An assessment of the lattice strain in the CrMnFeCoNi high-entropy alloy

L.R Owen,E.J Pickering,H.Y Playford,H.J Stone,M.G Tucker,N.G Jones

doi:10.1016/j.actamat.2016.09.032

L.R Owen, E.J Pickering + Show 4 more

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https://doi.org/10.1016/j.actamat.2016.09.032

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Abstract

The formation of single phase solid solutions from combinations of multiple principal elements, with differing atomic radii, has led to the suggestion that the lattices of high-entropy alloys (HEAs) must be severely distorted. To assess this hypothesis, total scattering measurements using neutron radiation have been performed on the CrMnFeCoNi alloy and compared with similar data from five compositionally simpler materials within the same system. The Bragg diffraction patterns from all of the studied materials were similar, consistent with a face-centered cubic structure, and none showed the pronounced dampening that would be expected from a highly distorted lattice. A more detailed evaluation of the local lattice strain was made by considering the first six coordination shells in the pair distribution functions (PDF), obtained from the total scattering data. Across this range, the HEA exhibited the broadest PDF peaks but these widths were not disproportionately larger than those of the simpler alloys. In addition, of all the materials considered, the HEA was at the highest homologous temperature, and hence the thermal vibrations of the atoms would be greatest. Consequently, the level of local lattice strain required to rationalise a given PDF peak width would be reduced. As a result, the data presented in this study do not indicate that the local lattice strain in the equiatomic CrMnFeCoNi HEA is anomalously large.

Highlights

High-Entropy Alloys (HEAs) differ from conventional metallic materials in that they are based upon multiple atomic species in near equiatomic ratios, rather than a single principal element
The level of local lattice strain in six single phase face-centered cubic materials, with varying compositional complexity, has been studied through neutron based total scattering measurements to assess the level of distortion present in the CrMnFeCoNi HEA
Detailed analysis of the pair distribution function (PDF) peak widths corresponding to the first six coordination shells was used to assess the extent of local lattice strain in the different materials

Summary

Introduction

High-Entropy Alloys (HEAs) differ from conventional metallic materials in that they are based upon multiple atomic species in near equiatomic ratios, rather than a single principal element. It might be expected that the microstructures of these alloys would contain several intermetallic phases, but much of the literature associated with these materials has reported only solid solutions with simple crystal structures, such as face- or body-centered cubic (fcc and bcc respectively) and their related superlattice structures [1,2]. These observations have given rise to the concept of entropic stabilisation, which suggests that the configurational entropy of these multi-component solid solutions can overcome the enthalpy of formation of competing intermetallic phases [1]. Owen et al / Acta Materialia 122 (2017) 11e18 to the lattice distortion in the literature is sparse and forms the basis of the current work [12]

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