Pin-on-disc testing of PE-CVD diamond-like carbon coatings on tool steel substrates

The present study deals with the tribological behaviour and the wear mechanisms of 2-μm thick diamond-like carbon coatings. The examined coatings were deposited by plasma-enhanced chemical vapour deposition (PE-CVD) on three tool steel substrates, of different hardnesses. Tribological studies against alumina were performed using a pin-on-disc apparatus under various normal loads (2–20 N) and sliding speeds (0.1–0.3 m s−1), while the relative humidity of the environment was kept constant, equal to 25%. The influence of the testing parameters (normal load and sliding speed) and the mechanical properties of the substrate on the wear lifetime of the coatings was determined and the involving wear mechanisms were identified. It was found that both the sliding conditions and the hardness of the substrate affect strongly the wear rate and the wear lifetime, but have no significant influence on the value of the friction coefficient, which was found to be lower than 0.15 for all the testing parameters.