The effect of chemical composition and current density on the properties of the pulse plated Ni-W coatings

In the last years, Ni-W coatings attracted a lot of attention because of high hardness and excellent corrosion resistance. At the current study, Ni-W coatings with different amounts of tungstate ion concentration and with the current density of 10-70 mA/cm2 were plated by pulse method on the copper substrates. The morphology and chemical composition of coatings were characterized by Scanning Electron Microscopy (SEM) and, Energy Dispersive X-Ray Analysis (EDS). Grain size calculations was conducted by means of X-ray diffraction (XRD). The hardness of coatings was analyzed by Vicker’s micro hardness tester. Tafel Polarization and electrochemical Impedance methods were used to evaluate the corrosion resistance behavior of the coatings in M3.5% NaCl solution. The results displayed that coatings were obtained from the bath with 60 g/l tungstate concentration, current density of 70 mA/cm2 and duty cycle of 20% showed highest microhardness (719 HV) and maximum corrosion resistance (7.39 KΩ.cm2). Also with decreasing the current density from 70 to 10 mA/cm2, microhardness decreased to (570 HV) and the corrosion resistance declined to 2.78 KΩ.cm2.