Ablation behavior of functional gradient ceramic coating for porous carbon-bonded carbon fiber composites

Highlights: • A novel functional gradient ceramic coating was prepared to improve the ablation resistance of CBCF composites at high temperature. This coating consists a two layer structure with a compact HfB₂-MoSi₂ outer layer (150∼200 μm in thick) and an inner Si-CBCF layer (2∼3 mm in thick). The ablation resistance of the coated CBCF composites was investigated with an arc-jet testing at temperature 1500-2200 °C. No macro-cracks and carbon fibers are detected in the cyclic ablation regions. The mass of sample was slightly reduced and the mass ablative rate was only 5.8′10⁻⁴g/(cm²∙s). Meanwhile, the thickness of the sample didn't change obviously, indicating good ablation resistance and good thermal shock resistance of the functional gradient ceramic coated CBCF composite. After ablation, the surface coating exhibit three different ablation regions due to the different ablation temperature. The formation of a dense silica glass layer embedded with HfO₂ particles or a molten HfO₂ layer was responsible for the good ablation resistant to the functional gradient ceramic coating. - Abstract: To improve the ablation resistance of low density carbon bonded carbon fiber (CBCF) composites at high temperature, a novel functional gradient ceramic coating was prepared. The coating exhibits a two layer structure with a compact HfB₂-MoSi₂ outer layer and an inner Si-CBCF layer with gradient transition structure. The high temperature ablation resistance of the coated CBCF composites was investigated with an arc-jet testing at temperature 1500–2200 °C. The results showed that the prepared functional ceramic coating exhibited good ablation resistance and good thermal shock resistance after four ablation cycles. After ablation, the surface coating exhibit three different ablation regions due to the different ablation temperature. The formation of a dense silica glass layer embedded with HfO₂ particles or a molten HfO₂ layer was responsible for the good ablation resistant to the functional gradient ceramic coating.