The tribological properties and mechanism of wear of Cu-based sintered powder materials containing molybdenum disulfide and molybdenum diselenite under unlubricated sliding against copper

Under certain conditions, the metals of some heavily loaded tribological units may slide against each other without the benefit of lubrication. In such cases, the heat or electrical conduction properties of the sliding materials are particularly important. Copper-based materials are relevant for such application. In this study, we investigated the wear and friction that occurs between copper-based composites and copper under dry sliding conditions. We varied the composition levels of molybdenum disulfide and molybdenum diselenite (from 1 to 15 percent) that were incorporated into a Cu-based substrate. The specimen composition (Cu+1; 5; 10 and 15 wt% MoS2 and MoSe2) was prepared by sintering powders with an average particle size of 35–40 μm into a hydrogen atmosphere at a temperature of 780 °C for 2 h. Pin-on-disk experiments were performed without any lubrication at a speed of 0.15 m/s while maintaining a contact pressure of 0.127–1 MPa. The prepared samples were used as flat-ended pins and slid against a copper plate to ensure contact conformability. The reference copper rapidly began scuffing and eventually experienced a catastrophic failure of the contact surfaces after a relatively short period of smooth sliding. Scuffing and catastrophic damage was prevented by using powder metallurgy technology to incorporate MoS2 and MoSe2 into the copper. Materials with MoS2 and MoSe2 had a coefficient of friction close to 0.2, undetectable linear wear under a contact pressure of less than 0.255 MPa, and an absence of material transfer between the pin and the copper plate. The solid lubricant embedded in the composite materials disintegrated and lubricated the surfaces; however, a protective layer did not form on the counterface. Heavier loads initiated substantial wear. Material removal resulted from adhesion between the sliding composite materials and the transferred material on the Cu counterface, which forms flaky debris. The mechanism of wear of the composite materials Cu–MoS2 and Cu–MoSe2 is consistent with the material removal process. As a function of composition, the lubricating effect is more pronounced at concentrations greater than 5 wt% of the solid lubricant.