Ultra-strong and ductile medium entropy alloy with a dual heterogeneous microstructure

Developing metallic materials with ultra-high strength and sufficient ductility, while retaining good work-hardening ability has always been a relentless pursuit. Architecting of heterogeneous microstructure ushers in a new way to achieve this goal. Hierarchical precipitation and partial recrystallization are two commonly used approaches to obtain heterogeneous microstructure. In this work, a dual heterogeneous microstructure was designed thorough combining partial recrystallization with hierarchical precipitation aiming to obtain high strength and ductile alloy with sufficient work hardening ability. The newly-developed VCoNi _1.2Al _0.2 medium entropy alloy (MEA) with dual heterogeneous microstructure exhibits ultra-high strength while retaining sufficient ductility ( σ Y S , σ U T S and ductility are 1857 MPa, 2191 MPa, 9.8 % for the sample annealed at 800 ℃, and 1461 MPa, 1934 MPa, 22.3 % for the sample annealed at 900 ℃, respectively), which is superior than most reported MEAs and high entropy alloys (HEAs). Such excellent mechanical properties in this work are attributed to the dual heterogeneous microstructure, which endows alloy with multiple strengthening mechanisms, and the strengthening mechanisms can be adjusted by controlling the microstructures. The uniform distribution of nano precipitated phase and partial recrystallized region not only enhances the crack tolerance ability, but also improves the dislocation storage capability, and prolongs strain hardening. This work offers more possibilities for the development of high-strength and ductile structural materials with sufficient work-hardening ability.