Ablation behavior of high-entropy boride (Hf-Zr-Ta-Ti)B₂ coating fabricated via supersonic atmospheric plasma spraying for carbon/carbon composites

Carbon/carbon (C/C) composites have the potential to fulfill the demands of thermal protection systems, whereas they are limited by oxygen susceptibility. Herein, a high-entropy boride (HEB) (Hf-Zr-Ta-Ti)B₂ coating was deposited on C/C composites via supersonic atmospheric plasma spraying for ablation-resistant applications. The coated C/C composites showed a linear recession rate of 1.14 μm/s after oxyacetylene torch testing for 60 s. The good ablation resistance is attributed to the multicomponent synergy effect. The Ti-dominated liquid phase sealed defects, resulting in a dense oxide scale, and the Ta-induced lamellar architecture potentially improved its thermal shock resistance. This study demonstrates that HEBs with compositional breadth are effective in protecting C/C composites from ablation at ultra-high temperatures.