In this paper, we report the development of rare-earth high-entropy alloys (RE-HEA) with multiple principle elements randomly distributed on a single hexagonal close-packed (HCP) lattice. Our work demonstrated that it is the entropy, rather than other atomic factors such as enthalpy, atomic size and electronegativity, that dictates phase formation in the current rare-earth alloy system. The high configuration entropy stabilized the crystalline structure from phase transformation during cooling, whereas a second-order magnetic phase transition occurred at its Neel temperature. The quinary RE-HEA exhibited a small magnetic hysteresis and the largest refrigerant capacity (about 627 J kg-1 at the 5T magnetic field) reported to date, along with respectable mechanical properties. Our analysis indicates that the strong chemical disorder resulted from the high configuration entropy makes magnetic ordering in the HEA difficult, thus giving rise to a sluggish magnetic phase transition and enhanced magnetocaloric effect. Our findings evidenced that RE-HEAs have great potential to be used as magnetic refrigerants and the alloy-design concept of HEAs can be employed to develop novel high-performance magnetocaloric materials.

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FexCrMnAlCu ( x = 0, 0.5, 1, 1.5, 2) high-entropy alloys were prepared by vacuum arc melting in this study. The effects of the element Fe on the microstructure evolution, mechanical properties, and wear behaviour of FexCrMnAlCu were evaluated. Results show that all FexCrMnAlCu consisted of dendrites (disordered BCC) and interdendritic (disordered FCC) structures. With an increase in Fe, uniformly distributed rod-like precipitates (Φ50 nm × 300 nm) rich in Al and Cu (ordered BCC) were formed in the dendrites; the volume fraction of the dendrites increased gradually, whereas the content of the interdendritic structures decreased. Through mechanical property testing, it was found that the content of precipitates significantly affected the strength and hardness of the FexCrMnAlCu.

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