Electrochemical characteristics of steel coated with TiN and TiAlN coatings

The corrosion protection characteristics of titanium nitride (TiN) and titanium-aluminum nitride (TiAlN) coatings produced on cemented carbon steel targets were investigated in aqueous sodium chloride solution. All coatings were produced by cathodic are plasma deposition. The results indicated that it was possible to follow the corrosion behavior of the coated systems over a period of 300-900 h of immersion. It was found that the TiN and TiAlN coatings had a lower corrosion rate (current density), about three orders of magnitude lower than the untreated steel substrates. The metal substrate was actually passive in these experimental conditions, and exhibited an electrochemical impedance response that could be described by means of the same equivalent circuit than for the coating. Nevertheless, the analysis of the impedance parameters allowed for direct information concerning the enhancement of the corrosion resistance of the coated system as compared to the passive uncoated metal substrate to be extracted. The major corrosion mechanism for the coated samples arises from electrolyte penetration in the pores of the deposits, which may eventually lead to the development of localized forms of corrosion. (C) 2000 Elsevier Science Ltd. All rights reserved.