Ni–Fe–Al2O3 electrodeposited nanocomposite coating with functionally graded microstructure

In this study, a Ni–Fe–Al2O3 nanocomposite coating was deposited on the substrate of low-carbon steel by electrodeposition from a sulphate-based bath. The effects of frequency and duty cycle were investigated to produce the functionally graded (FG) coating. For this purpose, first, the coatings with duty cycle-decreased method (DDM) were deposited in eight steps from 88 to 11%. At the second step, frequency-increased method (FIM) was utilized from 50 to 6400 Hz during eight steps. Assessing of coatings was carried out by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), potentiodynamic test, Vickers microhardness test and wear test. Microstructure evaluations gained by SEM and EDS demonstrated that the continuous alterations of duty cycle contribute for manufacturing of FG coatings, so that the maximum particle fraction was in the free surface of the coating and its amount was gradually decreased to the interface. These investigations showed that FIM had no effect on production of graded structure. Corrosion and wear tests indicated high corrosion and wear resistance of DDM coatings in comparison to FIM coatings. Investigating the best coatings obtained from both above methods exhibited 50 and 20% reduction in corrosion current density and wear rate, respectively, for DDM specimen in comparison to FIM sample.