Industrially deposited tetrahedral amorphous carbon coatings have been widely used for several years in numerous applications, for example on piston rings, piston pins and cutting and milling tools, due to their outstanding friction and wear properties.

Although the coatings are state of the art in some applications, particularly in engine oil lubricated internal combustion engines, there are still numerous unexplored interactions in the overall tribological system. This is especially true for interaction with lubricants and additives that are designed for iron-based surfaces.

Aside from oil-lubricated contacts, carbon coatings can show very interesting properties in more challenging environments, such as water, water-based lubricants, dry air and vacuum.

Furthermore, ta-C coatings also exhibit some special tribological phenomena that are still the subject of basic research. Of particular interest here is superlubricity, as well as other low-friction phenomena in aqueous media and vacuum.

In this contribution, tribological properties of ta-C coatings will be discussed in a broad range of lubrication scenarios, using conventional homogeneous ta-C coatings as well as several types of ta-C/MoS2 hybrid coatings. Coatings were tested with a ball-on-plate geometry in both a lubricated reciprocating tri-bometer as well as an ultrahigh vacuum tribometer with rotating movement. With respect to most engi-neering applications, counter body material was hardened steel. Friction and wear were measured in all scenarios and discussed with regard to potential applications.