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

Abstract

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.