Preparation And Tribological Performance Of Pulsed Laser Deposited WS_x/a-C Composite Films

Tungsten disulfide as a solid lubricant is often applied in the fields of vacuum equipments, aviation and space applications due to its low friction coefficient and good wear resistance; but the properties of films will debase in air especially in humid air. How to expand the application of WS2 thin films in the atmosphere has become one of the study directions of many scholars from home and abroad. It was found that nanocomposite films show low friction and long endurance in comparison to single-layer films.This thesis focuses on the preparation of WSx /a-C nanocomposite films fabricated by pulsed laser deposition (PLD) under co-deposition conditions, which developed by optimizing the PLD synthesis parameters of WSx and a-C film. The effects of carbon content on the microstructure and tribological properties of the films were investigated, and the tribological properties of the films in the atmospheric environment were improved effectively. The main achievements are as follows:1. A near-stoichiometric WSx film with dense structure could be grown under optimized growth conditions by orthogonal experimental method, including deposit temperature at 150℃, distance between target and substrate at 45 mm and laser flux at 5 J /cm-2 and argon pressure at 1 Pa. The ratio of sulfur to tungsten ranged from 1.05 to 3.75 and the film quality deteriorated dramaticly when the ratio of sulfur to tungsten exceeded 2.0.2. An amorphous structure of WSx films were deposited by PLD under room temperature, but the WS2 diffraction peak was found obviously when the temperature rasied to 300℃. The friction coefficient of the WSx film prepared under optimal conditions was the lowest,0.11, and the wear rate was an order of 10-6 mm3/Nm. A stoichiometric WSx film was more easily to be obtained by using a low substrate temperature and high deposited pressure, however, the ratio of sulfur to tungsten and the friction coefficient of the film was inversely proportional.3. Amorphous carbon films were deposited by ablation of graphite target, its friction coefficient was lower than pure WSx film and more smooth, more desen surface morphology.4. WSx /a-C composite films were fabricated by using fan-shaped WS2 and graphite combined target under co-deposition conditions. The ratio of sulfur to tungsten remained at 2.0 was benefit for the hexagonal layered structure of the films formed. The tribology performances of WSx/a-C composite films are better than those of single WSx film and a-C film. The composite films deposited at WS2/G (Graphite) ratio of 1.0 of combined target exhibits excellent wear resistance.5. A certain number of particles and holes were found on the surface of the WSx composite films by PLD, and lower binding force between film and substrate, affected the lubricating properties of the films. In order to achieve industrial applications, the relationship of the films between valence-bond structure and tribological properties should be further studied.