Atomistic simulation of kink structure on edge dislocation in bcc iron

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.     

First principles study of interactions of oxygen–carbon–vacancy in bcc Fe

Behaviors of C or O in bcc Fe and interactions of C–O and oxygen–carbon–vacancy(O–C–□) are investigated by first principles calculations. Octahedral interstitial site is the most stable position for an O atom in bcc Fe. The migration energy of an O atom in bcc Fe is 0.46 eV. The strength of O–Fe(1 nn) bond(0.32) is slightly greater than that of Fe–Fe metallic bond(0.26). Repulsive interactions of C–C, O–O, and C–O exist in bcc Fe. When the concentration of FIA(FIA refers to C or O) is relatively high, a vacancy can attract four FIAs and form stable FIAs–□ complex.     

Which stresses affect the glide of screw dislocations in bcc metals?

By direct application of stress in molecular statics calculations we identify the stress components that affect the glide of 1/2?111? screw dislocations in bcc tungsten. These results prove that the hydrostatic stress and the normal stress parallel to the dislocation line do not play any role in the dislocation glide. Therefore, the Peierls stress of the dislocation cannot depend directly on the remaining two normal stresses that are perpendicular to the dislocation but, instead, on their combination that causes an equibiaxial tension-compression (and thus shear) in the plane perpendicular to the dislocation line. The Peierls stress of 1/2?111? screw dislocations then depends only on the orientation of the plane in which the shear stress parallel to the Burgers vector is applied and on the magnitude and orientation of the shear stress perpendicular to the slip direction.     

A systematic study of irrational precipitation crystallography in fcc–bcc systems with an analytical O-line method

Precipitations that exhibit irrational transformation crystallography can often be explained in terms of the O-lines in the habit plane. The present work developed an analytical O-line method, which is more useful than the numerical O-line method to study the variation in the habit plane and its structure in a systematic manner. This method has an advantage that the orientation relationship (OR) is the output from the calculation, while in many other models interpreting precipitation crystallography the OR is either an input or is constrained by a prerequisite condition. This paper described the derivation of this method and its application to the study of the precipitation crystallography in fcc-bcc systems. Examples were given for three alloy systems, namely Cu-0.33wt%Cr and Ni-45wt%Cr alloys and a duplex-phase a-y stainless steel. The solutions include the OR between the precipitates and their matrix, the habit plane, the invariant line and the dislocation structure in the habit plane. The calculated results are in good agreement with the experimental observations reported in the literatures. Furthermore, the variation in the optimum O-line features with the lattice parameter ratio has also been studied systematically, providing some guidelines for estimating and understanding possible transformation crystallography from different fcc-bcc systems.     

温度对bcc铁中He行为影响的模拟

介绍了一种模拟bee铁中长期He行为的晶格动力学蒙特卡罗方法（LKMC），它采用分子动力学或第一性原理计算方法计算得到的金属中缺陷的迁移能、形成能、离解能等数据作为输入参数，根据这些参数计算得到模拟体系的事件集，然后通过抽样方法得到体系的下一状态，从而实现对金属中He和缺陷相互作用过程的模拟。根据Robison等描述的LKMC模拟步骤，编写了用于模拟bee金属中He行为的LKMC程序，采用该程序模拟研究了温度对bee铁中He行为的影响。     

室温下压致铁钴镍合金的bcc→hcp相变

 本文采用高压X光衍射方法在金刚石对顶压砧中在位地（in situ）研究了Fe₆₈Co₂₄Ni₈（wt%）合金在室温下的压致bcc→hcp结构相变和直到40.5 GPa的等温压缩行为。实验结果表明该合金在常压下为bcc结构，晶格常数a₀=(0.287 0±0.000 1) nm，体积V₀=(7.119±0.007) cm³/mol，密度ρ₀=(7.981±0.008) g/cm³；在20.9 GPa附近出现bcc→hcp结构相变，两相共存压力区约10 GPa，在此区域内有晶面间距d(002)_hcp=d(110)_bcc，且原子平面(002)_hcp//(110)_bcc，hcp相比bcc相体积减小(0.33±0.02) cm³/mol；高压相hcp结构的晶格参数比值c/a=1.608±0.004；相变后原子配位数的增加使得hcp相(002)平面内及(002)平面间的最近邻原子间距比bcc相最近邻原子间距分别增大约1.6%和0.5%；用Murnaghan状态方程对实验数据进行最小二乘法拟合，得到bcc相B₀=(130±13) GPa，B₀'=12.6±0.5；hcp相V₀=(6.62±0.04) cm³/mol，B₀=(243±21) GPa，B₀'=6.8±0.3；对于该合金的bcc→fcp相变时的结构转变机制做了详细的讨论。     

