Oxidation and ablation protection of multiphase Hf0.5Ta0.5B2-SiC-Si coating for graphite prepared by dipping-pyrolysis and reactive infiltration of gaseous silicon

A novel monolayer Hf0.5Ta0.5B2-SiC-Si coating with defect-free structure for protecting graphite materials was prepared by dipping-pyrolysis combined with reactive infiltration of gaseous silicon. The phase synthesis, microstructure, oxidation and ablation resistance properties of the prepared Hf0.5Ta0.5B2-SiC-Si coating were studied. Results demonstrated that the as-prepared coating exhibited excellent low and high temperature oxidation resistance, after isothermal oxidation at 900 degrees C and 1500 degrees C for 1320 h and 2080 h, respectively, the mass gains were 0.14% and 1.74%, respectively. The excellent anti-oxidation performance at 900 degrees C was ascribed to the defect-free structure of coating, while the formed compound Hf-Ta-Si-O glassy oxide layer on the coating surface was responsible for the excellent oxidation resistance at 1500 degrees C. Moreover, the Hf0.5Ta0.5B2-SiC-Si coating had good ablation resistance, after ablation for 60 s, the mass and linear ablation rates of the coated sample were 1.05 mg/s and -10.2 mu m/s, respectively. The ablation behaviors of the coated sample mainly included thermalphysical and thermal-chemical erosion along with thermos-mechanical denudation.