Pitting mechanism on lubricated surface of babbitt alloy/bearing steel pair under ac electric field

The mechanism of electrical pitting on the lubricated surface of babbitt alloy/steel pair is investigated, and the threshold condition to avoid the occurrence of electrical pitting is also established by using a static electrical pitting tester with high precision under the influence of ac electric field. According to the SEM micro-graph and EDS analysis are, the mechanism of electrical pitting is significantly influenced by the interface power and the oil film thickness. At the smaller oil film thickness, the eroded surface of babbitt alloy exhibits a concave crater with a few micro-porosity in the vicinity of center region with a plateau on its surrounding, especially at high supply current. The polished track can be observed at the plateau. A large amount of tin element transfers to the steel ball surface because the molten tin contacts the ball. At the higher oil film thickness, only a little amount of metal element transfers to each other. The major pitting area of the babbitt alloy is caused at the initial stage of the arc discharge. With increasing arc discharge time, the pitting area increases slowly, and finally reaches a saturated value. When the electrical pitting occurs, correlation formula for the electrical pitting area in terms of interface power and melting point of material has been established. It is found that the higher interface power and the lower melting point of material, the higher electrical pitting area. Two electrical pitting regimes are found, namely, pitting and no-pitting regimes. The boundary between the pitting and no-pitting regimes is called the threshold voltage. Correlation formula for the threshold voltage in terms of oil film thickness and melting point of material is derived.