Corrosion Behavior of Tungsten Carbide-Nickel Weld-Overlay

摘要

Plasma transfer arc welding (PTAW) is a cermet deposition method that may produce thick coating (up to 3 mm). Cermet deposit by this method has shown high wear and corrosion resistance. The tungsten carbide (WC) content used is 65 wt% to evaluate its morphology, chemical composition and corrosion behavior of the coating. Two techniques have been used to characterise the powders and coatings which are scanning electron microscopy (SEM) and X-ray diffraction (XRD). The potentiodynamic polarization with three electrodes was used to evaluate the corrosion behaviour of the weld-overlay. It is found that, XRD spectrum shows two type of tungsten carbide which are WC and W2C, nickel (Ni) and nickel boride (Ni_3B). The corrosion for cermet coating is due to removal of binder follow by carbide detachment. Removal of binder in acidic electrolyte is thicker (44±6μm) than in alkaline electrolyte (25± 2μm). Although the corrosion current in acidic electrolyte is more positive compares to in alkaline electrolyte, the removal of the binder in acidic electrolyte is higher due to less noble of nickel in the acidic than in alkaline electrolyte. In alkaline electrolyte, W is less noble, but due to large carbide size, the carbide is hard to removed.