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 ZrB2–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.