Oxygen free high conductivity (OFHC) copper was processed using equal channel angular extrusion (ECAE), drawing, swaging, or ECAE plus either drawing or swaging to a strain of 4. All processing was carried out at room temperature. The ECAE processing was carried out using route Bc with a die of 90° channel intersections. The influence of deformation path on the evolution of texture and microstructure in the as-deformed and annealed (at 250°C for 1 hour) conditions was documented using orientation imaging microscopy (OIM), X-ray diffraction, and Vickers hardness testing.
Processing by ECAE alone produced very fine and feathery microstructure (~ 1.2µm thickness) with weak <110>-<212> texture. Elongated grains parallel to the deformation direction were observed in wires processed by either drawing or swaging alone. Their texture was similar and can be described as <100>+<111>. Processing the wire by ECAE to a strain () of ~3 followed by drawing or swaging to a cumulative strain of ~4 resulted in a <100>+<111> duplex texture. The <111> texture in the ECAE plus swage wire was stronger than that of ECAE plus drawing. The Vickers hardness values for wires varied from 108 to 142 Hv, and difference in hardness was attributed to the variation in the substructure, which was minimal in the wires that underwent any form of swaging. Although the grain boundary character distribution (GBCD) of the wires in the as-processed condition was similar, the misorientation distribution function (MDF) was dependent on the processing method. While a high concentration of boundaries with 60 deg <111> were found in the swaged wires, it was relatively absent in other wires, which had lots of 30-45 deg <111> boundaries instead.
Subsequent annealing of these wires at 250 deg C produced diverse results: recovered microstructure in any form of swaged wires, partially recrystallized in drawn or ECAE+drawn wires and fully recrystallized in materials processed by ECAE alone. The annealing behavior of these wires were correlated with the density of substructure and the ratio of the mobile (60 deg <111>) to immobile (30-45 deg <111>) boundaries. A ratio of mobile boundaries to immobile boundaries was greater than or equal to one resulted in a fully to partially recrystallized microstructure upon annealing, while a ratio less than 1 resulted in limited to no recrystallization upon annealing.
