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

Authors: R.A. Khosroshahi; M.R. Kiyan Manesh; N. Parvini

Addresses: Department of Materials Engineering, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Iran. ' Department of Materials Engineering, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Iran. ' Department of Materials Engineering, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Iran

Abstract: 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.

Keywords: electrodeposition; trivalent chromium bath; nanocomposites; nanotechnology; nanocomposite coatings; mild steel substrates; nickel alloys; chromium alloys; aluminum oxide; nanoparticles; hardness; corrosion resistance.

DOI: 10.1504/IJSURFSE.2012.046845

International Journal of Surface Science and Engineering, 2012 Vol.6 No.1/2, pp.92 - 100

Published online: 20 Aug 2014 *

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