Corrosion resistance of titanium nitride and mixed titanium titanium nitride coatings on iron in humid SO2-containing atmospheres

The corrosion behavior in humid SO2-polluted atmospheres of three different TiN coatings on iron [single layer TiN (1000 nm), bilayer Ti(100 nm)/TiN(1000 nm) and multilayer Ti(100 nm)/TiN(100 nm)/Ti(100 nm)/TiN(100 nm)] have been investigated by means of x-ray photoelectron spectroscopy. Only the single layer coating shows some degradation in low concentration (0.001% v/v) SO2 atmospheres after 14 days of exposure, the other two coatings remaining stable. Exposure to higher SO2 concentration (0.04% v/v) for 7 days results in the total degradation of the single layer coating. Exposure to this latter atmosphere for 14 days brings about a considerable degradation of the bilayer and multilayer coatings, the results showing that the multilayer coating, even with the lowest total thickness, presents the highest resistance against these corrosion conditions. Corrosion of the TiN coatings results in the formation of TiO2 and several N species [probably of the type (NH4)(2)SO4 and species containing N-O bonds]. The degradation of the coatings results in the corrosion of the underlying iron. Fe2+ sulphates and sulphites, as well as FeOOH, are the main iron corrosion products. (C) 1997 American Vacuum Society. [S0734-2101(97)02206-9].