Environment dependent Ta-Mo synergy toward eutectic high-entropy alloys with strength and tunable corrosion resistance

Conventional alloy design often targets a single universally optimal composition. This paradigm is challenged by a ‘threat-matched’ synergistic alloying strategy in (CoCrFeNi)₈₅Ta_xMo_15-x eutectic high-entropy alloys (EHEAs), prepared by vacuum arc melting, enabling remarkable environment-specific performance. Systematic tuning of the Ta/Mo ratio yields a eutectic (CoCrFeNi)₈₅Ta₅Mo₁₀ alloy with exceptional properties of ∼1.7 GPa yield strength and 31.7 % fracture strain. Notably, corrosion resistance shifts with environment. In 0.6 M NaCl, a high-Ta alloy (TM10-5) offers a superior protection via a robust Ta₂O₅ barrier; in aggressive 0.6 M NH₄Cl, the optimal composition shifts to a balanced Ta/Mo ratio (TM7.5–7.5). This adaptability stems from a dynamic interplay where Mo's chemical stabilization is amplified to counter NH₄Cl's complex acidic and ion-complexing attack. This study validates a pathway for designing advanced EHEAs, where tailored synergistic alloying counters specific environmental threats, boosting reliability for demanding applications.