合成氟金云母单晶缺陷的X射线研究

本文报道了人工合成大面积氟金云母单晶中缺陷的X射线研究结果。X射线劳厄法的研究表明,在合成云母中存在着较大程度的一维无序,并因而出现许多堆垛错排区及其亚晶界。X射线衍射形貌术的研究表明,合成云母中的亚晶界和位错线大部分是从晶种起源并向生长表面的法线方向延伸的。晶体的靠近表面的区域缺陷较密集,中心部分较少。探讨了合成云母与天然云母中缺陷分布的差别。对用于制作电容器的合成云母片的缺陷与性能的关系作了分析和讨论。 关键词：     

高温应变下的晶界湮没机理的晶体相场法研究

应用晶体相场方法研究高温应变下的预熔化晶界位错湮没机理. 结果表明, 原预熔化晶界上的位错在应变作用下发生分离运动, 形成新晶界, 即亚晶界. 该过程的实质是生成了亚晶粒; 亚晶界的迁移过程的本质是亚晶粒长大、吞噬旧晶粒的过程; 亚晶界之间的湮没是亚晶粒完全吞噬旧晶粒过程的结束, 体系转变成为单个晶粒结构. 根据原子密度序参数沿x和y方向的投影值随应变量的变化特征, 可以揭示出高温应变作用下, 预熔化亚晶界相遇湮没的本质是两对极性相反的偶极子位错对发生二次湮没, 该湮没的微观过程是通过位错连续二次滑移湮没而实现的, 其湮没的速率较低温时的湮没速率要小许多.     

非对称倾侧亚晶界的晶体相场法研究

采用晶体相场法研究非对称倾侧亚晶界结构及其在应力作用下的微观运动机制.分别从温度、倾斜度角以及应力施加方向等方面对其结构及迁移过程进行分析和讨论.结果表明,非对称倾侧亚晶界由符号相同的一排刃型位错等距排列,部分出现由两个相互垂直排列的刃型位错构成的位错组;在应力作用下,非对称倾侧亚晶界迁移的微观机制包括位错的滑移和攀移、位错组分解、单个位错与位错组反应、单个位错分解以及位错湮灭;温度降低和倾斜度增大都会阻碍亚晶界的迁移过程;应力方向改变导致位错运动方向改变,从而改变晶界迁移形式.     

在氯化钠晶体中在亚晶界附近位错的分布

我们用交替抛光、浸蚀的方法,观察了由于应力作用在氯化钠晶体亚晶界附近出现的位错列的定性空间分布,看来这些位错是从亚晶界发出的。 实验所用晶体是北京大学物理系光学教研室用Czochralski法从分析纯的氯化钠制成的。 经过740℃退火60小时后,位错密度约10~3—10~41/厘米~2(不包括亚晶界的)。     

纳米铜薄膜塑性变形中空位型缺陷形核与演化的分子动力学研究

本文采用分子动力学方法模拟了纳米单晶铜薄膜在单向拉伸载荷作用下的塑性变形过程, 重点分析了空位型缺陷的形核过程和演化机理. 在模拟过程中, 采用镶嵌原子势描述原子间的相互作用. 模拟结果表明纳米铜薄膜中塑性变形起源于位错的表面形核, 而空位型缺陷的形核及演化都与晶体内部的位错运动密切相关. 空位型缺陷通常从位错割阶及层错交截处开始形核, 以单空位、层错四面体和不规则空位团等形式存在. 关键词： 纳米薄膜 塑性变形 空位 层错四面体     

阻热法引上生长Nd:YAG时界面转换前后出现的组分过冷和位错增殖现象

一、引 言 众所周知,平坦界面有利于抑制小晶面(核心和侧心)和位错的形成,是获得无缺陷单晶的基本条件[1].但晶体中已存在的位错则会延伸到晶体下部去.而在凸界面情况下,位错会沿大致垂直生长界面的方向伸展,最后排除于表面[2,3].但凸界面本身容易产生核心和其它缺陷[1].为综合     

