Abstract
Temperature dependent tribological properties of ultra-nanocrystalline diamond (UNCD) films were studied in ambient, dry and unlubricated conditions while sliding against Al 2 O 3 ball. In as-grown UNCD film, there is well defined grain/grain boundary interphase morphology. However, larger grains along with graphite/amorphous carbon (a-C) phase are formed in this film when subjected to tribo-test at 600 °C. These morphological aspects are evident from high resolution transmission electron microscopy (HRTEM). As revealed from micro-Raman spectroscopy, the inner region of wear tracks of high temperature tribo-tested film shows surface chemical changes accompanied with amorphization. In addition, micro-FTIR measurement confirmed pronounced surface oxidation in the wear track of high temperature tribo-tested film. Ultra-low friction coefficient and high wear resistance of these films were measured at room temperature and 200 °C. Such an ultra-low friction coefficient can be attributed to passivation of surface dangling bonds by the formation of weak van der Waals and hydrogen bonds. However, at high temperature (600 °C), the tribological performance of the film was found to degrade and at early sliding passes it deformed and failed abruptly due to accompanied oxidation and amorphization/polymerization. © 2014 by American Scientific Publishers.