Friction and wear behaviour of polymers in liquid hydrogen

The tribological behaviour of polymer composites were investigated in liquid hydrogen at -253 degrees C and compared with previous results obtained in gaseous hydrogen at ambient temperature. Experiments reveal that the friction and wear mechanisms in cryogenic conditions are related to the low temperature properties of polymers and to the formation or inhibition of the transfer film. For chemically stable polymers such as PEEK, that does not transfer in hydrogen gas, the tribological behaviour is improved in cryogenic liquids compared to ambient temperature. For tribo-reactive materials and graphite filled polymers that form a homogenous lubricating film in gaseous hydrogen, the sliding performance declines under cryogenic condition. The influence of hydrogen temperatures is discussed in this paper in relation to material compositions and transfer film formation.