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

Abstract The oxide layer formed by ultra‐high melt point oxides (ZrO 2 , HfO 2 ) and SiO 2 glassy melt is the key to the application of traditional thermal structural materials in extremely high‐temperature environment. However, the negative effect of ZrO 2 and HfO 2 phase transitions on the stability of oxide layer and rapid volatilization of low viscosity SiO 2 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/m 2 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) 2 O 17 combined with spherical particles and SiO 2 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 Ta 2 O 5 and are uniformly distributed in SiO 2 glassy melt, which hinder the flow of SiO 2 glassy melt and enhance its viscosity to a certain degree. And it reduces the volatilization of SiO 2 . In summary, the stable oxide layer was formed by irregular particles oxide and the SiO 2 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.