Achieving exceptional tensile strength in electrodeposited copper through grain refinement and reinforcement effect by co-deposition of few layered graphene

Abstract

Grain refinement which improves the mechanical strength of copper (Cu) results in substantial loss of its electrical conductivity. We demonstrate that synergistic effects of grain refinement and reinforcement of few layered graphene (Gr) can result in exceptionally high strength Cu without much degradation of electrical conductivity. For this study, the Cu-Gr composite foils are fabricated by pulsed electrodeposition from an additive-free copper sulphate bath. An aqueous suspension of few layer graphene, synthesized using a novel airless high-pressure exfoliation technique, was used as a reinforcement to copper. Electrodeposited pure Cu showed a strong columnar microcrystalline grain structure, and its grain size decreased slightly along with significant changes in the preferred growth direction upon increasing the current density and accordingly, the tensile yield strength improved moderately. Graphene reinforcement in copper resulted in significant grain refinement to ∼750 nm, increased growth-twin density and shift in crystallographic growth direction, and a remarkable tensile yield strength of ∼800 MPa which is much higher than previously reported values. The electrical conductivity of Cu-Gr composites was greater than 90% IACS and is comparable to pure copper. Detailed microstructural investigation and analysis suggest that uniformly dispersed graphene layers in conjunction with the reinforcement-induced microstructural features in electrodeposited Cu could have contributed to the observed high strength and good electrical conductivity.