126 Journal of New Materials for Electrochemical Systems Vol.25, No.2, April 2022, pp. 126-134 Journal homepage: http://iieta.org/journals/jnmes Pitting corrosion and mechanical properties of direct current and pulsed reverse current electrodeposited nickel-tungsten coatings M. Dadvand* and O. Savadogo Laboratory of New Materials for Electrochemistry and Energy Polytechnique Montréal, Montréal QC, H3T 1J4, Canada Corresponding Author Email: mina.dadvand@polymtl.ca, osavadogo@polymtl.ca https://doi.org/10.14447/jnmes.v25i2.a06 ABSTRACT Received: December 12-2021 Accepted: April 15-2022 The electrochemical corrosion and mechanical properties of direct current and pulsed reverse current electrodeposited nickel and nickel-tungsten were investigated by using cyclic polarization measurement and nano-indentation techniques. Direct and pulsed reverse current electrodeposited nickel-tungsten coatings revealed a significant higher resistance to pitting corrosion when compared to direct and pulsed reverse current deposited nickel. Furthermore, pulsed reverse current electrodeposited nickel-tungsten displayed the most noble corrosion potential and higher corrosion resistance compared to direct current electrodeposited nickel-tungsten. This was attributed to the more nano- crystalline structure of the pulsed-reverse current deposited coatings when compared to that of the direct current electrodeposited nickel-tungsten. The average modulus for both direct and pulsed reverse current deposited nickel-tungsten were found to be similar but the average hardness of direct current deposited nickel-tungsten was slightly higher than that of pulsed reverse current deposited nickel-tungsten. This was attributed to the higher tungsten content (35 wt.%) in the direct current deposited nickel-tungsten coating compared to that (25 wt.%) in the pulsed reverse current deposited nickel-tungsten and is supported by our energy dispersive X-ray spectroscopy results. Keywords: Nickel-tungsten coating, direct current, pulsed reverse current, electrodeposition, cyclic polarization. 1. INTRODUCTION Electrochemical deposition methods have been widely used to produce various coatings of nickel (Ni) alloys such as nickel-tungsten (NiW) in various engineering applications due to their simplicity and affordability [1]. In recent years, pulsed reverse current (PRC) electrodeposition method has gained considerable interest owing to its unique mechanical and corrosion properties. PRC technique has unique ability to produce coatings with greater uniformity, and finer grain size than the coatings obtained by using direct current (DC). It has been also reported that deposits with high tungsten content produced by means of PRC are superior with respect to being crack-free with lower defects compared to those produced by DC with the same tungsten content. Formation of residual tensile stress as a result of hydrogen evolution over the cathode was reported as the main cause for cracking of DC deposited NiW with high tungsten content, whereas in PRC technique, the reverse or anodic current consumes evolved hydrogen through its re-oxidation on the surface of cathode [1- 3]. In general, electrodeposited NiW coatings have demonstrated high hardness and high wear resistance. Therefore, improving their corrosion performance in various environments is in high interest. It is also imperative to investigate their corrosion behavior as well as corrosion mechanism and correlate them with their microstructures [1- 6]. There are a limited number of published articles about electrochemical investigation on corrosion behavior of electrodeposited NiW alloys [7–12] Majority of such studies are on investigation of general corrosion behavior of NiW alloys and their composites using potentiodynamic polarization technique in various corrosive environments and there is also not much information available regarding their pitting behavior [7-8, 13-17]. For example, Sriraman et al. [7] studied the influence of the tungsten content of the coatings on the corrosion resistance of the Ni-W and Ni-W-Fe alloys in 3.5 wt. % NaCl and sulfuric acid solution using polarization and electrochemical impedance spectroscopy techniques. They found that Ni-W with 7.54 at.%. tungsten and Ni-W-Fe with 9.20 at.% tungsten had the highest corrosion resistance. Yao et al. [13] investigated the general corrosion behavior of NiW-SiC composite by using anodic polarization and electrochemical impedance spectroscopy (EIS) techniques. They reported that the inclusion of SiC nano-particulates into the NiW alloy matrix increased the general corrosion resistance. The enhancement of corrosion resistance was explained by physical barrier behavior of the SiC particles to the corrosion process. Hosseini et al. [14] reported the corrosion characteristics of DC electrodeposited NiW-SiC composite coatings by using mass loss and electrochemical measurements, including open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization in a 3.5 wt. % NaCl solution. The results showed that the addition of SiC particle to the deposition bath of NiW significantly increased the corrosion resistance. To the best of our knowledge, no research has been reported to investigate the pitting corrosion behavior of pulsed reverse (PRC)