Hydrothermal corrosion of TiAlN and CrN PVD films on stainless steel

Abstract

Hydrothermal corrosion of thin TiAlN and CrN PVD films (of 3lm thickness) in 100MPa water over a temperature range of 20–950 C is compared to the behavior of TiN films over the same T–P conditions. Corrosion resistance increases in the sequence TiN! TiAlN !CrN. A FeTiO3 (ilmenite) layer on the surface of the TiAlN film is almost chromium-free and provides protective properties up to 700 oC, whilst u¨lvospinel formation leads to spallation of oxide scale due to high level growth stresses. Formation of a very stable spinel scale on the surface of the CrN films provides long-term corrosion protection in 100MPa water up to 800 oC. Nitride films on low-alloyed steel can substitute for expensive super alloy in wet air oxidation systems, with working temperatures up to 700 oC in the case of TiAlN, or 800 C in the case of CrN coatings.