C/C-(Hf0.5Zr0.3Ti0.2)C–W–Cu composites: Long-term ablation resistance based on active-passive protection at 2600 °C

Compared with the traditional C/C composites modified by ultra-high-temperature ceramics (C/C-UHTCs), those modified by metal/medium-entropy ceramics have excellent mechanical properties, thermophysical properties, and long-term ablation resistance. These composites have great potential towards improving the high-temperature resistance and service life of thermal protection systems for spacecraft. In this study, a new type of (Hf_0.5Zr_0.3Ti_0.2)C–W–Cu cermet-modified C/C composites (C/C-(Hf_0.5Zr_0.3Ti_0.2)C–W–Cu) was prepared at 1500 °C. Compared with C/C-UHTCs, the bending strength and fracture toughness of C/C-(Hf_0.5Zr_0.3Ti_0.2)C–W–Cu increased by 70 % and 110 % to 364.25 MPa and 14.64 MPa m^1/2, respectively. Due to the high thermal conductivity of Cu and W, the thermal conductivity of this new composite was 106 % higher than that of C/C-(Hf_0.5Zr_0.3Ti_0.2)C (44.26 versus 21.53 W/m·K). Under a high heat flow of 4.18 MW/m², this material exhibited very low mass and linear ablation rates (−0.163 mg/s and −0.193 μm/s, respectively). Active and passive protection occur during ablation due to the evaporative cooling of Cu, CuO, and WO₃ as well as a dense outer oxide layer that inhibits oxygen diffusion. The internal oxide layer forms a Hf-Zr-Ti-C-O framework mingled with Ti-rich Ti-Hf-Zr-C-O and an unoxidised W–Cu structure, effectively reducing the osmotic oxygen content. This work provides a new direction for developing thermal protection materials capable of long-term service in ultra-high-temperature environments.