The corrosion resistance of WC-Ni-Cr3C2 cemented carbides in acidic and neutral solutions had been shown to be improved at low carbon and high Cr3C2 content. Some remarkable peaks were observed in the polarization curves as the active dissolution, the passivation and over passivation regions, but they were not clear on what of the reactions cause.
In this report, WC-Ni-Cr3C2 cemented carbides were polarized and maintained at each potential in 3%NaCl + 0.1N H2S04 solution, and the partial polarization curves of W, Ni and Cr were calculated from the dissolved amounts of metallic elements in the test solution. The first peak in the vicinity of E ?? is due to the dissolution of Ni and Cr as binder metal. W starts to dissolve and an oxide or hydroxide film is formed as passivation film in this region. The reaction in the over passivation region is the dissolution of Ni, Cr, and W with the destruction and the disappearance of the passive film. The passivation film formed on low carbon content alloy has an excellent corrosion resistance at higher content of solid solution of W and Cr in the binder Ni phase.