Investigation On The Deformation Mechanism Of Silver Nanowires

Nanomaterials have attracted much attention in recent years due to their unique properties.With the development of nano science and technology,the preparation methods of nanomaterials have become more and more mature.However,due to the limitations of the experimental techniques,many microscopic details and the formation and deformation processes of nanomaterials cannot be obtained.In recent years,with the development of computer simulation technology,to obtain many important information on the experiment can be possible,although it cannot replace the experiment completely,it provides an important reference and guide experiment and validate some theoretical assumptions for researchers,reduce the blindness and low cost,especially molecular dynamics simulation has extensive and important applications in various disciplines.Molecular dynamics simulation is a very effective computer technology and has become one of the most important scientific research methods.This paper is based on the molecular dynamics simulation platform developed by the laboratory,through the study of tensile deformation mechanism of Ag nanowires,influencing factors gradually explore the mechanism of deformation of micro nanoscale materials,lay the foundation for further experimental study on nano materials.This paper designed a Ag nanostructure that the hole in the twin boundary,study the effect of the hole on the strength of nanomaterials;also designed a polycrystalline Ag nanostructure with different grain aspect ratio,studied the deformation mechanism of polycrystalline Ag nanowires with different grain aspect ratio,then change the system temperature,study the effect of temperature on the deformation mechanism of polycrystalline Ag nanowire.The conclusions are obtained as follows:1.Based on the molecular dynamics simulations,the plastic deformation of the silver nanowires under uniaxial tension has been studied systematically.In this part,the mechanical properties of[111]-oriented twin nanowires with different size of holes are studied.The existence of the hole has no effect in elastic deformation stage.The hole on the twin boundary has two main roles on the plastic deformation stage.In the initial plastic deformation,the main function of the hole is generating new dislocations as dislocation sources at small hole size.By raising the hole size,the main function of the hole is blocks dislocation slip.In the late stage of plastic deformation,the two functions of the hole complement each other,leading to the plastic of nanowires weaken.2.For the polycrystalline Ag nanowires with different aspect ratios,the deformation mechanism has a significant relationship with the aspect ratio.When the aspect ratio is greater than 1(Para2-8 and Para2-12),the dislocation slip is less than that of the nanowires,and the deformation mechanism is dominated by grain boundaries.The aspect ratio is less than 1(Para2-16,Para2-20 and Para2-24),the mechanism of deformation of nano wires mainly by the interaction between grain boundary and dislocation slip dominated in plastic deformation stage nanowires generated many dislocation slip,and accompanied by the grain boundary integration and rotation phenomenon.3.In this part,the effect of temperature on polycrystalline silver nanowires was studied using molecular dynamics analysis.It was found that for the polycrystalline Ag nanowires,larger of disorder atoms in the grain boundary environment make grain boundaries possess high energy.The smaller the grain size,the higher the energy,but with the increase of the temperature,atomic thermal motion increases,result in higher energy and lower yield strength.Also,due to atomic thermal motion increases,leading to the short-range and long-range order of the nanowire is reduced.However,in this work,the main finding is the deformation mechanism of polycrystalline Ag nanowires changed with the increase of temperature.At low temperature(T<200K)and large grain size,deformation tends to occur preferentially by grain sliding to dislocation slip.Due to the limited number of slip systems at low temperature,polycrystalline silver nanowire breaks by forming voids at grain boundaries upon tensile loading.In contrast,by raising the temperature(T>200 K),When the aspect ratio is greater than 1,grain boundary sliding becomes the primary deformation mechanism and the strength of the nanowires decreases.When the aspect ratio is less than 1,dislocation sliding becomes the primary deformation mechanism.The global plastic deformation is carried by both dislocations and grain boundary sliding.