Corrosion and tribocorrosion behaviour of cermet and cermet/nanoscale multilayer CrN/NbN coatings

Polarization curves recorded after 1 h of immersion and polarization resistance values monitored during 3 days exposures showed that under free corrosion conditions Cr3C2-37WC-18Me always exhibits low corrosion rates and efficiently protects the underlying steel substrate from corrosion. Even on WC-12Co-coated specimens, low corrosion rates are measured at long immersion times. Both cermet coatings suffer severe corrosion attack under tribocorrosion conditions. On the contrary, the duplex nanoscale multilayer CrN/NbN/WC-12Co deposit affords very good corrosion resistance both in the absence and in the presence of wear, within the studied exposure period. SEM observations and EDS analyses have also been carried out to characterize the original powder and coating microstructures and to assess the damage extent at the end of the corrosion and tribocorrosion tests.