Phase-specific tailoring strategy for synergetic and prolonged work hardening to achieve superior strength-plasticity in lamellar-structured alloy

Abstract

The pursuit of alloys that integrate high strength and substantial plasticity persists across various industries. Nevertheless, alloys engineered for elevated strength commonly manifest unsustainable work hardening, ultimately leading to a decline in plasticity. Dual- or even multi-phase systems offer vast potential for novel microstructural engineering aimed at harmonizing these inversely related property requirements. Here, heterogeneous lamellar structure consisting of alternating austenite and ferrite lamellae is explored to decouple and leverage the distinct roles of individual phases in a dual-phase system. This phase-specific tailoring strategy meticulously manipulates intra-phase microstructure, and tunes the lamella thickness to promote both high initial strength and prolonged work hardening. The significantly enhanced strength benefits from pre-existing defects, interfaces strengthening and quasi isostrain deformation mode while high plasticity originates from relatively uniform strain partitioning between phases across a wide strain range achieved through exploiting various hardening components. For austenite, prolonged work hardening is achieved by sequential utilization of dislocation hardening followed by martensitic transformation hardening. Moreover, the martensite laths in favorable configuration along with the retained austenite contribute to retarding cracking. For ferrite, wide-range work hardening is ensured by expanding the potential for dislocation activities which lowers initial density and raises peak density through reducing the space in the thickness dimension. Such innovation elevates the traditionally inferior work-hardening capability of high-strength BCC structure to an exceptional level. The resultant alloy, while boosting nearly twice the yield strength of its conventional counterpart, exhibits a total elongation of 45 %. This strategy holds potential for broad application across dual- and multi-phase systems and proposes a new avenue for enhancing plasticity in high-strength lamellar-structured alloys.