Tuning element distribution, structure and properties by composition in high-entropy alloys

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Abstract

High-entropy alloys are a class of materials that contain five or more elements in near-equiatomic proportions1,2. Their unconventional compositions and chemical structures hold promise for achieving unprecedented combinations of mechanical properties3,4,5,6,7,8. Rational design of such alloys hinges on an understanding of the composition–structure–property relationships in a near-infinite compositional space9,10. Here we use atomic-resolution chemical mapping to reveal the element distribution of the widely studied face-centred cubic CrMnFeCoNi Cantor alloy2 and of a new face-centred cubic alloy, CrFeCoNiPd. In the Cantor alloy, the distribution of the five constituent elements is relatively random and uniform. By contrast, in the CrFeCoNiPd alloy, in which the palladium atoms have a markedly different atomic size and electronegativity from the other elements, the homogeneity decreases considerably; all five elements tend to show greater aggregation, with a wavelength of incipient concentration waves11,12 as small as 1 to 3 nanometres. The resulting nanoscale alternating tensile and compressive strain fields lead to considerable resistance to dislocation glide. In situ transmission electron microscopy during straining experiments reveals massive dislocation cross-slip from the early stage of plastic deformation, resulting in strong dislocation interactions between multiple slip systems. These deformation mechanisms in the CrFeCoNiPd alloy, which differ markedly from those in the Cantor alloy and other face-centred cubic high-entropy alloys, are promoted by pronounced fluctuations in composition and an increase in stacking-fault energy, leading to higher yield strength without compromising strain hardening and tensile ductility. Mapping atomic-scale element distributions opens opportunities for understanding chemical structures and thus providing a basis for tuning composition and atomic configurations to obtain outstanding mechanical properties.

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Fig. 1: Aberration-corrected TEM imaging and mapping of element distributions in the CrMnFeCoNi Cantor alloy.
Fig. 2: Aberration-corrected TEM imaging and mapping of element distributions in the CrFeCoNiPd alloy.
Fig. 3: TEM observation of dislocations in the CrFeCoNiPd alloy.
Fig. 4: Comparison of mechanical properties of the CrFeCoNiPd alloy with other CrCoNi-based HEAs.

Data availability

All data generated or analysed during this study are included in the published article and Supplementary Information, and are available from the corresponding authors upon reasonable request.

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Acknowledgements

Q.Y. was supported by the National Natural Science Foundation of China (51671168), National Key Research and Development Program of China (2017YFA0208200), 111 project under grant no. B16042, and the State Key Program for Basic Research in China under grant no. 2015CB659300. T.Z. was supported by the US National Science Foundation under grant no. DMR-1810720. R.O.R. was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division and under contract no. DE-AC02-05CH11231 to the Mechanical Behavior of Materials program (KC13) at the Lawrence Berkeley National Laboratory. We thank E. Ma for providing the interatomic potential used for Monte Carlo simulations.

Author information

Q.Y., T.Z. and R.O.R. designed the research. Q.Y., Q.D., X.F., X.C., S.C., L.G. and F.W. performed TEM and in situ experiments. H.B. synthesized alloys and conducted mechanical testing. Y.Z., D.C., Y.G., M.W., T.Z. and Q.Y. conducted data analysis and modelling. Q.Y., T.Z., R.O.R., Q.D., Z.Z., J.L. and H.B. wrote the manuscript. All authors contributed to the discussion and revision of the paper.

Correspondence to Ting Zhu or Robert O. Ritchie or Qian Yu.

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The authors declare no competing interests.

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Peer review information Nature thanks Elena Pereloma and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Fig. 1

X-ray diffraction characterization showing the single-phase signal of the fcc structure of the CrFeCoNiPd alloy.

Extended Data Fig. 2 Atomistic Monte Carlo simulation.

