金纳米线拉伸力学行为和变形机制的模拟研究

发布时间：2018-08-24 20:54

【摘要】：金纳米线作为一维纳米材料的主要组成,由于其良好的化学稳定性和高电导率,较高的表面活性以及优良的生物亲和性,使其在纳米结构器件和生物传感器等方面具有广阔的应用前景。本文采用分子动力学方法,以一维金纳米线为研究对象,主要研究了单晶金纳米线和孪晶结构纳米线拉伸力学行为和微观形变机理,现主要结论如下:(1)单晶金纳米线在拉伸作用下弹性模量受直径的影响不大,受晶向影响较大,不同晶向弹性模量的大小顺序为E[111]E[110]E100],同时[100]晶向纳米线屈服应变和屈服应力远远高于其他晶向纳米线,是[110]晶向纳米线屈服应变和屈服应力的2.65倍和2.54倍。纳米线在低和中等拉伸应变率下,应变率对金纳米线弹性模量、屈服强度和断裂应变等力学特性影响较小,但在高应变率下这些力学特性都迅速提高。孪晶结构金纳米线的弹性模量受孪晶间距影响不大,屈服应力受孪晶面间距影响较大。随着孪晶面间距的不断增大,纳米线屈服应力不断减小,当孪晶间距达到一定值后,屈服应力则屈于平衡,不在改变。(2) [100]晶向单晶金纳米线在不同拉伸应变率下呈现不同力学行为和微观形变机理。低应变率(ε1.0×109s-1)下,应力-应变曲线在塑性变形阶段呈现周期性“锯齿状”变化特征,直至最后断裂,塑性变形主要由滑移引起,位错在每个屈服阶段产生、扩展并逃逸;中等应变率(1.0×109s-1ε≤1.0×1010s-1)下,应力-应变曲线塑性变形阶段平缓降低,直至最后断裂,塑性变形由滑移和孪生引起,位错在屈服过程不能充分扩展并逃逸,而是相互交截并驻留在纳米线内部;高应变率(ε1.00×1010s-1)下,应力-应变曲线在初始弹性变形阶段呈现一个明显凸起,在塑性变形阶段呈现“波浪状”起伏变化,直至最后断裂,塑性变形由非晶化引起,体系在屈服过程迅速转化为无序非晶态原子,而且断裂应变高达435.89%,呈现超塑性。(3)三种不同晶向纳米线在低应变率下的塑性变形机理均是由滑移引起。[100]晶向纳米线拉伸塑性变形过程中具有四个滑移系,但只有其中一个滑移面对塑性变形起主要作用;[110]晶向纳米线拉伸塑性变形过程中,层错间距随应变量增加不断增大,而后滑移方向改变,纳米线滑移加剧导致纳米线的最终断裂;[111]晶向金纳米线塑性形变主要由堆垛层错引起。(4)孪晶间距对金纳米线屈服应力影响较大,当TBS2nm(twin boundary spacing)时,位错和孪晶面共同作用使得纳米线颈缩区域孪晶间距增大,而后孪晶面阻碍滑移并改变滑移方向,对纳米线起强化作用;当TBS2nm时,纳米线被软化。(5)孪晶结构纳米线软化包括两种机制。当2nmTBBS5nm时,孪晶界未能有效阻止位错滑移,当位错在孪晶面处积累到一定程度时,位错打破孪晶面的限制,位错作为产生源在邻近孪晶块内再次生成位错,并同时伴有部分不全位错的分解和消失,纳米线未能过早形成应力集中,断裂应变相对较大;当TBS5nm时,位错的滑移使得纳米线孪晶面被破坏,形成剪切带,无序原子在孪晶面处大量堆积,使得纳米线断裂应变变小。
[Abstract]:As one of the main components of one-dimensional nanomaterials, gold nanowires have broad application prospects in nanostructured devices and biosensors due to their good chemical stability, high conductivity, high surface activity and excellent biocompatibility. In this paper, molecular dynamics method is used to study one-dimensional gold nanowires. The main conclusions are as follows: (1) The elastic modulus of single crystal gold nanowires is not affected by the diameter, but by the crystal orientation. The order of elastic modulus of different crystal orientations is E [111] E [110] E100, and [100] crystal. The yielding strain and stress of nanowires are 2.65 times and 2.54 times higher than those of other nanowires. The strain rate has little effect on the elastic modulus, yield strength and fracture strain of gold nanowires at low and moderate tensile strain rates, but at high strain rates. The elastic modulus of the twin-structured gold nanowires is not affected by the twin spacing, but the yield stress is greatly affected by the twin spacing. With the increasing of the twin spacing, the yield stress of the nanowires decreases continuously. When the twin spacing reaches a certain value, the yield stress yields to equilibrium and does not change. The stress-strain curves exhibit periodic "zigzag" characteristics at low strain rates (e 1.0 x 109 s-1), and finally fracture. The plastic deformation is mainly caused by slip, and dislocations are produced at each yield stage. At moderate strain rate (1.0 The stress-strain curves show a distinct bulge at the initial elastic deformation stage, a "wave-like" fluctuation at the plastic deformation stage, and finally fracture. The plastic deformation is caused by amorphous deformation. The system rapidly transforms into disordered amorphous atoms during the yield process, and the fracture strain is as high as 435.89%, showing superplasticity. The plastic deformation mechanism of homocrystalline nanowires at low strain rates is caused by slip. [100] There are four slip systems in the tensile plastic deformation of nanowires, but only one slip plane plays a major role in the plastic deformation. [110] In the tensile plastic deformation of nanowires, the stacking fault spacing increases with the increase of strain. (4) The twin spacing has a great influence on the yield stress of gold nanowires. When TBS2 nm (twin boundary spacing) is used, the dislocation and twin face act together to cause the twin in the necking region of the nanowires. When TBS2 nm, the nanowires are softened by two mechanisms. (5) The softening of twin nanowires includes two mechanisms. When 2 nm TBBS 5 nm, the twin boundary can not effectively prevent the dislocation slip. When the dislocation accumulates at the twin surface to a certain extent, the dislocation breaks the twin surface. Restriction, dislocation as the source of generation in the adjacent twin block again generated dislocations, and accompanied by partial decomposition and disappearance of incomplete dislocations, nanowires failed to form stress concentration prematurely, fracture strain is relatively large; when TBS5 nm, dislocation slip makes the twin surface of nanowires destroyed, forming a shear band, disordered atoms piled up in the twin surface. The fracture strain of nanowires decreases with product.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1;O341

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