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1.
徐振海  袁林  单德彬  郭斌 《物理学报》2009,58(7):4835-4839
采用分子静力学方法模拟了〈100〉单晶铜纳米线的拉伸变形过程,研究了纳米线屈服的机理. 结果表明:1) 纳米线初始屈服通过部分位错随机激活的{111}〈112〉孪生实现,后继屈服通过{111}〈112〉部分位错滑移实现;2) 纳米线变形初期不同滑移面上的部分位错在两面交线处相遇形成压杆位错,变形后期部分位错在刚性边界处塞积,两者都阻碍位错滑移,引起一定的强化作用. 关键词: 纳米线 屈服 位错 分子静力学  相似文献   

2.
Based on the general theory of dislocation and kink, we have constructed the three kink models corresponding to the 1/2 (111){011} and 1/2 (111){112} edge dislocations (EDs) in bcc Fe using the molecular dynamics method. We found that the geometric structure of a kink depends on the type of ED and the structural energies of the atom sites in the dislocation core region, as well as the geometric symmetry of the dislocation core and the characteristic of the stacking sequence of atomic plane along the dislocation line. The formation energies and widths of the kinks on the 1/2 (111){011} and 1/2 (111){112} EDs are calculated, the formation energies are 0.05eV and 0.04eV, and widths are 6.02b and 6.51b, respectively (b is the magnitude of the Burgers vector). The small formation energies indicate that the formation of kink in the edge dislocation is very easy in bcc Fe.  相似文献   

3.
周宗荣  王宇  夏源明 《物理学报》2007,56(3):1526-1531
运用分子动力学方法,对γ-TiAl金属间化合物的面缺陷能(层错能和孪晶能)进行了研究. 计算得到γ-TiAl不同滑移系(或孪生系)的整体堆垛层错能曲线,结果表明,γ-TiAl较一般fcc晶体结构的金属可动滑移系(孪生系)的数量减少,在外界条件下呈脆性. 研究孪生系(1/6)〈112〉{111}的弛豫的整体堆垛层错(GSF)能和整体孪晶(GTF)能曲线,对不稳定层错能γusf、稳定层错能γsf和不稳定孪晶能γusf值进行分析,可以预知, γ-TiAl的主要变形机理为孪生系(1/6)〈112〉{111}的孪生和普通滑移系(1/6)〈110〉{111}的滑移,以及超滑移系(1/2)〈011〉{111}的滑移. 关键词: γ-TiAl')" href="#">γ-TiAl 堆垛层错能 孪晶能 分子动力学  相似文献   

4.
用分子动力学方法计算模拟了单晶铜中纳米孔洞(约φ1.3nm)在〈111〉晶向冲击加载过程中的演化及其周围区域发生塑性变形的过程。模拟结果的原子图像如图1所示,其中活塞速度为500m/s,图中所示为4族连续三层穿过孔洞中心的{111}晶面在4000个时间步时(处于拉伸应力状态)的原子排列图像。从面心立方铜晶体中位错成核及运动特点可知,当位错在{111}面上成核和运动后,将产生层错和部分位错结构,我们正是根据此特点来判断在某{111}晶面上是否有位错的成核和运动。从图1可以看到,沿〈111〉晶向冲击加载后,  相似文献   

5.
 用分子动力学方法计算模拟了沿〈111〉晶向冲击加载过程中,单晶铜中纳米孔洞(直径约1.3 nm)的演化及其周围区域发生塑性变形的过程。模拟结果表明,在沿〈111〉晶向冲击加载后,在面心立方(fcc)结构中的4族{111}晶面中有3族发生了滑移。伴随孔洞的增长,在所激活的3族{111}晶面上,观察到位错在孔洞表面附近区域成核,然后向外滑移,其中在剪切应力最大的〈112〉方向上,其位错速度超过横波声速,其它〈112〉方向的位错速度低于横波声速。模拟得到的位错阻尼系数范围与实验值基本符合。由于孔洞周围产生的滑移在空间比较对称,孔洞增长形貌接近球形。在恒定的冲击强度下,孔洞半径增长速率近似保持恒定,其速率随着冲击强度的增加而增大。  相似文献   

