Effects of Y2O3 on HfO2 phase stability and ablation resistance of C/HfC-SiC composites

C/HfC-SiC composites show promise for thermal protection, but HfO₂ phase transformation-induced oxide spallation limits their reusability. In this study, Y₂O₃ was doped into C/HfC-SiC composites via a slurry-assisted precursor infiltration and pyrolysis (PIP) process to suppress oxide layer spallation, and their microstructure, mechanical properties, oxidation and ablation behavior were investigated. The incorporation of Y₂O₃ significantly improving the structural integrity of the oxide layer under high-temperature ablation. This enhancement is attributed to the substitution of Hf^4 + by Y³⁺, which stabilizes the tetragonal HfO₂ phase during cooling and inhibits phase transformation-induced stress. After 240 s of oxyacetylene torch exposure, with the composite containing 8 mol% Y₂O₃ achieving a linear ablation rate of 6.58 × 10⁻⁴ mm/s and a mass ablation rate of 1.35 × 10⁻³ g/s—representing reductions of approximately 95 % and 80 %, respectively, compared to the undoped composite. This study offers a useful strategy for the optimization of reusable ultrahigh-temperature materials.