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.


    

Effect of magnetic field on current efficiency and crystal orientation of NiCo alloy using pulse electrodeposition technique

Fig. 1: Electrodeposition process setup

The electrodeposition of NiCo alloy has been investigated in presence of various magnetic fields. The influence of superimposed magnetic field (0-0.5T) parallel to the electrode surface on current efficiency, surface morphology, preferred crystal orientation and electrochemical activity of Ni-Co alloy were studied. The maximum current efficiency was obtained by direct current at 100mA/cm2 with 0.4T. The optimized current density (100mA/cm2) was pulsed at four different frequencies (10, 25, 50 and 100Hz) with the same magnetic field (0.4T). However, the superimposition of magnetic field significantly favors the preferred crystal orientation of (220) phase. Pulsed current deposits exhibit single orientation of (220) at lower magnetic field (0.4T) whereas direct current deposition require higher magnetic field (0.5T). Tafel plot shows that electro-catalytic activity and corrosion resistance property has improved when the deposit is having a preferred orientation of (220).