Molecular Dynamics Simulation on Friction and Thermal Properties of FCC Copper in Nanoscale Sliding Contacts

In nanoscale sliding contact,adhesion effects and adhesive force are predominant,and high friction force will be produced.Friction energy is mainly converted into heat,and the heat will make nanomaterials become soft to affect friction behaviors,so it is important to investigate the friction and thermal properties of the nanoscale sliding contacts.A model of a nanoscale sliding contact between a rigid cylindrical tip and an FCC copper substrate is developed by molecular dynamics simulation.The thermal properties of the substrate and the friction behaviors are studied at different sliding velocities and different tip radii.The results show that at a low sliding velocity,the friction force fluctuation is mainly caused by material melting⁃solidification,while at a high sliding velocity the material melting is a main factor for the friction reduction.The average friction forces increase at initial phase and then decrease with increasing sliding velocity,and the average temperature of the substrate increases as sliding velocity increases.Increasing tip radius significantly increases the temperature,while the coupled effects of tip radius and temperature rise make friction force increase slightly.

Application of MoS_(2)in the space environment:a review

A considerable portion of space mechanism failures are related to space tribological problems.Cold welding in high vacuum;surface erosion and collision damage caused by various radiations,high temperature oxidation under atomic oxygen(AO)bombardment;and thermal stress caused by temperature alternation all alter the physical,chemical,and friction properties of materials.In particular,the space vibration caused by alternating temperatures and microgravity environments can alter the motion of the contact body,further affecting its friction properties.Improving the friction properties of contact surfaces in the space environment is an important way to extend the service life of spacecraft.Traditional lubricants can no longer meet the lubrication requirements of the space environment.This study describes the characteristics of the space environment and the applications of solid lubricants.The friction properties of MoS_(2),a solid lubricant widely used in space,are discussed.The synergistic lubrication of MoS_(2)with surface textures or metals is presented.Advances in research on the friction properties of collision sliding contacts in the space environment are reviewed.The combination of MoS_(2)and soft metals with surface textures is introduced to reduce the effects of vibration environments on the friction properties of moving parts in space mechanisms.Finally,the challenges and future research interests of MoS_(2)films in space tribology are presented.