Strong and ductile medium-entropy alloy via coupling partial recrystallization and hierarchical precipitation

Developing alloys with high strength and large ductility has always been a relentless pursuit. Employing hierarchical microstructures ushers in a crescendo of achieving this goal. Partial recrystallization and hierarchical precipitation are two commonly used approaches to producing hierarchical microstructures. However, employing one of them often embrittles the material and reduces work-hardening capability. Herein, we report that via coupling partial recrystallization and hierarchical precipitation, a strong and ductile medium-entropy alloy (MEA) can be successfully developed. In the model (Ni3CrV)100-xAlx (x = 0, 3, 6 and 9 at.%) MEAs, increasing the Al content not only retards recrystallization due to the resultant solute drag and Zener pinning, but also promotes hierarchical precipitation through elemental partitioning, which produces hierarchical precipitates embedded in the partially recrystallized matrix with large chemical complexity. As a result, the dual-hierarchical structure endows (Ni3CrV)91Al9 alloy with a tensile yield strength of 1151 +/- 33 MPa and an ultimate tensile strength of 1448 +/- 17 MPa, as well as a uniform elongation of 17% +/- 1%. The complex hierarchical structure brings multiple strengthening mechanisms, i.e., hetero-deformation-induced (HDI) strengthening, precipitation strengthening and dislocation strengthening, which lead to the observed high strength. Also, such complex structure heterogeneities facilitate multiple deformation behaviors, i.e., planar slip, wavy slip, stacking faults, dislocation networks and twinning deformation at different loading stages, which give rise to the large ductility and pronounced work-hardening capability.