Corrosion Behavior of Plasma Transferred Arc Fe-based Coating Reinforced by Spherical Tungsten Carbide in Hydrochloric Acid Solutions

Fe-based coatings reinforced by spherical tungsten carbide were deposited on 304 stainless steel using plasma transferred arc (PTA) technology. The composition and phase microstructure of the coatings were evaluated using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The corrosion behaviors of the coatings in 0.5 mol/L HCl solution were studied using polarization curve and electrochemical impedance spectroscopy (EIS) measurements. The experimental results shows that the tungsten carbide improves the corrosion resistance of the Fe-based alloy coating, but increase in the mass fraction of tungsten carbide leads to increasing amount of defects of holes and cracks, which results in an adverse effect on the corrosion resistance. The defects are mainly present on the tungsten carbide but also extend to the Fe-based matrix. The tungsten carbide, acting as a cathode, and binding material of Fe-based alloy, acting as an anode, create a galvanic corrosion cell. The binding material is preferentially corroded and causes the degradation of the coating.