TRIBOLOGICAL BEHAVIOR OF NANOCRYSTALLINE ZINC-OXIDE FILMS

This paper describes the room temperature tribological characteristics of nanocrystalline zinc oxide (ZnO) films. The films were grown onto 440C stainless steel substrates by pulsed laser deposition (PLD) using the 248 nm line from an excimer laser to ablate a hot pressed hexagon al ZnO target. The substrate temperature and oxygen partial pressure w ere varied to grow films with different stoichiometries and grain size s. Friction measurements were made against a 440C steel counterface in a ball-on-flat configuration. The friction coefficient of a conventio nal hot pressed ZnO disk was high, 0.65; the steel counterface after w ear testing was full of scratches. By contrast, the friction coefficie nts of PLD ZnO films were between 0.16 and 0.34; the steel counterface after testing was practically free of scratches. Extensive plastic de formation of ZnO was observed on the wear scars. The friction behavior of ZnO films was sensitive to Hertzian stress and sliding speed, but once a smooth wear scar was formed, the test conditions had no signifi cant effect on the friction. The improved tribological performance of the PLD ZnO films was attributed to their nanocrystalline grain struct ure and oxygen substoichiometry. (C) 1997 Elsevier Science S.A.