Frictional oxidation behavior of MoS2-Ti-LaF3 films under low temperature vacuum

Low temperatures induce novel effects and phenomena. Tribological studies of MoS₂-Ti-LaF₃ films in a low temperature vacuum environment revealed that trace water molecular condensation at a specific temperature promotes a unique MoS₂ tribochemical reaction, resulting in high friction and wear. The MoS₂-Ti-LaF₃ films were characterized using Raman spectroscopy, XPS, FESEM, TEM, and in situ vacuum quadrupole mass spectrometer. The results indicate that at 150 K, water molecules condense and physically adsorb on the film's surface, inhibiting MoS₂ shearing and rearrangement during friction. Under heavy load and friction heat, the adsorbed water molecules and trace O₂ further promote the chemical reaction with many damaged MoS₂ edge suspension bonds, defects, and other active sites, forming non-lubricious MoO₃. MoO₃ is transferred to the steel ball's surface, resulting in increased friction and wear, and its oxidation degree is positively correlated with the friction coefficient. This new discovery provides a reference for the research of low temperature solid lubrication materials and broadens the consideration and selection of actual working conditions.