Effects of Cr Concentration on the Morphology and Corrosion Resistance of Ni-Cr Coatings Prepared by the Electrodeposition Process on 25CrMo4 Steel

In the current study, Ni-Cr coatings with a various Cr concentrations from 0.1% Cr (up to 0.4 % Cr) were performed on the 25CrMo4 low steel, using the electrodeposition process. The deposition of the Ni-Cr coatings was carried out at temperature of 30°C , direct current density of 2 A/dm2 for 40 min , and a bath containing a Cr2(SO4)3 as source of chromium ions , Cr+. However, the effects of the Cr concentration on the morphology and the quality of the film were investigated. SEM, EDS and XRD analysis were used in order to characterize the Ni-Cr coatings. The SEM morphology analysis exhibited that the Ni-Cr with 0.2% Cr showed the lowest network of cracks and porosity with uniform and compact structure. The corrosion resistance of the Ni-Cr coatings has been investigated in 3.5 wt-% NaCl aqueous solution, using polarization curves and electrochemical impedance spectroscopy. According to the results, it was found that the variation of Cr content in the Ni-Cr coatings greatly affected the microstructure and the corrosion resistance of the coatings. Moreover, the coating developed with 0.2 % of chromium (Cr) can give excellent results as to quality , morphology and corrosion resistance in 3.5 wt-% NaCl environment.