Effect of sulphide concentration on corrosion behaviors of HVOF-sprayed WC-Cr3C2-Ni and WC-Ni coatings

Abstract

In this study, the WC-Cr3C2-Ni and WC-Ni coatings were processed on steels with the HVOF spray, and their corrosion behaviors in 3.5 wt% NaCl solution with 0, 20, 100 and 200 ppm Na2S were investigated. The corrosion resistances of both coatings in experimental solutions were measured by electrochemical tests including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, cyclic polarization and constant potential polarization. The morphologies of feedstock powders and as-sprayed coatings were captured by scanning electron microscope (SEM), and the components of corrosion products of both coatings after constant potential polarization were identified by X-ray Photoelectron Spectroscopy (XPS). Experimental outcome presented that the passivation of both coatings influenced their corrosion resistances. The increase of sulphide concentration decreased the corrosion resistances of both coatings by influencing the integrity of passive films. The WC-Cr3C2-Ni coating exhibited more stable properties resist corrosion than the WC-Ni coating in all tested corrosion solutions, this is attributed to the passive films with stable structure and high tendency toward repassivation on the WC-Cr3C2-Ni coating.