Corrosion and erosion damage mechanisms during erosion–corrosion of WC–Co–Cr cermet coatings

Experiments were performed in order to evaluate the behaviour of WC–Co–Cr coatings applied by the Super D-Gun™ (Trademark of Praxair S.T. Technology) thermal spray process in erosion–corrosion environments. The experiments were performed in 3.5% NaCl with different silica sand loadings (200 and 500 mg/l). The results were compared with UNS S31603 and UNS S32760 stainless steels. Measurements of the total material loss showed that the coating applied by Super D-Gun presented higher resistance to erosion–corrosion compared to both stainless steel materials as expected. The connection between the erosion–corrosion behaviour of the Super D-Gun coating and the microstructure is assessed. Scanning electron microscopy (SEM) images enabled the different mechanisms of tribo-corrosion to be understood. With cermet materials there has been much discussion relating to the role of corrosion in removing the hard phase particles which can breach tribological performance. The corrosion rate (icorr) of the coating was determined under erosion conditions and an evaluation of the influence of corrosion and synergistic processes on the erosion process was made using applied cathodic protection.