Cyclic ablation behavior of mullite-modified C/C-HfC-SiC composites under an oxyacetylene flame at about 2400 °C

Mullite-modified C/C-HfC-SiC composites were prepared via precursor infiltration and pyrolysis (PIP). The phase composition, microstructure, and cyclic ablation behavior under oxyacetylene flame with a heat flux of 4.18 MW/m² were investigated, and a comparison with the C/C-HfC-SiC composites showed that the mullite-modified composites have better ablation resistance. Results displayed a HfO₂ skeleton structure wrapped by SiO₂ and a dense layer of HfO₂-SiO₂ in the center and transition regions after the first ablation for 30 s, respectively. The structures transformed into HfSiO₄-wrapped carbon fibers and “island” shape HfO₂-HfSiO₄-SiO₂ layer after the second ablation for 30 s. Then both structures underwent severer peeling of HfSiO₄ and consumption of SiO₂ after the third ablation for 30 s. The modified composites exhibited better mass ablation rates after forming HfSiO₄, which were 0.36 mg/s cm² and 0.38 mg/s cm², respectively.