In-situ Observation and Discrete Element Simulation of Powder Lubrication Mechanism at Different Slip Velocities and Loads

Abstract

In this paper, the powder lubrication layer composed of graphite particles was prepared by spray method and the effect of velocity and load on the friction characteristics of graphite layer was investigated using a friction tester that can observe the friction interface in real time. Subsequently, 3D surface profilometer, SEM, and EDS were used to characterize the morphology and elements of worn surfaces. The friction results show that at low slip velocity (5 mm/s) and lower load (4N), only partial powder lubrication layer was formed in contact interface, the surface of the graphite layer exhibited obvious peeling characteristics. When slip velocity is too fast (20 mm/s), the dissipation of powder layer increases and the metal substrate is exposed, while there are serious abrasions and chip exfoliation. At the velocity of 12.5 mm/s, the graphite layer shows the best lubrication effect, and the worn surface is more flat compared with that of applying other velocities. The coordination number, the total number of force chains and high stress particles inside the graphite layer during friction process were calculated using the discrete element method at different velocities. With heavy load (8N) that dense force chains are formed at the interface. But the powder layer is easily damaged throughout that the substrate contact directly, thus the powder layer of interface is unevenness extremely. Trying to provide a reasonable explanation for the inherent mechanism of the influence of velocity and load on the lubrication effect of the powder layer.