Microstructural Evolution, Mechanical Properties, and Corrosion Behavior of an Al7.5Co20.5Fe24Ni24Cr24 High‐Entropy Alloy

Abstract

The relationship among microstructure, mechanical properties, and corrosion behavior of an Al7.5Co20.5Fe24Ni24Cr24 high‐entropy alloy (HEA) is systematically studied. The as‐cast HEA consisted of a single face‐centered cubic (FCC) phase with negligible chemical inhomogeneities of Al and Ni elements, whereas the homogenized HEA displayed a single FCC supersaturated solid‐solution phase with uniform distribution of constituent elements. Homogenization followed by aging at 900 and 700 °C leads to the formation of different precipitates in the FCC matrix. As the variety and volume fraction of precipitates increased, the HEA samples accordingly show enhanced strengths accompanied by slight losses in ductility. However, the formation of L12, B2, and σ precipitates is detrimental to the electrochemical properties of the HEAs. Improving the homogeneity of elemental distribution leads to a higher content of Cr oxides and Co(Fe,Cr)2O4 complex oxides in the passivation film, rendering an enhancement of corrosion resistance of the HEA in sulfuric acid. This work reveals the influence of chemical inhomogeneities and precipitates on the mechanical and electrochemical properties of the FCC‐structured Al7.5Co20.5Fe24Ni24Cr24 HEA via tuning phase composition, providing an interesting insight into how to balance the structural (strength and ductility) and functional (anti‐corrosion) properties of HEAs.