Electrochemical deposition and characterisation of NiTi alloy coatings for better corrosion protection

The present study reports the electrochemical deposition and characterisation of Nickel-Titanium (NiTi) alloy coatings on mild steel (MS) from citrate bath having nickel sulphate and titanium oxysulphate as salts, tri-sodium citrate as complexing agent and glycerol as the brightener. Bath composition and operating variables were optimised by the conventional Hull cell method for bright and uniform coating. NiTi alloy coatings were developed at varied current densities (1.0 A/dm2 to 4.0 A/dm2), keeping pH = 4.0. The corrosion behaviours of NiTi alloy coatings were evaluated by electrochemical AC and DC methods in a 3.5 per cent sodium chloride solution. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) techniques were used to study the phase structure, surface morphology and chemical composition of the coatings, respectively. The observed facts stand to the reason that the bath follows induced type co-deposition in the range of current density studied. Corrosion studies validated that NiTi alloy coating deposited at 4.0 A/dm2 is the most corrosion-resistant among all other current densities. This highest corrosion stability of NiTi alloy, corresponding to 4.0 A/dm2 is attributed to high wt.% of Ti (i.e. 3.5%). The decrease in corrosion rate towards high current density was analysed and discussed.