CORRELATION OF MICROSTRUCTURE AND PROPERTIES OF HARD COATINGS

If the maximum performance benefits are to be obtained for a particular coating/substrate system, it is of fundamental importance that the interrelationship between the microstructure and properties of the coating be understood. In physical vapor deposition (PVD) processes, the application of a substrate bias during deposition is used to control the degree of ion bombardment that the coating experiences during growth. This, in turn, affects the grain size, texture, morphology, composition and density of the coating. The control of coating microstructure is thus possible, to a limited extent, and this is illustrated for PVD titanium nitride films in this paper. The importance of the coating microstructure in dictating many of the physical properties of the coating (for example hardness, residual stress, adhesion, etc.), is highlighted. The implications of these microstructure/property relationships for the selection of optimised coatings for tribological applications is assessed, given the amount of microstructural control that is possible in PVD coating processes.