Towards high-entropy alloys with high-temperature corrosion resistance and structural stability

Abstract

Complex component alloys (CCAs) consisting of multiple principal elements potentially encompass superior mechanical properties and good corrosion resistance. Eutectic high-entropy alloys (EHEAs) stand out from CCAs as the desired candidates for high-temperature (HT) applications due to the combined advantages of HEA alloys and unique equilibrium eutectic structure. This work first explores the thermodynamic calculation route toward HEAs with eutectic structure. Series of pseudo-binary diagrams of transition metal (TM) CCAs were calculated with the Calphad approach to locate the potential eutectic points. The representatives of a CrFeCoNi2.2Al alloy with eutectic structure and a non-eutectic CrFeCoNiCu alloy were cast, and their HT performance was further evaluated by hot corrosion with Na2SO4 + 25 wt% NaCl molten salts at 700, 800 and 900 °C, respectively. The HT degradation mechanism was explicitly revealed from a comprehensive thermodynamic perspective. Relationships between the HT performance and the inherent physicochemical properties of the constituent phases and the alloying components were addressed for the first time. It was found that the mixing enthalpy (ΔHmix) and valance electron concentration (VEC) played more decisive roles in the hot corrosion resistance than the mixing entropy (ΔSmix) of CCAs. A strategy for tailoring and developing HEAs for HT application by modulating alloy chemistry and microstructural features was proposed.