Multiscale mechanism of Ta regulated ablation resistance in HfC-ZrC-TaC modified C/C composites

Abstract

To improve oxyacetylene flame ablation resistance, HfC-ZrC-TaC ceramic-modified C/C composites with varying Ta contents were prepared by precursor infiltration and pyrolysis. The effects of Ta content on phase composition, oxide-layer evolution, oxygen penetration, and ablation behavior were investigated by multiscale structural characterizations and first-principles calculations. Increasing Ta content promotes the formation of (Hf x Zr x Ta 1-2x )C solid solutions and induces lattice contraction. During ablation, the ceramic phases form Hf-Zr-Ta-O composite oxide layers, mainly composed of Ta-doped (Hf, Zr)O 2 and (Hf, Zr) 6 Ta 2 O 17 , while crystalline Ta 2 O 5 becomes evident in the high-Ta samples. Ablation resistance first increases and then decreases with rising Ta content. Under a heat flux of 4.18 MW/m 2 for 135 s, T2 exhibits the lowest linear and mass ablation rates of 1.65 μm/s and 1.32 mg/s, respectively. This improvement is attributed to a compact oxide layer composed of a continuous Ta-doped (Hf, Zr)O 2 solid skeleton and a suitable amount of molten Ta-containing intermediate oxide phase. The solid skeleton resists gas-flow scouring, while the molten phase fills pores and microcracks, thereby suppressing oxygen penetration. Insufficient Ta fails to seal defects, whereas excessive Ta promotes the formation of a Ta 2 O 5 -rich low-melting phase that is easily removed during ablation. First-principles calculations indicate that, within the optimal Ta content range, increasing Ta content raises the O migration energy barrier in the Ta-doped (Hf, Zr)O 2 skeleton, thereby enhancing the oxide layer's resistance to inward oxygen diffusion. This work offers a compositional strategy for designing ultra-high-temperature thermal protection C/C composites for extreme environments.

The authors' abstract, as published at the source. Composites Part B Engineering, 2026 · DOI ↗