Effects of Pulse-Reverse Currents on Nickel Deposited from Sulphamate Solutions

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Electroplating is widely used in many fields for decorative and engineering purposes. Nickel is mostly used for engineering applications beacause of its enchanced mechanical properties such as low internal stress and high corrosion and erosion resistance. It was reported that the use of pulse or pulse reverse currents instead of direct current produced homogenous deposits of better surface finish [1,2]. Nickel sulphamate bath was used in this study to attain better mechanical properties, lower internal stresses and good surface quality. The effects of pulse reverse current (PRC) method on the hardness, microstructure and roughness of the deposits were investigated and compared with direct current (DC) plating. In PRC electroplating, current value is alternated between anodic and cathodic currents to provide higher ion concentrations near electrodes compared to DC plating. In this way, the increased nucleation rate and the number of grains per unit area leads to a decrease in grain size [1]. In addition, the homogenity of the deposits can be improved and the growth of the planes can be controlled by the use of PRC coating [3]. In the design of experiments, special emphasis was given to the ratio of the anodic and cathodic current densities. Scanning electron microscopy (SEM) analyses, roughness measurements and vickers hardness tests were used to characterize the deposits. The results of selected DC and PRC deposits can be seen in Figure 1.