Comparative study of microstructure and corrosion properties in 3·5% NaCl solution of electrodeposited nickel obtained from various baths

A comparison was made between the electrochemical corrosion behaviour of electrodeposits prepared from sulphate, sulphamate and Watt's bath on mild steel substrate. Potentiodynamic polarisation tests, electrochemical impedance spectroscopy (EIS), SEM and XRD were the techniques used to characterise the corrosion behaviour. The potentiodynamic studies revealed the current density versus potential for the coated and uncoated substrates and the difference in their corrosion potentials E_corr. In all cases, the E_corr shifted to a more positive potential after the coatings were applied. The EIS measurements as a function of immersion time were carried out in a 3·5% NaCl solution at the E_corr. The corrosion parameters, such as lower corrosion current density I_corr and higher polarisation resistance R_p, were found in coating from sulphamate bath.