Abstract
The feasibility of reducing the friction coefficient of TiB 2-based coatings by the incorporation of carbon has been investigated for both multilayer and co-sputtered coatings. Characterisation was performed using pin-on-disk tribometry, nanoindentation, glancing angle X-ray diffractometry, X-ray photoelectron and Auger electron spectroscopy. The co-sputtered coatings were found to consist of two phases: a hexagonal TiB 2-type structure into which carbon is incorporated and a diamond-like carbon (DLC) phase. C is preferentially incorporated into the Ti(B,C) 2 phase and the lubricating DLC phase only starts to form once saturation is reached. Consequently, a reduction in the friction is only found at total C concentrations higher than 50 at%. For the multilayers, there was an increase in the overall carbon content required to obtain a friction-reducing effect from about 10–50 at% as the TiB 2 sublayer thickness was decreased from 100 to 1 nm. This was attributed to an increase in the relative proportion of carbon bonded with TiB 2 in the interface regions. Coatings with a hardness of about 20–30 GPa and friction coefficients of <0.2 against a steel ball could be obtained at a suitable composition.
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