Simultaneously enhancing the mechanical properties and corrosion resistance of FeMnCoCr high-entropy alloy via N-doping

FeMnCoCr high-entropy alloy (HEA) has attracted extensive attention due to its unique advantages in multi-principal element design, remarkable work-hardening capability, and diverse application potential. However, its relatively low yield strength and corrosion resistance limit the engineering applications. To simultaneously enhance the mechanical properties and corrosion resistance of FeMnCoCr HEA, we investigated the effect of nitrogen addition on its performance improvement. The results show that the addition of 1.8 at.% N increases the yield strength by 80 % while maintaining an elongation of over 50 %. The significant improvement in yield strength is attributed to the interstitial solid solution strengthening effect of N atoms, while N-induced transformation of the austenite and ε-martensite dual-phase structure to a single-phase austenite structure helps to maintain ductility. Additionally, N-doping significantly reduces the corrosion current density by an order of magnitude in a chloride-containing environment. The N addition promotes the formation of Cr oxynitride and oxide, suppresses Mn oxide formation, and increases the O²⁻/OH⁻ ratio in the surface film. This modification significantly restricts electron transport and enhances charge transfer resistance six-fold during anodic dissolution, thereby enhancing the electrochemical stability of the N-doped material. These findings not only provide new insights into the performance enhancement of FeMnCoCr HEAs but also establish the foundation for their application in complex service environments.