Phase Selection, Lattice Distortions, and Mechanical Properties in High-Entropy Alloys

High-entropy alloys (HEAs) composed of multiprincipal elements with near-equiatomic ratio have gained numerous attention in recent years. The design concept and unique microstructure make them exhibit a wide range of attractive properties, promoting them suitable for most structural and functional applications. HEAs have four core effects: severe lattice distortion, high entropy, sluggish diffusion, and cocktail effects, which are all interconnected. Among these core effects, severe lattice distortion is seen as the most key factor in determining the properties of HEAs. Recent findings prove that phase selection in HEAs cannot be described by the maximized entropy theory alone. As such, the phase formation principles in terms of single-phase and multiphase formation criteria are summarized. Severe lattice distortion affecting the mechanical properties and polymorphism of HEAs is reviewed. Several strategies, which have recently been successfully applied in overcoming the strength-ductility trade-off in HEAs, are discussed. Some key unsolved questions concerning the lattice distortion in HEAs which could be interesting research topics in the future are suggested.