Development of high strength pure copper wires by cryogenic deformation for magnet applications

A high strength pure copper conductor was fabricated by a cryogenic drawing process at 77 K where the dynamic recovery of copper was reduced. With this method, drawn pure copper wire achieved a strength level of 580 MPa and a conductivity of more than 96% IACS at room temperature. This strength level is about 45% higher than that obtainable by an equivalent room temperature deformation of copper. The material had a strength level of 680 MPa at 77 K and the resistivity ratio was larger than six. The interesting new basic science concerns the understanding of both strain hardening at low temperature, the attainment of high strength due to the stable accumulation of very high densities of dislocations, the change of the work hardening rate induced by cryogenic deformation, and the texture development in cryogenic deformation. In addition, the methodology has the potential to link the development of new approaches to materials selection and production to specific design needs in a variety of magnets. The potential of cryogenic deformation for the development of high strength conductors of pure copper is discussed in this paper.