6.
 采用周期性原子阵列方法建立bcc Fe中的刃型位错,利用分子动力学计算了0 K时bcc Fe的位错芯里氦-空位团的稳定性,并与理想Fe晶体里氦-空位团的稳定性进行比较发现,位错的作用导致氦-空位团不稳定。点缺陷(He、空位与自间隙Fe原子)与氦-空位团的结合能与团中氦-空位比例密切相关,当氦与空位数之比在3~6时,结合能趋于稳定。  相似文献   

7.
在球墨铸铁金属基体中建立α-Fe[100](010)刃型位错原子模型,利用基于密度泛函理论的CASTEP方法计算C原子在位错芯区的埋置能、亲和能、电荷布居数等电子参数.结果表明:α-Fe[100](010)刃型位错芯区局域效应集中范围较小并具有C2v点群对称性.位错芯区的能量低谷吸引轻质杂质C原子偏聚,C原子的2p轨道与刃型位错尖端Fe原子的4s价轨道之间发生电荷转移,具有较强的相互作用,使位错运动受阻.Fe-C原子间布居数较大、原子间距离较小表明,Fe-C原子间有生成渗碳体化合物的倾向.Si原子掺杂渗碳体的结合能及各原子轨道分波态密度表明,Si原子能够促使渗碳体分解,析出碳硅化合物成为石墨球化的核心,从而改善球墨铸铁的冲击韧性.  相似文献   

8.
 用分子动力学方法模拟计算了在冲击波加载条件下,单晶铁中的结构相变(由体心立方结构α相到六角密排结构ε相),相互作用势采用铁的嵌入式原子势(EAM),单晶铁样品的尺寸为28.7 nm×22.9 nm×22.9 nm,总原子数为1.28×106个。通过推动一个运动活塞对静止靶的作用来产生冲击压缩,加载方向沿单晶铁的[100]晶向。通过对原子位置的追踪,揭示了铁的冲击相变机制,计算结果表明相变机制包括两步:首先是在{011}面上的原子受到沿〈100〉晶向的压缩,使{011}面转化成正六角形密排面;然后是在{011}面上原子沿〈0-11〉晶向的滑移,完成由bcc结构到hcp结构的相变。同时发现滑移面只出现在与冲击波加载方向平行的(011)和(0-11)面上。  相似文献   

9.
Dislocations are thought to be the principal mechanism of high ductility of the novel B2 structure intermetallic compounds YAg and YCu.In this paper,the edge dislocation core structures of two primary slip systems 〈100 〉{010} and 〈100 〉 {011} for YAg and YCu are presented theoretically within the lattice theory of dislocation.The governing dislocation equation is a nonlinear integro-differential equation and the variational method is applied to solve the equation.Peierls stresses for 〈100 〉 {010} and 〈100 〉 {011} slip systems are calculated taking into consideration the contribution of the elastic strain energy.The core width and Peierls stress of a typical transition-metal aluminide NiAl is also reported for the purpose of verification and comparison.The Peierls stress of NiAl obtained here is in agreement with numerical results,which verifies the correctness of the results obtained for YAg and YCu.Peierls stresses of the 〈100 〉 {011} slip system are smaller than those of〈100 〉 {010} for the same intermetallic compounds originating from the smaller unstable stacking fault energy.The obvious high unstable stacking fault energy of NiAl results in a larger Peierls stress than those of YAg and YCu although they have the same B2 structure.The results show that the core structure and Peierls stress depend monotonically on the unstable stacking fault energy.  相似文献   

10.
利用离散变分方法和DMol方法,研究了P对bcc Fe中[100](010)刃型位错上扭折电子结构的影响,计算了杂质偏聚能、原子间相互作用能、电荷密度及态密度.计算结果表明:微量P引入体系后,电荷发生了重新分布,P原子得到电子,其周围Fe原子失去电子,由于P原子的3p轨道与近邻Fe原子的3d4s4p轨道之间杂化,使P原子与近邻Fe原子间有较强的相互作用,不利于扭折的迁移,使位错运动受阻,有利于材料强度的提高.同时,杂质P原子与基体原子间的成键主要是d,p轨道起作用,使得它们之间的成键有较强的方向性,有可能 关键词: 电子结构 刃型位错 扭折 杂质元素  相似文献   

