Characterizations of severely deformed and annealed copper

Abstract

The objectives of this study were to characterize severely plastically deformed and recrystallized oxygen free high conductivity copper, to determine texture transformation potential of Equal Channel Angular Extrusion (ECAE) and to investigate the possibility of converging different initial textures. The initial material was processed to have an average grain diameter of 50[u]m. The effects of different combinations of heat treatment, routes of extrusion (A, B and C) and plastic strains of 2.32 and 4.64 were examined. Hardness measurements were used to determine the recrystallization temperature of each ECAE path. Optical microscopy and X-ray diffraction were used for grain morphology and texture analyses. Optical microscopy revealed uniform microstructures for different processing routes. After recrystallization heat treatment, the nucleation of new grains from heavily deformed material was found to occur along sites with heavy distortions. Nucleation sites for recrystallized grains start in shear bands with subsequent growth in the direction of slip lines. Processing that causes intersection of shear planes creates more sites for nucleation and leads to a shifting of the recrystallization curve to lower temperatures. The one dimensional nature of shear bands lessens the opportunity for nucleation in route A decreasing consequently the beginning of nucleation. All recrystallization curves exhibit a slight increase in hardness prior to the sharp drop that accompanies recrystallization. Relatively weak textures are developed during processing of copper 101 via ECAE. The texture after multipass processing via route A is found to be near the {110}<122>. An intermediate rotation of the billet of ±90° during processing is found to produce a partial fiber texture: this texture is not as pronounced as a typical drawing texture and can be best described by partial fiber textures <122> and <100> along the extrusion direction. Route C leads to the formation of a sheet texture which is not removed when a reversal strain is applied during the even pass but rather is intensified by decreasing the component <100> parallel to the rolling direction. ECAE is found to be a powerful tool to converge different initial textures in copper. Recrystallization leads to similar textures for copper processed by different multipass routes.