The microstructure, texture and mechanical properties of AS-ECAE Interstitial-free steel and copper

Abstract

A comparison between the microstructure, texture and mechanical properties of bcc interstitial-free (IF) steel and fcc copper (Cu) for up to N = 8 passes Equal Channel Angular Extrusion (ECAE) via route BC processing was undertaken. Transmission Electron Microscopy (TEM) and Electron Back-Scattering Diffraction (EBSD) studies revealed that the deformation microstructures of both metals evolves from low-angled microbands and dislocation cells after N=2 passes towards more equiaxed, homogeneous subgrain/grain structures comprising higher-angles of misorientation after N = 8 passes. In both metals, the percentage rise in Σ3 and random boundaries are attributed to mechanisms that favour low-energy boundary configurations during ECAE. Texture evolution involves gradual changes in individual component strengths during multi-pass ECAE. The bcc and fcc textures are correlated by interchanging the Miller indices of the slip plane and slip direction between the two cubic crystal systems. The uniaxial tensile curves of both materials are representative of significant cold-working and depict higher 0.2% proof stresses, a small period of uniform elongation, necking and lastly, failure via geometrical softening. Constitutive modelling suggests that rather than a change in deformation mechanism, the preservation of ductility up to N = 8 passes is associated with an increase in the mean free path of dislocations; with slip via dislocation glide remaining as the dominant carrier of plastic strain in both metals.