Atomic-scale mechanisms of dislocation-driven ε→γtwin reversion in metastable compositionally complex alloys: insights from experiments and molecular dynamics simulations

JH Hou and PF Qu and YH Huang and DP Hua and CY Dong and Q He and WZ Bao and SH Zou and ZQ Mei and BN Qian and JW Zhang and WJ Lu, INTERNATIONAL JOURNAL OF PLASTICITY, 192, 104432 (2025).

DOI: 10.1016/j.ijplas.2025.104432

The epsilon ->gamma twin reversion process in metastable face-centered cubic (FCC) alloys remains poorly understood due to its complex, dislocation-mediated nature. In this study, we uncover the atomic-scale mechanisms governing this transformation in a metastable compositionally complex alloy (CCA) with Co34Cr23Fe25Ni18 wt.% through a combined experimental and computational approach. Quasi-in-situ electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and atomic-resolution imaging reveal that the reversion from epsilon- martensite to gamma nanotwins is not mediated by conventional mechanisms dominated solely by Shockley partial dislocation (SPD) glide. Instead, it proceeds via a cooperative sequence involving SPDs, full dislocations, and Frank partials, alongside boundary relaxation processes. Uniaxial compression along the (001) direction induces epsilon-martensite formation, which reverts to gamma nanotwins upon annealing. Molecular dynamics simulations further elucidate the energetics, showing that the epsilon ->gamma twin transformation is thermodynamically favored at elevated temperatures. The simulations also highlight the crucial role of stacking fault energy (SFE) in determining epsilon phase stability and twin formation kinetics. Our findings establish a new mechanistic framework for dislocation-assisted twin reversion in metastable alloys. It not only advances the fundamental understanding of transformation-mediated twinning but also provides strategic insights for microstructural engineering. By leveraging dislocation interactions and transformation pathways, this approach offers a pathway to design advanced materials with superior strength- ductility combinations.

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