Corrosion Behaviour of Substoichiometric TiNx Films Produced by DC Magnetron Sputtering E. Ariza 1 , L. A. Rocha 1,2 , F. Vaz 3 , L. Rebouta 3 , J. Ferreira 3 , E. Alves 4 , Ph. Goudeau 5 , J. P. Rivière 5 1 CIICS – Research Centre on Interfaces and Surfaces Performance, University of Minho, Campus de Azurém, 4800-058 Guimarães – PORTUGAL. Phone: +351 253 510220, Fax: +351 253 516007. e-mail: edith@dem.uminho.pt 2 DEM –Mechanical Engineering Department, University of Minho, Campus de Azurém, 4800-058 Guimarães – PORTUGAL 3 Dept. Physics, University of Minho, Campus de Azurém, 4800-058 Guimarães – PORTUGAL 4 ITN, Physics Department, E.N.10, 2685 Sacavém, PORTUGAL 5 Laboratoire de Métallurgie Physique, Université de Poitiers, 86960 Futuroscope, FRANCE Keywords : TiN coatings, reactive magnetron sputtering, corrosion resistance, EIS. Abstract. The present work describes the corrosion behaviour of substoichiometric TiN x films obtained by dc reactive magnetron sputtering. The coatings thickness ranged from 1.7 to 4.2 µm and the nitrogen content varied between 0 and 55 at. %. According to structural characterization by XRD, the films revealed a hexagonal α-Ti phase with a strong [002] orientation for low nitrogen contents. For nitrogen contents of 20% and 30%, the ε-Ti 2 N phase appears with a [200] orientation and further increasing of nitrogen content showed that the δ-TiN phase was dominant. Potentiodynamic polarisation and Electrochemical Impedance Spectroscopy (EIS) techniques were used to study the corrosion properties of TiN x films when immersed in artificial sweat solutions. Results of potentiodynamic polarisation tests showed that all films have a high corrosion resistance reflected by corrosion current densities values lower than 0.7µA/cm 2 . Also, EIS tests corroborated the results obtained in the polarisation tests, showing that films containing low percentages of nitrogen (less than 8 %) reveal the best corrosion resistance. Further increases in nitrogen content lead to a decrease in corrosion resistance. An exception to this behaviour was found for the film, with 30 % N. This sample presents an excellent corrosion resistance which increases with the immersion time. Higher nitrogen contents (52 and 55 %) promote a relative increase in the corrosion resistance when compared with 45 and 50 at % films, but never reaching values obtained for nitrogen contents lower than 30 % at. Introduction Stoichiometric titanium nitride (TiN) is actually one of the most important technological coating material, not only because of its excellent tribological properties but also due to a good chemical stability. It is certainly, in tribological terms, the most explored hard thin film material and most extensively used in industry. It is used in a wide range of applications, which range from protective material for machine parts and cutting tools [1] to diffusion barriers in semiconductor technology [2]. In the last decades there has been an increasing interest in elucidating the mechanisms, which lead to thin-film property modification caused by the so-called substoichiometric condition of TiNx films [3-5]. In recent years, properties of substoichiometric titanium nitride (TiN x ) have been studied by relatively few researchers considering only basic properties such as hardness, phase composition or lattice distortion [6-8]. All these investigations focused mainly on the δ- TiN-phase, whereas little attention was paid to the properties of α-TiN and ε-Ti 2 N phases, and especially to the corrosion properties of these films. In this paper, the corrosion behaviour of substoichiometric TiN x films, remarking the influence of nitrogen content, will be described.