Multi-healing behavior of (NbC-TaC)/ZrC/SiC triple-layer coated C/C composites enduring oxyacetylene flame

Herein, the ablation resistance of plasma-sprayed TaC-modified NbC (NbC-TaC) coatings on ZrC/SiC double-layer-coated C/C composites was firstly tested using an oxyacetylene flame. Next, the phase composition of ZrO₂-Ta₂O₅ (TaO_2.5) systems heat-treated at 2100 °C in an argon atmosphere was determined. The results demonstrated the formation of a free-standing Ta–O film that extended the effective ablation time of the TaC coating to >90 s. Among the NbC-TaC coatings, the 37.5 mol% TaC-addition produced a continuous film, achieving the best ablation property. Multi-healing behavior, comprised of interfacial, in situ, and surficial healing, further improved ablation performance. At 2100 °C, the solubility of TaO_2.5 in ZrO₂ was 15 mol%, and the stable phases were tetragonal ZrO₂ and Ta with face- and body-centered cubic structures. Furthermore, the interfacial bonding conditions of the heat-treated Zr-O-Ta system and the thermal stability mechanism of ZrO₂ to Ta₂O₅ were discussed.