Corrosion resistance of steel coated with Ti/TiN multilayers

The corrosion resistance behaviour of steel coated with TIN thin films deposited by physical vapour deposition (PVD) has been studied by electrochemical techniques in de-aerated 1 M sodium acetate solution at pH 5.6. Two different types of coatings deposited on carbon steel samples have been studied: (1) multilayered coatings of Ti/TiN in which the interfaces are compositionally abrupt, and (2) multilayered coatings of Ti/TiN in which there is a mixture between the two materials at the interfaces leading to gradual composition interfaces. The electrochemical results obtained have been correlated to structural defects studied by scanning electron microscopy. It has been observed that the corrosion resistance of coated steel was higher than the substrate resistance. The graded composition interface coatings showed a more protective character than the sharp interface. The corrosion resistance is mainly controlled by the occurrence of coatings defects and their presence can be easily detected by electrochemical measurements.