Effect of NiO-NiCr2O4 nano-oxides on the microstructural, mechanical and corrosion properties of Ni-coated carbon steel

Pure Ni and its composites with different percentages of Ni-Cr nano-oxides were coated over carbon steel to assess the coating features and mechanical and corrosion behavior. A nano-oxide composite of Ni-Cr was first synthesized through chemical coprecipitation with uniform distribution constituents. Electrodeposition was employed to coat pure Ni and Ni-(Ni-Cr) oxides (10, 20, 30, 40, and 50 g/L) on the steel sheets. Transmission electron microscope and field emission scanning electron microscope were adopted to examine the microstructure of powders and coatings, and X-ray diffraction analysis was employed to study the chemical composition. The microhardness, thickness, and wear resistance of the coatings were assessed, polarization and electrochemical impedance spectroscopy (EIS) tests were conducted to analyze the corrosion behavior, and the corresponding equivalent circuit was developed. Results showed flawless and crack-free coatings for all samples and uniform distribution of nano-oxides in the Ni matrix for the samples of 10-30 g/L. Agglomerated oxides were detected at high concentrations. Maximum microhardness (HV 661), thickness (116 mu m), and wear resistance of coatings were found at 30 g/L. A three-loop equivalent circuit corresponded satisfactorily to all EIS data. The corrosion resistance increased with the nano-oxide concentration of up to 30 g/L but decreased at 40 g/L. The sample of 50 g/L showed the best corrosion resistance.