Grain boundary modification of TiC ultrananocrystalline thin films: Improvement in tribo-physical properties

Abstract

This work reports on the influence of grain boundary modification on the tribological properties of nanocrystalline titanium carbide (nC-TiC) - amorphous carbon (a-C) nanocomposite films. TiC thin films were deposited by magnetron sputtering using TiC target in optimized hydrogen containing atmosphere. Nano/ultrananocrystalline TiC phase and short ranged ordered graphite phase were found to be dispersed in the a-C matrix in thin films. Chemical composition and also the chemical structure of the graphitized phase and a-C in the grain boundary were modified by controlling the substrate temperature. Raman spectroscopy showed that at room temperature, the films were dominated by a-C phase occupying the grain boundary. However, at moderate deposition temperature, graphitization of the film was observed and such modification was associated to the formation of short ranged crystalline graphite phase within a-C matrix. The friction coefficient was found to decreased with increase in the I(D)/I(G) ratio of Raman shift in the films. A sustainable ultralow value of friction coefficient was observed in the films with TiC nano/ultrananocrystalline phase surrounded by nanographitized domains. This could be associated to the layered lattice structure of short ranged graphite phase which readily shears and produces negligible frictional resistance. Sustainability of ultralow value of friction coefficient and high wear resistance are attributed to the formation of graphitized transfer film.