High temperature ablation behavior of pressureless sintered Ta0.8Hf0.2C-based ultra-high temperature ceramics

Ablation behavior of Ta0.8Hf0.2C and Ta0.6Hf0.2C-10 vol%SiC ceramics was investigated by plasma flame ablation test in air. Linear ablation rate was used for the characterization of ablation resistance and grazing-incidence Xray diffraction (GIXRD), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) were used for characterization. Ta0.6Hf0.2C-10 vol%SiC exhibited significantly higher ablation resistance, with ablation rate of 0.7 mu m/sec in comparison to the monolithic system with 3.5 mu m/sec. An unstable single oxide layer of monolithic Ta0.8Hf0.2C with thickness approximately 20 mu m was observed after ablation. Oxidation reactions happened individually as TaC and HfC while 'self-sacrificial' volatilization was mainly controlled by active oxidation of TaC. Hf6Ta2O17 was generated by the combination of HfO2 and TaO. A more stable double reaction-layer was observed after ablation of Ta0.5Hf0.2C-10 vol%SiC ceramic. Passive oxidation of TaC was dominant. Textured Ta2O5 skeleton, filled with Hf-containing TaO6, stopped consumption of SiC and hampered oxygen further diffusion.