Ablation resistance and mechanism of SiC/ZrC-ZrB2 double layer coating for C/C composites under plasma flame

Abstract

To improve the ablation resistance of carbon/carbon (C/C) composites, a SiC/ZrC-ZrB2 double layer coating was fabricated by pack cementation and slurry-sintering method. The ablation resistance of the SiC/ZrC-ZrB2 coating was tested under plasma flame above 2300 °C. The results indicate that the SiC/ZrC-ZrB2 double layer coating exhibits superior ablation resistance than the ZrC-ZrB2 single layer coating. After being ablated under the plasma flame for 20 s, the mass and linear ablation rates of the ZrC-ZrB2 coating are 0.89 mg/s and 15.3 µm/s, while those for SiC/ZrC-ZrB2 coating are 0.09 mg/s and 24.15 µm/s, respectively. During ablation, the SiC inner layer can generate SiO2 glass and result in the formation of ZrO2-SiO2 molten film. Compared with the ZrO2 molten film formed on the ZrC-ZrB2 coating surface, the ZrO2-SiO2 molten film with lower oxygen diffusion rate and viscosity enables the SiC/ZrC-ZrB2 coating to have better self-healing ability. Therefore, the enhanced ablation resistance of the SiC/ZrC-ZrB2 coating can be attributed to the formation of dense ZrO2-SiO2 molten film under the plasma flame.