High-Entropy Alloys: Fundamental and Frontiers

This chapter explores the fundamentals of high-entropy alloys (HEAs), covering an overview of their basic concepts such as compositional design, microstructural characterization, mechanical properties, thermal behavior, corrosion resistance, and coating applications. Since their introduction in 2004, HEAs have attracted significant research interest due to their unique compositions, random solid-solution (SS) structures, and exceptional properties. While traditional alloys such as stainless steels, high-speed steels, and superalloys rely on a base-element approach, HEAs incorporate five or more principal elements in near-equiatomic proportions, leading to higher mixing entropy. This high entropy contributes to the stabilization of simple SSs and enhances mechanical and chemical properties through effects such as SS strengthening, lattice distortion, and sluggish diffusion. The development of HEAs therefore represents a paradigm shift in alloy design, moving away from the conventional focus on single- or dual-element systems to explore multi-principal element systems. This shift enables the design of alloys with optimized structures, microstructures, and properties, including enhanced strength, ductility, thermal stability, and corrosion resistance. Last, the continued study and refinement of HEA principles have accelerated global research into these novel materials, paving the way for innovative applications in structural, high-temperature, and corrosive environments.