A VACUUM (10(-9) TORR) FRICTION APPARATUS FOR DETERMINING FRICTION AND ENDURANCE LIFE OF MOSX FILMS

The first part of this paper describes an ultrahigh vacuum friction ap paratus (tribometer). The tribometer can be used in a ball-on-disk con figuration and is specifically designed to measure the friction and en durance life of solid lubricating films such as MoS(x) in vacuum at a pressure of 10(-7) Pa, 10(-9) torr. The sliding mode is typically unid irectional at a constant rotating speed. The second part of this paper presents some representative friction and endurance life data for mag netron sputtered MoS(x) films, 110 nm thick, deposited on sputter-clea ned 440C stainless-steel disk substrates, which were slid against a 6- mm-diameter 440C stainless-steel bearing ball. All experiments were co nducted with loads of 0.49 to 3.6 N, average Hertzian contact pressure , 0.33 to 0.69 GPa, at a constant rotating speed of 120 rpm, sliding v elocity ranging from 31 to 107 mm/s due to the range of wear track rad ii involved in the experiments, in a vacuum of 7 x 10(-7) Pa, 5 x 10(- 9) torr, and at room temperature. The results indicate that there are similarities in friction behavior of MoS(x) films over their life cycl es regardless of load applied. The coefficient of friction mu decrease s as load W increases according to mu = kW-1/3, which is in agreement with the Hertzian contact model. The endurance life E of MoS(x) films decreases as the load W increases according to E = KW-1.4 for the load range. The load- (contact pressure-) dependent endurance life allows a reduction in the time needed for wear experiments and an acceleratio n of endurance life testing of MoS(x) films. For the magnetron-sputter ed MoS(x) films deposited on 440C stainless-steel disks, the specific wear rate normalized to the load and the number of revolutions was 3 x 10(-8) mm3/N.revolution; the specific wear rate normalized to the loa d and the total sliding distance was 8 x 10(-7) mm3/N.m; and the nondi mensional wear coefficient was approximately 5 x 10(-6). The values ar e almost independent of load in the range 0.49 to 3.6 N, average Hertz ian contact pressure of 0.33 to 0.69 GPa.