The characteristics of nickel film produced by supercritical carbon dioxide electroplating with ultrasonic agitation

This study uses a novel fabrication method of thin metal coatings by Ni electroplating combining ultrasonic agitation with supercritical CO2 (US-SC-CO2) mixed into conventional electrolyte. Coatings were also produced by the conventional and regular SC-CO2 electroplating methods for comparison. The characteristics obtained from the three fabrication methods such as surface morphology, hardness, roughness; crystallographic orientation, grain size; wear and corrosion resistance were all individually analyzed. Results show that plating quality achieved by US-SC-CO2 method is superior to that of regular SC-CO2 and conventional methods. With US-SC-CO2 process we achieved smoother and more compact surface morphologies, smaller grain size, lower surface roughness and higher microhardness, which also suggests good wear resistance. From XRD analysis we observed changes in preferred orientation due to application of the various methods. From the results of US-SC-CO2 electroplating and the operating mechanism of ultrasonic agitation we can confirm that this new type of ultrasonic agitation can indeed replace the role of surfactants to enhance coating aspect and properties, reducing their influence over the deposited metal coating, associated costs, and waste. In H2SO4 solution, the nickel coating fabricated by US-SC-CO2 method displayed the best polarization resistance among the three processes. More detailed experimental results and in depth discussion are presented in this paper.