Superhard amorphous carbon films for critical lubrication conditions

Carbon films are distinguished by their very low friction coefficient of about 0.1 under dry friction against metals. Hence, promising glide behaviour can be expected even without or with only limited lubrication. Amorphous tetrahedral bonded carbon films (ta-C) with a high fraction of diamond-like bonds and a corresponding very high hardness in the range above 40 GPa (or >HV 4000) show additionally a high resistance against abrasive wear. Such superhard amorphous carbon films can be deposited with high adhesion strength and at low temperatures <100 deg C. The corresponding specially developed deposition technologies based on pulsed vacuum arc discharges are now available on the industrial level. The tribological potential of the ta-C films has been evaluated by oscillating fretting tests for a broad variety of counter part materials and environments. The ta-C films are especially advantageous under dry friction or mixed/boundary lubrication. The resulting improvements are demonstrated by representative industrial applications. For components, e.g. in automotive industry, the ta-C coating of gears and for tools the machining of aluminium alloys are discussed in more detail. Future tasks concern the optimization of the surface topography, the adaptation of lubricants to the special chemistry of ta-C films and the modification of the film systems for the special demands of vacuum tribology.