The evolution of space equipment has been progressing to support heavier loads and longer durations of operation, necessitating the advancement of higher-performance lubricating materials. Currently, molybdenum disulfide (MoS2) films are predominantly used under low vacuum loads (< 0.5 GPa), underscoring the urgent need for developing MoS2 composite films that can perform under a wider range of vacuum loads, including medium and high loads. In this study, MoS2 / diamond-like carbon (DLC) composite films were carefully fabricated using non-equilibrium magnetron sputtering technology. A variety of analytical methods, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, transmission electron microscopy (TEM), and vacuum friction testing, were utilized to thoroughly assess the structure, morphology, tribological properties, and wear mechanisms of the films. The SEM images clearly show that the DLC film's surface is densely structured, consisting of closely packed small particles of similar sizes, without noticeable defects such as cracks or holes. Conversely, the surface of the MoS2 film features a worm-like structure, leading to a surface that is not smooth. When comparing the surface morphology of the MoS2 / DLC composite film to that of the DLC film, it is observed that both surfaces are composed of uniform small particles; however, the composite film's particles create a rough, island-like structure. This is attributed to the amorphous growth of the DLC film, which disrupts the one-dimensional growth pattern of MoS2. Compared to the MoS2 film, the cross-sectional organization of the composite film shows an improvement, with a less pronounced columnar structure leading to a denser film structure. The presence of amorphous carbon prevents the formation of the columnar structure in MoS2, effectively mitigating the issues of pores, cracks, and other defects in the MoS2 film. Notably, the XRD diffraction peaks of the composite film were primarily observed at the (002) crystal face, with amorphous carbon aiding the film's growth and promoting a preferred orientation on this crystal face, which enhances its lubrication effectiveness. The hardness of the composite film increased significantly to 8.13 GPa, marking an eightfold improvement over the pure MoS2 film. Additionally, the surface roughness of the composite film was significantly reduced to 1.66 nm, in contrast to the higher surface roughness of 5.89 nm exhibited by the pure MoS2 film. The hardness of the MoS2 / DLC film also showed a significant increase when compared to the MoS2 film. The inherent low hardness of the MoS2 film, which leads to high wear rates, is effectively countered by the addition of carbon, increasing the composite film's hardness and thereby reducing its wear rate. The elastic recovery rate of the composite film was also found to be improved over the MoS2 film. The integration of DLC with MoS2 modifies the MoS2 film's structure, incorporating the DLC film's high hardness advantage into the composite, enhancing its performance under medium to high loads. XPS analysis confirmed that the composite film is predominantly composed of 2H-MoS2, favoring effective lubrication. To evaluate the tribological properties of the composite film, comprehensive testing was conducted under a wide range of vacuum loads, from 0.73 GPa to 1.27 GPa, showing the film's ability to consistently maintain a low friction coefficient (0.02-0.06) and a low wear rate 10(-10) mm(3)<middle dot>N-1<middle dot>m(-1)). Comparative analysis has shown that, relative to MoS2 alone, the composite film significantly lowers both the friction coefficient and wear rate by three orders of magnitude. Further detailed examination revealed that the composite film is capable of undergoing a graphitization transformation, which leads to the creation of ordered graphite structures. These structures effectively lubricate MoS2 with a (002) orientation, a process induced by both the catalytic effect of MoS2 and contact stress. The development of layer-intercalated low shear stress graphite structures and layered MoS2, facilitated by the catalytic influence of MoS2 and contact stress, was identified as crucial for attaining both a low friction coefficient and wear rate. The incorporation of amorphous carbon into the composite film plays a significant role in enabling it to sustain a low friction coefficient and an ultra-low wear rate, even within a vacuum environment. Moreover, this study not only contributes practical insights but also offers valuable theoretical guidance for the future application, design, and development of MoS2 / carbon composite films.
