A bulk of uniform nanocrystalline copper with superior comprehensive mechanical properties electroformed in an ultra-low sulfate concentration bath without additives

Nanocrystalline copper has a high potential to meet high application requirement of a variety of new industries for its unique mechanical, physical and chemical properties. But its disappointingly low ductility limits its application. This paper provides a reliable and economical preparation method of nanocrystalline copper with superior comprehensive mechanical properties. In an ultra-low sulfate concentration bath (20 g/L) without additives, by strong electrolyte flushing and regulating cathodic working current density from 1 to 6 A/dm2, copper deposits with different nanostructure is electroformed because of high electrochemical polarization. The microstructure and mechanical properties of copper deposits are investigated. Except of the deposits of 6 A/dm2, the copper deposits exhibit good comprehensive mechanical properties in tensile tests at room temperature. In particular, a bulk of nanocrystalline copper obtained at 4 A/dm2, with uniform grains size (60-70 nm) and random grain orientation, exhibits superior comprehensive mechanical properties, with a high tensile strength of 526 MPa and a high elongation of 30%. The deformation mechanisms of copper deposits are discussed. Fracture observation indicates a feature of ductile fracture.