Ws <sub> 2 </ Sub> / Of Ag, Mo Sulfide / Ti Composite Films Environmental Friction Wear And Tear

Layered (2H-) MoS₂ and WS₂ are the most widely used as solid lubricants for space applications because of their low friction coefficient and good wear resistance. But pure MoS₂ and WS₂ films have poor tribological behavior in humid or oxygenous environments. To improve the tribological properties, in this work, the WS₂/Ag composite targets with different Ag contents were fabricated by pressing the ball-milling mixture of 2H-WS₂ and Ag powders, and then the WS₂/Ag composite films were deposited on medium carbon steel substrate by radio frequency (RF) magnetron sputtering. The effects of Ag content and sputtering pressure on the microstructure and tribological properties of the films were investigated. Meanwhile, Mo sulfide/Ti composite films were prepared by sulfurizing precursor Mo/Ti films. The influence of Ti content, sulfurizing temperature and time on the morphology, microstructure and tribological properties of the films were also discussed.The morphology, microstructure and chemical component of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The adhesion of the film to the substrate was determined by scratch test. The tribological behavior was investigated using a ball-on-disk tribometer in vacuum and in humid air, and the worn surface was characterized by scanning electron microscopy (SEM) to evaluate the wear resistance of the films.It was found that WS₂ and Ag were both amorphous in the WS₂/Ag composite films and pure WS₂ film. The microstructure and tribological properties of the films varied with the Ag content. Compared with the pure WS₂ film, the WS₂/Ag composite films had better compact microstructure and lower friction coefficient. Thereinto, the composite film with the content of 5.05 at.% Ag had the most compact microstructure, the lowest friction coefficient and the best wear resistance. So the addition of Ag in the films increased obviously the environmental stability of tribological behavior. At the same time, the high deposition pressure resulted in weakened densification, lower adhesion strength, film growth with column form, and increase in the ratio of S to W.The precursor films, sulfurizing temperature and time affected seriously the microstructure and tribological behavior of the Mo sulfide/Ti films. In the experiments, all the three precursor Mo/Ti films were sulfurized in the S vaporous ambience from 400℃ to 500℃ for different times (1～20 h). The results showed that 450℃ was the best sulfurizing temperature. S and Mo reacted more and more adequately when the sulfurizing time wasincreased, and the content of Mo sulfide increased synchronously. When the sulfurizing time was increased to 15 h, the Mo sulfide/Ti films had the most compact microstructure and the best tribological behavior. The film was sulfurized by the precursor Mo/Ti film with the content of 16.95 at.% Ti had the most compact microstructure and the lowest friction coefficient under the same sulfurizing condition. Thus the addition of Ti improved the tribological behavior of Mo sulfide/Ti films. In conclusion, the best sulfurizing temperature and time were 450℃ and 15 h.