Elemental distributions and substrate rotation in industrial TiAlN/VN superlattice hard PVD coatings

Chemical distribution of individual layers within a TiAlN/VN multilayer structure was characterised using a field emission gun transmission electron microscope, coupled with energy-filtered elemental mapping and high-angle annular dark field imaging. Bright field TEM micrographs using zero-loss electrons indicated the presence of alternating TiAlN and VN layers with a periodicity of ∼3 nm. Electron spectroscopic images (ESI) using the Ti-L2,3 and V-L2,3 edges were used to determine the Ti and V composition profiles of layers and confirmed the complementary distribution of Ti and V. ESI demonstrated an additional modulation super-imposed on the basic period of the coatings, which was confirmed by Z-contrast imaging using scanning transmission electron microscopy. The additional modulation was related to the threefold rotational geometry used in the deposition process. Film growth and elemental distributions were therefore theoretically predicted in association with substrate rotation. The experimental compositional profiles and the prediction showed good agreement. The implications of the compositional modulation on key process parameters are discussed.