Characterization of the microstructure and deformation substructure evolution in a hierarchal high-entropy alloy by correlative EBSD and ECCI

Abstract

We investigate the microstructure and deformation substructure evolution in an additively manufactured 1.8 at.% N-doped FeCoNiCr high-entropy alloy (HEA) by means of correlative electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI). The combinational use of EBSD and ECCI uncovers hierarchal structures of the HEA at multiple length scales, which consist of a bimodal grain structure, low angle boundaries, and dislocation networks, along with the quantitative evolution of geometrically necessary dislocations (GNDs) distribution. The ECCI technique shows comparable resolution to transmission electron microscopy (TEM) in terms of characterizing the dislocation substructures. We further clarify the strain hardening mechanisms by investigating the deformation microstructures. The excellent strain hardening rate of the HEA even at large strain is due to the jointly activation of slip bands and mechanical twining. The deformation induced twining shows strong orientation dependence.