Tribological behaviour of materials at cryogenic temperatures

Up to now interest in low temperature technology has been restricted to applications in space technology and superconductivity. However, some applications of cryotechnology are ready to take off in the near future. One example is the utilization of liquid hydrogen as an environmentally friendly energy carrier for transportation and energy supply systems. This technology involves new problems concerning the strength of materials as well as safety of equipment. For example, in hydrogen-fuelled aircraft, materials such as austenitic stainless steels or copper which are widely used in cryotechnical applications must be minimized or substituted because of their high density. On the other hand, the properties of light-weight materials, especially advanced composites, have not been examined sufficiently in cryogenic environment. Against this background, at the Federal Institute of Materials Research and Testing investigations on the low temperature behaviour of materials were started, including tribological investigations. It is the aim of the project to acquire data on materials' properties when stressed at low temperature and especially in low temperature gaseous hydrogen and liquid hydrogen. In addition to the thermal conditions, cryotechnical applications are also characterized by special environments. Different cryotribometers were constructed for different cooling and loading conditions as well as different environmental media in the temperature range from 4.2 K up to room temperature. Results are presented of low temperature investigations on the tribological behaviour of polymers and composites as well as of TiN and carbon coating systems. (C) 1998 Elsevier Science S.A. All rights reserved.