A Critical Review of Measures for an Effective Application of Nano-Structured Coatings in Milling

The evolution of the coating deposition technologies led, among others, to the production of nano-structured coatings. Such coatings are often deposited on cutting tools since they contribute to an impressive enhancement of the coated tool life. Hereupon, attention has to be given for avoiding a rapid crack propagation due to a potential coating brittleness increase and for achieving a sufficient film adhesion. In this context, film residual stresses and structure may affect the film adhesion. This paper introduces characteristic measures for an effective application of nano-structured PVD and diamond coatings on cemented carbide tools in milling. More specifically, the adhesion of PVD HPPMS nano-structured coatings can be improved via an appropriate adhesive interlayer. Besides, the coating brittleness can be restricted through the application of nano multi-layer film structures. Furthermore, for improving the diamond coated tool performance, the diamond film nano-structure may be interrupted by micro diamond layers. The introduction of successive nano- and micro-structured layers restricts the film brittleness since micro-structured layers are more deformable compared to nano-structured ones. Finally, the interfacial fatigue strength of diamond coatings is affected by the film residual stresses. Inclined impact tests supported by appropriate FEM simulations facilitate the quantitative adhesion characterization of such films.