Microstructural and Property Evolution of Continuous Columnar-Grained Polycrystalline Copper during Extreme Plastic Deformation at Room Temperature

An extreme extensibility with a true strain of 11.12 has been obtained for continuous columnar-grained (CCG) polycrystalline copper at room temperature, which was cold-drawn from a 10-mm-diameter as-cast rod into a 38.5-μm-diameter ultra-fine wire without any intermediate softening heat treatment. During the extreme plastic deformation, the ultimate tensile stress increased from 140 MPa for as-cast CCG copper to 525 MPa for the deformed sample at a true stain of 11.12, while the relative electrical conductivity maintained a high value of 97.6% IACS. On this basis, CCG copper is an excellent raw material for the fabrication of ultra-fine wires with both high strength and high electrical conductivity. The original columnar grains experienced grain subdivision and formed fibrous grains along the drawing direction with a fibrous longitudinal morphology and curly transverse microstructure at medium to high strain. The subdivision of the fibrous grains then went on as the extreme plastic deformation continued. Large amounts of strain-induced boundaries and microstructural refinement facilitated the storage of abundant glide dislocations created by extreme plastic deformation. Thus, extreme plastic extensibility can be achieved through continuous work hardening of CCG copper.