FRICTION BEHAVIOR OF PULSED-LASER DEPOSITED TUNGSTEN DISULFIDE FILMS

This research describes the friction behavior of pulsed laser-deposited tungsten disulfide films. A ball-on-flat apparatus, in which a 440C stainless steel ball was held on a rotating dish coated with a WS2 film, was used as the test configuration. Friction measurements were made in dry nitrogen and in laboratory air. Wear surfaces were characterized by scanning electron microscopy and Raman spectroscopy. The friction coefficient of the film in dry nitrogen was 0.04, and in laboratory air it rose to between 0.10 and 0.15. In the dry nitrogen case, friction induced some degree of crystallinity into the otherwise amorphous film, while rubbing in air mostly resulted in oxidation of the film. Transfer films formed in a dry environment were smooth, tenacious and firmly adherent to the steel counterface. By contrast, the films formed in air were patchy and powdery in nature.