Faculty Publications

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Electrodeposition of laminar coatings of Ni-W alloy and their corrosion behaviour
(Elsevier, 2015) Elias, L.; Hegde, A.
The attractiveness of electroplating for the synthesis of advanced materials is linked to large selection of plating conditions coupled with different mass transfer processes towards the cathode, and this allows the tailoring of different properties of many electrodeposited coatings. This theme has been exploited effectively in the development of a new class of coatings; called composition modulated multilayered (CMM), or in short laminar coatings. The work embodied in this paper is to demonstrate how the corrosion resistance of monolayer Ni-W alloys can be increased to many fold of its magnitude by multilayer deposition. Ni-W coatings have been deposited on mild steel (MS) in a laminar multilayer pattern from a citrate bath using single bath technique (SBT). Electrodeposits having alternate layers of alloys, having different compositions were developed by modulating the direct current (DC). CMM coating configurations have been optimized from a newly developed bath, in terms of current pulse height and thickness of each layer to maximize its corrosion protection ability, in relation to its monolayer coating, developed from same bath for same time. The process and product of the Ni-W coatings have been characterized using different instrumental methods, such as cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) study. The better corrosion resistance behaviour of CMM Ni-W coatings has been analysed in the light of increased surface areas of the coatings due to layering, and results are discussed. © 2015 Elsevier B.V.
Development of nanolaminated multilayer Ni-P alloy coatings for better corrosion protection
(Royal Society of Chemistry, 2016) Elias, L.; Bhat, K.U.; Hegde, A.
Nanolaminated multilayer Nickel-Phosphorous (Ni-P) alloy coatings were developed on mild steel from a citrate bath using glycerol as an additive. Multilayer Ni-P alloy coatings having nanolaminated layers of alloys of alternatively different compositions have been developed using pulsed direct current (DC) by cyclic modulation of the cathode current density. The composition and number (hence thickness) of the layers were tailored by periodic modulation of the current density (c.d.) and time using a programmable power source. The deposition conditions were optimized for both the composition and thickness of the individual layers for the best performance of the coatings against corrosion. Electrochemical corrosion study, evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) demonstrated that the multilayer Ni-P alloy coating with 300 nanolaminated layers, represented as (Ni-P)1.0/4.0/300 showed several fold better corrosion resistance compared to its monolayer counterpart (deposited using regular DC) from the same electrolytic bath. Drastic improvement in the corrosion protection efficacy of the nanolaminated multilayer Ni-P alloy coatings were attributed to an increase in number of interfaces, separating layers of alloys having different morphologies, compositions and phase structures, which was supported by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses, respectively. The corrosion rates of the multilayer Ni-P alloy coatings were decreased with increasing number of layers, only up to an optimal level and then increased. The increase in corrosion rates at a higher degree of layering were attributed to the diffusion of layers, due to the very short deposition time of each layer. © The Royal Society of Chemistry 2016.
Effect of magnetic field on corrosion protection efficacy of Ni-W alloy coatings
(Elsevier Ltd, 2017) Elias, L.; Hegde, A.C.
High corrosion resistant Ni-W alloy coatings were developed using magnetoelectrodeposition (MED) approach for the protection of mild steel substrates. The conditions for the development of more corrosion resistant MED Ni-W alloy coatings were optimized by inducing a magnetic field (B) during deposition, in terms of intensity and direction. The applied magnetic field was used as a tool to alter the crystallinity, composition and thereby the corrosion resistance of the coatings. It was demonstrated that the corrosion resistance of Ni-W alloy coatings can be improved to many folds of its magnitude by MED approach. Significant increase in corrosion resistance exhibited by MED coatings (under both parallel and perpendicular magnetic field, B) is attributed to the increased W content of the alloy affected by an increase in limiting current density (iL). The high corrosion resistance of the MED Ni-W alloy coatings was explained in the light of magnetohydrodynamic (MHD) effect, responsible for the increased W content, brought about by the enhanced mass transport. The inherent limitations of the bath like low iL and induced type of codeposition which impedes the development of W rich alloy coatings has been successfully resolved by MED method. Drastic improvement in corrosion resistance is ascribed to the basic difference in the process of electrocrystallization and phases formed during MED, confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) study. The results are discussed with greater insight into binary alloy deposition and mass transfer process at cathode/electrolyte interface. © 2017 Elsevier B.V.

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