Influence of MoS2 on the Rolling Contact Performance of Bearing Steels in Boundary Lubrication: A Different Approach

摘要

Effective lubrication has been achieved under vacuum conditions by employing MoS2 as a solid lubricant. The primary reason for its ability to reduce friction is attributed to its crystal structure, which allows easy shearing of MoS2 layers. This research explores the possibilities of utilizing MoS2 in soluble and insoluble forms to improve the performance of tribological systems. In this study, spherical rolling elements were coated with Ti-MoS2 and their tribological performance was evaluated in a ball-on-rod tribometer operating in boundary-lubricated (PAO ISO 10 oil) conditions. The results of these tests were compared with similar tests performed on uncoated steel specimens using PAO ISO 10 oil with and without a molybdenum dialkyldithiocarbamate (MoDTC) additive. The L-50 fatigue lives of M50 rods tested against Ti-MoS2 coated balls were found to be similar to those obtained from tests performed on uncoated steel specimens using oil with MoDTC (1 wt%); that is, the L50 fatigue lives of M50 rods were improved by more than a factor of 2 in both cases. Tribofilms generated on M50 rods during testing with Ti-MoS2 coated balls in neat oil and uncoated balls in MoDTC (1 wt%) mixed oil were observed to be similar. Wear track analysis on M50 rods tested against Ti-MoS2 coated balls indicated that the tribofilms are mixtures of MoS2 and amorphous hydrocarbon (a-C:H). A possible mechanism for the formation of the a-C: H on the counterface is proposed based on the experimental investigations in this study. Further, it is concluded that the Ti-MoS2 coating on the spherical rolling elements functions as an MoS2 additive source to the lubricating oil rather than as a tribological coating.