Domain structure and lattice effects in a severely plastically deformed CoCrFeMnNi high entropy alloy

An equiatomic high entropy CoCrFeMnNi alloy has been processed by caliber rolling and its microstructure studied by transmission electron microscopy (TEM). The cast dendritic structure and compositional inhomogeneity was reduced to a nanoscale microstructure. Domains as thin as 50 nm elongated in the rolling direction were formed after 19 rolling passes. Boundaries on {111} plane perpendicular to the rolling direction were also observed. FCC twins were observed in the cross-section of the rolled rods, about 50 nm in thickness. A stack of twins and other planar faults result in a periodicity of three times the interplanar spacing of the {111} twinning plane to about 6.2 Å. Lattice imaging shows interference fringes and diffraction effects which can be attributed to domain formation at a very fine scale. These give rise to diffraction streaks and additional spots. Extra diffraction spots and associated diffuse intensity also point to an underlying lattice not fully ordered. The nanoscale domain boundaries are often on {111} planes which are not simple stacking faults but complex in structure.