Semi-ordered high entropy materials: The case of high entropy intermetallic compounds

Intermetallic compounds (ICs) have been actively investigated since the early twentieth century due to their high strength, especially at high temperatures, as well as a variety of other complex features. However, lack of ductility at ambient temperature has continually hampered their practical applications. In recent years, the concept of entropy stabilization in multicomponent materials or high entropy materials (HEMs) has revolutionized the design of various materials including disordered solid solution alloys, ordered ceramics, and ICs. Ordered high entropy ICs (HEICs) are one type of these materials, which incorporate the benefits of HEMs and ICs into a singular material. HEICs exhibit a long-range ordered structure and well-defined multicomponent compositions with complex sublattice occupancy. This could open up a new avenue for tackling the long-standing brittleness of ICs at low temperatures. This review article aims to provide a comprehensive overview of the present state of design and unique features of HEICs. We classify nearly all developed multicomponent ICs based on ordering types and focus on microstructural features in these HEICs, such as ordered superlattice structure, nanoscale multi-element segregation, and tailoring disorder degree. These characteristics may result in improved mechanical and functional properties. Finally, we summarize the current state and future prospects of material design challenges and opportunities in ordered multicomponent alloys.