Ablation Mechanism of HfC-HfO2 Protective Coating for SiC-Coated C/C Composites in an Oxyacetylene Torch Environment

To prevent the C/C composites from ablation, HfC-HfO₂ protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO₂ coating were characterized by X-ray diffraction and scanning electron microscopy. The ablation resistance test was carried out by an oxyacetylene torch. The results show that the as-prepared coating is dense with little pinholes and crack free. The elements Hf, C and O were uniformly distributed in the cross-section. After ablation for different time, the mass ablation rate fluctuated along with the change of ablation time. The ablation process of the surface coating could be divided into rapid oxidation and solid state sintering stages. During ablation, an HfC_xO_y-HfO₂ transitional layer was generated in the coating, which resulted from the active oxidation of HfC. After cooling, some microcracks were observed on the surface of coating, and the structure of cross-section was broken, which were due to the phase transition of HfO₂.