Friction and Wear Behaviors of Ag/MoS2/G Composite in Different Atmospheres and at Different Temperatures

Abstract

Silver-based composite with 15 vol% MoS2 and with 5 vol% graphite was prepared by powder metallurgy method. The impacts of the counterface materials, atmosphere, and temperature on the tribological behavior of the composite were investigated. It was found that when sliding against brass less effective lubricating film formed, causing a higher friction and wear comparing with ASTM-1045 steel. With the increasing proportion of oxygen in the O2/N2 atmosphere, the wear rate and friction coefficient ascended slightly. At 200 °C, the combination lubrication of graphite, MoS2, and Ag contributed to a low friction coefficient (0.07) and wear rate (6.56 × 10−6 mm3/Nm). At 400 °C, graphite lost its lubricating role, while silver became excessively soft. Large amount of MoS2 was oxidized into MoO3, and the residual MoS2 formed some island-like lubricating films. Severe adhesive wear occurred on the contact surface, which led to a high friction coefficient (0.25) and a great increase of the wear rate (23.2 × 10−6 mm3/Nm). At 600 °C, a relatively low friction coefficient (0.1) was obtained because of the formation of high-temperature solid lubricants, (Ag2Mo4O13 and Ag2Mo2O7) and liquid Ag2Mo2O7. However, the wear rate at 600 °C was the highest (32.6 × 10−6 mm3/Nm) due to the thick transfer layer.