Corrosion resistance of tungsten carbide-based cermet coatings formed by sinter-brazing

WC-Ni composite coatings were prepared by on the mild steel substrates by high-temperature sinter-brazing. The microstructure of the brazing coatings was characterised by the scanning electron microscopy (SEM). The chemical composition was determined by energy dispersive X-ray (EDX). The corrosion behaviours were investigated by using electrochemical impedance spectroscopy and potentiodynamic polarisation curves in 0.5M HCl solution. It shows that the brazed WC/Ni coatings have good corrosion-resistance property in acidic chloride media. The anodic polarisation process reflects mainly the behaviour of Ni binder. The general corrosion degradation of the brazed WC/Ni coatings presents a preferential dissolution of Ni binder. The insoluble oxidation products deposit on the WC/Ni coatings surface. This leads to a pesuo-passivity property and reduces the dissolution rate of the brazed WC/Ni coatings.