Tribological properties of PVD titanium carbides

Abstract

The influence of the acetylene flow rate on the tribological properties of TiC films produced by cathodic arc plasma deposition (CAPD) on the high-speed steel substrates was investigated. The following properties of films were tested: phase and chemical composition, microhardness, adhesion characterised by the scratch method, thickness, fracture morphology (by SEM), surface roughness, friction coefficient and abrasive wear (by ball-on-disk method). The flow rate of acetylene was changed between 20–250 sccm by constant substrate bias voltage of −70 V. The highest values of microhardness of coatings were obtained at a flow rate between 70 and 140 sccm. The maximum of 43 GPa value was achieved at a flow rate of 70 sccm. At flow rates of 20 and above 180 sccm, the microhardness was about 16 GPa. The friction coefficient reaches the value of 0.2, its decreasing is caused by the increase in flow rate of acetylene. Coating abrasive wear also decreases. The highest values of abrasive wear were obtained at the acetylene flow of 20 sccm, for which the dry friction coefficient was 0.54. The abrasive wear of the counter-specimen (ball) gets also bigger for higher values of the dry friction coefficient. By X-ray examination of crystalline structure, reflexes from (1 1 1)TiC and (2 2 0)TiC planes were recorded; they disappear at higher acetylene flow rates. This may be the result of an amorphisation process of the film structure.