Functionally-graded high-entropy alloy coatings: New frontiers in cutting edge industrial applications

High-entropy alloy-based industrial coatings have gained rapid recognition and advancement over the past decade due to their outstanding properties. This review paper presents the current status of functionally graded HEA-based coatings, including their concepts, design principles, and structural and strength evolution during manufacturing and post-treatment processes. Additionally, functionally-graded high-entropy alloy (FG-HEA) coatings have gained significant attention from researchers due to their unique mechanical, thermal, electrical, and tribological properties. FG-HEA coatings are a type of coating containing metallic materials where the distribution of compositions/phases forms a smooth gradient structure, making them ideal for specific industrial and engineering applications. Beyond summarizing recent progress, this review provides a critical synthesis of fabrication–microstructure–property relationships in FG-HEA coatings. Particular emphasis is placed on identifying dominant strengthening, wear, corrosion, and thermal-stability mechanisms across different compositional gradients and deposition routes. By comparatively evaluating fabrication techniques and highlighting unresolved challenges related to scalability, cost, and long-term durability, this work offers practical guidance for both academic research and industrial deployment of FG-HEA coating systems. In addition, this review explores potential applications of FG-HEA coatings and outlines key future challenges in the field. The outcomes of this work aim to provide a fundamental guideline for those interested in the field of FG coatings, helping them make informed decisions for better choice in the protection of industrial parts.