In-situ EBSD investigation of excellent strength-ductility synergy mechanism achieved by thermal-mechanical processing of Al0.25FeCoNiV high-entropy alloy

The development of high-entropy alloys (HEAs) is plagued by a trade-off between strength and ductility. In this study, we investigated the effects of different cold rolling ratios and subsequent heat treatments on the microstructures and mechanical properties of the Al0.25FeCoNiV HEA. An efficient and economical thermal-mechanical processing route was successfully explored to prepare multiscale, multiphase heterogeneous structures consisting of heterogeneous grain structures and duplex structures. Yield strength, ultimate tensile strength, and fracture elongation of 1277.3 MPa, 1633.6 MPa, and 26.4%, respectively, could be achieved. The strength-ductility trade-off was avoided. Detailed information on the evolution of grain boundary distribution, grain orientation changes, and grain rotation under stress and strain fields were obtained with in-situ electron backscatter diffraction (EBSD) tensile tests. The mechanism of coordinated plastic deformation and the intrinsic mechanism of excellent strength and ductility were investigated by quantitatively calculating the activation of the slip system, slip transfer at the phase boundaries (PBs), and grain rotation paths. It was found that the excellent mechanical properties can be attributed to multistage hetero-deformation-induced (HDI) strengthening and strain-hardening coupling mechanisms. In this study, an effective method for designing novel HEAs with excellent strength-ductility combinations and an analytical method based on in-situ tests are proposed.