Passive film formation, stability, and breakdown in high-entropy alloys: a critical review of corrosion mechanisms and electrochemical performance

Abstract

Abstract Corrosion remains a critical limitation in advanced engineering materials, particularly under aggressive and multi-environment conditions. High-entropy alloys (HEAs) have emerged as promising candidates for corrosion applications due to their multi-principal-element design and their ability to form chemically complex passive films. However, a unified, mechanism-driven understanding of passive film behavior in HEAs remains lacking. This review systematically examines passive film formation, stability, and breakdown in HEAs. It further evaluates electrochemical characterization methods, identifies corrosion mechanisms in aggressive environments, and proposes design strategies to enhance corrosion resistance. A systematic review was conducted using the Scopus database following Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines. A total of 487 records were identified, of which 369 met the inclusion criteria. Bibliometric analysis using VOSviewer and thematic classification was applied to identify dominant research clusters, mechanisms, and emerging trends. The findings show that corrosion resistance in HEAs is governed by multi-component passive films with complex chemistry and layered structures. Their performance is strongly dependent on composition, microstructure, and environment. Cr plays a dominant role in film formation, while Mo significantly enhances pitting resistance and stability in chloride- and acidic-environments. Electrochemical characterization consistently links low corrosion current density and high charge transfer resistance to stable passive films. Microstructural uniformity is also critical. Under aggressive conditions, including mixed-ion environments and tribocorrosion, degradation mechanisms shift from passivation-controlled behavior to dynamic film breakdown and repassivation. The ability of HEAs to rapidly reform passive films emerges as a key performance advantage. Future research should focus on multi-environment corrosion mechanisms, tribocorrosion behavior, and in-situ characterization of passive film evolution.