Magnetoelectrodeposition of Ni-Mo-Cd alloy coating for improved corrosion resistance

Abstract

The attractiveness of electroplating in the production of high performance coatings is linked to large selection of operating variables coupled with diffusion controlled mass transport process at cathode-solution interface, and this allows tailoring of different properties of the coatings. In this direction, the present communication reports the effect of magnetic field ( B) on electrodeposition of Ni-Mo-Cd alloy coatings and their corrosion performances. Magnetoelectrodeposited (MED) coatings developed under different conditions of superimposed magnetic field ( B ), in both direction and intensity were found to exhibit far less corrosion rates (CR's), compared to conventionally electrodeposited (ED) coatings. Experimental results demonstrated that CR's MED coatings decreased with intensity of B only up to 0.3T (optimal intensity), and then started increasing. Better corrosion protection efficacy of MED coatings were explained on the basis of increased noble metal (Ni) content of the deposit, affected due to the combined effect of natural convection and Lorentz force. The effect of B on the surface morphology, composition, and phase structure, responsible for better corrosion resistance of MED coatings were discussed in the light of diffusion controlled mass transfer of Ni +2 ions, affected due to magnetohydrodynamic (MHD) effect. The constancy of diffraction peaks of ED and MED Ni-Mo-Cd coatings of all configurations indicated that crystallinity of the coating is controlled by induced B at given c.d. The effect of B on surface morphology, composition, phase structure and corrosion performance of MED coatings were analysed, using X-ray diffraction (XRD),energy-dispersive X-ray (EDX), and scanning electron microscopy (SEM) and electrochemical analyses, and results are discussed Diagrammatic representation showing the increase of limiting current density (iL) of Ni due to change of electrodeposition from: a) natural convection to b) combined effects of natural convection and MHD resulting in drastic decrease of EDL thickness (δ). Below are the surface morphology of Ni-Mo-Cd alloy coatings developed by electrodeposition (ED) and magneto-electrodeposition (MED) methods