Tribological systems have become one limiting factor in spacecraft performance. For tribological components working under extreme conditions, such as in a vacuum, or under broad temperature ranges, the problem is to achieve acceptable endurance of their friction parts. New material requirements are involved for these tribo-systems, in particular regarding operability and reliability.
At the Federal Institute for Materials Research and Testing, Berlin, several projects were conducted in the past few years, dealing with the tribological behaviour of friction couples in vacuum environment. This paper describes the experiments carried out with polyetheretherketone (PEEK), filled with carbon fibres and solid lubricants (polytetrafluoroethylene (PTFE), graphite or MoS2), against X5CrNi1810 steel (similar to AISI 304). Tests were performed with a pin-on-disc configuration in oscillating and continuous sliding. Friction tests were carried out in vacuum in the temperature range between -40°C and +160°C and in ultra high vacuum at room temperature.
Surface analyses of the worn polymer pin and of the transfer film on the steel disc were performed after the experiments by means of optical microscopy, SEM, AFM, EDX and XPS.
Results indicate that MoS2 filled PEEK show the best tribological performance. Particularly, in the lower temperature range and at higher loads the friction behaviour is improved by the MoS2 content.
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