Microstructure evolution of in-situ SiC-HfB₂-Si ternary coating and its corrosion behaviors at ultra-high temperatures

An in-situ SiC-HfB₂-Si ternary coating was deposited on C/C composites (C/Cs) via slurry panting plus gaseous Si infiltration composite method, to improve the oxidation and ablation resistance of C/Cs above 1773 K. The coating formation mechanism was investigated by microstructural analyses and thermo-dynamic calculations. The oxidation behavior of the coated specimens subjected either to high-temperature testing at 1773 K and 1973 K in static air furnace or to ablation testing with oxyacetylene torch upon ultra-high temperature service were studied, base on thermo-dynamic computations, numerical simulations and microstructure evolution. The SiC-HfB₂-Si coating protected C/Cs against oxidation at 1773 K for more than 1507 h which is longer than that of the reported SiC-HfB₂-based coatings, due to the as-prepared compact mosaic coating filled with HfB₂-rich Si-based multiphase and the consequently formed dense Hf-Si-O oxide layer. Moreover, a good ablation resistance with relatively low linear and mass ablation rates of −0.72 μm/s and 0.07 mg/s, respectively, was achieved due to the stable oxide scale with high viscosity.