Corrosion behavior of thermal‐sprayed WC cermet coatings in SO 4 2− environment

Abstract A series of the electrochemical and long‐term corrosion tests was carried out in a 3.5 wt% Na 2 SO 4 solution on thermal‐sprayed WC‐17Co and WC‐10Co‐4Cr cermet coatings in order to examine the effect of composition of binder materials on the corrosion behavior. The results reveal that the overall corrosion resistance of the WC‐17Co coating is inferior to that of the WC–Co–Cr coatings due to the corrosion of binder materials which induce WC particles to fall off. CoO and WO 3 oxide films form on the surface of WC‐17Co coating in Na 2 SO 4 solution electrochemical corrosion process, which will protect the coating in the process of corrosion. Cr 2 O 3 oxide film formed on the WC‐10Co‐4Cr coating surface has a strong hindered role to corrosion. The corrosion mechanism of WC‐17Co coating in Na 2 SO 4 solution is entire corrosion of Co matrix, while it is film‐hole corrosion mechanism for WC‐10Co‐4Cr coating.