Structure and high-temperature tribological behavior of Ti–Si–C nanocomposite thin films

Multiphase, thin Ti–Si–C films have been deposited from elemental targets (Ti, Si) by pulsed, double source, reactive magnetron sputtering in argon–acetylene atmosphere on steel substrates. Optical emission plasma spectroscopy was used to control deposition conditions. The composition of the coatings was determined by electron microprobe working in energy/wave dispersive spectroscopy mode, based on reference samples analyzed by Rutherford Backscattering Spectroscopy. X-ray diffraction indicates the coexistence of TiCx and traces of Ti5Si3Cx, TiSi2 and SiC phases in dependence on nominal composition of the coatings. Low-temperature (400 °C) deposits transform from nanocrystalline to amorphous with increasing silicon content. Microhardness of 2-μm-thick films on AISI 440C steel substrates have been tested by means of Vickers indentation and ranges from 7.5 to 16 GPa. Tribological behavior during dry friction in air of normal humidity was studied in the wide temperature range (20 to 450 °C) using ball-on-disc configuration. The lowest, room temperature friction (μ<0.3) was observed for samples containing less than 15 at.% of silicon. These films, consisting of TiCx nanocrystallites, encapsulated in amorphous SiC/aC:H matrix, show also the best high-temperature properties. Results are discussed in terms of chemical and phase composition of studied films.