Efficient fabrication of light C _f/SiHfBOC composite with excellent thermal shock resistance and ultra-high temperature ablation up 1800 °C

In this paper, a high-yield Hf-modified SiHfBOC ceramic precursor was developed, and a high-pressure assisted impregnation pyrolysis method was proposed to achieve the preparation of 3D PyC-C_f/SiHfBOC composites. This high-pressure assisted impregnation method significantly improves the impregnation filling effect of the precursor in and between fiber bundles compared to dozens of traditional impregnation cycles. After undergoing just 9 PIP cycles, the composites achieved a relative density of approximately 90% and a density of 1.64 g/cm³. The critical temperature difference of 3D PyC-C_f/SiHfBOC composites after the shock of RT-1000 °C is as high as 650 °C, which is twice that of the traditional ceramic material, showing good thermal shock resistance. Under the effect of Hf modification, a dense HfO₂-SiO₂ oxide layer (thickness 93μm) was formed in situ on the surface of the 3D PyC-C_f/SiHfBOC composites, effectively preventing further erosion of the composite matrix by high-temperature oxidation gas. Even in the ultra-high temperature oxygen-containing environment at 1800 °C, it still exhibits an excellent non-ablative result (with a linear ablation rate of 0.83×10^-4 mm·s^-1). This work not only enriches the basic research on lightweight ultra-high temperature ceramic composites converted from Hf ceramic precursors but also provides strong technical support for their application in ultra-high temperature non-ablative thermal protection materials for high-speed aircraft.