In situ Observation of the Formation of MoDTC-Derived Tribofilm on a Bearing Steel with Different Surface Roughness by Using a Reflectance Spectroscopy and Its Effects on Friction

In this paper, we evaluated the formation of MoDTC-derived tribofilm and its effects on friction reduction. We conducted in situ observation using reflectance spectroscopy to monitor the tribofilm's evolution during friction, allowing us to estimate its thickness and composition. The results revealed that the rough specimen ( R_a=12.7 nm) maintained a smaller friction coefficient and a larger volume fraction of MoS 2 compared to the smooth specimen ( R_a=2.6 nm). Additionally, using the in situ observed composition and contact state, we inferred changes in the frictional properties of the tribofilm formed on both specimens. This analysis suggested that the pronounced direct contact of asperities, especially evident in the rough specimen, promoted the formation of a low-friction tribofilm (primarily MoS 2 ), enabling the rough specimen to sustain lower friction. Graphical abstract