Corrosion behaviour of WC-10% AISI 304 cemented carbides

Corrosion behavior of WC-Co coatings deposited by cold gas spray onto AA 7075-T6

“…8b), generating deep attack in these areas (Fig. 8c (B)), as observed previously [66]. A comparison of the cross-sectional SEM images at 20 μm from the top, for both coatings and at the end of the E OCP measurements (Fig.…”

“…The corrosion potential of the WC-12Co coating shifted to more positive values, with E corr = −0.33 V vs. Ag|AgCl|KCl 3mol/L and i corr = 1.2 μA cm −2 , while the corresponding values for the WC-25Co coating were -0.42 V vs. Ag|AgCl|KCl 3mol/L and 2.9 μA cm −2 . These values were slightly lower than the E corr values obtained for WC-Co with similar composition in aqueous solutions of 0.5 mol L −1 H 2 SO 4 [68] and 0.05 mol L −1 NaCl [66]. The anodic and cathodic processes of WC-Co corrosion in chloride solution correspond to the following reactions: dissolution of Co (Eq.…”

“…The values then stabilized at around −0.32 V vs. Ag|AgCl|KCl 3mol/L (WC-12Co) and −0.42 V vs. Ag|AgCl|KCl 3mol/L (WC-25Co). Under E OCP conditions, the behavior of WC-Co cermets is dominated by dissolution of the less noble component (pure metallic cobalt) and by selective dissolution of metal from the binder phase (Co + WC) [7,14,66,67]. The exposed metallic phase oxidizes from the beginning of the immersion, with the reduction of dissolved O 2 mainly occurring at the WC.…”

“…The exposed metallic phase oxidizes from the beginning of the immersion, with the reduction of dissolved O 2 mainly occurring at the WC. Galvanic coupling with the WC component of the material may enhance the rate of dissolution of the Co binder present in the coating, and hydrolysis of the metal cations can lead to acidification of the solution in regions where oxygen access is limited, creating conditions that accelerate corrosion of the cobalt [14,66]. On the other hand, the reduction of oxygen on the carbide phase increases the local pH, and due to the relatively long distance between anodic and cathodic sites, the increase of the pH in the cathodic regions may destabilize the carbide surface [14].…”

“…7), the E OCP value at 1 h of immersion was around −0.70 V vs. Ag|AgCl|KCl 3mol/L , followed by a decrease to ∼−0.95 V vs. Ag|AgCl|KCl 3mol/L and then an increase to −0.85 V vs. Ag|AgCl|KCl 3mol/L . This indicated that native oxides and oxides initially formed on the substrate surface when exposed to the aqueous solution were responsible for the relatively high open circuit potential [66,72]. However, this oxide film was not sufficiently protective, and the potential decreased to around −0.8 V vs. Ag|AgCl|KCl 3mol/L at 24 h, with attainment of a minimum value of −0.95 V vs. Ag|AgCl|KCl 3mol/L at ∼70 h (due to localized corrosion that exposed the aluminum surface to the electrolyte), followed by an increase for longer immersion times, reaching −0.85 V vs. Ag|AgCl|KCl 3mol/L after 196 h of immersion.…”