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

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 degrees 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.