Structure and properties of molybdenum-disulfide/amorphous carbon composited coatings deposited by co-sputtering method

Molybdenum-disulfide/amorphous carbon (MoS2/a-C) composite coatings with different MoS2 contents were deposited by a co-sputtering system. The MoS2 content in the coatings was adjusted by changing the sputtering power of the MoS2 target. Growth morphology, composition, and chemical bond structure of the coatings were investigated by scanning electron micrograph, energy dispersive X-ray detector and X-ray photoelectron spectroscopy. Mechanical properties and tribological behavior of the coatings were also studied by nanoindentation and ball-on-disk tribometer, respectively. The results show that the MoS2 content of the coatings increases as the sputtering power of the MoS2 target increases. The incorporation of MoS2 promotes the graphitization and causes the increase of the sp(2)/sp(3) ratio, which results in the decrease of the coating hardness. However, the graphitization on the friction contact surface causes the MoS2/a-C coating with small content of MoS2 to present a superlow friction at ambient air. Furthermore, the MoS2/a-C coating with high content of MoS2 exhibits the super-low friction at the elevated temperature due to the formation of MoS2 crystalline that can serve as lubricant. This indicates that we can acquire the MoS2/a-C coatings with low friction coefficient at different conditions (such as ambient air and dry air) through controlling the addition content of MoS2.