Insights into strain delocalization and plasticity in pre-deformed metastable dual-phase medium-entropy alloys

Abstract

The interplay between strength and ductility in metallic materials has long been a paradox, particularly in microstructures laden with high-density dislocations where catastrophic plastic instability often undermines their mechanical potential. In this study, we unveil the origin of deformation mechanism that transforms this limitation into an advantage, enabling exceptional uniform elongation (∼45%) in hot-rolled metastable medium-entropy alloys (MEAs) under cryogenic conditions. By leveraging the dynamic coupling of deformation-induced martensitic transformation (DIMT) and strain rate sensitivity (SRS), we reveal how strain localization evolves into global strain delocalization, fundamentally altering the plastic response of dual-phase MEAs. Our findings show that low SRS at the early stage of deformation initiates the strain localization, triggering localized DIMT. As tensile deformation progresses, DIMT amplifies SRS, redistributing strain and enhancing ductility while maintaining high strength. This interdependence between SRS and DIMT, validated through strain rate jump tests and microstructural analyses, sheds unprecedented light on mesoscale deformation phenomena. Unlike traditional studies focusing on recrystallized microstructures, this work pioneers the investigation of pre-deformed, hot-rolled MEAs, correlating strain-hardening behavior with microstructural evolution in a high-dislocation-density matrix. These insights not only elucidate the mechanisms underpinning strain delocalization but also offer a transformative pathway for designing advanced alloys capable of exceptional performance in extreme environments.