Ablation behavior and mechanisms of Cf/(CrZrHfNbTa)C‒SiC high-entropy composite at temperatures up to 2450°C

Abstract

The oxide layer formed by ultra-high melt point oxides (ZrO₂, HfO₂) and SiO₂ glassy melt is the key to the application of traditional thermal structural materials in extremely high-temperature environment. However, the negative effect of ZrO₂ and HfO₂ phase transitions on the stability of oxide layer and rapid volatilization of low viscosity SiO₂ melt limit its application in aerospace. In this study, the ablation behavior of C_f/(CrZrHfNbTa)C‒SiC high-entropy composite was explored systematically via an air plasma ablation test, under a heat flux of 5 MW/m² at temperatures up to 2450°C. The composite presents an outstanding ablation resistance, with linear and mass ablation rates of 0.9 µm/s and 1.82 mg/s, respectively. This impressive ablation resistance is attributed to the highly stable oxide protective layer formed in situ on the ablation surface, which comprises a solid skeleton of (Zr, Hf)₆(Nb, Ta)₂O₁₇ combined with spherical particles and SiO₂ glassy melt. The irregular particles provide a solid skeleton in the oxides protective layer, which increased stability of the oxide layer. Moreover, the spherical particles have a crystal structure similar to that of Ta₂O₅ and are uniformly distributed in SiO₂ glassy melt, which hinder the flow of SiO₂ glassy melt and enhance its viscosity to a certain degree. And it reduces the volatilization of SiO₂. In summary, the stable oxide layer was formed by irregular particles oxide and the SiO₂ glassy melt with certain viscosity, thereby resulting in the impressive ablation resistance of the composite. This study fills a gap in ablation research on the (CrZrHfNbTa)C system.