Nanostructured copper matrix composite with extraordinary strength and high electrical conductivity produced by asymmetric cryorolling

Abstract

A novel method for fabricating nanostructured copper matrix composite with extraordinary strength and high electrical conductivity using casting, homogenization, and asymmetric cryorolling has been proposed. Microstructural observations were performed by optical microscopy (OM) and scanning electron microscopy (SEM) equipped by energy dispersive spectroscopy (EDS). A nanostructured (grain size < 100 nm) copper matrix composite due to the occurrence of discontinuous dynamic recrystallization (DDRX) and particle stimulated nucleation (PSN) mechanisms with a uniform dispersion of copper oxide particles achieved after 96% asymmetric cryorolling. The yield strength, ultimate tensile strength, and hardness of the 96% deformed copper matrix composite increased from 31.7 MPa, 206.2 MPa, and 29.4 HB (for the annealed sample) to 836.6 MPa, 841.7 MPa, and 103.4 HB, demonstrating 2539%, 308%, and 252% enhancement, respectively. The significant increase in strength and hardness was attributed to severe strain hardening, remarkable grain refinement, uniform dispersion of particles, and effective load transfer. At the same time, the improvement on yield and ultimate tensile strength did not cause serious deterioration in electrical conductivity so that the 96% deformed composite exhibited a high conductivity of 82.10% IACS (international annealed copper standard). Consequently, the copper matrix composite exhibited a good balance in strength and electrical conductivity. With increasing the thickness reduction, the number, and depth of dimples and the sharpness of tearing edges decreased and the failure mode changed from typical ductile fracture (for annealed, 30% and 60% rolled samples) to a combination of shear ductile and brittle fracture (for 90% and 96% deformed samples).