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Coating of Sic on Titanium Aluminide
Published online by Cambridge University Press: 01 January 1992
Abstract
Coating of silicon carbide on the surface of structural materials is being used in industry to improve the oxidation resistance and wear resistance properties. In this study, silicon carbide coatings were applied on titanium aluminide by both chemical vapor deposition and sputter deposition techniques. Chemical vapor deposition of SiC was accomplished by reacting methyl trichlorosilane (MTS) and hydrogen in the presence of argon on the substrate surface at 1100 C under 1 atm pressure. Sputter deposition of SiC was completed in a Cooke sputter deposition system using a SiC target at 10 mTorr argon total pressure and 100 watt power. Under the experimental conditions of this study, the deposition rate of CVD SiC is about 1 μm per hour whereas that of sputtered SiC is about 1 urn per hour. To minimize the thermal residual stress between the aluminide substrate and SiC coating as a result of the coefficient of thermal expansion mismatch and temperature variation, a thin layer of TiC was coated prior to the SiC coating. For sputter deposited SiC, it was found that when the coating was done at room temperature, the adhesion of coating to the aluminide substrate was poor. The coating layer spalled off when the coated specimen was thermal cycled to 900 C. By coating the carbides at an elevated temperature, e.g. 560 C. strong adhesion between carbide coating and the substrate was obtained. The coating survived many thermal cyclings. The degree of surface roughness ranging from #80 to #800 grit surface polish did not affect the adhesion of coating.
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- Copyright © Materials Research Society 1995
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