High-entropy alloy coatings for surface protection and thermal barrier applications: fundamentals, recent advances, and a critical assessment of their potential as alternatives to conventional coatings

High-entropy alloy (HEA) coatings have recently emerged as highly promising materials for next-generation thermal barrier and surface protection systems, due to their exceptional thermal stability, oxidation resistance, and compositional flexibility. This review presents a comprehensive overview of recent advances in HEA coatings for thermal barrier coating (TBC) applications, highlighting their unique microstructural characteristics, deposition methods, and high-temperature performance in comparison with conventional MCrAlY-based coatings. The fundamental principles of HEAs—including core effects, phase stability, and diffusion behaviour—are systematically discussed to establish the scientific basis for their superior performance. In addition, the oxidation kinetics, thermally grown oxide (TGO) morphology, and interfacial adhesion mechanisms of HEA bond coats are critically analysed to explain how multicomponent chemistries influence durability and spallation resistance under cyclic thermal conditions. Recent progress in self-healing HEA coatings is also reviewed, with a focus on atomic-scale evidence of selective oxidation and crack-sealing mechanisms. Finally, the challenges, current limitations, and future research directions for optimizing HEA compositions and deposition strategies are outlined, guiding for design of damage-tolerant, high-temperature protective coatings for aerospace and energy applications.