ZrB₂-SiC gradient oxidation protective coating for carbon/carbon composites

To improve the oxidation protective ability of carbon/carbon composites, ZrB₂-SiC gradient coating was prepared on the surface of C/C composites by an in-situ reaction method. The ZrB₂-SiC gradient coating consisted of an inner ZrB₂-SiC layer and an outer ZrB ₂-SiC-Si coating. The phase composition and microstructures of the multiphase coating were characterized by XRD, EDS and SEM. Results showed that the inner coating is mainly composed of ZrB₂ and SiC, while the outer multiphase coating is composed of ZrB₂, SiC and Si. The multilayer coating is about 200 μm in thickness, which has no penetration crack or big hole. The oxidation behavior of the coated C/C composites at 1773 K in air was investigated. Results show that the gradient ZrB₂-SiC oxidation protective coating could protect C/C from oxidation for 207 h with only (4.56±1.2)×10^-3 g/cm² weight loss, owing to the compound silicate glass layer with the existence of thermally stable phase ZrSiO₄.