In-Situ Observation and Discrete Element Simulation of Solid Graphite Lubrication Mechanism

Solid lubrication is a green manufacturing technology with high efficiency, which saves energy and material and thus it is suitable for extreme conditions in mechanical engineering fields such as aerospace and high temperature mold. In this study, a graphite layer of specified thickness was prepared on the end face of the upper specimen by the directional spray method. The effect of velocity and load on the friction characteristics of the graphite layer were investigated using a friction tester capable of real time observation of the friction interface. Subsequently, a 3D surface profilometer, SEM, and EDS were used to characterize the morphology and elemental composition of the worn surfaces. The results show that the lubrication performance of the graphite layer is most effective with a flatter worn surface (S_a and S_Z are smaller) and higher carbon content when the velocity is 12.5 mm/s and the load is 4N. Meanwhile, force chains are short, numerous and lasting for a long time, while being uniformly distributed in all directions and velocity fluctuates greatly, with slowly decreased coordination numbers. This study aims to provide a reasonable explanation for the mechanisms by which velocity and load influence the lubrication effect of the powder layer.