Microstructure of chemical vapor deposition SiC-B_xC coatings in high temperature simulated environments

SiC-B_xC composite coatings deposited by chemical vapor deposition on graphite substrates were subjected to simulated combustor environments at 700, 1000 and 1200°C, respectively, in a wet atmosphere of O₂(8 kPa)/H₂O(14 kPa)/Ar(78 kPa) for 10 h. The microstructures of the coatings were investigated by scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, micro-Raman spectroscopy and Fourier transform infrared spectroscopy. The results show that the BxC layer of the composite coatings can be completely oxidized to form B₂O₃ and H₃BO₃ in wet oxygen at the temperature range between 700 and 1000°C, and the oxidation products of B_xC are volatilized rapidly between 1000 and 1200°C. After treatment in high temperature simulated environments, there is borosilicate glass on the surface of the composite coatings, and the crystallinity of all the oxidation products and SiC layers decrease with the increase of test temperature. Based on the results of microanalysis, the anti-oxidation performance of the self-healing properties of composite coatings is discussed.