Strengthening the FeCoCrNiMo0.15 high entropy alloy by a gradient structure

Abstract

In present work, a gradient structured FeCoCrNiMo0.15 high entropy alloy (HEA) is processed by shot peening treatment. Microstructures of the gradient structured HEA are characterized by electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM). Complex microstructures consisting of nanograins, nanotwins, with high densities of dislocations are formed on the surface of the shot peening treated HEA. With the increase of depth from surface to center, a planar dislocation slip occurs while no deformation twin is observed. Un-deformed grains were observed in the regions of ∼100 μm–150 μm depth from the surface. Such gradient structured HEA shows an increase of yield strength from 418 MPa to 486 MPa when compared to the one with homogeneous structure, with a slight decrease in tensile elongation from 50.9% to 46.8%. During tensile deformation, strong deformation twinning including the formation of hierarchical nanotwins occurs in the gradient structured HEA. These unique deformation microstructures are associated with high strain hardening and show increased ductility, which creates excellent combination of strength and tensile elongation. Our work offers valuable insight into achieving high-performance HEAs.