The influence of B4C and SiC additions on the morphological, physical, chemical and corrosion properties of Ni coatings

Microhardness, internal stresses, Scanning Electron Microscopy (SEM) and Electrochemical Impedance Spectroscopy (EIS) measurements were used to compare nickel matrix composite coatings - Ni-B4C and Ni-SiC - with a pure nickel coating. The influence of incorporated carbides on Ni electro-co-deposition, the surface morphology, physical and chemical strength and corrosion ability of Ni coatings has been studied. Ni coating properties differ from those of Ni-Sic and even more from Ni-B4C properties. Their microhardness is lower than that of Ni-SiC coatings but their corrosion resistance is twice higher than that of Ni-B4C coating. The correlation between physical properties of the surface of incorporated carbides and coating surface properties exists: due to the conductive B,C the activity of the surface increased and its stability decreased. As a result. the corrosion resistance ability of hydrophobic metallic Ni surface decreases, hard and corrosion resistant compact matrix is formed with nonconductive SiC particles. High temperature does not change the integrity of Ni composites. (C) 2002 Elsevier Science B.V. All rights reserved.