The effects of oxygen and water vapor on lubrication, transfer, and failure were investigated. In general, it was found that the lubrication mechanism was the formation of thin, metallic-colored, coalesced MoS2 films on each sliding surface and the plastic flow of these films between the sliding surfaces in relative motion. In the air, the failure mechanism was the transformation of the metallic-colored, coalesced MoS2 films to a black, powdery material. Water in the air atmosphere appeared to accelerate this transformation rate. In argon, no transformation of MoS2 was observed (with a microscope), but cracking and spalling of the coalesced M0S2 film resulted in its gradual depletion. The second part of this study (reported herein) investigated the effect of substrate surface roughness (1) on the lubrication mechanism; (2) on the failure mechanism and the chemical composition of the black, powdery material on the wear track; (3) on the wear life; (4) on the friction coefficient; and (5) on the rider wear rate. Rubbed MoS2 films were applied to polished disk substrates (0.09kO. 02 pm CLA (centerline average)), sanded (0.3050.05 ym CLA), and sandblasted (1.210.2 pm CLA). To separate any effects caused by oxidation of the MoS2 film, experiments were conducted in both moist air (10 000-ppm H20) and dry argon. The tests were stopped at preset sliding intervals, and then the sliding surfaces were examined by optical microscopy at magnifications to 1100. A pin-on-disk sliding friction apparatus and 440C HT steel specimens were used. The experimental conditions were:A temperature of 25' Cy.A sliding speed of 2.6 meters per second (1000 rpm).A load of 1 kilogram.
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