Assessment of Topography Parameters During Running-In and Subsequent Rolling Contact Fatigue Tests

Rolling contact fatigue (RCF) is one of the major problems observed in gear mechanisms, which leads to high friction, ultimately resulting in high energy consumption. This paper demonstrates the evolution of surface topography during running-in and subsequent RCF tests under boundary or mixed-elastohydrodynamic lubrication regimes. The case-hardened disks of equal surface finish and hardness are used in the experiments, and the evolution of surface topography is investigated using a white light interferometer. Surface topography at different load stages is measured at three distinct points, on the disks and average roughness and topography parameters are reported. Semi-quantitative techniques are used to determine the asperity-level parameters at different load stages. From the running-in experiment, it is found that running-in is a fast process where substantial change in surface topography occurs due to plastic deformation of most prominent asperity. From the RCF test, it is concluded that within range of the fatigue cycles, the root-mean-square (RMS) roughness (Sq) is negatively correlated with the summit radius (R) and the autocorrelation length (Sal) and positively correlated with the summit density (Sds) and the RMS slope (Sdq). Scanning electron microscope (SEM) analysis reveals the disappearance of grinding ridges, the formation of micropits at a very small scale, and pit growth in the sliding direction.