LiNbO_3晶体中缺陷的X射线形貌研究

用X射线透射扫描形貌方法观察了直拉法生长LiNbO~3晶体中各种类型点阵缺陷,诸如铁电畴壁、生长层、位错、亚晶界和胞状组织等;用不同衍射矢量对[001]和[210]方向生长的晶体的形貌消象规律,结合X射线铁电异常散射效应和光学显微观察,讨论了晶体中180°铁电畴和生长层的衬度及其分布,并研究了LiNbO~3晶体中180°畴壁形成及其相互关系。     

钼单晶体中亚晶界位错结构的研究

本文应用蚀象法对电子束浮区区熔法制得的原生态钼单晶体中的亚晶界位错结构进行了直接观测。对于实验结果进行了细致的分析,并与亚晶界的Frank公式的一些预期结果比较,全面地证实了理论预测。对(111)面上平行蚀线方向的测量表明,它们大体沿着1/2〈111〉刃型位错的滑移面及攀移面的交线,从而证实了它们是这种位错所组成的一组位错倾侧型晶界。通过对蚀斑三叉亚晶界的分析,检验了推广后的Read-Shockley公式,同时表明存在着两组位错的倾侧晶界。对于(111)面上观察到的15组蚀线网络进行了分析,结果表明其中5组是1/2〈111〉/〈100〉网络,9组是〈100〉/〈110〉网络。分析中,除去应用Carrington等所发展的极图分析法以外,我们还根据Frank公式所规定的网线间距的关系式,提出了进一步定量检验的分析方法。实践证明,当极图分析不能获得唯一的结果时,这种定量检验法可以有效地确定位错网络的Burgers矢量。此外,我们还观察到奇位错和亚晶界交互作用的事例,特别是奇位错在亚晶界上引起“台阶”以及夹杂物和亚晶界交互作用的迹象。不同类型的亚晶界交接以及非平衡态的亚晶界也是经常可以观察到的。以上结果表明,蚀象法对于定量地研究原生态晶体中的亚晶界位错结构是极其有效的,其能力并不亚于电子显微镜薄膜透射法。     

晶体相场法研究晶粒缩小过程中的位错湮灭与晶界迁移

通过晶体相场法模拟了与基体三种不同取向圆形晶粒在缩小过程中晶界上的位错湮灭机制与晶界迁移机制.研究结果表明:当圆形晶粒和基体的取向差17°时,圆形晶粒和基体形成位错核心重叠的大角晶界,用位错模型难以解释该演化过程,但结果表明圆形晶粒半径的平方与演化时间成线性关系,该关系与弯曲晶界迁移理论相互印证;当取向差为4°时,圆形晶粒和基体形成由分离位错构成的小角晶界,在该晶粒缩小的过程中,位错以径向攀移为主且会发生晶粒转动以调整位错间距,随着位错间距的减小相互靠近的位错发生反应;当取向差为10°时,晶界既有位错核心重叠较小的部分也有由分离位错构成的部分,在晶粒缩小时晶界演化表现为位错径向攀移和切向运动,两种运动的耦合运动使得能相互反应的位错相互靠近并发生反应.     

LiNbO3晶体中缺陷的X射线形貌研究

用X射线透射扫描形貌方法观察了直拉法生长LiNbO₃晶体中各种类型点阵缺陷,诸如铁电畴壁、生长层、位错、亚晶界和胞状组织等;用不同衍射矢量对[001]和[210]方向生长的晶体的形貌消象规律,结合X射线铁电异常散射效应和光学显微观察,讨论了晶体中180°铁电畴和生长层的衬度及其分布,并研究了LiNbO₃晶体中180°畴壁形成及其相互关系。 关键词：     

High temperature superconducting behaviour in PbTePb system

We have observed a strongly field dependant diamagnetic susceptibility in PbTe up to temperatures reaching 20° K. This could be explained through anomalous superconductivity of lead precipitates in subgrain boundaries of PbTe crystals.     

Mechanisms and Kinetics of Recrystallisation: A Two Dimensional Vertex Dynamics Simulation

The recrystallisation process in single phase materials is investigated using a vertex dynamics simulation. The situation is idealised (two dimensional and isotropic) to better understand the role of physical parameters (energy and mobility of subgrain and grain boundaries, shape and relative size of grains) on the competition between recrystallisation and recovery. Simulations show that subgrain growth can be very heterogeneous in the vicinity of grain boundaries, i.e. that recrystallisation develops following the bulging mechanism. Bulging is enhanced for low mobilities of subgrain boundaries, high relative desorientation and small relative sizes. The recrystallisation kinetics is well described by an Avrami law of low exponent.     

