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

The ϵ→γ_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 ϵ-martensite to γ 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 ϵ-martensite formation, which reverts to γ nanotwins upon annealing. Molecular dynamics simulations further elucidate the energetics, showing that the ϵ→γ_twin transformation is thermodynamically favored at elevated temperatures. The simulations also highlight the crucial role of stacking fault energy (SFE) in determining ϵ 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. © 2025 Elsevier Ltd.