Influence of lamellae thickness on the corrosion behaviour of multilayered PVD TiN CrN coatings

The corrosion behaviour of two multilayered TiN/CrN coatings with different chemical modulation period (10 and 125 nm, respectively) have been investigated in a 0.1 M H2SO4 solution. Single layered TiN and CrN have been included in the investigation and used as reference coatings. All coatings have been deposited on single crystalline Si in commercial PVD equipment. The multilayered coatings with thin lamellae showed superior corrosion resistance as compared to the coating with thicker lamellae. This is concluded from the following; it was observed that TiN oxidised to a solid passivating Ti(N,O), whereas CrN was oxidised and dissolved. Furthermore, it has been shown that the oxidation rate of the multilayered coatings is determined by the rate of CrN dissolution. The rate is directly related to the number of lamellae since the dissolution of CrN lamellae propagates laterally, rather than the vertically. From this it can be concluded that the higher the number of lamellae in the multilayered coating, the lower the oxidation rate, in the present H2SO4 solution. (C) 1999 Elsevier Science S.A. All rights reserved.