Corrosion- and wear-resistant properties of Ni-Al2O3 composite coatings containing various forms of alumina

This article describes the effect of the addition of different phases of alumina particles on the properties of electrodeposited Ni-Al2O3 composite coatings. The corrosion- and wear-resistant properties of Ni-Al2O3 composite coatings electrodeposited from a nickel sulfamate bath containing (i) alpha-alumina particles (Ni-Al2O3-1), (ii) gamma-alumina particles (Ni-Al2O3-2), and (iii) mixture of alpha, gamma, and delta alumina particles (Ni-Al2O3-3) have been studied. The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies showed superior corrosion resistance of Ni-Al2O3-2 composite coatings compared with other two coatings. The SEM images and EDAX spectra also corroborated well with the observed corrosion results. The pin-on-disk wear studies showed improved wear resistance of Ni-Al2O3-1 composite coating containing alpha alumina compared with other two coatings. The transfer of material from the pin onto the disk was evident from the optical microscopy images of the wear tracks and Raman spectra of the wear track. This study shows that the addition of pure gamma-alumina particles enhances the corrosion resistance, and that pure alpha-alumina particles enhance the wear resistance of Ni composite coatings to a greater extent.