Effect of MoS2 additive on electrical pitting mechanism of lubricated surface for Babbitt alloy/bearing steel pair under ac electric field

In this study, a static electrical pitting tester, SEM, and EDS are employed to investigate the effects of supply voltage, supply current, MoS2 concentration, and oil film thickness on the mechanism of electrical pitting for the lubricated surface of Babbitt alloy/bearing steel pair under ac electric field. The pitting regimes, consisting of pitting and no-pitting regimes, have been established in terms of the supply voltage, the oil film thickness, and MoS2 concentration at different supply currents. The area of pitting regime increases with increasing MoS2 concentration and supply current. It is seen from the pitted surfaces of the Babbitt alloy block that there exists an obvious concave crater with a few plateaus. According to the force measurement, the formation process of the metal column is proposed. The cross-sectional area of the plateau significantly increases with increasing oil film thickness and MoS2 concentration. Moreover, the ratio of pitting area to interface power (Ap/P) increases with increasing MoS2 concentration and oil film thickness at the oil film thickness less than 6 μm. When the oil film thickness increases from 6 to 10 μm, the value of Ap/P quickly increases to about 10 times, because MoS2 powders can sufficiently suspend on the oil across the gap.