温度对bcc铁中He行为影响的模拟研究

温度对bcc铁中的He行为有重要的影响,基于bcc晶格的晶格动力学蒙特卡罗（Lattice Kinetic Monte Carlo,LKMC）方法,模拟研究了298—1298 K范围内温度对bcc铁中He行为的影响.结果表明：温度对bcc铁中He行为的影响可以分为4个阶段：（1）298—598 K,（2）598—798 K,（3）798—998 K,（4）998—1298 K.第一阶段随着温度的增加,晶粒内He原子浓度略有降低,但He泡中平均He原子个数迅速增加;第二阶段随着温度的增加,晶粒内的He原子浓度迅速降低,但He泡中平均He原子个数几乎不变;第三阶段随着温度的增加,晶粒内的He原子浓度和He泡中平均He原子个数均迅速减少;第四阶段随着温度的增加,晶粒内He原子浓度以及He泡中平均He原子个数均有所增加,到1298 K时,晶粒内He原子浓度与室温时相近,几乎没有He原子从铁晶粒内逃逸出.模拟结果与文献正电子湮灭实验结果有很好的吻合. 关键词： bcc铁 He 晶格动力学蒙特卡罗 温度     

bcc Fe中刃型位错的结构及能量学研究

基于位错理论，利用分子动力学方法建立了〈100〉{010}，〈100〉{011}，1/2〈111〉{011}和1/2〈111〉{112}刃型位错的芯结构，并计算了这四种刃型位错的形成能、位错芯能量和芯半径.计算结果表明：〈100〉{010}和〈100〉{011}刃型位错的形成能比1/2〈111〉{011}和1/2〈111〉{112}刃型位错的要高，这表明〈100〉刃型位错比1/2〈111〉刃型位错更难形成.而〈100〉{010}和〈100〉{011}刃型位错的芯半径比1/2〈111〉{011}和1/2〈111〉{112}刃型位错的小，这说明在1/2〈111〉刃型位错中位于奇异区的原子数多于〈100〉刃型位错，而这些原子要比完整晶体中的原子具有更大的活性.可见，1/2〈111〉刃型位错比〈100〉刃型位错更易运动，且〈100〉刃型位错在bcc Fe中难以形成. 关键词： bcc Fe 刃型位错 分子动力学模拟     

Disordered bcc γ-phase to δ-phase transformation in Zr-rich U-Zr alloy

The transformation mechanism of hexagonal delta phase from the disordered bcc gamma phase has not been reported before in the Zr-rich U–Zr alloy system. With the help of X-ray diffraction, transmission electron microscopy (TEM) and high-resolution TEM analyses it was shown that the gamma to delta conversion takes place by the lattice collapse mechanism of omega transformation. It was also ascertained that a higher aging temperature or time promotes the growth of all four variants of the delta phase within a parent gamma grain. In addition, ab initio electronic structure calculations showed that the bcc to hexagonal transformation, involving partial ordering of the parent bcc phase followed by (111) plane collapse, is energetically favorable.     

单轴应变驱动铁bcc—hcp相转变的微观模拟

用分子动力学方法模拟了沿〈001〉晶向应变加载和卸载情况下单晶铁中体心立方(bcc)与六方密排(hcp)结构的相互转变,分析了相变的可逆性和微结构演化特征.微观应力的变化显示样品具有超弹性性质,而温度变化表明在相变和逆相变过程中均出现放热现象.相变起始于爆发式均匀形核,晶核由块状颗粒迅速生长为沿{011}晶面的片状分层结构; 而卸载逆相变则从形核开始就呈现片状形态,且相界面晶面指数与加载相变完全一致,表现出形态记忆效应.在两hcp晶核生长的交界面易形成面心立方(fcc)堆垛层错. fcc通过在hcp晶粒内     

Compositional effect of bcc Co100−x Fe x electrodes on magnetoresistance in AlO x -based magnetic tunnel junctions

The effect of the composition of ferromagnetic bcc Co_100−x Fe _x electrodes on tunneling magnetoresistance (TMR) of Co_100−x Fe _x /AlO _x /Co_100−x Fe _x /IrMn magnetic tunnel junctions was studied. The epitaxial growth of the bottom Co_100−x Fe _x electrode leads to a high-quality electrode and interface, which significantly enhances the TMR ratio and the desired effect for study. Other factors that could also affect TMR, such as interface roughness, tunneling barrier properties, and exchange-bias properties, were kept the same within the uncertainty of the experiment in order to minimize their effects. The observed TMR dependence on composition is attributed to the variation of the s-like electron densities of state of the bcc Co_100−x Fe _x electrodes with different compositions.     

