Probing solid-state diffusion and its synergistic role with preferential oxidation in enhancing the ablation performance of multiphase multicomponent carbide

Multiphase multicomponent ultrahigh-temperature ceramics (UHTCs) hold great promise for achieving better ablation performance because of their broader structure and compositional tunability. However, the knowledge gap with respect to ablation mechanisms hinders the design and optimization of these materials. Here, through studying the ablation behavior of a multiphase multicomponent carbide (i.e., Hf–Zr–Ti–Ta–C) composed of Hf-rich carbide, Ta-rich carbide, and Ti-rich carbide phases, a thermodynamic-driven solid-state diffusion process between the constituent multicomponent phases during ablation was revealed. The solid-state diffusion of metal ions (mainly Zr and Ti) occurred among the oxidation-affected three-phase regions beneath the oxide layer, leading to the formation of Zr- and Ti-rich oxides. More importantly, the resulting Ta enrichment of the residual carbide phase enabled their thermodynamic stability to be sustained at a relatively high oxygen partial pressure, thus improving the oxidation resistance. Moreover, the coupling between the solid-state diffusion process and preferential oxidation behavior facilitated the in situ formation of a micron-sized Hf-rich oxide network, which effectively enhanced the mechanical properties of the oxide layer, thereby offering better protection against the scouring of hot high-speed flow. In summary, the synergistic effect of the solid-state diffusion process and preferential oxidation behavior optimized the ablation performance of the multiphase multicomponent carbide under extreme conditions.