Ws <sub> 2 </ Sub>-ag Nanocomposite Thin Film Preparation And Tribological Performance

Great challenges have been confronted with the lubricant in severe operating environments (e.g., high temperature or vacuum, or circle between high & low temperature) where lubricating oil cannot be used. Solid lubricating films are often applied as an alternative lubricant and are finding greater practical uses in the fields of vacuum equipments, aviation and space applications. Due to excellent tribological properties and higher oxidation resistance temperature than M0S2, WS₂ has been practical solution for more rigorous application occasion. However, humidity susceptibility plays a key role in preventing the WS₂ lubricating films from being widely used. Various attempts have been carried out to enhance humidity susceptibility resistance, and metal additives have been demonstrated to meet the challenge.In this work, WS₂-Ag composite targets with different Ag contents were fabricated by pressing the ball-milling mixture of 2H-WS2 and Ag powders. The WS₂-Ag composite films with different Ag contents were deposited with the composite targets by both direct current magnetron sputtering and radio frequency (RF) magnetron sputtering under different deposition pressures of argon.The morphology, microstructure and chemical component of composite films were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) and energy dispersive X-ray spectroscope (EDS) respectively. Scratch tests were performed to determine the adhesion of as-deposited films with the substrates. The nanoscale WS₂ and Ag in the films deposited with DC magnetron sputtering were both amorphous, while the films deposited by RF magnetron sputtering was either dual nanoscale amorphous phases at low Ag content or amorphous WS2 accompanied with nanocrystalline Ag phase at high Ag content. The addition of Ag facilitated the densification of films and increased the adhesion strength. By RF magnetron sputtering, 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 tribological properties for WS₂-Ag nanocomposite films were investigated by ball-on-disk trobometer in vacuum and in humid air. The effects of Ag content, deposition pressure, test environment, applied load and rotating frequency on the friction and wear behavior were discussed. Ag in films has improved the humidity susceptibility resistance andstability of friction. The composite films deposited by RF magnetron sputtering the tagart containing 15 at.% Ag presented the lowest friction coefficient and highest durability. The decrease in friction coefficient at low Ag content owed to the improvement of contact condition cause by plastic rheologic deformation of Ag;the increase in durability was resulted from both densification and dispersion-strengthen effect of Ag in the nanocomposite films.