Surface fatigue behaviour mapping of PVD coatings for mechanical purposes

Most mechanical components used for transmission of movement are subjected to repeated impacts or cyclic stress. If these elements are well designed and the materials well chosen, their durability is linked to surface fatigue mechanisms. In order to improve the fatigue behaviour of these parts, hard coatings, such as physical vapour deposition (PVD) or plasma-assisted chemical vapour deposition (PACVD) coatings, can be appropriate. Unfortunately, such hard coatings cannot be used for elements whose replacement is more difficult than, say, cutting tools. An understanding of failure mechanisms should make it possible to optimise the fatigue behaviour of hard coatings. In order to study the surface fatigue behaviour of thin, hard PVD coatings, a special apparatus has been developed to carry out repeated impacts over a broad range of speeds. The possibility of mapping the fatigue behaviour of different coatings is illustrated through the examples of TiN and TiN/CrN multilayer coatings of different thicknesses deposited on several substrates.