Role of transfer film formation on the tribological properties of polymeric composite materials and spherical plain bearing at low temperatures

Polymeric composites show promising self-lubricating properties for low temperature applications, yet the lubrication mechanism still remains unresolved. Here, we report the friction and wear behaviors and mechanisms of a hybrid composite based on polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE) at temperatures ranging from 20 degrees C to -100 degrees C in vacuum with relatively large load of 10 N. The friction coefficient maintains lower than 0.1 over this wide temperature range with a minimum value at -70 degrees C due to the combined effects of transfer film formation and thermally activated sliding. As for self-lubricating spherical plain bearings lubricated by Nomex/PTFE fabric, we show direct evidence of transfer film formation on the outer surface of the inner ring after tribotest at -160 degrees C in nitrogen gas.