Microstructural Development of Silicon Carbide Containing Large Seed Grains

Fine (}0.1μm) β‐SiC powders, with 3.3 wt% large (}0.44μm) α‐SiC or β‐SiC particles (seeds) added, were hot‐pressed at 1750°C and then annealed at 1850°C to enhance grain growth. Microstructural development during annealing was investigated using image analysis. The introduction of larger seeds into β‐SiC accelerated the grain growth of elongated large grains during annealing, in which no appreciable β→α phase transformation occurred. The growth of matrix grains in materials with β‐SiC seeds was slower than that in materials with α‐SiC seeds. The material with β‐SiC seeds, which was annealed at 1850°C for 4 h, had a bimodal microstructure of small matrix grains and large elongated grains. In contrast, the material with α‐SiC seeds, also annealed at 1850°C for 4 h, had a uniform microstructure consisting of elongated grains. The fracture toughnesses of the annealed materials with α‐SiC and β‐SiC seeds were 5.5 and 5.4 MPa·1/2, respectively. Such results suggested that further optimization of microstructure should be possible with β‐SiC seeds, because of the remnant driving force for grain growth caused by the bimodal microstructure.