Direct laser interference patterning of tetrahedral amorphous carbon films for tribological applications

In this work, the influence of surface topography and micro structural changes on the tribological properties of tetrahedral amorphous carbon coatings (ta-C) structured using a holographic technique the direct laser interference pattering (DLIP) is investigated. By utilizing a nanosecond pulsed UV-laser (wavelength 355 nm), both ablation and graphitization thresholds were determined as a function of the pulse number. Incubation effects for the ablation threshold (~ 205 mJ cm- 2) were found to be negligible. However, for the graphitization of the film thresholds varying from 47 to 74 mJ cm - 2 were observed depending on the number of laser pulses utilized (from 1 to 30) and thus obtaining an incubation factor of 1.13. Using two- and three-beam interference setups, dot- and line-like periodi c arrays were fabricated. The tribological performance of these patterns was investigated under reciprocating sliding with a ball on disk method under non-lubricated conditions showing that coefficient of friction can be reduced from ~ 0.089 (un-patterned) to ~ 0.055 patterned ta-C (~ 30% reduction). The results can be explained based on the reduction of surface contact area combined with high hardness as well as the good intrinsic tribological properties of the ta-C films