Multicomponent and multiphase hard coatings for tribological applications

Plasma vapour deposition (PVD) processes are often used to deposit coatings and thin films in order to reduce wear and friction of tools and machine parts. These techniques especially allow the deposition of a broad spectrum of materials, particularly covering the nitrides and carbides of the transition metals and some borides and oxides as well as carbon-containing coatings like diamond, diamond-like, metal-carbon and carbon-nitrogen coatings. On the basis of the binary compounds TiN and TiC, various strategies were developed to improve or adapt the hard coatings to a specific tribological problem. This was first realized in multicomponent coatings by adding other metallic or non-metallic elements — also with graded concentrations. Further developments were focussed on the deposition of multiple-layer and multilayer coatings and most recently on nanostructured coatings where in addition to hard components also soft and lubricating materials are simultaneously deposited. The paper reviews the recent developments of tribological coatings giving examples of their structure, properties and performances.