Properties and performance of commercial TiCN coatings. Part 1: coating architecture and hardness modelling

Several PVD and CVD TiCN coatings on a cemented carbide substrate have been obtained from commercial suppliers and subjected to a range of analysis and characterisation techniques to determine the effects of coating composition and architecture on performance. The majority of suppliers produce coatings with a C/N ratio approximately equal to 1, although one supplier increases this to 2. For all the PVD coatings, the supplier initially deposits a layer of TiN to promote adhesion and then gradually increases the nitrogen content of the process gas to make TiCN with a graded composition running from pure TiN to TiCN over a few 100 nm of coating growth. This graded layer may or may not be capped with a layer of TiCN with fixed composition. The hardness behaviour of these layers is more complex than a simple, single layer on the substrate. In this study, an existing predictive hardness modelling analysis developed at Newcastle, UK has been extended to deal with coatings of graded composition. The potential for optimising the hardness of TiCN coatings by changing coating architecture is discussed.