Zonal synergistic protection behavior of C _f –HfC–HfB ₂ –SiC composites under 2600–2700 °C long-duration plasma ablation

Abstract Carbon fiber-reinforced ultrahigh-temperature ceramic matrix composites (Cf/UHTCs) suffer from limited structural continuity, regional protection mismatch, and unstable failure mechanisms in oxidative plasma ablation environments above 2500 °C, where single-phase UHTC systems (e.g., HfC or HfB2) fail to maintain wide-temperature synergistic stability. To address this ablation-limit imbalance, a dual-UHTC-phase Cf–HfC–HfB2–SiC composite is designed, achieving a wide-temperature synergistic protection effect. The composite exhibits an ultralow linear ablation rate of 1.88×10−4 mm·s−1 at 2600 °C for 1500 s, increasing only slightly to 2.32×10−4 mm·s−1 at 2700 °C. Structural analyses reveal a stable triple-layer oxidation architecture consisting of a dense HfO2 outer layer, an HfO2–SiO2 intermediate layer, and a porous inner buffer layer with spatially partitioned responses. First-principles calculations show that the HfC–HfB2 interface facilitates the formation of a continuous oxygen coordination network, supporting the evolution of a continuous protective oxide scale. These findings suggest a zonal synergistic protection behavior associated with the cooperative evolution of different ablation regions under nonuniform ultrahigh-temperature environments.