Preparation of oxidation protective ZrB2–SiC coating by in-situ reaction method on SiC-coated carbon/carbon composites

•ZrB2–SiC coating was prepared by in-situ reaction method on SiC-coated C/C.•ZrB2 was synthesized through in situ reaction by reducing ZrO2 using B2O3 and C.•The coating could protect C/C for 550 h with only 0.22% mass loss at 1773 K in air.•The “embedding structure” causes the occurrence of crack deflecting and termination.•Dual protection of SiO2 glass layer and “pinning phases” causes excellent resistance.

In order to reduce production cost and effectively improve the oxidation protection ability of the ultra-high temperature ceramics (UHTCs) ZrB2–SiC coating for the SiC-coated carbon/carbon (C/C) composites, a ZrB2–SiC outer coating was prepared by in-situ reaction method on SiC-coated C/C. Instead of costly ZrB2 powder, inexpensive B2O3, ZrO2, Si and C powders were used as raw materials to prepare the outer ZrB2–SiC coating with well-developed microstructures. The ZrB2 and SiC phases in the outer coating were synchronously obtained during the preparation of the coating. The isothermal oxidation behavior of the coated C/C composites at 1773 K was investigated. The double-layer ZrB2–SiC/SiC coating could prevent C/C composites from oxidation at 1773 K for 550 h. During oxidation, a kind of ‘embedding structure’ containing ZrO2 and ZrSiO4 will be formed on the surface of the compound silicate glass layer, which is responsible for the excellent oxidation resistance of the ZrB2–SiC outer coating.