Sintering of Silicon Carbide Powder Containing Metal Boride

Abstract

α(6H)-SiC powders mixed with 11 types of metal boride, B and C were sintered at high temperatures (1800-2200°C for 30min). MoB, NbB₂, TaB₂, TiB₂, VB₂, WB, and ZrB₂ promoted the densification of SiC powder and sintered SiC had a high fracture toughness (4.07-4.75MPa·m^1/2). The addition of metal boride enabled us to control the grain growth and densify SiC powder containing a fairly large amount of B. Metal borides dispersed in SiC grains, precipitated in triple points, and appeared to obstruct grain growth and crack propagation. CaB₆, CrB, LaB₆, and YB₆ did not promote sintering of SiC powder. These latter metal borides resulted in highly exaggerated grain growth and the SiC powder became porous after sintering. The starting 6H-SiC powder tended to be partially transformed into a 4H polytype which was accompanied by grain growth.