Induced codeposition of Ni-W alloy coatings using glycerol as additive and their characterization

Abstract

As a promising coating material to replace hard chromium coating, the development of nickel–tungsten (Ni-W) alloy coatings of good corrosion protection is of great interest in surface coating technology. Further, the effect of plating variables, including additive on the composition of alloys of induced co-deposition is more vagarious than in other types of alloy deposition. In this regard, an alkaline citrate bath has been formulated for electrodeposition of Ni-W alloy through conventional Hull cell method, using glycerol as additive. Electrodeposition following the induced type of codeposition of Ni–W alloy was carried out onto mild steel (MS) substrate at different current densities (c.d.’s) at room temperature, taking a basic bath. Influence of bath constituents and operating parameters on the appearance, hardness, thickness and composition of the deposits were studied as a measure of their performance against corrosion. Corrosion behaviours of Ni-W coatings, having hard-adherent mirror bright appearance were studied using Tafel’s polarization and electrochemical impedance spectroscopy (EIS) method in 5 wt. % NaCl solution. Experimental results revealed that corrosion protection efficacy of Ni-W coatings increased with deposition c.d., in proportion of its W content. The coating developed at 4.0 A dm-2 was found to exhibit the least corrosion rate (5.3 x 10-2 mm y-1), compared to those at other c.d.’s. The process and product of electrodeposition have been studied using different instrumental methods, such as Cyclic voltammetry (CV), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) study. Experimental observations were analyzed in the light of induced codeposition of Ni-W alloy due to stimulation by Ni+2 ions, and results are discussed.