Plasma torch ablation performance of Ta_0.8Hf_0.2C-SiC gradient coating fabricated by LPPS and pack cementation for C/C composites

The Ta_0.8Hf_0.2C solid solution inherits the outstanding oxidation and ablation resistance of both TaC and HfC, making it a promising material for ultra-high-temperature applications. In this work, a Ta_0.8Hf_0.2C-SiC gradient coating was fabricated on carbon/carbon (C/C) composites via pack cementation followed by low-pressure plasma spraying (LPPS). The resulting gradient coating exhibited outstanding ablation resistance under a plasma heat flux of 13 MW/m², withstanding a peak surface temperature of 2670 ℃. Such outstanding ablation resistance is attributed to a combination of synergistic mechanisms, including: heat dissipation through the volatilization of Ta₂O₅ and SiO₂; defect sealing by a low-vapor-pressure Ta–Hf–Si–O glassy phase; structural anchoring by the high-melting Hf₆Ta₂O₁₇ skeleton; and the gradient distribution of Ta_0.8Hf_0.2C and SiC, which effectively mitigates thermal stress. This study provides a viable strategy for developing high-performance thermal protection coatings for hypersonic and re-entry aerospace applications.