Prolonged martensitic transformation induced by heterogeneous deformation in a heterostructured metastable high-entropy alloy

We report prolonged martensitic transformation in heterostructured metastable high-entropy alloy composed of non-recrystallized (NRX) and recrystallized ultrafine-grained (UFG) zones. This distinctive transformation behavior is attributed to heterogeneous deformation inherent in heterostructures. The high stress concentrations at the hetero-zone boundaries facilitate preferential nucleation and stable evolution of martensite within the NRX zones. This process accommodates stress localization and establishes a pronounced strain gradient between the NRX and UFG zones. Additionally, the activation of shear bands, driven by the high dislocation density in the UFG zones, initiates and extends the martensitic transformation to higher strain levels. As a result, this prolonged martensitic transformation significantly extends high work-hardening into high applied strains, thereby producing an excellent strength-ductility combination.