五重孿晶銀納米線形變機(jī)理的分子動(dòng)力學(xué)模擬研究
發(fā)布時(shí)間：2019-01-01 20:21
【摘要】：銀納米線被認(rèn)為是最有可能取代銦錫氧化物(IT0)的材料,它們?cè)趯淼娜嵝怨怆娮悠骷I(lǐng)域展現(xiàn)出了巨大的應(yīng)用前景。五重孿晶結(jié)構(gòu)是銀納米線內(nèi)的一種常見結(jié)構(gòu),盡管過去的實(shí)驗(yàn)和模擬強(qiáng)有力地證實(shí)了納米孿晶界能作為一種有效的途徑來提高納米材料的綜合性能,人們對(duì)于五重孿晶界對(duì)一維金屬納米材料力學(xué)性能影響的認(rèn)識(shí)依然不是很清晰。本文采用分子動(dòng)力學(xué)方法研究了單晶和五重孿晶銀納米線在拉伸、壓縮、彎曲、扭轉(zhuǎn)載荷下的力學(xué)行為,尤其關(guān)注孿晶界相關(guān)的形變機(jī)理。主要結(jié)論如下： 1.拉伸時(shí),單晶銀納米線的塑性變形由不全位錯(cuò)滑移和孿生實(shí)現(xiàn)；五重孿晶界有效地阻擋了不全位錯(cuò)的運(yùn)動(dòng)。大量位錯(cuò)被困在五重孿晶納米線內(nèi)部,隨著變形增加,位錯(cuò)間會(huì)發(fā)生復(fù)雜的反應(yīng)并產(chǎn)生大量的不可動(dòng)位錯(cuò)。孿晶界在變形過程中逐漸失去它們的共格特性和平整性,甚至伴隨著孔洞出現(xiàn)在孿晶界交匯處來釋放位錯(cuò)塞積引起的應(yīng)力集中。 2.壓縮時(shí),單晶銀納米線的塑性變形以全位錯(cuò)滑移為主,全位錯(cuò)能完全滑出納米線表面從而導(dǎo)致位錯(cuò)匱乏狀態(tài)；五重孿晶界的存在導(dǎo)致了全位錯(cuò)必須與孿晶界發(fā)生交互作用。非螺型全位錯(cuò)穿過孿晶界后會(huì)沿著{100}面滑移,最終交滑移到與加載軸平行的{111}面上。在整個(gè)塑性過程中,由于位錯(cuò)和孿晶界以及位錯(cuò)之間的交互作用,五重孿晶納米線內(nèi)的位錯(cuò)密度顯著上升。 3.彎曲時(shí),單晶納米線的塑性變形主要由孿生實(shí)現(xiàn),孿生導(dǎo)致納米線的{100}側(cè)表面重新取向到{110}晶面；五重孿晶納米線的塑性變形則完全集中在中部和端部很小的范圍內(nèi)。位錯(cuò)的運(yùn)動(dòng)受到孿晶界的阻礙,大量位錯(cuò)塞積在孿晶界附近,為了釋放由局域化變形和位錯(cuò)塞積引起的應(yīng)力集中,五重孿晶納米線較早開始斷裂。五重孿晶銀納米線相對(duì)單晶銀納米線而言具有更高的強(qiáng)度,但是明顯更低的塑性。 4.五重孿晶納米線的扭轉(zhuǎn)塑性變形分為兩個(gè)階段：當(dāng)載荷不大時(shí),塑性變形完全由五個(gè)孿晶不全位錯(cuò)滑移實(shí)現(xiàn),若在這個(gè)階段卸載,塑性可以完全恢復(fù),五重孿晶納米線展現(xiàn)出偽彈性行為；繼續(xù)增加載荷,各個(gè)晶區(qū)內(nèi)開始出現(xiàn)同軸Shockley不全位錯(cuò)形核和滑移,與孿晶不全位錯(cuò)一樣,這些位錯(cuò)同樣從形核端不斷向納米線另一端擴(kuò)展,卸載后可以恢復(fù)。與此同時(shí),在加載端附近還會(huì)出現(xiàn)不可恢復(fù)的非螺型位錯(cuò),阻礙了納米線卸載后回到初始狀態(tài)。
[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.
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB383.1;O614.122
本文編號(hào)：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.
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB383.1;O614.122
【參考文獻(xiàn)】
相關(guān)期刊論文 前1條
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
，本文編號(hào)：2398069
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