FRICTION AND WEAR MECHANISMS OF SMOOTH DIAMOND FILMS DURING SLIDING IN AIR AND DRY NITROGEN

Under the influence of extreme contact pressure and high frictional he ating, the real contact areas of diamond films may undergo phase trans formation and gradual wear during long-duration dy sliding contacts. T he wear debris particles that accumulate at the contact interface can then dominate the long-term sliding friction and wear performance of t hese films. In this study, employing a combination of transmission ele ctron microscopy, electron diffraction, Raman spectroscopy, and electr on energy loss spectroscopy, the authors explored the structural chemi stry of the diamond debris particles and the sliding contact interface s of smooth diamond films (surface roughness: 20-40 nm, root mean squa re (RMS)) and described their friction and wear mechanisms in open air and dry nitrogen (N-2) The results of tribological tests indicated th at the friction coefficients of Si3N4 balls against smooth diamond fil ms were 0.04 in dry N-2 but 0.1-0.15 in air. Friction fluctuated subst antially in dry N-2, especially during long-duration tests. The wear r ates of Si3N4 balls were by factors of 5 to 6 lower in dry N-2 than in air, but a reverse situation was observed for diamond films; their we ar rates were significantly higher in dry N-2 than in air. The results of the surface and structure analytical studies have suggested that t he sp(3)-bonded crystalline diamond had transformed to a sp(2)-bonded amorphous slate, but not to crystalline graphite.