Simulation shows formation of concentration waves in a model equiatomic ternary alloy under annealing at a temperature of 800 K. a, Initial fcc structure with a random distribution of the three constituent elements; yellow, grey and green atoms represent A, B and C elements, respectively. b, Relaxed structure showing the formation of a mixture of an element-A/B dominant phase (mixed yellow and grey atoms) and an element-C dominant phase (green atom clusters). c, Simulated EDS map for element C based on the structure in b. d, Plots of pair correlation functions S(r) of individual elements against concentration wavelength r.

Extended Data Fig. 3 Atomic structure of a simulated dislocation dipole.

The structure consists of two closely spaced 60° dislocations of opposite signs in an fcc Ni single crystal, for comparison with similar dislocation core structures in Fig. 3a. Atoms are coloured by their coordination numbers (CN = 12, yellow; CN = 11, blue), so as to display 30° and 90° partial dislocations (atoms in blue) in the core of an extended 60° full dislocation.

Extended Data Fig. 4 High-resolution TEM images of the cores of dissociated 60° dislocations in the CrFeCoNiPd alloy.

The number in each image indicates the measured stacking fault width in the core of dissociated dislocation. The average stacking fault width is d = 3.37 nm. The stacking-fault energy γsf can be estimated as \({\gamma }_{{\rm{sf}}}=\frac{\mu {b}_{{\rm{p}}}^{2}}{8{\rm{\pi }}d}\left(\frac{2-\nu }{1-\nu }\right)\left(1-\frac{2\nu \cos 2\theta }{2-\nu }\right)\), where θ is the angle between the dislocation line and the Burgers vector of the full dislocation, bp is the length of the Burgers vector of the partial dislocation, μ is the shear modulus and ν is Poisson’s ratio. The γsf of the CrFeCoNiPd alloy is estimated to be 66 mJ m−2.

Extended Data Fig. 5 Kocks–Mecking plots.

The plots of strain hardening rate against true strain at 293 K and 77 K show the strong hardening capability of the CrFeCoNiPd alloy.

Extended Data Fig. 6 Aberration-corrected TEM imaging and mapping of element distributions in the Cr20Fe20Co18Ni30Al12 alloy.

a, HAADF images and associated EDS maps (taken along the [110] zone axis) for individual elements of Cr, Fe, Co, Ni and Al. b, Line profiles of atomic fraction of individual elements taken from respective EDS maps in a; each line profile represents the distribution of an element in a (002) plane projected along the [110] beam direction. c, Cross-slip of dislocations in the Cr20Fe20Co18Ni30Al12 alloy, from in situ straining experiment.

Extended Data Fig. 7 Comparison of element distributions in CrCoNi alloy and in CrCoNi alloy containing 5 at% W.

a, HAADF image and corresponding EDS maps of the CrCoNi alloy containing 5 at% W, taken along the [110] zone axis, showing the distribution of individual elements of Cr, Co, Ni and W. b, Line profiles of atomic fraction of elements Cr, Co and Ni taken from respective EDS maps in a for the CrCoNi alloy containing 5 at% W; each line profile represents the distribution of an element in a \(\left(1\bar{1}1\right)\) plane projected along the [110] beam direction. c, Line profiles of atomic fraction of individual elements taken from the corresponding EDS maps of the CrCoNi alloy; each line profile represents the distribution of an element in a \(\left(1\bar{1}1\right)\) plane projected along the [110] beam direction.

Extended Data Table 1 Properties of the CrMnFeCoNi, CrFeCoNiPd, Cr10Mn30Fe50Co10 and CrCoNi alloys

Supplementary information

Reporting Summary

Video 1

In situ TEM showing the sluggish motion of dislocations in the primary slip plane in the CrFeCoNiPd alloy. The leading dislocation in the pile-up stopped moving in the middle of the strained sample, indicating that the glide of dislocations was strongly hindered (scale bar: 500 nm).

Video 2

In situ TEM showing massive cross slip as the primary slip stopped in the CrFeCoNiPd alloy (scale bar: 200 nm).

Video 3

In situ TEM showing secondary cross slip from the first cross-slipped dislocations in the CrFeCoNiPd alloy (scale bar: 500 nm).

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