Corrosion behaviour of WC-Co based hardmetal in neutral chloride and acid sulphate media

A comparative study of the corrosion behaviour of WC-Co based hardmetals with Ni and Cr3C2 additions is carried out. The aggressive environments are neutral and acidic aerated aqueous solutions of NaCl and H2SO4. This study is based on electrochemical (linear sweep voltammery), compositional (surface EDX analyses, AAS analyses of attack solutions), structural (XRD) and morphological (SEM) investigations. Electrochemical figures of merit were computed from linear sweep voltammograms in order to rank the corrosion behaviour close to free-immersion conditions in the studied environments and with presence of oxidising agents. EDX and XRD analyses allow to accurately characterise the penetration depth of the attack as well as the preferential dissolution of the constituents. Binders containing Ni show a significantly improved corrosion resistance in the studied systems. The amount of Ni in the binder is the single most important factor affecting corrosion performance. Cr3C2 additions to hardmetals with lower-Ni binders cannot balance the effect of Ni, but give an improved resistance in neutral chloride-containing solutions.