First-principles Study On The Interfacial Friction Between Ag Or Cu And Its Combination With Graphene

Friction phenomenon on human production and life has a significant impact.About 1/3-1/ 2world’s primary energy is consumed in the friction process.Industrial developed countries account for 5% to 7% of GDP is depleted due to friction and wear.Therefore,the study of friction is essential about four centuries ago people have begun to study the friction,the most basic law of tribology is the law of Amundon.With the development of science and technology,the size of modern precision devices is getting smaller and smaller,the specific surface area is getting bigger and bigger,the friction has a decisive influence on the normal operation and service life of the device.Scientists have found a super-lubrication phenomenon from some material studies,and the ultra-lubricating fingers have a friction factor of zero or a wireless close to 0.Ultra-lubrication brings hope for the design and manufacture of modern micro-nano mechanical systems.Two-dimensional material graphene,molybdenum disulfide due to the intergranular atoms between the strong chemical bonds,between the crystal surface is not easy to deformation,while the layer between the weak van der Waals force,the friction between the interface more easily close to zero.This theory was also confirmed in the experiment.The excellent lubricating properties of soft metals Ag and Cu make them suitable for the manufacture of high precision instruments.However,with the need for ultra-low friction or even no friction in the mechanical system or in the micro-nano-scale,the soft metal Ag,Cu lubrication performance has been unable to meet the needs.The modification of the soft metal surface by graphene is expected to solve this problem.In this paper,the first-principles are used to systematically study the frictional properties of metal-metal interface,metal-to-graphene interface and graphite-modified metal interface at the micro-nano scale.Our study found that the metal and metal interface still obeys the Amonton law at microscale.The very low frictional force between the metal and the graphene interface is caused by the weak physical adsorption between the interfaces.The graphite-modified metal interface produces superlubricity phenomenon,the composite interface is easier to achieve ultra-lubricating than the individual graphene interface.