Corrosion of stainless steel coated with TiN, (TiAl)N and CrN in aqueous environments

The corrosion behaviour of TiN, (TiAl)N and CrN coated on 304 stainless steel by physical vapour deposition was examined in borate solution (pH 9.0) and in 0.5 M NaCl solution. The study was performed by using open circuit potential, potentiodynamic polarization and cyclic polarization techniques, complemented with XRD and laser microscopy. The measurements were also performed on the uncoated substrate for comparison. Nitrided coatings significantly improve the corrosion performance of the steel; however, they are prone to corrosive attack as a consequence of the presence of microstructure defects such as pinholes and pores. Galvanic corrosion between the coatings and the substrate result in significant attack of the substrate, allowed by the penetration of small pinholes into the substrate. In borate solution, (TiAl)N possesses the highest corrosion resistance, However, CrN possessed the highest corrosion resistance in NaCl solution. (C) 2002 Elsevier Science Ltd. All rights reserved.