Three-body Contact Friction of MoS2 Thin Films in Space Rolling Bearings

Because of the weightless environment of space, space dust can easily enter the spacecraft. In the long time running, the friction pair will produce debris. Space dust and debris can affect mechanical lubrication. It is difficult to reveal the failure mechanism of solid lubricated bearings caused by space dust and debris. The friction characteristics of MoS2 (molybdenum disulfide) lubricated film of space rolling bearing were studied by molecular dynamic simulation. Fe-Ni-Cr alloy was used as the reference bearing material in the simulation to explore the interaction between the film and the substrate. Firstly, the atomic model of MoS2 film and Fe-Ni-Cr alloy was established. Based on this, the friction contact conditions of MoS2 film were divided into two-body contact and three-body contact according to the actual scene. Secondly, the friction and wear mechanism of MoS2 film under three-body contact condition was explored by comparing the friction results of two-body contact and three-body contact. Finally, the effect of rough substrate on three-body contact wear of MoS2 film was explored by changing the substrate structure. For the surface,under the condition of two-body contact, the abrasive particles will tear the film, and the ploughing phenomenon will appear under the action of load. Under the condition of three-body contact, there is no tearing or ploughing phenomenon on the surface of the film. The wear of three-body contact is less than that of two-body contact. The friction coefficient of three-body contact is less than that of two-body contact. Under the condition of three-body contact, the rough surface of the substrate is not conducive to the adsorption of thin films and accelerates the wear of thin films. The effect of load on the adsorption of rough substrate and thin film is obvious. When the load exceeds 300 nN, the adsorption energy of rough substrate and thin film will change abruptly. The friction and wear mechanism of three-body contact is different from that of two-body contact. Under the condition of two-body contact, the abrasive particles lead to sliding friction. During the process of motion, the abrasive particles accumulate and release tangential force on the surface of the film (stick-slip phenomenon). When the accumulated tangential force exceeds the strain limit of the film, the film will be destroyed. Under the condition of three-body contact, the abrasive particles have both rolling friction and sliding friction. When the abrasive slip velocity is kept constant, the abrasive spin velocity will affect the friction and wear of the film. In the process of three-body contact friction, there is no ploughing phenomenon on the surface of the film, which leads to the tear of the film. At atomic scale, the spin effect of abrasive particles weakens the accumulation of tangential force on the surface of the film, thus effectively reducing the friction force and the wear of the film. In the process of three-body contact friction, the slight convexity on the rough substrate obstructs the motion of the film and increases the friction force, and the reduction of the contact area between the film and the substrate weakens the absorbability of the substrate and the film. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.