Corrosion Resistance of CVD Coatings on Superalloys. Topical Report, September 1,1990-August 31, 1992

摘要

This project was co-funded by GRI and Eniricerche, and was intended to assess thecorrosion resistance of silicon carbide coatings on Nimonic 80 superalloys in oxygen and SO2, H2O, CO2, and sodium containing environments at 800-1100 deg. C. Eniricerche was to supply the coated superalloys. CVD SiC coated tungsten carbide cutting tool inserts were supplied for initial oxidation studies of the coatings. This TiN-Ti(C,N)/Al2O3/SiC tri-layer coating system was about 11 micrometers in thickness, with the SiC layer about 5 micrometers. Chemical and microstructural characterization was followed by a qualitative analysis of residual thermal stresses in the coating. Oxidation studies on the coated tools for times of 100 to 4000 minutes were performed in an atmosphere of high purity oxygen at 800 and 900 deg. C; single crystal Si and reaction-bonded SiC were also examined for comparative purposes. Samples of SiC-coated Nimonic superalloys were never supplied, so careful studies of the 800 to 1100 deg. C oxidation of single crystal and CVD SiC were performed to extend the temperature range for the authors' baseline data which is utilized in analyses of additive and impurity effects on the oxidation of commercial silicon carbides.