Tribological properties of amorphous diamond-like carbon coatings

Abstract

A wide range of different amorphous diamond-like carbon (ADLC) coatings are now commercially available. Centre Suisse d'Electronique et de Microtechnique (CSEM) made a tribological characterization of amorphous carbon coatings obtained from seven different suppliers. Pin-on-disk tests using a CSEM tribometer showed generally lower friction and longer life in humid air than in dry air and/or vacuum. Tests are carried out with AISI 52100 ball bearing steel balls, under the conditions of 5 N load at 10 cm s -1 sliding speed, in dry air (relative humidity (RH), less than 3%) or humid air (RH, greater than 97%). Only one supplier proposed a coating showing self-lubricating properties in both dry and humid air. In vacuum, the friction of steel against hard coatings such as TiC or ADLC is high, but the sliding against each other shows good tribological properties. For sliding operation in air as well as in vacuum, the combination of a TiC coating against an ADLC coating can lead to stable and low friction and very low wear, under environmental conditions ranging from vacuum to humid air. In fact, the friction and wear behavior of this couple is even better than that of MoS 2-coated pairs.