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

Abstract

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.