A hybrid PACVD SiC/CVD Si3N4SiC multilayer coating for oxidation protection of composites Original Research Article

Chemical vapor deposition (CVD) coatings used for the oxidation protection of carbon-carbon (CC) composites provide inadequate oxidation protection due to extensive thermal cracking. One method to reduce the thermal cracking is to use plasma-assisted chemical vapor deposition (PACVD). In this study a PACVD SiC coating and a hybrid PACVD SiC/CVD Si3N4 multilayer coating were deposited on two-dimensional CC substrates. Oxidation behavior of coated and uncoated CC composites was studied using a thermogravimetric analyzer (TGA) in both the isothermal and kinetic modes. The PACVD coating exhibited an inadequate oxidation protection of the CC substrate while the hybrid PACVD SiC/CVD Si3N4 coating provides excellent oxidation protection at temperatures up to 1400 °C. Microstructural and chemical characterizations of coated composites were performed using SEM, optical microscopy, EDS, XRD, FTIR, XPS and TEM. A correlation between coating microstructure, composition and oxidation behavior is discussed.