Oxidation of Al2O3-/Cr2O3-Forming High-Entropy Alloys and Role of Trace Reactive Elements: A Review

Abstract High-entropy alloys (HEAs), with their intrinsically complex compositions and distinctive microstructures, present unique challenges in high-temperature applications. The simultaneous oxidation of multiple principal elements leads to thermodynamic competition and kinetic pathways that are highly sensitive to local chemical fluctuations, which may result in oxide scales with significant chemical heterogeneity and structural non-uniformity. These features can undermine scale stability and accelerate interfacial degradation, limiting the long-term performance of HEAs in high-temperature environments. Recent studies show that the deliberate addition of trace amounts of reactive elements (REs) can substantially improve the oxidation resistance of HEAs, akin to the reactive element effect (REE) seen in conventional alloys. This review systematically explores the oxidation behavior of HEAs, focusing on their characteristic challenges as well as the role of RE doping across the entire oxidation process: from initial stages (including selective oxidation and alumina phase transformation) to steady-state regimes (encompassing scale growth kinetics and adhesion). The analysis provides valuable insights into the design of high-performance HEAs with enhanced oxidation resistance.