Tribological characterisation of hard carbon films produced by the pulsed vacuum arc discharge method

Hard diamond-like carbon (DLC) films were deposited on silicon and high-speed steel substrates using a pulsed vacuum arc discharge method. The plasma plume was focused on the substrate using a direct electromagnetic coil. Several methods were used for coating characterisation. The film composition was analysed using Rutherford backscattering spectroscopy and forward recoil spectroscopy. About 0.5 at.% oxygen and about 1 at.% hydrogen was detected in the film. The tribological properties of the carbon films were studied using pin-on-disc tests. The counterface materials employed were alumina and hardened steel (AISI 52100 and M50) pins, which were slid against the coated substrates. The friction coefficient was measured and the wear surfaces were studied. The sliding speed was in the range 0.02-0.6 m/s and the load in the range 5-20 N. The tests were carried out in air with a relative humidity of 50±2% and at a temperature of 24±3 °C. The test results show that the DLC coatings produced for this study generally had a coefficient of friction (μ) of about 0.2. The lowest value measured was μ=0.14. The wear resistance of the coatings was good, provided that the adhesion to the substrate was sufficient. The comparative tests with titanium nitride and titanium aluminium nitride coatings showed that DLC films are considerably more wear resistant than titanium-based coatings.