bcc Fe的刃型位错中氦-空位团的稳定性

 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。     

On the binding energies and configurations of vacancy and copper–vacancy clusters in bcc Fe–Cu:a computational study

The properties of trapping centres in – as grown – Tl₄GaIn₃S₈ layered single crystals were investigated in the temperature range of 10–300 K using thermoluminescence (TL) measurements. TL curve was analysed to characterize the defects responsible for the observed peaks. Thermal activation energies of the trapping centres were determined using various methods: curve fitting, initial rise and peak shape methods. The results indicated that the peak observed in the low-temperature region composed of many overlapped peaks corresponding to distributed trapping centres in the crystal structure. The apparent thermal energies of the distributed traps were observed to be shifted from ~12 to ~125 meV by increasing the illumination temperature from 10 to 36 K. The analysis revealed that the first-order kinetics (slow retrapping) obeys for deeper level located at 292 meV.     

氦泡在bcc钨中晶界处成核长大的分子动力学模拟

钨(W)是潜在的聚变堆面向等离子体材料.聚变反应中产生的氦(He)不溶于金属W,并在其中易聚集形成He泡,使W基体发生脆化,从而导致W基体的性能发生退化.在前人工作的基础上,本文采用分子动力学研究了He泡在单晶bcc-W中以及bcc-W中∑3[211](110)和∑9[110](411)晶界处He泡形核长大初期的演化过程.结果发现,晶界处He泡的长大机制和单晶W中有所不同.单晶W中He泡通过挤出位错环促进长大.而He泡在∑3[211](110)晶界处的长大机制为:首先挤出并发射少量自间隙W原子,而后挤出1/2⟨111⟩位错线,随后,该位错线会沿晶界面上[111]方向迁移出去;在∑9[110](411)晶界处,He泡在我们的模拟时间尺度范围内没有观察到W自间隙子的发射和位错的挤出.     

氧与bcc相Co（100）表面相互作用的光电发射研究

通过在ＧａＡｓ（１００）表面生长具有弱有序的ｂｃｃ相Ｃｏ超薄膜，利用同步辐射光电发射和ＸＰＳ，研究了室温下不同氧暴露量时Ｃｏ膜的氧吸附行为。价带谱和Ｃｏ３ｐ发射谱结果表明，当暴露氧量低于４Ｌ时，氧解离吸附；更高的氧暴露量导致表面ＣｏＯ相的成核与生成。     

高压下Fe从bcc到hcp结构相变机理的第一性原理计算

采用基于密度泛函理论的第一性原理方法, 分别研究了压力作用下Fe从体心立方 (bcc,α 相) 结构到六角密排(hcp, ε相) 结构相变的两种不同的相变机理: 相变过程中出现亚稳定的面心立方(fcc) 结构(bcc-fcc-hcp) , 以及相变过程中没有出现亚稳定的fcc结构(bcc-hcp) . 计算结果表明: 静水压力条件下, 相变过程中并不会产生亚稳定的fcc结构, 这与最近的原位XRD实验测量结果相一致. 随着压力的增加, fcc-hcp的相变势垒逐渐增加, 压力趋向于阻止Fe从fcc结构到hcp结构的相变. 计算得到了相变过程中原子磁性和结构的详细信息, 分析表明相变过程中涉及复杂的磁性转变, 并且讨论了原子磁性对结构转变影响的物理机理. 此外, 对分子动力学模拟中产生亚稳定的fcc结构的原因也进行了讨论. 关键词： 相变机理 静水压力 第一性原理 铁     

第一性原理计算Fe从bcc到hcp结构的相变路径及其磁性边界

本文采用基于密度泛函理论的第一性原理方法,计算了压力作用下Fe从bcc到hcp结构相变的势能面、相变路径以及相变过程中的磁性相边界.结果表明:与Burgers路径不同,相变过程中bcc结构(110)bcc面的剪切和相对滑移相互耦合,并伴随有(110)bcc面间距的减小;这一相变机制可以解释Fe的静高压实验中在相变初期观察到的hcp结构异常.因此,并不需要像Wang和Ingalls提出的那样,在相变过程中引入一个亚稳定的fcc相来解释这些实验结果.对相变势能面的计算表明剪切对相变的发生有激活作用.此外,分析表明相变过程中涉及复杂的磁性转变,相变过渡态位置正好位于磁性相边界上,并对原子磁性对结构转变影响的物理机制进行了讨论.