC and β-SiC powders, and they were hot pressed with sintering aids. From the microstructure, some elongated grains were found among equiaxial grains. The anisotropic grain growth was resulted from phase transformation of the β-SiC to the α-SiC with 4H polytype during sintering or heat treatment. Volume fraction, maximum length, and aspect ratio of elongated grains were the highest at 50 vol.% β-SiC in the starting SiC powder, which showed the highest fracture toughness about 6.0 MPa m 1/2.