Effects of Gd₂O₃ Content on the Infrared Emissivity and Ablation Resistance of HfB₂/SiC/TaSi₂ Coating at 4400 kW/m²

To improve the infrared emissivity and the ablation resistance of HfB₂/SiC/TaSi₂ coatings for serving in heat flux of 4400 kW/m², HfB₂/SiC/TaSi₂ coatings with different contents of high-emissivity Gd₂O₃ were prepared using atmospheric plasma spraying. The highest emissivity in 3–5 μm can reach up to 0.92 at 1273 K when the Gd₂O₃ content is at 10 vol.%. The increase in the emissivity is attributed to the additional electronic transitions induced by oxygen vacancies, which are generated by substituting Hf⁴⁺ with Gd³⁺. Due to the high emissivity, the surface temperature of the coating modified with 10 vol.% Gd₂O₃ was decreased by ~100 K. Meanwhile, the mass and the liner ablation rate are confirmed to be 4.28 × 10⁻⁷ kg/s and 2.15 × 10⁻⁷ m/s, respectively, which are decreased by 80% and 31% compared to the undoped HfB₂/SiC/TaSi₂ coating. During ablation, HfB₂/SiC/TaSi₂/Gd₂O₃ coating was oxidized to HfO₂, Gd₂Ta₂O₇, HfSiO₄, and GdTaO₄. A stable Hf–Ta–Gd–Si–O multiphase glass was formed on the surface of the coating, which could restrain oxygen penetration. However, the excessive amount of Gd₂O₃ is detrimental to the ablation performance due to its consumption of the SiO₂ glass layer. These findings indicate that the addition of an appropriate amount of Gd₂O₃ could improve the anti-ablation performance of the modified coating.