Abstract
Nanosized silicon nitride (Si3N4) particles reinforced Nickel-tungsten composite coatings were deposited on the surface of C45 steel sheet by pulse electrodeposition. The effect of duty cycle, frequency, current pattern and presence of Si3N4 nanoparticles on microstructure, phases and corrosion resistance and mechanical properties of the coatings were investigated. The Si3N4 phase was incorporated into Ni-W alloy matrix uniformly and the inclusion content of in the coating was analyzed by energy dispersive x-ray spectrometer (EDS). The structure, microhardness and surface roughness of the coatings was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers micro-indenter and atomic force microscopy (AFM). The corrosion protection of steel by the coatings was evaluated by weight loss and electrochemical impedance spectroscopy (EIS). Corrosion rates of the coatings were determined using the Tafel polarization test. The results indicated that the duty cycle of 60%, pulse frequency of 1000Hz, average current density of 5A/dm−2, and Si3N4 nanoparticles concentration of 30g/L were the optimal plating conditions. The amount of Si3N4 particles incorporated into the coating that were produced under the optimum plating conditions was 2.1wt%, and the microhardness was 1031Hv as well as the crystallite size of this coating was 27nm.
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