Electrochemical corrosion behaviors of straight WC–Co alloys: Exclusive variation in grain sizes and aggressive media

Abstract

The electrochemical corrosion behaviors of straight WC–10Co cemented carbides with grain sizes of 1.2, 2.6, 6.1 and 8.2μm, were comparatively investigated in the solutions of NaOH (pH=13), Na2SO4 (pH=7) and H2SO4 (pH=1) respectively. To insure a sole variable of WC grain sizes, specific magnetic saturation values of the alloys are adjusted to be identical. The results show a good linear dependence for Rct (charge transfer resistance) and Icorr (corrosion current density) against the grain sizes. A high sensitivity of the grain sizes to both Rct and Icorr are identified in NaOH and H2SO4. In the solutions of NaOH and Na2SO4, the alloys with smaller WC grain sizes exhibit better corrosion resistances, while the alloys with larger WC grain sizes exhibit better corrosion resistances in H2SO4. Additionally, in terms of the corrosiveness, NaOH is the weakest and H2SO4 is the most aggressive for all the alloys. The corrosion mechanisms were discussed in light of the SEM surface observation, X-ray photoelectron spectroscope analysis and the electrical equivalent circuits for electrochemical impedance spectroscopy.