Lattice distortions in high-entropy alloys

One of the founding concepts of the high-entropy alloy (HEA) field was that the lattice structures of multicomponent solid solution phases are highly distorted. The displacement of the constituent atoms, away from their ideal locations (local lattice strain), has been widely cited as the reason for a number of the observed physical and mechanical properties. However, very little data directly characterizing these lattice distortions exist and, thus, the validity of this hypothesis remains an open question. Here, the concept is reviewed by considering the underlying principles of the lattice distortions, the suitability of different assessment methods, and the direct experimental data currently available. It is found that, at present, there is no clear evidence that the lattice distortions in HEAs are significantly greater than those of conventional alloys. However, so few alloys have been appropriately characterized that this conclusion cannot be considered overarching and further research is required.