Self-lubricating materials play a critical role in space mechanisms, where they are commonly used in bushings, guides, slip rings, gears, and ball bearing cages.
At the European Space Tribology Laboratory (ESTL), we recently assessed two widely used self-lubricating materials, PGM-HT and its newer replacement TECASINT 8591, under representative vacuum conditions using our Vacuum Mini Traction Machine (VMTM).
The VMTM is a unique ESTL facility designed to study lubricant and material behaviour in space-relevant tribological contacts. It uses a single ball loaded against a disc, with independently driven motors allowing conditions from pure rolling through to sliding. Its in-situ optical capability also enables direct observation of transfer film formation in real time.
Our study showed that both materials formed transfer films and maintained a moderate traction coefficient of around 0.05 throughout testing in vacuum at room temperature. However, TECASINT 8591 rapidly formed a more consistent and durable transfer film than PGM-HT. In one test, the PGM-HT transfer film failed mid-test, leading to substrate wear, which was directly observed using the VMTM’s optical system.
We also investigated the interaction between these self-lubricating materials and ESTL’s MoS₂ solid lubricant. The results for both materials showed a significant extension in low-traction lifetime of the lubricated contact, when used in conjunction with the MoS2 alongside a reduced running-in friction period for the MoS₂ itself.
This synergistic behaviour is particularly important for ball bearings, where torque and lifetime performance are key drivers in solid-lubricated space mechanism design.
A technical memorandum detailing this study is freely available to download from the ESTL Members Area (accessible upon registration to entities within the ESA Member and Cooperating States): ESA-ESTL-TM-0469 01-: Optical Investigations of SLM Transfer Film Formation
If you would like to learn more about self-lubricating materials for space, the Vacuum Mini Traction Machine, or other research undertaken at ESTL, please feel free to get in touch.
