Achieving superior ductility with ultrahigh strength via deformation and strain hardening in the non-recrystallized regions of the heterogeneous-structured high-entropy alloy

Abstract

Developing metallic structural materials with ultrahigh strength and exceptional ductility remains a significant challenge due to the trade-off between both properties. This study presents a heterogeneous-structured high-entropy alloy achieving a superior combination of strength and ductility compared to the reported heterogeneous-structured high entropy alloys through deformation and strain hardening in the non-recrystallized regions. The cold rolling followed by annealing at 760 °C resulted in a heterogeneous microstructure consisting of a small fraction of ultrafine recrystallized grains and extensive non-recrystallized regions, with a significant amount of L12 precipitates throughout the alloy. The architected microstructure led to a significant enhancement of yield strength through mechanisms including dislocation strengthening, L12 strengthening, and grain boundary strengthening. During the deformation, the non-recrystallized regions accommodated substantial strain through the reactivation of pre-existing deformation bands and the synergistic deformation of the FCC and L12 phases, thereby markedly enhancing ductility. Moreover, the metastable FCC matrix underwent FCC→BCC phase transformation, leading to the formation of numerous short-range BCC domains, which further contributed to the pronounced strain hardening. Consequently, the alloy annealing at 760 °C achieved a yield strength of 1.73 GPa, an ultimate strength of 2.05 GPa, and an elongation of 21.0 %. This study underscores a novel strategy for the concurrent enhancement of strength and ductility and provides valuable insights for the design of high-performance alloys.