Corrosion behavior of nanolayered TiAlN/CrN multilayer coatings prepared by reactive DC magnetron sputtering process

TiN, TiAlN, CrN and TiAlN/CrN multilayer coatings were deposited on steel substrates using a multi-target reactive DC magnetron sputtering process. The coatings were characterized using X-ray diffraction and scanning electron microscopy. The corrosion behaviors of these coatings were studied in 0.5 M NaCl solution using linear polarization, potentiodynamic polarization and impedance analysis. About 1.5 m thick coatings of TiN, CrN, TiAlN and TiAlN/CrN multilayers showed good corrosion protection of the steel substrate and multilayer coatings performed better than single layered coatings. Although, the transition metal nitride coatings are chemically inert the corrosion protection of these coatings is greatly influenced by micropores present in the coatings. The size and the density of the micropores in the physical vapor deposited transition metal nitride coatings can be controlled by - (1) Alloying of the coating (e.g. addition of Al in TiN). (2) Small crystallite size (e.g. ion bombardment of the growing coating). (3) Incorporation of a large number of interfaces in the coating (e.g. multilayer deposition). In this paper we will discuss the effect of these parameters on the corrosion protection of nanolayered TiAlN/CrN multilayer coatings