Amorphous carbon coatings and their tribological behaviour at high temperatures and in high vacuum

Abstract

The aim of this research work is a comparative study of three different types of amorphous, diamond-like carbon (DLC) coating, performing under high temperature and high vacuum conditions. A series of hard carbon coatings have been produced by PVD magnetron sputtering and plasma decomposition (low-pressure PACVD) using standard in-house equipment. Sputtered amorphous hydrogen free carbon (a-C), r.f. plasma deposited hydrogen containing amorphous carbon (a-C:H) and titanium doped hydrogen containing amorphous carbon (Ti–C:H) have been prepared on steel disks. Different tests have been carried out for the characterisation of the mechanical properties and the tribological behaviour at high temperatures (up to 450°C) and/or in high vacuum (up to 3×10⁻³ Pa). A recently self-built vacuum pin-on-disk test rig was used for the investigations. The examined tribological coatings show good microhardness and excellent friction properties, when sliding against steel at ambient air. Unfortunately, in high vacuum and at high temperatures the friction coefficients are high and the coatings fail rapidly. After a running-in at ambient air, however, the coatings depict initially ultralow friction in vacuum and during heating. The coefficients of friction fall to values of about 0.02 to 0.04. The results of the tribological model tests will be discussed.