Oxidation behavior of SiC-HfB₂-Si coating on C/C composites prepared by slurry dipping combined with gaseous Si infiltration

An effective monolayer SiC-HfB₂-Si coating for long-time oxidation protection of C/C composites was designed and prepared by a combined technique of slurry dipping and gaseous Si infiltration (SD + GSI). This coating is dense and adheres well with the C/C substrate, which is ascribed to the formed zigzagged SiC transition layer. After oxidation at 1773 K in static air for >538 h, the mass loss of SiC-HfB₂-Si coated samples is only 0.69%. By thermodynamic calculation, the oxidation process of SiC-HfB₂-Si coated samples is mainly controlled by oxygen diffusion, and the stable oxidation products are HfO₂ + B₂O₃ + SiO₂ + CO. The excellent oxidation protective ability is mostly attributed to the formation of a composite Hf-Si-O glass layer on the coating surface to heal cracks and pores.