Awakening the metastability of an interstitial high entropy alloy via severe deformation

The metastability of a typical non-equiatomic FeMnCoCr high-entropy alloy (HEA) system was demonstrated to be dormant upon co-doping with C and N interstitials, i.e., displacive gamma-epsilon phase transformation disappears during tensile deformation. Interestingly, we found in the present study that the displacive phase transformation prevails again in the C-N co-doped HEA upon severe deformation via cold-rolling. The generation of epsilon-phase lamellae is found to be motivated by strain localization which facilitates the formation of shear bands. Such highly concentrated strains significantly intensify the local elastic fields to neighboring gamma matrix and finally eke out the driving force to overcome the interstitials-enhanced energy barrier of epsilon-martensite transformation. The results suggest that the suppressed phase metastability is awakened, which inspires efforts to tune the phase metastability via modifying the strain state during alloy processing and gives new insights into the development of HEAs with desirable phase stability and mechanical properties. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

In this study, the metastability of a non-equiatomic FeMnCoCr high-entropy alloy was shown to be dormant when co-doped with C and N interstitials, disappearing during tensile deformation but re-emerging after severe deformation via cold-rolling. The generation of epsilon-phase lamellae was found to be driven by strain localization, intensifying local elastic fields to overcome the energy barrier of epsilon-martensite transformation. These findings suggest that phase metastability can be controlled by adjusting the strain state during alloy processing.