Raman spectroscopy as a tool to study cubic Ti–C–N CVD coatings

A series of CVD TiC1 − xNx coatings has been deposited on cemented carbide. The choice of precursors (CH4 or CH3CN) and deposition temperature (850–1000 °C) influenced the microstructure, crystallinity, microhardness and chemical composition.Laser Raman spectroscopy was used to investigate the coatings, since it has been shown to be a very sensitive technique regarding composition differences. Even small changes in the C:N ratio resulted in systematical Raman shifts. This frequency shift was found to be particularly pronounced in the range of the acoustical phonons, wherein the peaks shifted about 30 cm− 1 to higher frequencies with increasing carbon content.In order to gain better understanding of the tribochemical reactions and high temperature oxidation, Raman spectroscopy was used to determine oxidation processes of TiC, TiN and TiC1 − xNx coatings. Depending on the annealing temperature different amounts of anatase and rutile could be found, and a correlation between carbon content and oxidation product was observed.The extent of oxidation at 500 °C could be explained by decreasing oxidation resistance with increasing carbon content. The opposite behavior was obtained at 700 °C due to differences in the oxide layer composition and the formation of a denser oxide layer.We proved that Raman spectroscopy is a very useful non-destructive tool for a qualitative characterization of CVD TiCN coatings. However, effects of laser power had to be taken into account carefully.