Atomic Simulation of Plastic Deformation Behavior and Mechanics Strengthening Property for Cu / graphene Material

Copper metal is widely used in micro / nano-electromechanical systems, such as mechanical controllers, precision measuring instruments, power appliances, and other important engineering applications because of its excellent mechanical properties, electrical conductivity, and heat dissipation. However, in practice, copper metal materials are often not conducive under complex and harsh service conditions, such as high temperature, high pressure, high speed, high fatigue, corrosive media, and other harsh environments, which cause severe wear and tear of metal parts. Therefore, higher requirements should be imposed on the mechanical strength of copper metal in service, and the main causes of its dynamic contact deformation and strengthening properties should be evaluated. Graphene can improve the mechanical surface/interface contact properties of copper owing to its excellent mechanical properties, high carrier concentration, good thermal conductivity, and low shear properties. The static and dynamic contact behavior of the graphene membrane-substrate interface is primarily studied through atomic force microscopy, finite element calculations, and molecular dynamics simulations; however, finite elements cannot satisfy the requirements of nanoscale space-time and energy-scale calculations, and precision experimental measurements are very limited in revealing the dynamic contact behavior of the atomic-scale interface and costly in studying the mechanism. The molecular dynamics method can be used to study dynamic contact properties and reveal the strengthening mechanism of the membrane-substrate interface at the atomic scale, which can effectively prevent the shortage of precision instrumentation and finite element calculations and is useful for studying the constitutive correlation between dynamic microstructural deformation and mechanical properties. Thus, understanding this plastic deformation information and mechanical strengthening of copper surfaces covered with multilayer graphene is useful for improving the metal material performance of membrane-base interface coupling. Furthermore, it can provide meaningful insights into the performance of copper materials with strengthened and toughened features. Hence, in this study, the dynamic contact characteristics between an indenter and Cu/graphene were explored using a nanoindentation method. The effects of some influencing factors on the copper deformation characteristics were analyzed, such as the copper surface with or without the graphene layer, number of graphene layers, and various crystal planes. The wrinkle contribution of graphene with a fixed double boundary(XY) and single boundary(Y) to the interface contact mass distribution and strengthening was investigated. The analysis results indicated that the elastic deformation of graphene produced load-displacement curves with a linearly increasing trend during the nanoindentation process. The calculation results showed that the Cu surface with the graphene layer effectively improved the material-bearing capacity compared with the surface without graphene. The mechanical properties (hardness and elasticity modulus) exhibited a linear increase with the addition of graphene layers. In addition, the hardness and Young' s modulus were almost 7.4 times those of pure copper, and the strengthening mechanism was derived from the synergistic effects between graphene deformation and homogenization features induced by external loads and the interface contact mass distribution. In terms of double-boundary fixed graphene. The loading-induced wrinkle deformation for single-boundary fixed graphene was larger, and the interface contact quality improved. Furthermore, the corresponding enhancement effect was reduced by 28% compared with that of single-boundary fixed graphene. For the same number of graphene layers, the mechanical properties and plastic deformation of the membrane-base interface exhibited evident anisotropy features for a copper base covered by graphene with different crystal planes. The results of this study can be used to significantly improve the mechanical properties of metallic devices used in microelectromechanical systems.