刃型位错形成对面心立方金属Cu体积的影响

使用分子动力学方法,采用嵌入原子势（EAM）,在0K下模拟了面心立方金属Cu单晶的刃型位错,研究了刃型位错产生对晶体体积的影响．模拟结果表明,无论使用推入还是抽出原子层的方法获得刃型位错,平衡状态时刃型位错的存在使晶体体积增大．     

温度对镍基单晶高温合金γ/γ'相界面上错配位错运动影响的分子动力学研究

用分子动力学方法研究了温度对镍基单晶高温合金γ/γ'相界面上错配位错运动的影响.研究结果表明:无论是在低温还是在高温下,错配位错的运动都是通过扭折的形核及扭折沿位错线的迁移来实现;在低温时错配位错的相互作用有利于错配位错的运动;然而在高温时错配位错的相互作用可以阻碍错配位错的运动,从而阻碍γ和γ'相界面的相对滑动,有利于提高镍基单晶高温合金的高温力学性能. 关键词： 镍基单晶高温合金 相界面 错配位错 分子动力学模拟     

温度对超薄铜膜疲劳性能影响的分子动力学模拟

用嵌入原子势的分子动力学方法模拟了温度对超薄铜膜疲劳性能的影响. 通过模拟, 首先给出了超薄铜膜的总能及应力随循环周次的变化曲线; 根据叠加经验式得出的叠加量随循环周次变化曲线, 判断出各种恒定温度下超薄铜膜的疲劳寿命. 由 200–400 K温度范围内超薄铜膜的疲劳寿命-温度变化曲线, 可以发现存在两个温度区域: 在约370 K以下, 超薄铜膜的疲劳寿命随温度升高缓慢增加, 而在约370 K以上增加较快. 建立了模型并用位错演化机制解释了超薄铜膜疲劳寿命的温度依赖关系. 关键词： 分子动力学 疲劳 温度效应 位错     

刃型位错形成对面心立方金属Cu体积的影响

使用分子动力学方法,采用嵌入原子势(EAM),在0K下模拟了面心立方金属Cu单晶的刃型位错,研究了刃型位错产生对晶体体积的影响.模拟结果表明,无论使用推入还是抽出原子层的方法获得刃型位错,平衡状态时刃型位错的存在使晶体体积增大.     

基于连续介质位错理论的位错原子分布构造方法

基于连续介质位错理论提出一种新的位错原子分布构造方式,理论上可以构造出任意形状和任意Burgers矢量的位错结构.利用该方法,选用FCC单晶铜为模拟介质,构造Burgers矢量为b=[110]/2的刃型全位错和Burgers矢量为b=[112]/6圆环形不完全位错环,并使用分子动力学方法模拟全位错的扩展分解过程和不全位错环在自应力作用下的收缩过程,模拟结果与理论分析一致.该方法的优点在于可以方便地构造出其他传统方法难以构造的位错闭合结构——位错环,从而使位错环的细致研究成为可能.     

铜晶体中类层错四面体的结构及其演化

运用分子动力学方法,研究了金属铜单晶中不同形状的Frank位错环演化形成的各种类层错四面体稳定构型.对其形成过程的细致分析表明,这些稳定构型都可以用统一的位错分解和位错反应过程来解释.模拟结果表明,在零温下各种Frank位错环存在各自的临界尺寸,小于临界尺寸的Frank位错环不能长成类层错四面体结构.对梯形、六边形等Frank位错环演化过程的模拟表明,在形成稳定类层错四面体的过程中,存在位错生长和回缩的振荡现象.振荡现象是由于位错间的排斥和吸引相互作用不同步或弹性波传播的延迟效应引起的. 关键词： 层错四面体 位错 分子动力学     

冲击条件下含纳米空洞的单晶铜的塌缩

利用分子动力学方法研究了单晶铜中不同大小的球形空洞在冲击波下的演化过程.模拟结果表明不同大小空洞的塌缩过程不同.模拟中冲击波由空洞左边扫向空洞右边.在较大尺寸的空洞塌缩过程中会产生系列的位错环.当空洞半径较小时,先在空洞的右侧形成位错环,当空洞半径增大到某一临界大小时,在空洞左右两侧同时产生位错环,当空洞半径较大时,先在空洞左侧形成位错环.当空洞左右两侧的位错环均形成以后,其右侧位错环前端的生长速度大于其左侧的.空洞半径增大,相应的位错环前端的生长速度变化不大.当空洞半径增大时,空洞中心指向位错源的矢量方 关键词： 纳米空洞 位错环 冲击波 塑性变形     