Formation of fragments with medium-angle boundaries in shear bands: Computer simulation

The conditions for the formation of fragments with medium-angle boundaries in shear bands are analyzed using computer simulation. It is shown that the main condition for the transformation of weakly disoriented dislocation structures into a fragmented structure is the suppression of active plastic deformation in a subgrain by the elastic fields of disclinations appearing at subgrain boundary junctions as a result of mismatch of plastic rotations in individual subgrain boundaries. Under these conditions, during continued straining in the surrounding matrix, such a subgrain behaves as an undeformed inclusion and experiences a crystallographic rotation. The disorientation of the subgrain continuously increases, thereby transforming initial small-angle dislocation boundaries into medium-angle and (in the limit) large-angle boundaries.     

On defects in aluminium single crystal thin films

Defects in Al single crystal thin films prepared by epitaxial growth on mica were investigated by transmission electron microscopy. Dislocations, subgrain boundaries, grain of different orientation and separated polycrystalline regions were observed in the single crystal matrix with density dependent on the pressure of residual gases.     

Dislocation structure of copper single crystals in high-temperature creep test

It has been shown that in the high-temperature creep test at 0·85 kp mm^?2 and 0·7T _m (T _m is the melting temperature in °K) the dislocation substructure of copper single-slip oriented crystals is formed practically at the early stage of the test. The subsequent changes of substructure consist in the growth of subgrain misorientation and in the transformation of tangled subgrain boundaries into regular dislocation networks. There is a pronounced tendency to the formation of subboundaries in the {111} and {110} planes.     

Solute-diffusion-controlled dislocation creep in pure aluminium containing 0.026 at.% Fe

Pure aluminium containing about 200?at.ppm Fe in solution is shown to creep about 10⁶ times slower at 200°C than the same aluminium containing a negligible amount of iron in solution. The high creep resistance of the Al–200?at.ppm?Fe alloy is attributed to the presence of subgrain boundaries containing iron solute atoms. It is proposed that the opposing stress fields from subgrain boundaries and from the piled-up dislocations during creep are cyclically relaxed, by iron solute diffusion, to allow climb of the lead dislocation in the pile-up. The mechanism is a form of mechanical ratcheting. The model is applied to Al–Fe alloys and correctly predicts that the creep rate is controlled by the rate of iron solute diffusion and by a temperature dependence equal to the activation energy for iron diffusion, namely Q _c?=?221?kJ?mol^?1. Basic creep studies on solid-solution alloying with solute atoms that diffuse slowly in the lattice of aluminium (e.g. manganese, chromium, titanium and vanadium) appear worthy of study as a way of enhancing creep strength and of understanding creep mechanisms involving solute-atom-containing subgrain boundaries.     

铁硅合金(110)[001]单晶体的形变和再结晶

本文研究了含硅3.25％铁硅合金(110)[001]的单晶,在压下量为5—50％范围内的形变和再结晶。沿样品轴向冷轧2—16％后,测出的滑移面为(101),(101),(011)和(011),孿生面为(112)和(112),这很好地解释了本文所得冷轧机构的来源。样品经过35％和50％冷轧后,在退火时再结晶晶粒形成的部位和生长的情况有所不同:前者在孿晶界上领先形成,并沿孿晶界择尤生长;而后者除了观察到在孿晶界和形变带附近形成外,还观察到一种通过亚晶粒长大而成的晶粒,它们择尤生长的趋势也不如前者明显。     

Etch pits on fresh and grown-in dislocations and etching of antiphase domain boundaries in Fe-Si alloys

The etching of fresh and grown-in dislocations on the chemically polished (100) surface of Fe-3% Si alloy single crystals and fresh dislocations on the same surface of Fe-7% Si alloy single crystals in a 1–2% nital is described. Antiphase domain boundaries are revealed by the same etching on the surfaces of Fe-7% Si alloy single crystals with different crystallographic orientation.