High Entropy Materials

High entropy materials (HEMs) are considered to be a new ‘avatar’ in physical metallurgy and materials engineering. After their seminal discovery in 2004 (refs 1, 2), research activity in HEMs and related materials has been vigorous for the last 13 years. In recent times, HEMs have gained tremendous attention due to their attractive and adjustable properties with a large compositional range and fascinating microstructures. Although the initial discovery was on high entropy alloys (HEAs) consisting of different metals, the research areas have been expanded to different classes of materials such as high entropy refractory alloys, high entropy superalloys, high entropy metallic glass and high entropy ceramics (oxides/nitrides/carbides). Therefore, these are now termed as HEMs.