Protectiveness of CVD Al2O3 Films Against High-Temperature Oxidation

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Abstract
Protectiveness of CVD Al2O3 films deposited on SUS 304 stainless steel coupons precoated with CVD TiN films was studied by isothermal and cyclic oxidation tests in pure oxygen under atmospheric pressure. The deposition temperatures were 1073, 1173 and 1273K, and the oxidation temperatures were 1173 and 1273K. The adherence of the Al2O3 film to the TiN film is so good that the partial spallation takes place almost always at the interface between the TiN film and the substrate, The Al2O3 films on flat areas of the specimens are protective during the isothermal oxidation, and hence the TiN film and the substrate do not oxidize. Contrary to this cracks are developed in the films on and near the specimen edges, where the exposed substrate surface oxidizes. The degree of this cracking depends on the deposition and oxidation temperatures. During the cyclic oxidation test with a maximum temperature of 1273K, partial spallation of the film takes place over relatively wide areas when the deposition temperature was 1173K. However, when the deposition temperature is 1273K the spallation is very limited. The above observations were explained mainly in terms of the thermal stresses.

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