11.
The effect of dislocation stress fields on the sink efficiency thereof is studied for hydrogen interstitial atoms at temperatures of 293 and 600 K and at a dislocation density of 3 × 1014 m–2 in bcc iron crystal. Rectilinear full screw and edge dislocations in basic slip systems 〈111〉{110}, 〈111〉{112}, 〈100〉{100}, and 〈100〉{110} are considered. Diffusion of defects is simulated by means of the object kinetic Monte Carlo method. The energy of interaction between defects and dislocations is calculated using the anisotropic theory of elasticity. The elastic fields of dislocations result in a less than 25% change of the sink efficiency as compared to the noninteracting linear sink efficiency at a room temperature. The elastic fields of edge dislocations increase the dislocation sink efficiency, whereas the elastic fields of screw dislocations either decrease this parameter (in the case of dislocations with the Burgers vector being 1/2〈111〉) or do not affect it (in the case of dislocations with the Burgers vector being 〈100〉). At temperatures above 600 K, the dislocations affect the behavior of hydrogen in bcc iron mainly owing to a high binding energy between the hydrogen atom and dislocation cores.  相似文献   

12.
Changes in the shape and emission characteristics of the atomically sharp trihedral 〈111〉 angle of a tungsten tip reconstructed in an electric field are studied by continuous-mode field desorption microscopy during high-current-density field emission. The main changes in the tip shape and the slope of the Fowler-Nordheim characteristic occur at an emission current of 1–5 μA. At a current of 50–100 μA taken from the angle, the tip shape and emission characteristics stabilize and remain unchanged in the range 0–150 μA. The new tip shape is characterized by the widening of the angle edges; the appearance of {112} and {001} plane steps in them; a decrease in the sizes of the {011} planes forming the angle faces; and the appearance of steplike transition regions between {011}, {001}, and {112} faces. These changes in the tip shape are related to the fact that the emission field is weaker than the electric field used for preliminary tip reconstruction, the weakening of the field by the space charge of emitted electrons, and a nonuniform temperature distribution in the tip.  相似文献   

13.
The method of etching dislocations is used to study the distribution of dislocations and twins in Fe-3% Si alloy single crystals prepared from the melt after plastic deformation with higher speed. The crystals are deformed by twinning in the 〈111〉 directions along the {112} planes and by slip in the 〈111〉 directions along the {110} planes. The results prove that the dislocations causing plastic deformation move in the {110} planes during both fast and slow deformation. The difference in the slip surfaces during fast and slow deformation is explained by the different number of cross slips per unit dislocation path.  相似文献   

14.
郭常霖 《物理学报》1982,31(11):1526-1533
用腐蚀法研究了β-SiC外延层中的晶体缺陷。腐蚀剂为熔融氢氧化钾。三角形尖底蚀坑对应于位错。在β-SiC中的全位错为立方晶系的73°位错和60°位错。不同堆垛方式的β-siC生长层相遇时将形成{111}交界层错,其腐蚀图象为平行于<110>方向的直线。60°位错可分解为两个1/6<112>SchockLey不全位错,并夹着一片{111}层错构成扩展位错。三个1/6<110>压杆位错与三片{111}层错可构成层错锥体。正、反堆垛的β-SiC可形成尖晶石律双晶,双晶面为(111)。腐蚀法和X射线劳厄法证实了这种双晶的存在。 关键词:  相似文献   

15.
The Peierls-Nabarro barrier and stress of thea/2〈111〉 edge dislocation on {112} and {110} plane inα-Fe at O K is calculated within the Peierls-Nabarro model. The method proposed by Nabarro is used, however, the sine force law is replaced by more general force laws based on two central interionic potentials inα-Fe. The values of the Peierls-Nabarro stress corresponding to one of the chosen interionic potentials, 3·5×10?4 μ and 1×10?4 μ on {112} plane (in the twinning direction) and on {110} plane, respectively, seem to be good estimates of the stress necessary to move edge dislocations inα-Fe at O K.  相似文献   

16.
The effect of externally applied stress on the dislocation bias factor (BF) in bcc iron has been studied using a combination of atomistic static calculations and finite element integration. Three kinds of dislocations were considered, namely, a0/2〈1 1 1〉{1 1 0} screw, a0/2〈1 1 1〉{1 1 0} edge and a0〈1 0 0〉{0 0 1} edge dislocations. The computations reveal that the isotropic crystal expansion leads to an increasing or constant dislocation bias, depending on the Burgers vector and type of dislocation. On the other hand, compressive stress reduces the dislocation bias for all the dislocations studied. Variation of the dislocation BF depending on dislocation type and Burgers vector is discussed by analysing the modification of the interaction energy landscape and the capture efficiency values for the vacancy and self-interstitial atom.  相似文献   

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