High entropy alloys (HEAs) were first reported in the early 2000s. High mixing entropy of the HEAs makes it present good thermal stability. Meanwhile, the large lattice distortion in the HEAs leads to significant solution strengthening. Additionally, cluster structures are formed within grains due to the large negative enthalpy. Consequently, the movement of dislocation is effectively hindered, and the strength of the HEAs is remarkably improved. Given to these unique characteristics, the HEAs is expected to have excellent physical and chemical properties at low and high temperatures. As a result, the HEAs have become a hot area with lots of published research papers. Based on existing physical and mechanical properties of the HEAs with BCC and FCC structure, relation among electron concentration, lattice constant, atomic mismatch, mixing enthalpy, hardness, elasticity modulus and normalized hardness were analyzed to develop a formula calculating elasticity modulus and hardness of the HEAs. On this basis, the composition design method of the HEAs with BCC and FCC structures is established by considering density, ductility and working environment. Finally, it is pointed out that the persistent strength of HEAs, the uniformity of composition and properties of large-sized ingots, and the preparation of large-sized alloy ingots are key issues that need to be addressed in the engineering application of HEAs.
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