单晶Cu冲击加载及卸载下塑性行为的微观模拟

使用分子动力学方法对室温下单晶铜沿［001］和［111］方向冲击加载及卸载下的塑性行为进行了模拟,得到了Hugoniot关系以及冲击熔化压力,与实验基本符合. 加载过程中,较高的初始温度有利于位错的形核与发展. 通过对冲击波在自由表面卸载过程的模拟和分析发现：卸载过程呈现“准弹性卸载行为”;沿［001］方向卸载后大量不全位错环与堆积层错消失,而沿［111］方向卸载后只有少量层错消失,部分层错甚至会发展扩大. 关键词： 分子动力学 冲击波 塑性     

镍基单晶高温合金界面位错网在剪切载荷作用下的演化

运用分子动力学方法,研究了镍基单晶高温合金γ/γ' 相界面错配位错网在剪切载荷作用下的演化特征.结果表明:(100),(110) 和 (111) 三种相界面形成的位错网在载荷作用下有不同形式和不同程度的损伤,其变形和损伤随温度的增加而增加.在相同的剪切载荷和温度作用下,(100) 相界面形成的正方形位错网最稳定. 关键词： 镍基单晶高温合金 界面位错网 分子动力学     

α-Fe中刃型位错与空洞相互作用的分子动力学模拟

本文通过分子动力学方法（MD）,采用嵌入原子势法（EAM）,沿[111]方向插入一层（0-11）半原子面形成位错,然后在模型中插入空洞,模拟了BCC 铁中刃型位错与空洞相互作用,研究了空洞对位错运动的影响机理。模拟结果表明,当温度设定为10K时,位错运动速度快,但空洞直径的大小对位错运动速度的影响不太明显,当高温设定为100K时,由于位错线密度增大并随着空洞直径的增加位错运动速度减小,临界剪切应力也随着减小。最后将模拟计算结果与Osetsky的研究数据及连续体理论模型进行了对比分析。     

晶体缺陷规范场方法处理运动螺型位错

本文用晶体缺陷规范场方法分析了运动螺型位错的性质,在一定规范条件下求解了螺型位错的动力学方程,得到了匀速运动螺型位错的应力场。在K=μ/s(s为耦合常数)趋于零的情况下,其结果与匀速运动的Volterra螺型位错的应力场形式上是一样的,但螺型位错运动的极限速度是2^1/2c。在螺型位错速度为零的情况下,其应力场与Volterra螺型位错的应力场完全一样。最后对所得结果进行了讨论。 关键词：     

In源流量与Ⅲ族流量之比对InGaN/GaN多量子阱性质的影响

利用x射线三轴晶衍射和光致发光谱研究了生长参数In源流量与Ⅲ族流量之比对InGaN/GaN多量子阱结构缺陷(如位错密度和界面粗糙度)和光致发光的影响.通过对（0002）对称和（1012）非对称联动扫描的每一个卫星峰的ω扫描，分别测量出了多量子阱的螺位错和刃位错平均密度，而界面粗糙度则由（0002）对称衍射的卫星峰半高全宽随级数的变化得出.试验发现多量子阱中的位错密度特别是刃位错密度和界面粗糙度随In源流量与Ⅲ族源流量比值的增加而增加，导致室温下光致发光性质的降低，从而也证明了刃位错在InGaN/GaN 关键词： x射线三轴晶衍射 界面粗糙度 位错 InGaN/GaN多量子阱     

Structure, stability, and motion of dislocations in double-wall carbon nanotubes

In this paper,a novel double-wall carbon nanotube(DWCNT) with both edge and screw dislocations is studied by using the molecular dynamics(MD) method.The differences between two adjacent tubule indexes of armchair and zigzag nanotubes are determined to be 5 and 9,respectively,by taking into account the symmetry,integrality,and thermal stability of the composite structures.It is found that melting first occurs near the dislocations,and the melting temperatures of the dislocated armchair and zigzag DWCNTs are around 2600 K-2700 K.At the premelting temperatures,the shrink of the dislocation loop,which is comprised of edge and screw dislocations,implies that the composite dislocation in DWCNTs has self-healing ability.The dislocated DWCNTs first fracture at the edge dislocations,which induces the entire break in axial tensile test.The dislocated DWCNTs have a smaller fracture strength compared to the perfect DWCNTs.Our results not only match with the dislocation glide of carbon nanotubes(CNTs) in experiments,but also can free from the electron beam radiation under experimental conditions observed by the high resolution transmission electron microscope(HRTEM),which is deemed to cause the motion of dislocation loop.     

Mechanisms of stacking fault tetrahedra destruction by gliding dislocations in quenched gold

The destruction processes of stacking fault tetrahedra (SFTs) induced by gliding dislocations were examined by transmission electron microscopy (TEM) in situ straining experiments for SFTs with edge lengths ranging from 10 to 50 nm. At least four distinct SFT destruction processes were identified: (1) consistent with a Kimura–Maddin model for both screw and 60° dislocations, (2) stress-induced SFT collapse into a triangular Frank loop, (3) partial annihilation leaving an apex portion and (4) complete annihilation. Process (4) was observed at room temperature only for small SFTs (～10 nm); however, this process was also frequently observed for larger SFTs (～30 nm) at higher temperature (～853 K). When this process was induced, the dislocation always cross-slipped, indicating only screw dislocations can induce this process.     

