Corrosion resistance of WC–Co and WC–Ni type sintered carbides in acetic acid water solution

Corrosion resistance of sintered WC carbides products is an important factor determining their service properties. As an alternative to cobalt binders mainly nickel based matrices are introduced to increase corrosion resistance. To assess the effect of the metallic binder and carbide grain size on electrochemical corrosion susceptibility two grades with conventional cobalt matrices and two sinters with nickel were investigated. The gravimetric (weight) as well as electrochemical (potentiodynamic, potentiostatic, and galvanostatic) measurements in a 10% water solution of acetic acid were performed. The cobalt samples were characterized by lower corrosion resistance in comparison with the nickel containing grades. In most cases the investigated samples revealed a tendency to self-passivation, the phenomena being more intense in the nickel sinters. Both electrochemical and gravimetric measurements showed that the increased fraction of the metallic phase and microstructural inhomogeneity lowered the corrosion resistance. The variation in grain size in <1 μm ÷ 3 μm interval did not significantly affect the corrosion intensity.