Preparation and characterisation of low-friction TiB 2-based coatings by incorporation of C or MoS 2

Abstract

Hard, low-friction, TiB 2-based coatings incorporating C or MoS 2 have been synthesised by magnetron co-sputtering from TiB 2 and C or MoS 2 targets. The coating microstructure was characterised by glancing angle X-ray diffractometry and photoelectron spectroscopy. The friction coefficient was measured using pin-on-disk tribometry and hardness by nanoindentation. Our TiB 2–C coatings were found to consist of two phases, diamond-like carbon (DLC) and a hexagonal TiB 2 type structure into which carbon is incorporated. A friction-reducing effect was observed only at C concentrations above 66%, where a significant quantity of DLC phase was able to form. For TiB 2–MoS 2 coatings, a reduced friction was observed, even at low concentrations of MoS 2. With both types of lubricants, a trade-off between hardness and friction coefficient was found. Coatings exhibiting a relatively high hardness of 20 GPa and friction coefficients as low as 0.05 could be obtained by choosing a suitable composition. Low friction could be obtained for temperatures as high as 400 °C for the TiB 2–MoS 2 coatings, whilst the TiB 2–C coatings exhibited a sharp increase in friction coefficient above 150 °C.