Investigation of Dual-phase Nanocrystalline Ni-Cu Electrodeposits

Ni-Cu alloys are employed on a large scale in the marine industry due to their excellent corrosion resistance in natural sea water. In an effort to enhance the erosion resistance of these alloys as well, nanocrystalline Ni-Cu specimens were synthesized by electrodeposition. However, surface and bulk characterization revealed an unexpected macrostructure that displayed separate Ni- and Cu-rich phases. Detailed characterization showed significant differences between the two phases in terms of chemical composition, grain size distribution, and localization of bulk defects. Furthermore, inhomogeneity of this electrodeposit in terms of hardness was found as well, hindering the application of such electrodeposits in industry. The formation of this macrostructure was investigated through assessing key characterization results, and a formation mechanism is postulated which is related to the diffusion-controlled deposition of uncomplexed Cu species, due to inadequate stability of complexing agents in the electrolyte. Some steps to eliminate this undesirable macrostructure are proposed.M.A.S