Microstructure evolution and phase interface characterization in anti-ablation (Hf1/4Zr1/4Ta1/4Ti1/4)C-coated C/C composites

Ta and Ti elements are often used as modified components to densify the loose oxide film for HfC/ZrC coatings after long-term ablation, while the synergistic effect among their multi-phase oxides on the ablation resistance of the coatings for C/C composites is still being explored. In this work, a (Hf 1/4 Zr 1/4 Ta 1/4 Ti 1/4 )C high-entropy carbide ceramic was proposed as an advanced anti-ablation coating for C/C composites and the multicomponent synergistic effect on the ablative behavior was investigated. At the initial ablation, the O atoms first reacted with Hf and Zr elements to form m-(Hf, Zr)O2. 2 . The TiO2 2 was prone to decompose into TiO and then evaporated from the coating during ablation, slowing down the volatilization of Ta2O5. 2 O 5 . The remaining TiO2 2 and Ta2O5 2 O 5 diffused to m-(Hf, Zr)O2 2 and produced a phase transition from Ta/Ti-doped m-(Hf, Zr)O2 2 to o-(Hf, Zr)6Ta2O17/o- 6 Ta 2 O 17 /o- (Hf, Zr)TiO4. 4 . The formation of nanotwin between (Hf, Zr)6Ta2O17 6 Ta 2 O 17 and (Hf, Zr)TiO4 4 enhanced the toughness of the oxide film. Although excessive Ta2O5 2 O 5 broke the stability of the oxide film, the Hf-Zr-rich oxide skeleton (Ta/ Ti-doped (Hf, Zr)O2, 2 , (Hf, Zr)6Ta2O17 6 Ta 2 O 17 and (Hf, Zr)TiO4)) 4 )) ensured that C/C substrates were intact after ablation for 180 s, showing superior ablation resistance.