The interface interaction within multi-phase oxides on the ablation behavior of the (Hf_0.25Zr_0.25Ti_0.5)C-coated C/C composites

To investigate the effect of the multi-phase Ti-containing oxides on the ablation behavior of (Hf-Zr-Ti)C coating, the (Hf_0.25Zr_0.25Ti_0.5)C coating was prepared on the SiC-coated C/C composites, and their ablation resistance was investigated. After ablation, Ti-poor and Ti-rich areas appeared on the coating surface, corresponding to the Ti-doped m-(Hf, Zr)O₂ and o-(Hf, Zr)TiO₄, respectively. Their interface interaction on the ablation resistance, microstructural evolution and defect initiation of the coating during ablation was discussed. The combination of the experimental results (SEM/TEM), first-principle calculation (VASP) and finite element simulation (ABAQUS) indicated the latter had poor plastic deformation to resist crack initiation and propagation compared to the former. The mechanical denudation produced the stress concentration, which resulted in some damaged areas appearing at the phase interface between Ti-doped m-(Hf, Zr)O₂ and o-(Hf, Zr)TiO₄, as well as the grain boundaries of different o-(Hf, Zr)TiO₄ grains, in the forms of phase interface cracks and intergranular pores/cracks, respectively. Although these ablative defects accelerated the damage to the coating, without exposed carbon fibers and broken SiC coating after ablation for 120 s, the intact interface between SiC and C/C composites indicated that (Hf_0.25Zr_0.25Ti_0.5)C coating had good ablation protection for C/C composites.