CAJ | 학술논문

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。
채용분자동역학방법모의료불동련정계밀도은납미선적랍신형변행위，분석료련정계밀도대다정은납미선굴복강도、탄성모량화소성변형궤리적영향。재탄성형변구역，련정계적존재대양씨모량변화적작용불명현。재소성형변계단，수선종표면변연개시산생위착성핵，연후연신병수조우련정계。재진일보랍신재하작용하，련정계장작위위착원산생신적위착。모의결과표명，은납미선적강도여련정계화정립적척촌유관。련정계밀도교소(즉정립적장경비대우1)시，차납미선적굴복응력비단정납미선환요소，지유당련정계밀도교대시(즉정립적장경비소우1)，련정계사득납미선득도강화。종합분석료련정계화정립척촌대은납미선적영향，위구건고강도금속납미선타하기출。최후토론료온도화랍신속도대련정납미선굴복응력소산생적영향，수착온도적승고，련정납미선여단정납미선적굴복응력차선승고후추우은정；당랍신속도축점증대，련정납미선여단정납미선적굴복응력차선은정후증대。
The deformation mechanisms and mechanical tensile behavior of Ag nanowires containing different densities of paral el twin boundaries were investigated using molecular dynamics simulations. The effect of twin boundaries on the Young′s modulus in nanowires was not obvious in the elastic deformation stage. After the elastic deformation stage, the initial dislocation from the edge of the free surfaces in nanowires resulted in plastic deformation. The existence of the twin boundary in nanowires wil cause the spread of the dislocation and act as sources of dislocations with the assistance of the newly formed defects with further tension load. The simulation showed that the mechanical strength of Ag nanowires was highly dependent on the twin boundary spacing and the size of the grain, resulting from the aspect ratio between the spacing distance and the length of the cross-section. In particular, twinned Ag nanowires with smal twin density (aspect ratio>1) had smal yielding stresses, even less than that of the single crystal Ag nanowires. Only with large twin density (aspect ratio<1) can the nanowires be strengthened by the structure of the twin boundaries. We also investigated the effects of tensile rate and temperature on the yielding strength of the Ag nanowires. With increasing temperature, the difference of yielding stress between twinned nanowires and single crystal nanowires first increased and then decreased to a stable level. With increasing tensile rate, this difference showed the opposite trend.