A study of the erosion-corrosion of PVD CrN/Nb superlattice coatings in aqueous slurries

New generation PVD coatings include advanced superlattice structures in which the combination of tribological and corrosion properties may optimized. Such coatings of the CrN/NbN type offer the possibility of enhanced wear and corrosion resistance. However, there has been little work carried out to date to identify the mechanisms of wear of these coatings in environments where solid particles may impact the surface in corrosive conditions. In this paper, the erosion-corrosion performance of M2 tool steel coated with PVD CrN/NbN superlattice coatings, produced by unbalanced magnetron sputtering with bias voltage of -75 V, was assessed and compared to the uncoated tool steel substrate. The results indicated that the performance of the coating depended on the impact angle and the applied potential. The overall erosion-corrosion resistance of the coated samples was found to be superior to that of the uncoated samples; however, the relative protection depended on the impact angle and the applied potential. Possible reasons for such behaviour are described in this paper.