LUBRICIOUS ZINC-OXIDE FILMS - SYNTHESIS, CHARACTERIZATION AND TRIBOLOGICAL BEHAVIOR

Solid lubricants that are effective over an extreme range of operating temperatures are necessary for the development of new generation high -performance gas turbine engines with increased propulsion capability. While oxides have the potential to perform as high-temperature lubric ants, they typically have high friction and create abrasive wear debri s at low temperature. The objective of this work was to create oxides that have good tribological properties at room temperature through con trol of microstructure and stoichiometry. Zinc oxide films were grown by pulsed-laser deposition. The stoichiometry and microstructure of th e films were controlled by adjusting substrate temperature and oxygen partial pressure during pulsed-laser deposition. Chemistry and microst ructure were probed using SEM, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Friction coefficients and wear li fe were measured using a ball-on-flat tribometer. The degree of simila rity of the coatings to bulk ZnO was RT, vac < RT, O-2 < 300 degrees C , vac < 300 degrees C, O-2 Coatings with oxygen deficiency and nanosca le structure have low friction (i.e. mu < 0.2) and long wear lives (i. e., greater than 10(6) cycles) at room temperature. As the chemistry a nd crystal structure of a coating approaches that of bulk ZnO, its tri bological properties degrade and can become load/speed sensitive. An i mportant result of this study is that oxides can be made to provide go od tribological properties at room temperature. Thus, there is signifi cant potential to produce low-friction, low-wear oxide coatings for wi de-temperature range applications by controlling nanostructure and oxy gen vacancies.