Accelerated water-oxygen corrosion mechanism of HfB₂-SiC/SiC coating on the surface of C / C composites

Ultra-high temperature ceramic modified SiC-based coatings have been widely used for high-temperature oxidation protection of C/C composites. However, the corrosion of the coating by water vapor in the real aircraft engine environment cannot be ignored. In this paper, the HfB₂-SiC coating was prepared on the surface of SiC coated C/C composite by slurry painting and heat treatment technology, and the composite structure of ceramic mosaic glass was successfully constructed. The coating's corrosion behavior and failure mechanism in a water-oxygen coupled environment were investigated. The results indicated that the presence of water vapor accelerated the corrosion rate of HfB₂-SiC coatings compared to dry oxygen corrosion, which was mainly attributed to the micropores within the coatings, which encompassed both the coating itself and the corroded SiO₂ layer on the surface of the coatings. These micropores provided an effective channel for the diffusion of corrosive gases. At the same time, regardless of the oxygen or water vapor atmosphere, the HfSiO₄ phase could inhibit the crystallization of the surrounding SiO₂ glass, thereby reducing the risk of coating cracking.