五重孪晶银纳米线形变机理的分子动力学模拟研究
发布时间：2019-01-01 20:21
【摘要】：银纳米线被认为是最有可能取代铟锡氧化物(IT0)的材料,它们在将来的柔性光电子器件领域展现出了巨大的应用前景。五重孪晶结构是银纳米线内的一种常见结构,尽管过去的实验和模拟强有力地证实了纳米孪晶界能作为一种有效的途径来提高纳米材料的综合性能,人们对于五重孪晶界对一维金属纳米材料力学性能影响的认识依然不是很清晰。本文采用分子动力学方法研究了单晶和五重孪晶银纳米线在拉伸、压缩、弯曲、扭转载荷下的力学行为,尤其关注孪晶界相关的形变机理。主要结论如下： 1.拉伸时,单晶银纳米线的塑性变形由不全位错滑移和孪生实现；五重孪晶界有效地阻挡了不全位错的运动。大量位错被困在五重孪晶纳米线内部,随着变形增加,位错间会发生复杂的反应并产生大量的不可动位错。孪晶界在变形过程中逐渐失去它们的共格特性和平整性,甚至伴随着孔洞出现在孪晶界交汇处来释放位错塞积引起的应力集中。 2.压缩时,单晶银纳米线的塑性变形以全位错滑移为主,全位错能完全滑出纳米线表面从而导致位错匮乏状态；五重孪晶界的存在导致了全位错必须与孪晶界发生交互作用。非螺型全位错穿过孪晶界后会沿着{100}面滑移,最终交滑移到与加载轴平行的{111}面上。在整个塑性过程中,由于位错和孪晶界以及位错之间的交互作用,五重孪晶纳米线内的位错密度显著上升。 3.弯曲时,单晶纳米线的塑性变形主要由孪生实现,孪生导致纳米线的{100}侧表面重新取向到{110}晶面；五重孪晶纳米线的塑性变形则完全集中在中部和端部很小的范围内。位错的运动受到孪晶界的阻碍,大量位错塞积在孪晶界附近,为了释放由局域化变形和位错塞积引起的应力集中,五重孪晶纳米线较早开始断裂。五重孪晶银纳米线相对单晶银纳米线而言具有更高的强度,但是明显更低的塑性。 4.五重孪晶纳米线的扭转塑性变形分为两个阶段：当载荷不大时,塑性变形完全由五个孪晶不全位错滑移实现,若在这个阶段卸载,塑性可以完全恢复,五重孪晶纳米线展现出伪弹性行为；继续增加载荷,各个晶区内开始出现同轴Shockley不全位错形核和滑移,与孪晶不全位错一样,这些位错同样从形核端不断向纳米线另一端扩展,卸载后可以恢复。与此同时,在加载端附近还会出现不可恢复的非螺型位错,阻碍了纳米线卸载后回到初始状态。
[Abstract]:Silver nanowires are considered to be the most likely materials to replace indium tin oxide (IT0). They will be widely used in the field of flexible optoelectronic devices in the future. The quintuple twin structure is a common structure in silver nanowires, although past experiments and simulations have strongly confirmed that nanocrystalline twinning boundaries can be used as an effective way to improve the comprehensive properties of nanomaterials. The effect of the five-fold twin boundary on the mechanical properties of one-dimensional metal nanomaterials is still unclear. In this paper, the mechanical behavior of single crystal and five twin silver nanowires under tensile, compression, bending and torsional loads has been studied by means of molecular dynamics, with particular attention to the deformation mechanism related to twin boundaries. The main conclusions are as follows: 1. The plastic deformation of monocrystalline silver nanowires is realized by the slip of incomplete dislocation and twinning, and the movement of incomplete dislocation is effectively blocked by the five-fold twin boundary. A large number of dislocations are trapped inside the five-fold twin nanowires. With the increase of deformation, complex reactions occur between the dislocations and a large number of immovable dislocations occur. The twin boundaries gradually lose their coherence and smoothness in the deformation process, and even release the stress concentration caused by the dislocation slug accumulation by the appearance of the holes at the twinning boundary junctions. 2. During compression, the plastic deformation of single crystal silver nanowires is dominated by total dislocation slip, which can slip completely out of the surface of nanowires, which leads to the lack of dislocation, and the existence of five-fold twin boundary leads to the interaction between the total dislocation and the twin boundary. The non-screw full dislocations will slip along the {100} plane after crossing the twin boundary and eventually cross to the {111} plane parallel to the loading axis. During the whole plastic process, the dislocation density in the five-fold twin nanowires increases significantly due to the interaction between dislocations and twin boundaries and dislocations. 3. During bending, the plastic deformation of single crystal nanowires is mainly realized by twinning, which leads to the reorientation of {100} side surface to {110} plane, while the plastic deformation of five-fold twin nanowires is completely concentrated in the middle and end of the nanowires. The movement of dislocation is hindered by the twin boundary, and a large number of dislocation plug deposits are near the twin boundary. In order to release the stress concentration caused by localized deformation and dislocation slug accumulation, the five-fold twin nanowires began to fracture earlier. The five-fold twin silver nanowires have higher strength than single crystal silver nanowires, but obviously lower plasticity. 4. The twisting plastic deformation of the five-fold twin nanowires is divided into two stages: when the load is small, the plastic deformation is completely realized by the slip of the five twin incomplete dislocations, and if unloaded at this stage, the plasticity can be completely restored. The quintuple twin nanowires exhibit pseudo-elastic behavior. With increasing load, coaxial Shockley incomplete dislocation nucleation and slippage begin to occur in each crystal region. Like twin incomplete dislocations, these dislocations extend from the nucleation end to the other end of the nanowire, and can be recovered after unloading. At the same time, unrecoverable non-screw dislocations occur near the loading end, which prevents the nanowires from returning to their initial state after unloading.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;O614.122
