Low-friction TiN coatings deposited by PACVD

Hard coatings like TiN are widely used to protect cutting and forming tools against wear and corrosion. The aim of this study was to develop TiN coatings deposited by PACVD (plasma-assisted chemical vapor deposition) with different chlorine contents to optimize their friction and wear properties. Coating structure and chemical composition were characterized using scanning electron microscopy (SEM), wavelength-dispersive electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The tribological properties of the coatings were evaluated using a ball-on-disc tribometer. Hardness measurements with a nanoindenter gave values of 17.9 … 24.8 GPa for TiN according to the chlorine content. Extremely low friction coefficients against ball-bearing steel of 0.17 … 0.22 have been obtained for those TiN coatings showing a chlorine content in the range of 3.2 … 6.3 at.%. For lower chlorine contents, the friction coefficient increases to 0.75. The wear tracks were investigated with an optical profiler where mainly material transfer was found for low chlorine contents whereas for higher chlorine concentrations the dominant wear mechanism was mild abrasion. The addition of low chlorine impurity levels by PACVD allows one to tailor friction and wear properties of TiN coatings.