Hydrothermal corrosion of TiAlN and CrN PVD films on stainless steel

Hydrothermal corrosion of thin TiAlN and CrN PVD films (of 3μm thickness) in 100 MPa 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 °C, whilst ülvospinel 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 100 MPa water up to 800 °C. Nitride films on low-alloyed steel can substitute for expensive super alloy in wet air oxidation systems, with working temperatures up to 700 °C in the case of TiAlN, or 800 °C in the case of CrN coatings.