Coupling Reversion and Partial Recrystallization for Hetero-Structured Metastable Microstructural Design

Achieving a desirable strength-ductility synergy in metallic alloys indispensably relies on the understanding and control of crystalline defects and the interplay involved therein. An effective pathway to approach this is to activate plastic strain-induced martensitic transformation because of the salient strain hardenability resulting from massive dislocation-phase boundary interactions. Provided the appreciable attempts to maximize the mechanical benefits of such a displacive transformation, microstructural design concepts based on its complementary part, <i>i.e.</i> martensite reversion via thermal annealing appear rather scant. Here we present a microstructural design strategy by combing plastic strain-induced epsilon-martensite reversion and partial recrystallization. We will show that by exploiting the displacive nature of epsilon-martensite reversion to promote strength, and by activating partial recrystallization to balance ductility, a feasible pathway to overcome the rule-of-mixture bound can be paved. Through <i>in situ</i> tensile tests under synchrotron X-ray diffraction and post-mortem electron channeling contrast imaging (ECCI) characterization, we underpin the dominant role of mechanical faulting throughout the entire strain hardening process. Assessments of individual strengthening mechanisms will also be presented to shed a bit more quantitative light on the heterogeneous microstructures by design.