Electrochemical corrosion behaviour of nickel chromium-chromium carbide coating by HVOF process

摘要

To overcome the corrosion problem in marine industry, coatings are one of the most economical solutions. In this paper, the corrosion behaviour of 25(NiCr)-75Cr_3C_2 cermet coating on low carbon steel substrate by HVOF process is studied. Different phases such as Cr_7C_3 and Cr_3C_2, along with Ni and chromium oxide(Cr_3O_2) constituents present in the coating were revealed by X-Ray Diffraction (XRD) analysis. The morphology of the coating obtained by scanning electron microscope (SEM) gave confirmation for the XRD analysis. Electrochemical corrosion techniques such as Linear Polarization Resistance (LPR) and Electrochemical Impedance Spectroscopy (EIS) were used to study the corrosion behaviour of the cermet in 3.5wt% NaCl electrolyte solution. The corrosion current density of the coated sample and substrate were found to be 6.878μA/cm~(-2) and 21.091μA/cm~(-2) respectively. The Nyquist Impedance spectra were used to derive an equivalent circuit to analyze the interaction between the coating and electrolyte. The Bode Impedance plots obtained by EIS for the coating showed a typical passive material capacitive behaviour, indicated by medium to low frequency with phase angle approaching -60°, suggesting that a stable film is formed on the tested material in the electrolyte used.