A functionally graded C/C–HfC–SiC composite sharp leading edge merging lightweight and superior ablation resistance

To accommodate the severe temperature gradients encountered by the sharp leading edges (SLEs) in hypersonic vehicles, a functionally graded (FG) C/C–HfC–SiC composite SLE was fabricated using a combined process of precursor infiltration and pyrolysis and chemical vapor infiltration. The resulting architecture exhibits a continuous compositional gradient of HfC–SiC modifiers and pyrolytic carbon (PyC) along the thermal gradient. Under oxyacetylene torch testing at a heat flux of 4.2 MW/m² for 3 × 40 s, the FG SLE maintained structural integrity and achieved a low linear recession rate of 3.10 ± 0.26 μm/s. It achieved ablation resistance comparable to conventional UHTC-modified C/C composite SLEs and bulk components, while maintaining a significantly lower density of only 1.83 ± 0.06 g/cm³, enabling lightweight design. A dense HfO₂ scale formed on the nose, while a protective HfO₂–SiO₂ composite scale covered the middle section. Furthermore, the PyC deposited in the middle and base sections enhanced thermal conduction, alleviating heat accumulation at the nose. The functionally graded architecture merges superior ablation resistance and lightweight characteristics, demonstrating its promise for advanced thermal protection systems in hypersonic applications.