The matrix corrosion of tungsten carbide/carbon steel metal matrix composites

Metal matrix composites (MMCs) have been prepared by melting in an argon arc two high carbon tool steels in the presence of particles of fused tungsten carbide. The microstructures were examined using scanning electron microscopy (SEM) and energy dispersive analysis (EDA). The corrosion characteristics were ascertained in both acidic and alkaline environments by potentiodynamic polarisation. SEM showed that the tungsten carbide collects mainly along the grain boundaries where it appears as dendritic-like deposits. The tungsten is present as iron tungsten carbide, Fe 3W 3C. The polarisation studies, in conjunction with SEM, showed that in acid environments the MMC is susceptible to general corrosion along the grain boundaries. However, in aerated alkaline corrodents containing aggressive chloride ions, spontaneous passivation will occur followed by pitting corrosion of the iron-rich grains.