Searching for Next Single-Phase High-Entropy Alloy Compositions

Abstract

There has been considerable technological interest in high-entropy alloys (HEAs) since the initial publications on the topic appeared in 2004. However, only several of the alloys investigated are truly single-phase solid solution compositions. These include the FCC alloys CoCrFeNi and CoCrFeMnNi based on 3d transition metals elements and BCC alloys NbMoTaW, NbMoTaVW, and HfNbTaTiZr based on refractory metals. The search for new single-phase HEAs compositions has been hindered by a lack of an effective scientific strategy for alloy design. This report shows that the chemical interactions and atomic diffusivities predicted from ab initio molecular dynamics simulations which are closely related to primary crystallization during solidification can be used to assist in identifying single phase high-entropy solid solution compositions. Further, combining these simulations with phase diagram calculations via the CALPHAD method and inspection of existing phase diagrams is an effective strategy to accelerate the discovery of new single-phase HEAs. This methodology was used to predict new singlephase HEA compositions. These are FCC alloys comprised of CoFeMnNi, CuNiPdPt and CuNiPdPtRh, and HCP alloys of CoOsReRu.

Deviation from high-entropy configurations in the atomic distributions of a multi-principal-element alloy

“…6e). Similar results are seen at different temperatures 47 . These CSRO trends in the liquid can be viewed as precursors for nucleating the segregated Al-Ni-enriched, Cr-Fe-enriched and Cu-rich phases (Fig.…”

“…AIMD simulations are emerging as a predictive tool for the phase formation from the liquid 47 and have served here to identify the local-ordering trends in the liquid, particularly the CSRO, which influence the formation of the solid phases in Al 1.3 CoCrCuFeNi. Strong evidence of the local structural similarity between the liquid and solid phases has been provided by the present combined AIMD, experimental PDF and complementary temperature-dependent neutron and synchrotron X-ray diffraction studies.…”

“…These findings have generated great interest, and intense efforts are underway to further develop high-entropy alloys for practical applications. The goal is increasingly focused on obtaining single-phase solid solution microstructures 26,27,47,50 . However, multiphase microstructures should not be dismissed, not only because they provide valuable test cases for understanding phase separation in high-entropy alloys, but also because many are technologically significant in their own right.…”

“…Similar trends in the diffusion constants was observed at T ¼ 1,600°C (ref. 47). This high diffusion rate for Cu may facilitate its precipitation from the matrix, as observed in the present microscopy studies (Figs 1 and 2).…”

“…The AIMD simulations can predict the local atomic structure of the liquid and give insight into the solidification behaviour of complex alloys 46,47 . In the present study, AIMD simulations were run, both with and without constraints from the experimental input.…”