Influence of Al2O3 addition on the ablation behavior of SiC coatings fabricated on C/C composites

SiC–Al2O3 composite coatings were fabricated on C/C composites by the combination of vacuum plasma spraying (VPS) and heat-treatment in the present paper. The influence of Al2O3 addition on the ablation behavior of coatings was investigated as well. Si–Al2O3 mixed powders with different contents of Al2O3 (10 wt.% and 30 wt.%, respectively) were preliminarily deposited on the C/C substrates by using the VPS method, and then heat-treated in an argon atmosphere at 2073 K. Phase composition and microstructure of the coatings were characterized, while their high temperature ablation behaviors were studied by using a H2–O2 flame. The results implied that reactions between Al2O3 and Si, C or SiC occurred during heat-treatment. The reaction product aluminum has low viscosity and help liquid silicon to penetrate into the deeper region of C/C substrates, while some non-reacted Al2O3 remained on the coatingsʹ surface. Consequently, an outer layer of SiC–Al2O3 and a conversional layer of SiC–C–Al were formed on the C/C composites. The size of the SiC grains in the coating was decreased with the addition of Al2O3. In addition, Al2O3 have an accelerative effect on the glass formation for SiC coatings during the ablation process. The ablation resistance of SiC coatings has been improved by the addition of 10 wt.% Al2O3, which could protect the C/C substrate efficiently and withstand the H2–O2 flame (2773 K, atmosphere) for 300 s with a low mass loss of 2.95% in this study.