Anomalous codeposition of NiCo alloy coatings and their corrosion behaviour

Abstract

Here, we report the electrodeposition NiCo alloy coatings from a new bath using the glycine, as additive. A bright and uniform coatings NiCo alloy have been developed at different current densities and their corrosion performances have been evaluated. The surface morphology, composition and phase structure of alloy coatings have been analyzed using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray diffraction (XRD) techniques, respectively. The compositional information of NiCo alloy coatings revealed that the proposed bath follows anomalous type of codeposition over range of current density studied (1.0–4.0 A dm−2), by demonstrating more Wt. % of Co in the deposits, than in the bath. A constant increase in the Wt. % of Ni with current density was found, supported by XRD analyses; and it may be attributed to the depletion of more readily depositable Co+2 ions at cathode film by following the principle of codeposition of NiCo alloy. The corrosion study revealed that NiCo alloy deposited at 4.0 A dm−2, represented as (NiCo) 4.0 A dm-2 coating is the most corrosion resistant compared to all other coatings. The highest corrosion stability of (NiCo) 4.0 A dm-2 alloy attributed to its highest Ni content (38.6 wt%) and increased surface smoothness, supported by EDS and SEM study.