Velocity effects of erosion-corrosion of CrN/Nb superlattice PVD coatings

Erosion-corrosion or tribo-corrosion poses a threat to materials which are subjected to conditions involving corrosive slurries. Industries suffering from erosion-corrosion include the automotive, aviation, pump, mining and petroleum industries. The rate of material removal due to erosion-corrosion can be very different to the damage caused by the individual components, i.e. erosion and corrosion. Hard and corrosion resistant coatings have been produced to resist this combined attack. Coatings include thermally sprayed coatings, composite cermets, multilayer and monolithically grown PVD coatings. They have improved wear and corrosion resistance owing to their high hardness and use of noble metals. Previous work on the erosion-corrosion of CrN/NbN superlattice coatings has shown variation in the erosion-corrosion mechanisms and volume loss with change in impact angle and applied potential. Yet the effect of velocity on the transitions between erosion-corrosion mechanisms of superlattice CrN/NbN PVD coatings is unexplored. The present work investigates the velocity effects on erosion-corrosion behaviour of range of multilayer CrN/NbN "superlattice" PVD coatings against that of uncoated M2 tool steel. This work discusses the possible interaction between erosion-corrosion for CrN/NbN PVD coatings. Erosion-corrosion mechanism maps and wastage maps have been generated based on the results to depict the changing mechanisms of material degradation with impact angle and changing velocity.