Effect of WC on electrodeposition and corrosion behaviour of chromium coatings

To study the effect of WC particles on corrosion behaviour of chromium coating steel samples were plated in Cr(VI) baths with various concentrations of WC. XPS, EPM and XRD were used to study the chemical composition, morphology and texture of the coatings. The corrosion behaviour was studied at different exposure times in solution containing 0.01 mol L-1 H 2SO4 + 0.5 mol L-1 Na2SO4 using cyclic voltammetry and impedance spectroscopy. Cyclic polarization measurements suggest that WC particles slow down the processes of passive film dissolution and penetration of aggressive ions to the substrate. Electrochemical impedance spectroscopy (EIS) was used to reveal the details of the corrosion process at the solution/electrode interface. The simulation of EIS data with a proposed equivalent circuit model made it possible to obtain quantitative valuation of the Y0 (Qc), Y0 (Q5) and Rpore parameters, reflecting corrosion behaviour of samples at the solution/electrode interface. Samples plated in a Cr(VI) bath with WC provided better resistance to corrosion than those plated in a bath without WC. Analysis of the data obtained suggests that WC particles enhance corrosion resistance due to the microstructural features of the coatings.