Strengthening mechanisms in high entropy alloys: Fundamental issues

High entropy alloys (HEAs), offering a multi-dimensional compositional space, provide almost limitless design opportunities surpassing the frontiers of structural materials development. However, an in-depth appraisal of the fundamental materials physics behind strengthening in HEAs is essential in order to leverage them to achieve greater flexibility in application oriented materials design. This viewpoint paper concentrates on issues regarding inherent compositional fluctuations in HEAs and corresponding impact on strengthening is highlighted. In particular, metal physics based design criteria in multi-phase HEAs are discussed and comparisons between multi-phase and single-phase HEAs are drawn.