Ablation behavior of non-equimolar C_f/(Hf_1/2Zr_1/3Ta_1/6)C-SiC composites under varying oxyacetylene flame conditions

Non-equimolar C_f/(Hf_1/2Zr_1/3Ta_1/6)C-SiC composites were fabricated using a precursor impregnation and pyrolysis process. The phase composition and microstructure were characterized by XRD, TEM, and SEM, and the ablation behavior was evaluated under oxy-acetylene flame conditions with heat flux densities ranging from 4 to 9 MW/m2. The synthesized (Hf_1/2Zr_1/3Ta_1/6)C powder exhibited a uniform nanoscale elemental distribution. The resulting composites showed a density of 2.84 g/cm3 and a porosity of 11.71 %, together with excellent mechanical properties, achieving tensile and compressive strengths of 286.74 MPa and 235.58 MPa, respectively. Under a heat flux of 4 MW/m2, a continuous and protective oxide layer formed on the surface, resulting in only minor ablation damage. After ablation under a heat flux of 7 MW/m2, the surface temperature increased to 2320 °C. The oxide layer formed on the specimen surface effectively inhibited oxygen penetration. The inner oxide layer was firmly bonded to the substrate and consisted of a high-melting (Hf,Zr,Ta)O₂ oxide skeleton and a SiO₂ healing phase containing dispersed spherical (Hf,Zr)₆Ta₂O₁₇ particles. The alternating coexistence of these two phases facilitated the formation of a dense and protective oxide layer. When the heat flux increased to 9 MW/m2, the combined effects of extreme temperature and high-velocity gas flow led to severe erosion of the oxide layer.