Oxidation behavior and microstructure evolution of SiC-ZrB2-ZrC coating for C/C composites at 1673 K

To protect carbon/carbon (C/C) composites against oxidation, a SiC-ZrB2-ZrC coating was prepared by the in-situ reaction between ZrC, B4C and Si. The thermogravimetric and isothermal oxidation results indicated the as-synthesized coating to show superior oxidation resistance at elevated temperatures, so it could effectively protect C/C composites for more than 221 h at 1673 K in air. The crystalline structure and morphology evolution of the multiphase SiC-ZrB2-ZrC coating were investigated. With the increase of oxidation time, the SiO2 oxide layer transformed from amorphous to crystalline. Flower-like and flake-like SiO2 structures were generated on the glass film during the oxidation process of SiC-ZrB2-ZrC coating, which might be ascribed to the varying concentration of SiO. The oxide scale presented a two-layered structure ~130 µm thick after oxidation, consisting of a SiO2-rich glass layer containing ZrO2/ZrSiO4 particles and a Si-O-Zr layer. The multiphase SiC-ZrB2-ZrC ceramic coating exhibited much better oxidation resistance than monophase SiC, ZrB2 or ZrC ceramic due to the synergistic effect among the different components.