Ni-WC-TiO2 Nanocomposite Coating on Steel Substrate by Reverse Pulse Plating Method and its Comparison with Pulse Plating

In this study, Ni-WC-TiO2 coating was produced by pulsed current (PC) on St-37 samples (1-5) and by pulsed reverse current (PRC) on samples (6-9). In order to investigate the morphology of the coatings, field emission scanning microscopic (FE-SEM) images were used. The coating resulting from the pulsed reverse current has more uniformity and fineness than the pulsed current. The EDS results showed that Carbon, tungsten, titanium, oxygen and nickel elements were formed on the surface in both plating currents. The anti-corrosion performance of the coatings was investigated through EIS and polarization tests. The analysis of the results of these tests showed the improvement of the anti-corrosion performance of PRC samples compared to PC samples. The results indicated that the presence of WC and TiO2 nanoparticles decreased the Rct (charge transfer resistance) of sample 6, Rct=99.77 (ohm.cm2 ) compared to other samples, this sample also has the lowest Rp (polarization resistance) , Rp=233.57 (ohm.cm2 ) and the highest icorr (corrosion current) is icorr=3.46E-5 (μA/cm2 ) compared to other tested samples. Decreasing the current density from 0.4 to 0.3 amps caused the non-uniform distribution of nanoparticles and the crystal size in this coating and finally increased the corrosion current density in the sample. According to the results, it was observed that sample 9 (pulse reverse current coating) has better anti-corrosion performance than other samples, RP=4933.1 (ohm.cm2 ). Vickers hardness test was used to check the mechanical properties of the coatings and the results indicated that the hardness of the samples in the PRC plating current is higher than that of the PC plating current.