Crossing the limits of electric conductivity of copper by inducing nanotwinning via extreme plastic deformation at cryogenic conditions

Abstract

Cu features excellent electric conductivity, although typically at the expense of favourable mechanical properties. Nevertheless, by optimizing the processing procedure, the mechanical properties can be enhanced while maintaining advantageous electric conductivity, which consequently increases the efficiency of copper wires and leads to their lower weight, as well as lower costs of material and production. The presented study investigates the effects of a thermomechanical manufacturing procedure involving rotary swaging, an industrially applicable intensive plastic deformation method imparting shear mixing and intensive (sub)structure modifications, performed at cryogenic conditions on the microstructures and mechanical and electric properties of Cu conductors. The results showed that the cryogenic swaging resulted in formation of significantly elongated grains with heavily refined cross-sections, which featured the mechanical properties enhanced by almost 200%, and, simultaneously, the electric conductivity of 104.9% IACS (International Annealed Copper Standard). By applying an optimized heat treatment, the electric conductivity even increased to 105.8% IACS, primarily due to structure homogenization and development of twins in the micro, and also nano scales.