High-Entropy Alloys: A Critical Review of Aqueous Corrosion Behavior and Mechanisms

Advances in corrosion-resistant alloys have primarily been driven by new corrosion mechanisms and new alloys. As a new class of structural and functional materials, high-entropy alloys (HEAs) represent a novel compositional design concept, which not only enhances the in-depth understanding of the corrosion mechanisms of traditional corrosion-resistant alloys, but also broadens the spectrum of high-performance corrosion-resistant alloys with better damage tolerance. HEAs break through the characteristics of a single component of traditional corrosion-resistant alloys, and their copious degrees of freedom in the selection of alloying elements provide a broad compositional design space for alloys with various chemical structures. Among them, the fascinating solid-solution microstructures of single-phase HEAs and the outstanding mechanical properties exhibited by dual-phase HEAs have facilitated the study of the corrosion of HEAs. In this review, the corrosion behavior and mechanisms of the currently reported HEAs have been summarized in consideration of microstructures and phase structures by comparing with traditional corrosion-resistant alloys, such as Fe-based stainless steels (SS) and Ni-based superalloys. In terms of aqueous corrosion behavior, HEAs can exhibit corrosion properties comparable or even superior to traditional corrosion-resistant alloys via controlling composition and phase structure. This comprehensive review of the composition–structure–corrosion relationship of HEAs will allow for continuous advancement in corrosion-resistant alloys.