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1、[Article]www.whxb.pku.edu.cndoi:10.3866/PKU.WHXB201409101不同孪晶界密度银纳米线拉伸形变行为的分子动力学模拟孙倩杨熊博高亚军赵健伟*(南京大学化学化工学院,生命分析国家重点实验室,南京210008)摘要:采用分子动力学方法模拟了不同孪晶界密度银纳米线的拉伸形变行为,分析了孪晶界密度对多晶银纳米线屈服强度、弹性模量和塑性变形机理的影响.在弹性形变区域,孪晶界的存在对杨氏模量变化的作用不明显.在塑性形变阶段,首先从表面边缘开始产生位错成核,然后延伸并受阻于孪晶界.在进一步拉伸载荷
2、作用下,孪晶界将作为位错源产生新的位错.模拟结果表明,银纳米线的强度与孪晶界和晶粒的尺寸有关.孪晶界密度较小(即晶粒的长径比大于1)时,此纳米线的屈服应力比单晶纳米线还要小,只有当孪晶界密度较大时(即晶粒的长径比小于1),孪晶界使得纳米线得到强化.综合分析了孪晶界和晶粒尺寸对银纳米线的影响,为构建高强度金属纳米线打下基础.最后讨论了温度和拉伸速度对孪晶纳米线屈服应力所产生的影响,随着温度的升高,孪晶纳米线与单晶纳米线的屈服应力差先升高后趋于稳定;当拉伸速度逐渐增大,孪晶纳米线与单晶纳米线的屈服应力差先稳定后增大.关键词:银纳米线;
3、孪晶界;单轴拉伸;分子动力学模拟;纳米器件;长径比中图分类号:O641MolecularDynamicsSimulationoftheDeformationBehaviorofAgNanowireswithDifferentTwinBoundaryDensityunderTensionLoadingSUNQianYANGXiong-BoGAOYa-JunZHAOJian-Wei*(SchoolofChemistryandChemicalEngineering,StateKeyLaboratoryofAnalyticalChemis
4、tryforLifeScience,NanjingUniversity,Nanjing210008,P.R.China)Abstract:ThedeformationmechanismsandmechanicaltensilebehaviorofAgnanowirescontainingdifferentdensitiesofparalleltwinboundarieswereinvestigatedusingmoleculardynamicssimulations.TheeffectoftwinboundariesontheYo
5、ung′smodulusinnanowireswasnotobviousintheelasticdeformationstage.Aftertheelasticdeformationstage,theinitialdislocationfromtheedgeofthefreesurfacesinnanowiresresultedinplasticdeformation.Theexistenceofthetwinboundaryinnanowireswillcausethespreadofthedislocationandactas
6、sourcesofdislocationswiththeassistanceofthenewlyformeddefectswithfurthertensionload.ThesimulationshowedthatthemechanicalstrengthofAgnanowireswashighlydependentonthetwinboundaryspacingandthesizeofthegrain,resultingfromtheaspectratiobetweenthespacingdistanceandthelength
7、ofthecross-section.Inparticular,twinnedAgnanowireswithsmalltwindensity(aspectratio>1)hadsmallyieldingstresses,evenlessthanthatofthesinglecrystalAgnanowires.Onlywithlargetwindensity(aspectratio<1)canthenanowiresbestrengthenedbythestructureofthetwinboundaries.Wealsoinve
8、stigatedtheeffectsoftensilerateandtemperatureontheyieldingstrengthoftheAgnanowires.Withincreasingtemperature,thedifferenceof
