Effects of Equal Channel Angular Extrusion on the Microstructure and Mechanical Properties of CoCrFeMnNi

Abstract

The present work aims at revealing the effect of grain size on the post processing mechanical behavior of the equiatomic CoCrFeMnNi high entropy alloy (HEA) upon severe plastic deformation (SPD). SPD has been applied using the equal channel angular extrusion (ECAE) process where the billets are extruded through a 90° corner die achieving near simple shear deformation. The microstructure and mechanical properties of successfully extruded billets were reported using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS), tension experiments and microhardness measurements. The effects of extrusion conditions, such as temperature, processing route and extrusion rate on the microstructure and mechanical properties, are investigated for the extrusion and flow plane of each billet. The ECAE deformation of CoCrFeMnNi at high homologous temperatures results in deformation twinning. Refined mean grain size leads to significant increase in tensile flow stresses at room temperature. Further work is needed to find processing schedules at low temperatures to refine the grain size further to determine the lower limit of grain size one can achieve in bulk HEAs.