It is well known that tribological systems operating in vacuum environments present severe challenges to be overcome. MoS₂ is one of the most well-known materials for providing low friction in both ambient and vacuum environments. However, it has a low wear resistance and a limited ability to withstand higher contact pressures. Super-hard hydrogen-free tetrahedral amorphous carbon coatings (ta-C) are a possible wear-resistant alternative. While they have low friction and wear properties in air at normal atmospheric conditions, their vacuum performance is limited when self-paired or in combination with steel.

In this work, the impact of various counter body materials is studied when paired with ta-C coatings. The evaluated counter body materials include brass, bronze, copper, silicon carbide, as well as aluminum oxide (Al₂O₃), steel and ta-C coated. In particular, brass was found to be the most promising counterbody material, and it was put to the test in direct comparison to steel as well as in long-term performance tests. In the short term, regardless of pressure, the brass/ta-C friction pair exhibits low friction (~0.1) and high wear, whereas in the long term, the friction coefficient increases (up to 0.52) due to a change in wear mechanism. Al₂O₃ was found to be a promising sliding partner against ta-C, with a higher friction coefficient (0.3) but significantly lower wear than brass.