Microstructure and mechanical properties of cold drawing CoCrFeMnNi high entropy alloy

The present study investigated the effects of cold drawing deformation on the microstructure and mechanical properties of CoCrFeMnNi high entropy alloy. The results showed that at low strain (≤0.28), the plastic deformation is dominated by planar slip with the formation of slip bands, Lomer-Cottrell locks and Taylor lattices. While at medium to high strain (between 0.28 and 1.96), the microstructure consisted of dislocation cells, deformation twins (including the primary and secondary twins) and irregular dislocation (i.e. randomly distributed dislocation clusters). At high strains (＞1.96), deformation is mainly mediated by twinning and shear banding causing the formation of lamellae structures parallel to metal flow direction. Texture evolution showed that the <111> fiber texture was the stable texture component and the <100> fiber texture became unstable at low strain. At strains higher than 1.96, the texture component content remained unchanged even under further increased strain, and the volume fractions of <111>, <100> and complex texture components were 57.4%, 30.7% and 11.9%, respectively. Additionally, the microhardness and yield strength increased monotonically with increased strain. At the early stages of deformation, activation of planar slip causes the initial HEA to display a very high strain hardening rate. The hardness value saturated at 430 HV at the strain of 2.77, which is about 3 times larger than the initial hardness value. Pre-strain by cold drawing deformation can significantly enhance the yield strength of the CoCrFeMnNi high entropy alloy by twinning and texture strengthening.