Novel gradient ZrB₂–MoSi₂–SiC dense layer with enhanced emissivity and long-term oxidation resistance at ultra-high temperatures

The rapid evolution of hypersonic vehicle technologies necessitates robust thermal protection systems capable of withstanding extreme oxidative ablation. This study introduces a novel gradient-architected ZrB₂–MoSi₂–SiC dense layer embedded within a lightweight three-dimensional (3D) needled carbon fiber composite. Utilizing the volatility of ethanol and polycarbosilane, the ceramic slurry is selectively infused into targeted regions of the fibrous structure, optimizing the ZrB₂ to MoSi₂ ratio to enhance performance. The resulting dense layer exhibits exceptional emissivity, surpassing 0.90 in the 1–3 μm range and exceeding 0.87 in the 2–14 μm range. Moreover, it demonstrates remarkable oxidative ablation resistance. Specifically, at an optimized ZrB₂ to MoSi₂ ratio of 6:4, the dense layer achieves a minimal linear ablation rate of 0.015 μm·s⁻¹ under a 1.5 MW·m⁻² oxyacetylene flame for 1000 s. Even after exposure to oxyacetylene ablation at surface temperatures of approximately 1750 °C for 1000 s, the dense layer retains its structural integrity, highlighting its enduring oxidation resistance. The incorporation of MoSi₂ not only enhances emissivity but also fortifies the ZrO₂ and SiO₂ oxide layers, crucial for environments with elevated oxygen levels, thereby mitigating the active oxidation of SiC. This combination of high emissivity and long-term oxidation resistance at ultra-high temperatures positions the ZrB₂–MoSi₂–SiC dense layer as an exceptionally promising candidate for advanced thermal protection in hypersonic vehicles.