Simplifying the erosion–corrosion mechanism map for erosion of thin coatings in aqueous slurries

Abstract

A significant advance in the study of erosive wear in recent years has been the construction of erosion mechanism maps showing the transitions between the erosion–corrosion regimes as a function of the main process parameters. The various corrosion regimes, ranging from active to passive conditions, have been incorporated on the map. Hence, the map is more complex than that in dry oxidizing conditions where the predominant corrosion process is film growth. The object of this work has been to study the combined effects of increasing erodent velocity and applied potential on the erosion of PVD coatings, i.e., Ti 2N and CrN in aqueous conditions. The substrate was mild steel, the particles alumina and the solution, a carbonate–bicarbonate buffer. Mechanisms of erosion–corrosion were identified on the basis of the results. The erosion mechanism maps generated from the results provided a means of differentiating between erosion–corrosion behaviour of the coating and the substrate. Significant shifts in the boundaries were identified for different coatings. The stages in the construction of such maps, in addition to the various approaches towards simplifying the nomenclature and the format, are described in this paper.