Vibrational properties of straight dislocations in bcc and fcc metals within the harmonic approximation

We calculate the vibrational spectra of straight screw and edge dislocations in several body-centered cubic (bcc) (Mo and Fe) and face-centered cubic (fcc) (Cu and Al) metals within the harmonic approximation. We take advantage of the translational symmetry of straight dislocations to efficiently calculate their phonon eigenstates in the harmonic limit. This allows us to calculate the low-temperature contribution of straight screw and edge dislocations to the heat capacity of each respective metal, and show that the dominant temperature dependence below 5 K is linear. Comparison with heat capacity measurements of heavily cold-worked Cu reveals very good agreement with our calculations. At higher temperatures, the contribution from the non-linear terms becomes significant. As a result, maxima in the straight dislocation heat capacities are observed in the temperature range from 9% to 16% of the Debye temperature. We investigate the appearance of localized and resonance peaks in the vibrational spectra induced by dislocations, and study in detail their spatial spread around the dislocation cores by projecting vibrational eigenstates onto individual atoms. We study the deviation of these atomic-level vibrational free energies from that of the perfect crystal as a function of distance to the dislocation cores, and establish that, similar to the dislocation energy, the vibrational free energy of an isolated dislocation behaves logarithmically in the long-range limit. Finally, we obtain vibrational spectra for propagating waves along the dislocation line and find that the dispersion for these waves is consistent with the notion of kink formation and motion for screw dislocations.     

Influence of topology in a quantum ring

In this Letter we study the quantum rings in the presence of a topological defect. We use geometric theory of defects to describe one and two-dimensional quantum rings in the presence of a single screw dislocation. In addition we consider some potential in a two dimensional ring and calculate their energy spectrum. It is shown that the energy spectrum depend on the parabolic way on the burgers vectors of the screw dislocation. We also show that the presence of a topological defect introduces a new contribution for the Aharonov-Bohm effect in the quantum ring.     

Molecular dynamics simulation of the interaction between a mixed dislocation and a stacking fault tetrahedron

A high number-density of nanometer-sized stacking fault tetrahedra are commonly found during irradiation of low stacking fault energy metals. The stacking fault tetrahedra act as obstacles to dislocation motion leading to increased yield strength and decreased ductility. Thus, an improved understanding of the interaction between gliding dislocations and stacking fault tetrahedra are critical to reliably predict the mechanical properties of irradiated materials. Many studies have investigated the interaction of a screw or edge dislocation with a stacking fault tetrahedron (SFT). However, atomistic studies of a mixed dislocation interaction with an SFT are not available, even though mixed dislocations are the most common. In this paper, molecular dynamics simulation results of the interaction between a mixed dislocation and an SFT in face-centered cubic copper are presented. The interaction results in shearing, partial absorption, destabilization or simple bypass of the SFT, depending on the interaction geometry. However, the SFT was not completely annihilated, absorbed or collapsed during a single interaction with a mixed dislocation. These observations, combined with simulation results of edge or screw dislocations, suggest that defect-free channel formation in irradiated copper is not likely by a single dislocation sweeping or destruction process, but rather by a complex mix of multiple shearing, partial absorption and defect cluster transportation that ultimately reduces the size of stacking fault tetrahedra within a localized region.     

一维六方准晶中螺形位错与楔形裂纹的相互作用

采用保角映射方法和扰动技巧,研究了一维六方准晶中螺形位错和半无限楔形裂纹的相互作用. 讨论了位错的位置和楔形角对作用在位错上的力的影响,得到了应力强度因子和作用在 位错上的力的解析解.此外,还详细地讨论了位错对裂纹的影响.当楔形角参数λ=1/2时, 半无限楔形裂纹退化成半无限尖裂纹,相应的结果 可以作为特殊情况而直接得到.     

On the elastic fields produced by non-uniformly moving dislocations: a revisit

We investigate the non-uniform motion of straight dislocations in infinite media using the theory of incompatible elastodynamics. The equations of motion are derived for non-uniformly moving screw dislocations, gliding edge and climbing edge dislocations. The exact closed-form solutions of the elastic fields are calculated. The fields of the elastic velocity and elastic distortion surrounding the arbitrarily moving dislocations are given explicitly in the form of integral representations free of non-integrable singularities. The elastic fields describe the response in the form of non-uniformly moving elastic waves caused by the motion of the dislocation.