HVOF spray of Cr3C2–NiCr coating for enhancing the corrosion resistance of nickel aluminium bronze in 3.5% NaCI solution with different sulphide concentrations

Abstract

In this study, the corrosion resistances of the HVOF sprayed Cr3C2–NiCr coating and nickel aluminium bronze (NAB) were tested in 3.5 wt.% NaCl solution with different Na2S concentrations, which included 0, 20, 100 and 200 ppm. Their corrosion behaviors were investigated by potentiodynamic polarization, cyclic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and constant potential polarization. The obtained data was used to analyze the effect of sulphide on corrosion mechanisms of the Cr3C2–NiCr coating. The potentiodynamic polarization outcome showed that the corrosion resistances of the Cr3C2–NiCr coating and NAB in the NaCl solution without sulphide were close to each other. However, the Cr3C2–NiCr coating exhibited more stable corrosion resistance in the NaCl solution containing sulphide than the NAB, which is attributed to the formation of passive film as confirmed by the cyclic polarization and EIS tests. The corrosion mechanism of the Cr3C2–NiCr coating and NAB showed different evolution with increasing sulphide in corrosion solution. Even if the NAB exhibited more stable current density than the Cr3C2–NiCr coating during constant potential polarization, the corrosion resistance of the NAB was inferior to that of the Cr3C2–NiCr coating.