Preparation and characterisation of electrodeposited Ni-Cr/Al2O3 nanocomposite coatings from a trivalent chromium-based bath

Ni-Cr/Al2O3 composite coatings were co-deposited on mild steel substrates by co-electrodeposition of Ni-Cr alloys and Al2O3 nanopowders from a trivalent chromium plating bath. Variations of Cr and Al2O3 nanoparticles in nanocomposite coatings as a function of Al2O3 concentration in electrolyte, cathode current density, stirring rate and temperature of plating bath was investigated. It was found that these parameters strongly affect the weight percentage of Cr and Al2O3 nanoparticles in the coatings. Microstructural characterisation of the coatings was performed by x-ray diffraction (XRD), scanning electron microscopy and energy-dispersive x-ray analysis (EDX). The corrosion behaviour of the nanocomposite coatings was evaluated by charting the Tafel curves of the solution of H2SO4 (5%) at room temperature. The results showed that the amount of Al2O3 nanoparticles in the coating increases with increasing Al2O3 concentration in electrolyte. This also enhances the co-deposition of Ni and Cr. It was also found that the presence of Al2O3 nanoparticles leads to an increase in hardness and corrosion resistance of the coatings. The distribution of Al2O3 nano-particles across the coatings was uniform even in those cases which resulted from baths of higher concentrations of Al2O3.