High-entropy alloys

Abstract

Alloying has long been used to confer desirable properties to materials. Typically, it involves the addition of relatively small amounts of secondary elements to a primary element. For the past decade and a half, however, a new alloying strategy that involves the combination of multiple principal elements in high concentrations to create new materials called high-entropy alloys has been in vogue. The multi-dimensional compositional space that can be tackled with this approach is practically limitless, and only tiny regions have been investigated so far. Nevertheless, a few high-entropy alloys have already been shown to possess exceptional properties, exceeding those of conventional alloys, and other outstanding high-entropy alloys are likely to be discovered in the future. Here, we review recent progress in understanding the salient features of high-entropy alloys. Model alloys whose behaviour has been carefully investigated are highlighted and their fundamental properties and underlying elementary mechanisms discussed. We also address the vast compositional space that remains to be explored and outline fruitful ways to identify regions within this space where high-entropy alloys with potentially interesting properties may be lurking.

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Fig. 1: Possible mixing reactions for three alloying elements.
Fig. 2: Damage-tolerant properties of the Cantor CrMnFeCoNi alloy.
Fig. 3: Tuning the stacking-fault energy and the phases in a set of non-equimolar derivatives of the Cantor alloy.
Fig. 4: A mechanistic approach to the design of high-entropy alloys.
Fig. 5: Mechanical properties of the dual-phase, high-entropy, transformation-induced plasticity alloy Fe50Mn30Co10Cr10.
Fig. 6: Role of local chemical ordering on the stacking-fault energy calculated by density functional theory for solid-solution CrCoNi alloys.

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Acknowledgements

This study was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, through the Materials Science and Technology Division at the Oak Ridge National Laboratory (E.P.G.) and the Materials Sciences Division at the Lawrence Berkeley National Laboratory (R.O.R.). D.R. was supported by the European Research Council (ERC) through the 7th Framework Programme (FP7/2007–2013) ERC Advanced Grant SMARMET (grant agreement 290998) and through the German Research Foundation (DFG) through the Priority Programme ‘Compositionally Complex Alloys – High Entropy Alloys (CCA-HEA)’ (special priority programme (SPP) no. 2006).

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George, E.P., Raabe, D. & Ritchie, R.O. High-entropy alloys. Nat Rev Mater 4, 515–534 (2019). https://doi.org/10.1038/s41578-019-0121-4

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