The nanocrystalline and high density dislocation-Enabled ultrahigh strength and ductility of Al0.4Co0.5V0.2FeNi high entropy alloy

The evolution of the microstructure and mechanical properties of a vacuum arc melted non-equiatomic Al0.4Co0.5V0.2FeNi high-entropy alloy (HEA) subjected to severe plastic deformation was investigated experimentally and by simulations. The present work explored duplex HEAs, comprising a face-centered cubic (FCC) matrix and a body-centered cubic (BCC) phase, towards outstanding their mechanical responses. The Al0.4Co0.5V0.2FeNi alloys had a duplex structure, i.e., with dispersed B2-phase islands (with sizes of dozens of microns) in several hundred micron-, even millimeter-sized FCC grains. The mechanical properties of this HEA were strongly deformation dependent, i.e., when deformation increased from 30 % up to 60 %, the yield strength and ultimate strength tensile increased from ∼0.9 GPa and 1.0 GPa to ∼1.2 GPa and 1.3 GPa, respectively. During tensile deformation, initial fractures occurred in the FCC phase located close to the interface between the FCC and BCC phases. With an increase of deformation, the fracture degree in the FCC phase got larger, and fractures also appeared in the BCC phase. Combined with the geometric dislocation density calculation results from an electron backscatter diffraction (EBSD) analysis, it can be seen that the dislocation density near the phase interface of FCC was higher, making it more likely to produce defects.