Ablation behavior of mullite modified C/C-SiC-HfC composites under oxyacetylene torch for single and cyclic ablations with two heat fluxes

To investigate the ablation mechanism of the mullite modified C/C-SiC-HfC composites prepared by precursor infiltration pyrolysis, a 60 s single ablation and 30 s × 3 cyclic ablations were carried out at heat fluxes of 2.38 and 4.18 MW/m², respectively. Results showed that the ablation temperatures played a vital role in the ablation process. Under the lower heat flux condition, the single ablation behavior was mainly influenced by the escape of gaseous oxidation products and slight airflow erosion, while cyclic ablation was influenced primarily by the stresses induced by crystallization transformation during the heating-cooling process. Under the higher heat flux condition, HfSiO₄ was gradually generated at the interface between HfO₂ and SiO₂, which stabilized the crystallization of HfO₂. The ablation behavior under higher heat flux was mainly influenced by thermal-induced stresses and mechanical forces of high-velocity airflow.