Synergistic strength-ductility enhancement of CoCrFeNi high-entropy alloys with regulated Co/Cr atomic ratios

In this paper, the mechanical properties and deformation mechanisms of the non-equimolar high-entropy alloy Co35Cr25Fe20Ni20 35 Cr 25 Fe 20 Ni 20 (Co35) are investigated. Compared with the equimolar high-entropy alloy Co25Cr25Fe25Ni25 25 Cr 25 Fe 25 Ni 25 (Co25), the high-entropy alloy Co35 exhibits higher yield strength, tensile strength, and work-hardening rate. During tensile process, the deformation mechanisms of Co35 are: stacking faults, deformation twins and fcc-hcp martensitic phase transition. The appearance of these complex mechanisms is the main reason for the superior performance of Co35. Subsequently, generalized stacking fault energies (GSFEs) of the two alloys are calculated by molecular dynamics simulation, the results show that the Co35 demonstrates lower stacking fault energy (SFE) than Co25. The deformation twins and hcp phase transformation are activated easily in the Co35 with low SFE, while the high SFE will suppresses these processes. The Warren-Cowley parameter (WCP) shows that the increasing proportion of Cr atoms favor Ni and Co atoms as the nearest neighbors, which enhance the chemical short-range ordered structure (CRSO) and the enhancement of CRSO affects the SFE. Finally, the cohesion energies of the fcc and hcp structures of the two alloys were calculated by density functional theory, the results show that hcp phase of Co35 (-0.15945 eV/atom) is more favorable, suggests that Co35 is more likely to generate hcp phases during deformation.