High-Entropy Alloys: A Review of Mechanical and Thermal Properties

Abstract

High-entropy alloys (HEAs) represent a paradigm shift in metallurgical design, replacing the conventional one-principal-element strategy with multi-principal-element compositions occupying near-equiatomic proportions. Since the concept gained momentum in the alloy design community, research activity has expanded rapidly, driven by the combination of high strength, ductility, thermal stability and phase simplicity that a large compositional space can, in principle, deliver [1]. This review synthesizes current understanding of the mechanical behavior of HEAs — including strengthening mechanisms such as severe lattice distortion, sluggish diffusion and solid-solution hardening — alongside their thermal characteristics, covering high-temperature strength retention, oxidation resistance and phase stability in refractory HEA systems. Face-centered-cubic (FCC) HEAs such as CoCrFeMnNi are shown to combine excellent low-temperature ductility with moderate strength, whereas body-centered-cubic (BCC) refractory HEAs based on Nb, Mo, Ta, W, Ti, Zr and Hf offer superior high-temperature strength but often at the cost of room-temperature ductility. The review further discusses compositional design rules, processing routes, current engineering applications in aerospace, nuclear and coating technologies, and the outstanding challenges — including oxidation behavior above 1000 °C, processing cost and the strength–ductility trade-off — that continue to guide research in this field. Only literature published between 2014 and 2025 is considered.