Influence of high-entropy solid-solution structures on the oxidation and ablation resistance of boride coatings

Compared with single-component systems, high-entropy boride (HEB) coatings exhibit superior oxidation resistance and ablation performance, yet the role of the high-entropy solid solution remains unclear. In this study, (Ti₁/₄Zr₁/₄Hf₁/₄Ta₁/₄)B₂ HEB coatings and mixed single-component boride (MIX) coatings were compared using air plasma ablation experiments and first-principles calculations to reveal initial oxidation and product evolution. HEB coatings show slightly lower oxidative weight gain but nearly 50% lower linear ablation rate than MIX coatings. Their oxidation products are dense, continuous multi-component oxide solid solutions, whereas MIX coatings form mixtures of discrete single-component oxides. Calculations indicate that oxygen adsorption is slightly inhibited in the high-entropy system and that oxidation proceeds sequentially among constituent elements before forming multi-component oxide solid solutions at high temperature. These dense oxide layers possess enhanced structural continuity and resistance to gas-flow erosion, accounting for the improved ablation performance. The results demonstrate that the high-entropy solid-solution structure facilitates the formation of stable protective oxide layers and thereby improves coating performance in ultra-high-temperature environments. This study highlights the crucial role of high-entropy solid solutions in enhancing ultra-high-temperature boride coating performance and offers guidance for their design and application.