Microstructure, ablation behavior and thermal retardant ability of C/C-HfB₂ composites prepared by precursor infiltration pyrolysis combined with chemical vapor infiltration

C/C-HfB₂ composites were fabricated by precursor infiltration pyrolysis combined with chemical vapor infiltration. Ablation behavior, oxidation performance and thermal retardant ability of the prepared composites were investigated. The results showed that the oxidation products of HfB₂ could enhance the oxidation performance and ablation property of C/C-HfB₂ composites. During ablation in the heat flux of 2.38 MW/m² under oxyacetylene torch, a protective HfO₂ layer was covered on ablated surface, acting as an efficient barrier to heat transfer and denudation of the oxyacetylene torch. As the heat flux increased to 4.18 MW/m², thermal energy concentration and denudation enhancement of the oxyacetylene torch resulted in the spalling of the HfO₂ layer. Based on microstructure evolution, thermal retardant ability test, thermogravimetric analysis and measurement of residual flexural strength, oxidation as well as ablation mechanism of the C/C-HfB₂ composites was discussed.