Effect of Initial α‐Phase Content on Microstructure and Mechanical Properties of Sintered Silicon Carbide

By using α‐ and β‐SiC starting powders with similar particle sizes, the effects of initial α‐phase content on the microstructure and the mechanical properties of the liquid‐phase‐sintered and subsequently annealed materials were investigated. The microstructures developed were analyzed by image analysis. When β‐SiC powder was used, the grains became elongated. The average diameter decreased with increasing α‐SiC content and the aspect ratio showed a maximum at 10%α‐SiC and decreased with increasing α‐SiC content in the starting powder. Such results suggest that microstructure can be controlled by changing α‐phase content in starting powders. The strength increased with increasing α‐SiC content in the starting powder while the fracture toughness decreased with increasing α‐SiC content. There may be a trade‐off in improving both the strength and toughness in SiC ceramics sintered with oxide additives.