Relationship between discoloration, condensation, and tribology behavior of steel surfaces at cryogenics in vacuum

Cryogenic temperature is an extreme condition that challenges the lubrication properties of materials, but it’s currently under-recognized due to the difficulty of characterizing material behavior online and obtaining
cryogenic temperature. A new phenomenon, the condensation of trace gas molecules, exists in cryogenic vacuum environments and affects the color and tribology behavior of the steel surface. Several thermal cycles, prolonged vacuuming, and online detection by mass spectrometer demonstrated that discoloration was mainly caused by water condensation, and the condensation content was positively correlated with the color’s intensity. The condensation increases the wear life of the steel/steel friction partner by a factor of at least 100, and wear can be further reduced by actively controlling the amount of nitrogen and oxygen condensed.