Electrochemical Corrosion Behavior of Near-Nano and Nanostructured WC-Co Cemented Carbides

Abstract

In this paper, the electrochemical corrosion resistance of near-nano and nanostructured WC-Co cemented carbides was investigated. WC powders with an average grain size dBET in the range from 95 nm to 150 nm and with an addition of vanadium carbide (VC) and chromium carbide Cr3C2 as grain growth inhibitors were used as starting powders. The mixtures with 6 wt. % and 9 wt. % Co were consolidated by two different processes; sintering in hydrogen atmosphere and the sinter-HIP process. WC-Co samples were researched by direct current and alternating current techniques in the solution of 3.5% NaCl at room temperature. Corrosion parameters such as corrosion potential (Ecorr), corrosion current density (jcorr) and polarization resistance (Rp) were determined by electrochemical techniques. From the conducted research, it was found that the consolidation processes and microstructural characteristics—grain growth inhibitors, grain size of the starting WC powders and η-phase—influenced the electrochemical corrosion resistance. η-phase enhanced the formation of a passive layer on the samples’ surfaces, thereby reducing the tendency of the sample dissolution and increasing the stability of oxides forming therewith a passive layer on the sample surface.

Keywords

• near-nano and nanostructured cemented carbides
• corrosion potential
• corrosion current density
• polarization resistance
• grain growth inhibitors
• η-phase
• WC grain size