Real-time observations of TRIP-induced ultrahigh strain hardening in a dual-phase CrMnFeCoNi high-entropy alloy

Sijing Chen,Robert O Ritchie,Hyun Seok Oh,Ze Zhang,Sang Jun Kim,Bernd Gludovatz,Qian Yu,Eun Soo Park

doi:10.1038/s41467-020-14641-1

Abstract

Strategies involving metastable phases have been the basis of the design of numerous alloys, yet research on metastable high-entropy alloys is still in its infancy. In dual-phase high-entropy alloys, the combination of local chemical environments and loading-induced crystal structure changes suggests a relationship between deformation mechanisms and chemical atomic distribution, which we examine in here in a Cantor-like Cr20Mn6Fe34Co34Ni6 alloy, comprising both face-centered cubic (fcc) and hexagonal closed packed (hcp) phases. We observe that partial dislocation activities result in stable three-dimensional stacking-fault networks. Additionally, the fraction of the stronger hcp phase progressively increases during plastic deformation by forming at the stacking-fault network boundaries in the fcc phase, serving as the major source of strain hardening. In this context, variations in local chemical composition promote a high density of Lomer-Cottrell locks, which facilitate the construction of the stacking-fault networks to provide nucleation sites for the hcp phase transformation.

Highlights

Strategies involving metastable phases have been the basis of the design of numerous alloys, yet research on metastable high-entropy alloys is still in its infancy
We find that the strain-hardening results from the formation of three-dimensional stacking-fault networks that impede dislocation motion and further provide preferred sites for the formation of the hcp phase via a transformation-induced plasticity (TRIP) effect, phenomena that appear to be promoted by variations in local chemical composition
Deformation-induced phase transformations are known to occur in DP-HEAs12–16, our current in situ transmission electron microscopy (TEM) studies demonstrate that the phase transformation from fcc to hcp is based on the formation of three-dimensional (3D) stackingfault networks comprising multiple stacking faults (SFs) and a 1100 b c

Summary

Introduction

Strategies involving metastable phases have been the basis of the design of numerous alloys, yet research on metastable high-entropy alloys is still in its infancy. Direct experimental evidence of the dynamic microstructure evolution the phase transformation and its direct impact on mechanical behavior is still lacking, since most experimental studies to date have been relatively large-scale and have involved only post-mortem investigations of the structure and dislocation activity With such DP-HEAs, as the local chemical environment varies everywhere, combined with a deformation-induced change in crystal structure, there is a scientific imperative to understand the relationships between deformation mechanisms in their dualphase structure and the chemical distribution of atoms. We find that the strain-hardening results from the formation of three-dimensional stacking-fault networks that impede dislocation motion and further provide preferred sites for the formation of the hcp phase via a TRIP effect, phenomena that appear to be promoted by variations in local chemical composition

Methods

Results

Conclusion