本文编号：2398069
[Abstract]:Silver nanowires are considered to be the most likely materials to replace indium tin oxide (IT0). They will be widely used in the field of flexible optoelectronic devices in the future. The quintuple twin structure is a common structure in silver nanowires, although past experiments and simulations have strongly confirmed that nanocrystalline twinning boundaries can be used as an effective way to improve the comprehensive properties of nanomaterials. The effect of the five-fold twin boundary on the mechanical properties of one-dimensional metal nanomaterials is still unclear. In this paper, the mechanical behavior of single crystal and five twin silver nanowires under tensile, compression, bending and torsional loads has been studied by means of molecular dynamics, with particular attention to the deformation mechanism related to twin boundaries. The main conclusions are as follows: 1. The plastic deformation of monocrystalline silver nanowires is realized by the slip of incomplete dislocation and twinning, and the movement of incomplete dislocation is effectively blocked by the five-fold twin boundary. A large number of dislocations are trapped inside the five-fold twin nanowires. With the increase of deformation, complex reactions occur between the dislocations and a large number of immovable dislocations occur. The twin boundaries gradually lose their coherence and smoothness in the deformation process, and even release the stress concentration caused by the dislocation slug accumulation by the appearance of the holes at the twinning boundary junctions. 2. During compression, the plastic deformation of single crystal silver nanowires is dominated by total dislocation slip, which can slip completely out of the surface of nanowires, which leads to the lack of dislocation, and the existence of five-fold twin boundary leads to the interaction between the total dislocation and the twin boundary. The non-screw full dislocations will slip along the {100} plane after crossing the twin boundary and eventually cross to the {111} plane parallel to the loading axis. During the whole plastic process, the dislocation density in the five-fold twin nanowires increases significantly due to the interaction between dislocations and twin boundaries and dislocations. 3. During bending, the plastic deformation of single crystal nanowires is mainly realized by twinning, which leads to the reorientation of {100} side surface to {110} plane, while the plastic deformation of five-fold twin nanowires is completely concentrated in the middle and end of the nanowires. The movement of dislocation is hindered by the twin boundary, and a large number of dislocation plug deposits are near the twin boundary. In order to release the stress concentration caused by localized deformation and dislocation slug accumulation, the five-fold twin nanowires began to fracture earlier. The five-fold twin silver nanowires have higher strength than single crystal silver nanowires, but obviously lower plasticity. 4. The twisting plastic deformation of the five-fold twin nanowires is divided into two stages: when the load is small, the plastic deformation is completely realized by the slip of the five twin incomplete dislocations, and if unloaded at this stage, the plasticity can be completely restored. The quintuple twin nanowires exhibit pseudo-elastic behavior. With increasing load, coaxial Shockley incomplete dislocation nucleation and slippage begin to occur in each crystal region. Like twin incomplete dislocations, these dislocations extend from the nucleation end to the other end of the nanowire, and can be recovered after unloading. At the same time, unrecoverable non-screw dislocations occur near the loading end, which prevents the nanowires from returning to their initial state after unloading.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;O614.122
【参考文献】
相关期刊论文 前1条
1 Weiwei He;Changhui Ye;;Flexible Transparent Conductive Films on the Basis of Ag Nanowires:Design and Applications:A Review[J];Journal of Materials Science & Technology;2015年06期
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