Electrofabrication of Composition Modulated Multilayer Alloy (CMMA) of Co-Ni for Better Corrosion Protection

Electrofabrication of multilayer Co-Ni alloy coatings were accomplished successfully on mild steel (MS) for better corrosion protection. Multilayer comprised of alternatively formed ‘nano-size’ layers of Co-Ni alloy of different composition have been produced from single electrolyte having Co+2 and Ni+2 ions using modulated (i.e. periodic pulse control) current density. The deposition conditions were optimized for both composition and thickness of individual layers for best performance against corrosion. The process and product of depositions were analyzed using cyclic voltammetry and SEM, PXRD, Hardness Tester, electrochemical AC and DC methods, respectively. The corrosion behavior of multilayer coatings was found to be improved drastically when the thickness of individual layer approached nano regime. The coating having 300 layers, deposited at cyclic cathodic current densities of 2.0 and 4.0 Adm-2 was found to show the least corrosion rate (CR = 0.02 mmpy) compared to monolayer (Co-Ni)4 alloy coating (CR = 2.8 mmpy) deposited from the same bath for same deposition time. Drastic improvement in the corrosion performance of multilayer coatings were explained in the light of changed kinetics of mass transfer at cathode and increased surface area due to layering, respectively.