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This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License
Article
Author(s)
Oloyede Olamilekan Razaq1, Zhu Liu1 and Hong Liu2
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DOI:10.17265/2161-6221/2014.02.002
Affiliation(s)
1. Corrosion and Protection Centre, School of Materials, The University of Manchester, ManchesterM13 9PL, United Kingdom 2. School of Mechanical and Automobile Engineering, Shandong Polytechnic University, Ji’nan 250100, P.R. China
ABSTRACT
The emergence of electroless Ni-P based ternary coatings and consequence duplex deposition possibilities, now offer more excellent corrosion and functional properties in acidic and alkaline environment. In this study, medium and high phosphorus Ni-P and duplex Ni-W-P coatings were produced and sequentially deposited on mild steel using plating baths with 10 g/L and 25 g/L of sodium hypophosphite as reducing agent (RA) with composition of the resulting deposits to be 91.5 Ni: 8.5 P and 87.6 Ni: 12.4 P, respectively. From the field-emission scanning electron microscope (FE-SEM) examination, the deposit morphology was found to change from nodular with some surface porosity to become more dense and smoother after heating treatment between 200-600 °C. The cross-section reveals firm adhesion of the as-plated and the merging of the top duplex layers of the heat treated sample as a result of tungsten diffusion. The potentiodynamic polarization test shows that the coating demonstrated significant improvement of corrosion resistance in 3.5% NaCl solution with optimum performance at 600 °C. The noted improved corrosion resistance of the coating came as a result of annealing which strengthened the layer and broaden its application.
KEYWORDS
Electroless plating, Ni-W-P, duplex coating, heat treatment, corrosion, electrochemical potential.
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