Mechanisms of the Ti-enhanced ablation resistance in a Zr-Si-B-C ceramic achieving the reduced ablation rate and long-term durability

During atmospheric re-entry, thermal protection systems (TPS) are subjected to prolonged oxygen-rich, high-temperature exposure and complex thermo-mechanical loads. Ultra-high temperature ceramics (UHTCs) stand out due to their high melting points, oxidation resistance and structural stability. Among them, multiphase Ti-containing ceramics exhibit superior ablation resistance above 2000 °C compared to conventional UHTCs. However, the underlying mechanism by which Ti enhances ablation performance is still obscure. In this work, Zr-Si-Ti-B-C multiphase UHTCs with varying Ti contents were fabricated via spark plasma sintering and evaluated under dissociated oxygen at a heat flux of 3.5 MW·m⁻² in a high-frequency plasma wind tunnel. Ti addition significantly improved ablation resistance, as confirmed by thermodynamic analysis of the underlying mechanisms. Ti incorporation refined the oxide solid-solution grains and promoted the formation of a columnar (Zr,Ti)O₂ gradient structure, featuring interwoven microporous channels filled with SiO₂, and a Ti-rich dense band formed near the substrate. This architecture established a robust “solid skeleton–liquid filler” composite barrier that markedly enhanced structural integrity. Furthermore, active oxidation of the underlying SiC generated SiO gas that diffused through the microporous channels and reoxidized to SiO₂ in regions of higher oxygen partial pressure, filling pores and acting as an effective oxygen barrier. This self-reinforcing cycle further promoted the active oxidation of the underlying SiC, continuously supplying SiO to the channels and providing long-term protection. The optimized Ti-doped ceramic exhibited a 34.5 % reduction in linear ablation rate compared with the undoped counterpart, highlighting the nonlinear synergistic mechanism of Ti addition and providing new insights for next-generation TPS design.