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Pb/H-DLC coatings with varying Pb content were deposited using a unbalanced magnetron sputtering system, and their tribological properties were tested in vacuum. For the two coatings exhibiting superior performance, the surface damage caused by space irradiation was investigated in ground-simulated space environments, including atomic oxygen (AO) erosion and ultraviolet (UV) irradiation. The irradiation damage and friction mechanisms were analyzed using surface/interface characterization techniques. The results reveal that the hydrogen content and the ratio of I D /I G in the Pb/H-DLC coatings initially decrease and then increase with increasing the Pb content. The Pb/H-DLC coatings show improved mechanical and vacuum tribological properties when the Pb content is 0 at% and 2.4 at%. The lowest average friction coefficient is 0.014, and the lowest wear rate is 3.8 × 10−8 mm3N−1m−1. AO erosion induces graphitization and oxidation on the Pb/H-DLC coating surfaces, and the tribological properties of coating are deteriorated, while Pb doping effectively mitigates damage to the coatings' surface properties caused by AO erosion. The reduction in friction coefficient of the Pb/H-DLC coatings after UV irradiation can be mainly attributed to the formation of a soft layer consisting of HO-C O groups on the surface due to irradiation. [Display omitted] • Pb-H/DLC coatings with various Pb contents were deposited and the coefficients of friction were less than 0.05. • After atomic oxygen erosion, the Pb-H/DLC coating underwent significant oxidation and graphitization. • The coefficient of friction of the Pb-H/DLC coating decreased after UV irradiation. [ABSTRACT FROM AUTHOR]

To investigate atomic oxygen effects on tribological properties of Mo/MoS2-Pb-PbS film and further enlarge application range, atomic oxygen exposure tests were carried out for 5 h, 10 h, 15 h, and 20 h by the atomic oxygen simulator with atomic oxygen flux of 2.5 × 1015 atoms/cm2·s. The exposure time in test was equivalent to the atomic oxygen cumulative flux for 159.25 h, 318.5 h, 477.75 h, and 637 h at the height of 400 km in space. Then, the vacuum friction test of Mo/MoS2-Pb-PbS thin film was performed under the 6 N load and 100 r/min. By SEM, TEM, and XPS analysis of the surface of the film after atomic oxygen erosion, it was observed that atomic oxygen could cause serious oxidation on the surface of Mo/MoS2-Pb-PbS film, and the contents of MoS2, PbS, and Pb, which were lubricating components, were significantly reduced, and oxides were generated. From AES analysis and the variation in the main element content, Mo/MoS2-Pb-PbS thin film showed self-protection ability in an atomic oxygen environment. Hard oxide generated after atomic oxygen erosion such as MoO3 and Pb3O4 could cause the friction coefficient slight fluctuations, but the average friction coefficient was in a stable state. [ABSTRACT FROM AUTHOR]

MoS 2 film plays an important role in the field of space lubrication due to its excellent tribological properties, but the complex and changeable space environment has increasingly higher requirements for the lubricating layer. In order to improve the spatial tribological properties of the MoS 2 film, the Mo-X (X = Pb, PTFE, C) binary composite films were prepared by radio frequency magnetron sputtering technology. Then, Mo/MoS 2 –Pb–PbS, Mo/MoS 2 -PTFE and Mo/MoS 2 –C films were obtained through the treatment of binary films by "low-temperature ion sulfurizing" technology. The structure, morphology and composition properties of the three films were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS).The tribological properties of the three films were tested through ultraviolet (UV), atomic oxygen (AO) and high-vacuum simulated space environment, and the results showed that the Mo/MoS 2 –Pb–PbS film has better comprehensive spatial tribological properties. The Mo/MoS 2 –Pb–PbS film was applied to practical bearings, which were simulated for life test after exposure to space environment. The wear life of the new bearing is an order of magnitude higher than that of the active bearing. Therefore, Mo/MoS 2 –Pb–PbS film has broad application prospects in the field of space solid lubrication. • Three kinds of multi element Mo-based films were prepared by a simple method. • Mo/MoS 2 –Pb–PbS film have good comprehensive tribological properties in space environment. • The solid lubricated bearing using Mo/MoS 2 –Pb–PbS film is better than some bearings in service. [ABSTRACT FROM AUTHOR]