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

Abstract

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 (Hf1/4Zr1/4Ta1/4Ti1/4)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. The TiO2 was prone to decompose into TiO and then evaporated from the coating during ablation, slowing down the volatilization of Ta2O5. The remaining TiO2 and Ta2O5 diffused to m-(Hf, Zr)O2 and produced a phase transition from Ta/Ti-doped m-(Hf, Zr)O2 to o-(Hf, Zr)6Ta2O17/o-(Hf, Zr)TiO4. The formation of nanotwin between (Hf, Zr)6Ta2O17 and (Hf, Zr)TiO4 enhanced the toughness of the oxide film. Although excessive Ta2O5 broke the stability of the oxide film, the Hf-Zr-rich oxide skeleton (Ta/Ti-doped (Hf, Zr)O2, (Hf, Zr)6Ta2O17 and (Hf, Zr)TiO4)) ensured that C/C substrates were intact after ablation for 180 s, showing superior ablation resistance.