The tribological and structural characterization of nano-structured Ti-Si-N films coated by pulsed-d.c. plasma enhanced CVD

Multiphase nanocomposite thin films composed of nanocrystalline TiN, nanosized amorphous Si3N4, and occasionally amorphous or nanocrysralline TiSi2, were deposited on high-speed steel substrate at 550 °C, using an industrial setup of pulsed-d.c. plasma-enhanced chemical vapor deposition technique. Feed gases used were TiCl4, SiCl4, N2, and H2. The composition of the films could be controlled well, through adjustment of mixing ratio of chlorides. The Si contents in films varied in the range 0-35 at%. It was found that Si contents in coatings play a great role on the quality of Ti-Si-N coatings. Ti-Si-N coatings of high Si contents were less dense than that of low Si contents. Ti-Si-N coatings with coarse grains show poor adhesion to substrates and high electrical resistance. The results indicated clearly that wear-resistant properties of TiN coating remarkably increase with addition of silicon, while friction coefficient remains high (about 0.8) at room temperature and reduces only slightly at elevated temperature (about 0.7 at 400 °C). There was a much lower wear resistance in higher-Si-content films due to coarse mirostructure during formation of coating.