Surface and bulk phase analysis of the tribolayer of nanocrystalline diamond films sliding against steel balls

Abstract

Low friction coefficient of nanocrystalline diamond (NCD) films deposited on steel alloys was observed in highvacuum at high-temperature (HV HT) tribological conditions. High wear resistance of the film was observed in high-vacuum at room temperature (HV RT) condition. However, high friction and low wear resistance of the films were measured in ambient atmosphere at room temperature (AA RT) conditions and this was associated to the formation of metal-oxide (Fe2O3 and Fe3O4) layer in the sliding interfaces. Micro-Raman spectra of wear tracks of deformed films and ball scars showed the formation of a carbonaceous bulk tribolayer and this was the main reason for the improved frictional properties in the HV HT conditions. Bulk form of such tribolayer was absent on the ball scar in AA RT condition. The Fe2O3 peak was absent in HV HT which could be one of the important reasons for the low friction coefficient in this conditions. A comprehensive analysis of X-ray photoelectron spectroscopy showed limited oxidation of NCD films and the elimination of contaminated surface layer in HV HT condition which was correlated as a major cause for low friction.