Fabrication and Vickers Hardness of Electrodeposited Ni-Cu Alloy with Composition Gradient

A Ni-Cu alloy film with high composition gradient was fabricated by electrodeposition technique. Because the chemical composition of the electrodeposit depends on the applied electrochemical potential in solution containing nickel and copper ions, we could grow the gradient composition Ni-Cu alloy film by applying a continuously variable potential wave. To obtain a relatively thick film on a substrate, the Ni-Cu layers with high positive and negative gradients were stacked alternately during the electrodeposition. In X ray diffraction analyses, the gradient composition film exhibited a very broad peak lying between Ni and Cu peaks, although two diffraction peaks appeared in an electrodeposited Ni/Cu multilayer fabricated using a rectangular potential wave. This broad X ray peak was consistent with the gradient composition. Vickers hardness of the gradient composition film was higher than that of the Ni/Cu multilayer with 100 nm layer thickness, by a factor of 1.8. The strength increment in the gradient composition film could be explained by high density misfit dislocations which uniformly distributed in the film.