Towards ultrastrong and ductile medium-entropy alloy through dual-phase ultrafine-grained architecture

• Novel V 0.5 Cr 0.5 CoNi medium-entropy alloy with fully-recrystallized dual-phase UFG architecture. • Formation of local chemical ordered structure in HCP solid solution and the significant strengthening effects. • Ultrahigh yield strength of 1476 MPa and promising uniform elongation of 13.2% at room temperature. Advanced materials with superior comprehensive mechanical properties are strongly desired, but it has long been a challenge to achieve high ductility in high-strength materials. Here, we proposed a new V 0.5 Cr 0.5 CoNi medium-entropy alloy (MEA) with a face-centered cubic/hexagonal close-packed (FCC/HCP) dual-phase ultrafine-grained (UFG) architecture containing stacking faults (SFs) and local chemical order (LCO) in HCP solid solution, to obtain an ultrahigh yield strength of 1476 MPa and uniform elongation of 13.2% at ambient temperature. The ultrahigh yield strength originates mainly from fine grain strengthening of the UFG FCC matrix and HCP second-phase strengthening assisted by the SFs and LCO inside, whereas the large ductility correlates to the superior ability of the UFG FCC matrix to storage dislocations and the function of deformation-induced SFs in the vicinity of the FCC/HCP boundary to eliminate the stress concentration. This work provides new guidance by engineering novel composition and stable UFG structure for upgrading the mechanical properties of metallic materials.