Effect of Electrodeposition Current and Pulse Parameter on Surface Mechanical and Electrochemical Behavior of Ni–W Alloy Coatings

Abstract

Ni–W alloy coatings have various applications because they are capable of replacing hard chromium coatings due to their corrosion, oxidation, wear, and hardness properties. Moreover, these alloys demonstrate excellent mechanical and thermal stability at high temperatures leading to possible specialized applications of such coatings. In this study, the effect of pulse frequency and current density on the structure and properties of electrodeposited Ni–W coating were investigated. Pulse electro-co-deposition technique was employed to synthesize Ni–W alloy coatings by varying pulse frequency and current density. The deposition process was performed in the newly established deposition bath that does not contain surfactants and stress-relieving agents. The Ni–W-coated samples were evaluated to determine surface mechanical (microhardness and wear) and electrochemical properties. Phase formation, microstructure, and compositional analysis of Ni–W alloy coatings were examined by XRD, SEM, and EDS, respectively. Microstructure examination revealed that morphology of the coating varied with pulsed frequency and current density. An increase in the current density at fixed pulse frequency improved the surface mechanical properties (hardness and wear properties) owing to higher W content, fine, and dense structure of the coating. The maximum hardness (920 HV) and wear resistance were observed in the Ni–W coating that was obtained at the current density of 60 mA cm−2 and frequency of 2 kHz. Electrochemical polarization test and EIS study carried out in 3.5 wt pct NaCl solution reveal that a decrease in corrosion resistance of the coating is due to finer morphology or strained matrix whereas higher W content improves the corrosion resistance.