The slurry erosive wear of physically vapour deposited TiN and CrN coatings under controlled corrosion

The erosion-corrosion of mild steel (BS6323), in the presence and absence of physically vapour deposited (PVD) TiN and CrN coatings, was studied, in comparison with that of AISI 304 stainless steel, in an aqueous alkaline slurry solution containing alumina particles. The influence of applied potential and particle velocity on the total erosion-corrosion loss was examined, and the respective corrosion and erosion damage (both contributing to the overall weight loss) then assessed by means of microscopical investigation of the morphology of the damaged surface, and subsequently evaluated quantitatively. The superior erosion-corrosion resistance of both the coatings compared to that of the uncoated mild and stainless steels was shown to be due to their resistance to both wear and corrosion. According to the detailed corrosion mechanisms revealed and different responses to wear, schematic diagrams were proposed to outline the main features of the corrosion-erosion process and the individual roles of erosion and corrosion. Discrete differences, in terms of the respective erosion and corrosion processes, between the TiN and CrN coatings, and between the mild and stainless steels, were also investigated and discussed.