TRIBOLOGY OF CARBONACEOUS FILMS FORMED BY ION-BEAM-ASSISTED DEPOSITION OF ORGANIC MATERIAL

By combining the vapour deposition of a silicone oil (pentaphenyltrimethyltrisiloxane) and simultaneous energetic ion irradiation, carbonaceous films (i-silicone films) 0.1-0.3-mu-m thick were coated on disc samples of hardened SUJ2 (AISI 52100). As the ions for irradiation, 1.5 MeV Ar+, 400 keV N+ and 200 keV Ti+ were used. The frictional properties of the i-silicone coated disc, in particular the dependence of the friction coefficient mu on humidity, were tested with a pin-on-disc method using a hardened SUJ2 pin. All the i-silicone coatings prepared by using the three ion beams exhibited similarly low values of mu almost-equal-to 0.05 in ambient atmosphere. In both air and nitrogen gas the i-silicone coating exhibited a low value of mu almost-equal-to 0.05 for a relative humidity range from 70% to 20%, the lowest humidity available. On the contrary, diamond-like carbon prepared by plasma-enhanced chemical vapour deposition displayed a value of mu almost-equal-to 0.2 for the same humidity range. In dry nitrogen, both the i-silicone and the diamond-like carbon exhibited an extremely low value of mu less-than-or-equal-to 0.02. Reasons for the moisture-insensitive frictional properties of i-silicone and features of the ion-beam-assisted deposition coating process of organic materials are discussed.