High pressure synthesis of a hexagonal close-packed phase of the high-entropy alloy CrMnFeCoNi

TL;DR

This study demonstrates the high-pressure synthesis of a metastable hexagonal close-packed phase in the high-entropy alloy CrMnFeCoNi, revealing a new pathway to tune alloy structures beyond conventional methods.

Contribution

It reports the first high-pressure induction of an hcp phase in a high-entropy alloy, with the phase remaining stable at ambient conditions, enabling novel material property tuning.

Findings

HCP phase begins at 14 GPa during compression.

HCP phase remains metastable after decompression.

Transformation is sluggish and involves magnetic moment suppression.

Abstract

High-entropy alloys, near-equiatomic solid solutions of five or more elements, represent a new strategy for the design of materials with properties superior to those of conventional alloys. However, their phase space remains constrained, with transition metal high-entropy alloys exhibiting only face- or body-centered cubic structures. Here, we report the high-pressure synthesis of a hexagonal close-packed phase of the prototypical high-entropy alloy CrMnFeCoNi. This martensitic transformation begins at 14 GPa and is attributed to suppression of the local magnetic moments, destabilizing the initial fcc structure. Similar to fcc-to-hcp transformations in Al and the noble gases, the transformation is sluggish, occurring over a range of >40 GPa. However, the behaviour of CrMnFeCoNi is unique in that the hcp phase is retained following decompression to ambient pressure, yielding metastable fcc-hcp mixtures. This demonstrates a means of tuning the structures and properties of high-entropy alloys in a manner not achievable by conventional processing techniques.