Fine (}0.1m) -SiC powders, with 3.3 wt% large (}0.44m) α-SiC or -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 -SiC accelerated the grain growth of elongated large grains during annealing, in which no appreciable →α phase transformation occurred. The growth of matrix grains in materials with -SiC seeds was slower than that in materials with α-SiC seeds. The material with -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 -SiC seeds were 5.5 and 5.4 MPa·1/2, respectively. Such results suggested that further optimization of microstructure should be possible with -SiC seeds, because of the remnant driving force for grain growth caused by the bimodal microstructure.
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Document Type: Research Article
Department of Materials Science and Engineering, Seoul City University, Seoul 130-743, Korea
National Institute for Research in Inorganic Materials, Ibaraki 305, Japan
Research Center, Denki Kagaku Kogyo Company, Tokyo 194, Japan
Publication date: 01 January 1997