Characterisation of PVD TiCN layers by physical and electrochemical methods

Abstract

TiCN coatings were deposited by magnetron sputter ion plating onto high speed AISI M2 steel. The physical vapour deposition TiCN coatings were produced with various partial pressures of nitrogen and methane, at a constant substrate bias of 0, 50 or 100 V and constant deposition temperature of 300, 350, 400 or 450°C, respectively. Next, the substrate bias was varied for constant ratios of partial pressures and constant temperature. The amount of methane flow affects the coating composition as well as its lattice parameters and residual stresses. These properties are also affected by the substrate bias. The joint effect of increasing the substrate bias, the presence of interstitial carbon and the formation of CN–Ti bonds could probably be responsible for strong fcc lattice distortion and consequently high residual stresses of the TiC_xN_y coatings. The deposition temperature affects the lattice parameters and the residual stresses only to a small extent. The substrate bias of 0 to −100 V yields known strong effects on the lattice parameters and residual stresses, because this deposition parameter is adjusted more or less independently of the other deposition parameters. Electrochemical analysis confirms the effects of different deposition parameters. Coating–substrate systems produced at low bias exhibit better corrosion resistance compared with those manufactured at −100 V. Coating embrittlement from hydrogen incorporation, the formation of CN–Ti bonds and large numbers of defects from high bias obviously favour corrosion attack, and high values of compressive residual stresses are not able to prevent early electrolyte attack on the substrate.