Study on Pitting Fatigue Properties of DLC Coating under Pure Rolling Conditions

Abstract

To extend the cruising range of electric vehicles (EV), it is necessary to improve the power consumption rate in EV. By rotating the motor at high speed, it is possible to reduce the size and weight, which leads to an improvement in the power consumption rate. However, the fatigue life of the bearings and gears will decrease; therefore, pitting will increase. Diamond-like carbon (DLC) film is expected as one way to prevent the pitting of bearings and gears. DLC has various excellent tribological properties such as low friction and high wear resistance. However, there are few studies to evaluate the pitting resistance of DLC films. In addition, in the contact surface of gears, sliding and rolling contact occur at the same time. Therefore, it is necessary to evaluate the pitting resistance of DLC films at pure rolling condition. In this study, we applied two types of DLC film (ta-C, a-C:H) to the surface of balls. Ball-on-disk tests were conducted under the conditions of lubrication of base oil and pure rolling contact to investigate the effect of these types of DLC film on pitting resistance. We confirmed that the ta-C type DLC film suppresses pitting.