Effect of AlN and Al2O3 Additions on the Phase Relationships and Morphology of SiC Part II: Microstructural Observations
Additions of AlN and Al2O3 to -SiC hot pressed at 2100°C strongly effect the - to -SiC phase transformation and the resultant -SiC polytypes which are formed. Scanning and transmission electron microscopy were utilized to investigate the microstructural changes occurring in SiC due to these additions and to correlate these observations to their mechanical properties. The results suggest that Al2O3 additions stabilize the formation of the 6H-polytype of -SiC which grows rapidly into an elongated plate-like morphology, while AlN additions stabilize the 2H-polytype of -SiC resulting in fine equiaxed 2H-SiC: AlN solid solution grains. It is speculated that the elongated growth of 6H-SiC with Al2O3 additions can be controlled through the simultaneous addition of AlN. The formation of 2H-SiC : AlN solid solution grains inhibits the growth of the 6H-SiC grains since AlN(2H) will not go into solid solution in the SiC(6H) structure, effectively pinning the growth of the 6H-SiC grains.
T. Tien and G. Hilmas, "Effect of AlN and Al2O3 Additions on the Phase Relationships and Morphology of SiC Part II: Microstructural Observations," Journal of Materials Science, Springer Verlag, Nov 1999.
The definitive version is available at http://dx.doi.org/10.1023/A:1004745419321
Materials Science and Engineering
United States. Department of Energy
Keywords and Phrases
SiC; Microstructural Changes; Aluminum nitride; Aluminum oxide
Article - Journal
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