Development of Monolayered Low Friction PVD Ceramic Coatings for Application on Tools and Mechanical Components

Ceramic carbon based coatings have become common on tools and machine components, mainly because they offer a greatly reduced friction, as compared to uncoated steel contacts, in combination with a considerable wear protection. Very often they contain alloying elements such as different metals to control properties like hardness, wear resistance and lubricity. Applied to component surfaces, also properties relating to the running-in behaviour become important since an efficient running-in is crucial for their long term steady-state functionality. Also, even though component coatings are meant to provide low friction in dry sliding, they are increasingly used also in lubricated situations. This raises demands for compatibility with common lubricants. All these aspects have to be considered when developing new tribological coatings and some of these are addressed in this work. Results from different sliding tests with coated and uncoated surfaces in both dry and boundary lubricated contacts are presented. The generated tribofilms and their influence on the tribological properties are compared for the different sliding conditions. It is also shown how lubricants and their additives can affect the running-in, the tribofilm formation, and alter the steady state friction.