Ablation Mechanism of Carbon/Carbon Composites Modified by HfC–SiC in Two Conditions Under Oxyacetylene Torch

C/C–HfC–SiC composites prepared by precursor infiltration and pyrolysis process were ablated by oxyacetylene torch under two different flame conditions. The ablation performance of the composites was investigated in the heat flux of 2.38 MW/m² (HF-L) and 4.18 MW/m² (HF-H) for 60 s. The mechanical denudation in 4.18 MW/m² (HF-H) was higher than that in 2.38 MW/m² (HF-L), while the results indicated that the composites had a similar and good ablation property under two different flame conditions. C/C–HfC–SiC composites can adapt the heat flux from 2.38 MW/m² to 4.18 MW/m². The HfO₂ was not melted completely in the heat flux of 2.38 MW/m² (HF-L). So, both HfO₂ and SiO₂ layers acted as an effective barrier to the transfer of heat and oxidative gases into the underlying carbon substrate. SiO₂ was severely consumed in 4.18 MW/m² (HF-H), where the HfO₂ molten layer played a more important role in protecting the inner composite.