Molecular Dynamics Simulation of Cu2S Crystal in Sliding: Atomistic Friction Behavior and Temperature Dependence

摘要

As substitution of high-lead bronze material which is prohibited around the world, new copper alloys including a sulfide precipitate (Cu_2S) have been developed so far. The alloys have prospect for their nice performance in lubricating behavior under severe condition of friction materials. In order to clarify the basic mechanism, in this study, Cu_2S crystal in sliding motion is investigated from atomic scale. An interatomic potential for hexagonal Cu_2S crystal is constructed based on the first-principle (DFT) calculation. Then it is applied to classical molecular dynamics (MD) simulations, where Cu_2S crystals are sliding each other. Shear resistance and friction between crystalline surfaces of Cu_2S depend largely on temperature as well as the crystalline direction and the sliding velocity. In low temperature, the sliding motion of Cu_2S crystal shows a kind of "stick and slip" behavior, whereas, in high temperature, the atomic movement turns into somewhat fluidic state and becomes smooth. Besides, the sliding resistance depends on the combination of chemical elements (sulfur or copper) of surface layer at the contact. In general, the interaction between sulfur atoms results in low friction under shear. This atomistic mechanism agrees with other metal sulfides (e.g. MoS_2).