The running-in mechanisms of binary brass studied by in-situ topography measurements

In this study, we investigate the running-in behavior of brass (i.e. 95% Copper and 5% Zinc) sliding against 100Cr6 under lubricated conditions. Prior to the tribological tests, the materials are characterized using microindention, nanoindentation, Focused Ion Beam analysis (FIB), X-Ray Photoelectron Spectroscopy (XPS), and White Light Interferometry (WLI) in order to quantify the mechanical properties, grain sizes, chemistry, and topography. The sliding experiments are performed using "real time" tribometry with a pin on plate tribometer with varying contact pressures (1-4. MPa) and sliding velocities (10-20. mm/s).We found that a significant reduction in friction during running-in occurs only at a small range of pressure (2.4-2.9MPa). We suggest that two main mechanisms are favorable for running-in. The first mechanism is the presence of ZnO in the near-surface region of the wear track, which acts as lubrication and reduces the friction. The second mechanism is the pr esence of C/CHX within the first 200nm of the pin which acts as a passivation layer and thus keeps the transfer film thin and stable.