Microstructure Characterization of Gas-Pressure-Sintered β-Silicon Nitride Containing Large β-Silicon Nitride Seeds |
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Authors: | Naoto Hirosaki Yoshio Akimune Mamoru Mitomo |
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Affiliation: | Materials Research Liboratory. Nissan Research Center, Nissan Motor Company, Ltd., Yokosuka 237, Japan; National Institute for Research in Inorganic Materials, Tsukuba-shi, Ibaraki 305, Japan |
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Abstract: | Fine β-Si3N4 powders with or without the addition of 5 wt% of large β-Si3N4 particles (seeds) were gas-pressure sintered at 1900°C for 4 h using Y2O3 and Al2O3 as sintering aids. The microstructures were examined on polished and plasmaetched surfaces. These materials had a microstructure of in situ composites with similar small matrix grains and different elongated grains. The elongated grains in the materials with seeds had a larger diameter and a smaller aspect ratio than those in the materials without seeds. A core/rim structure was observed in the elongated grains; the core was pure β-Si3N4 and the rim was β-SiAION. These results show that the large β-Si3N4 particles acted as seeds for abnormal grain growth and the rim was formed by precipitation from the liquid containing aluminum. |
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