Simultaneously enhancing strength–ductility synergy in refractory high entropy alloys by a heterogeneous structure design

Abstract

Improvement in the strength of metallic materials is often achieved at the expense of material ductility; this long-standing conflict is referred to as the strength–ductility trade-off. In this study, the composition design of high-entropy alloys was combined with the design of multiscale microstructures, and heterogeneous refractory high-entropy alloys (RHEA) with multi-sized grains were fabricated via a simple rolling-annealing treatment process, which significantly alleviates the strength–ductility trade-off. The RHEA annealed at 970 ℃ was composed of fully-recrystallized grains of size 25 μm surrounded by nanosized grains. Owing to the heterogeneity in the structure, dislocations preferentially accumulated at soft recrystallization grain boundaries, thus inducing dislocation interactions such as cross-slip and jog, strengthening the soft region grains, and resulting in Heterogeneous deformation-induced (HDI) strengthening. This mechanism resulted in a significant increase in the work hardening rate during tensile deformation and ensured a high tensile strength of 905 MPa, while improving its uniform elongation to 10.6%. Thus, the proposed heterogeneous design accomplished by simple thermal treatments presents a novel strategy to develop a new generation of high-strength and high-ductility high-entropy alloys.