An investigation on corrosion resistance of as-applied and heat treated Ni-P/nanoSiC coatings

Abstract

EN-SiC coatings are recognized for their hardness and wear resistance. in this work electroless Ni-P coatings containing nano Sic particles were co-deposited on St37 tool steel substrate. Scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray diffraction (XRD), polarization and electrochemical impedance spectroscopy (EIS) were used to analyze morphology, structure and corrosion resistance of the coatings. The results showed that Sic nano-particles co-deposited homogeneously, and the structure of Ni-P-SiC nano-composite coatings as deposited was amorphous. Heat-treatment at 400 degrees C for 1 h induced crystallization of the electroless Ni-P coatings. Microhardness of electroless Ni-P-SiC composite coatings increased due to the existence of nano-particles, and reached to a maximum value after heat-treatment Corrosion tests showed that both electroless nickel and electroless nickel composite coatings demonstrated significant improvement of corrosion resistance in salty atmosphere. Proper post heat-treatment significantly improved the coating density and structure, giving rise to enhanced corrosion resistance. (C) 2009 Elsevier Ltd. All rights reserved.