Research On Tensile Deformation Property Of Cu-Pb Alloy Based On Molecular Dynamics

With the transition of MEMS(micro-electromechanical systems)to NEMS(nano-electromechanical systems),the device size gradually reaches the nanometer scale,showing different characteristics from macroscopic materials.Cu-Pb alloys are often used in bearings because of the excellent wear-resisting and self-lubricating property.When the Cu-Pb alloys bear heavier mechanical loads,the working surface of the bearings would deforms,resulting a decrease of the movement precision and stability of the system.Due to lack of deformation characteristics of Cu-Pb alloys at nanoscale,material instability and failure problems are not clear,the structure design of NEMS is unreasonably.Thus,it's necessary to study the deformation characteristics under load of nano Cu-Pb alloys and provide technical support for the structure design bearing and efficacy lose prevention in NEMS.At first,polycrystalline Cu-Pb alloys simulation models are built using the Voronoi method based on molecular dynamics.The embedded atom potential(EAM)is used to describe the atom interactions in Cu-Pb alloys and verified correctly by comparing the simulated elastic constants and cohesion energy with experimental values.Secondly,simulation models were relaxed enough and deformed by imposing tensile load in LAMMPS.The relaxation results show that Pb atoms have an important influence on grain boundary(GB)characteristics.With the increase of Pb concentrations,the shear stresses of different structures in GB decrease linearly,while potentials of them increase linearly.The tensile deformation results show that,as the increase of Pb concentrations,the modulus of elasticity decreased and maximum strength first decreased then increased,Pb atoms have an obvious suppression on dislocations.The potential curves are totally different for grain and GB during tensile deformation.Both the stress distribution and potential distribution are different at different structures.The GBs play a main role in polycrystalline deformation.Pb atoms have an effect on GB strength,leading to a different dieection of crack propagation accompanied by the increase of Pb concentration.Finally,simulation models that contain hole defects were deformed by tensile simulation,the location,radius and amount of hole defects in Cu-Pb alloys were researched.The results show hole defects can reduce the strength of Cu-Pb alloys and increase the dislocations whatever the hole defects locate.The stress of Cu-Pb alloys with grain hole defects is higher than that with GB hole defects.When hole defects are at GB,the increase of hole defects' radius and hole defects' amount reduce the strength of Cu-Pb alloys at plastic deformation and crack propagation stage.When hole defects are at grain interior,the reductions only occur at plastic deformation and early crack propagation stage,while the increase of hole defects' amount have an increase effect on strength of Cu-Pb alloys at crack propagation stage.