Effect of flame environment on the ablation behavior and mechanisms of C/C-Hf_0.4Ta_0.6C composites

C/C-Hf_0.4Ta_0.6C composites were prepared using the precursor infiltration and pyrolysis method. The effects of different ablation environments on the composites' composition, microstructure, and ablation behavior were investigated. The material exhibited significantly greater ablation resistance under plasma flame conditions (linear and mass rates of 3.84 μm/s and 0.001 mg/s) than under oxyacetylene ablation conditions (linear and mass rates of 13.34 μm/s and 3.98 mg/s). This discrepancy is primarily attributed to the disparate flame characteristics, as quantified by finite element simulations. These characteristics lead to different ablation surface temperatures and subsequent oxide layer formation. In the process of oxyacetylene ablation, the strong scouring effect and the resultant higher surface temperature (2300 °C) lead to substantial loss of the protective liquid phase and the formation of HfO₂. In contrast, the plasma flame environment results in a lower surface temperature (1800 °C) and permits the formation of a denser, more effective oxide layer. Hf₆Ta₂O₁₇ acts as a framework that retains the higher-viscosity liquid phase, filling pores and cracks. High-resolution transmission electron microscopy (TEM) and geometric phase analysis (GPA) revealed that this dense layer exhibits a more uniform micro-strain distribution, which correlates to its structural integrity. This process effectively seals diffusion channels and enhances resistance to diffusion.