共查询到18条相似文献,搜索用时 578 毫秒
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本文计算了铌酸锶钡(SBN)晶体中沿光轴的位错双折射像的反衬,计算中考虑了光弹系数的各向异性,结果表明与各向同性计算相比刃位错双折射像中的花瓣有伸长的趋势,螺位错无反衬,并与实验结果作了比较。 相似文献
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利用X射线投影貌相术观察和分析了硅蹼中的位错和层错。在生长态硅蹼中,除观察到柏氏矢量为1/2<110>的刃型、螺型与60°全位错以及柏氏矢量为1/6<112>的Shockley刃型半位错外,还观察到平行于硅蹼表面的大面积层错和蹼中的60°,30°Shockley半位错。位错在热处理过程中运动并发生位错反应形成近六角形的位错网络。热处理改变生长态硅蹼中层错的组态和衬度,并由于杂质聚集破坏了Shockley半位错的消象法则。还观察到层错象中的位错。对所观察的结果都分别作了分析和简要的讨论。
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为研究激光冲击材料内部位错组态和晶粒细化的关系,用脉冲激光对690高强钢试样进行了冲击强化处理,采用扫描电镜和透射电镜分别获得了冲击后试样的扫描电子显微像和透射电子显微像、高分辨电子显微像,并对高分辨电子显微像进行快速傅里叶逆变换,从位错组态角度建立了激光冲击690高强钢晶粒细化模型.结果表明,690高强钢试样经功率密度为5.09 GW/cm^2的激光冲击加载后,其材料内部位错增殖、表层晶粒细化,截面晶粒尺寸大小分布在80~200 nm;析出相与基体保持半共格关系,基体中分布着众多刃型位错、位错偶以及扩展位错等缺陷,其中位错偶是由带割阶的螺型位错运动形成;通过由位错、扩展位错、空位等构成的几何位错界面扩展交汇把原始大晶粒分割成细小晶粒;激光冲击690高强钢晶粒细化模型可以描述激光冲击690高强钢位错运动主导的晶粒细化过程. 相似文献
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考虑到晶体的离散点阵结构,滑移只能在原子之间进行,因此位错中心永远没有原子,位错中心附近分摊到每个原子的离散弹性能量处处有限。在刚性位错假定下,直接应用位错弹性理论解析结果,求出了晶体直奇异位错等效内切半径及其随位错中心位置的周期变化。对于简单四方晶体中奇异螺型位错,一级近似与Peierls模型结果巧合。计算了fcc和bcc两种晶系中各种位错的自能和等效位错内切半径,并初步考虑了各向异性弹性效应。结果表明:位错滑移面不是几何平面,bcc螺型位错滑移面类似于蜂巢结构。指出了用这种离散弹性方法进一步估算各种次级效应的可能。
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This paper addresses the question as to whether the core structure of screw dislocations in Mo in the bulk can be obtained from high-resolution electron microscopy (HREM) images of such dislocations viewed end-on in a thin foil. Atomistic simulations of the core structure of screw dislocations in elastically anisotropic Mo were carried out using bond order potentials. These simulations take account automatically of the effects of the surface relaxation displacements (anisotropic Eshelby twist). They show that the differential displacements of the atoms at the surface are different with components perpendicular to the Burgers vector about five times larger than those in the middle of the foil, the latter being characteristic of the bulk. Nye tensor plots show that the surface relaxation stresses strongly affect the incompatible distortions. HREM simulations of the computed structure reflect the displacements at the exit surface, modified by interband scattering and the microscope transfer function. Nye tensor plots obtained from the HREM images show that interband scattering also affects the incompatible distortions. It is concluded that it would be very difficult to obtain information on the core structure of screw dislocations in the bulk Mo from HREM images, even under ideal experimental conditions, and that quantitative comparisons between experimental and simulated images from assumed model structures would be essential. 相似文献
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This paper describes how the sign of a screw dislocation or of the screw component of a mixed dislocation in a thin elastically isotropic foil, viewed end-on, can be determined from the dark-field weak-beam diffraction contrast arising from surface relaxation displacements. The contrast consists of black-white lobes, with the line of no-contrast parallel to g , similar to that found previously by Tunstall et al . [Phil. Mag. 9 99 (1964)] for bright-field imaging of screw dislocations in thick foils. Unlike weak-beam images of inclined dislocations, the image profiles are very broad (~10?nm for the strongest) owing to the long-range nature of surface relaxation strain-field. For dislocations spaced at ~10?nm or less, the overlap of the strain-field from nearby dislocations has to be taken into account. The paper also discusses the nature of the contrast from mixed dislocations slightly tilted from the incident beam direction, when contrast from the edge component is expected, and the possibility of determining the sign of the screw component in this case. 相似文献
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E. G. Galieva O. V. Antonova P. E. Panfilov A. N. Titov 《Physics of the Solid State》2011,53(5):1047-1055
The dislocation structure of titanium dichalcogenide single crystals has been investigated. It has been established that the basis of the structure consists of dislocations that lie in the basal plane, are predominantly edge dislocations, and are responsible for the strain behavior of the material. There are also growth dislocations that are predominantly screw dislocations and form dislocation networks. A relationship is revealed between the nature of the chalcogen and the character of the defect structure. 相似文献
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M. M. Myshlyaev 《Doklady Physics》2012,57(3):107-109
Dislocation reactions, including dislocation intersections during various processes in crystals, play an important and often
crucial role. This is most pronounced during plastic deformation of crystalline solids, which attracts particular interest
from researchers. Intersection of screw dislocations in fcc crystals during their deformation by uniaxial tension and compression
was studied by A. Cottrell [1]. It was shown that the intersection of similar screw dislocations moving toward each other
results in the formation of interstitial thresholds on them; in the case of intersection of opposite screw dislocations, vacancy
thresholds are formed on them. 相似文献
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Section topographs of edge and screw dislocations with an axis along [0001] in 6H-SiC are taken and interpreted, and the image formation is explained for this case. The contrast induced by various arrangements of dislocations within the Borrmann triangle is experimentally studied. The sign of the Burgers vector of an edge or screw dislocation normal to the crystal surface is shown to be unambiguously determined from the section-topograph image of this dislocation. The sign of the Burgers vector of a screw dislocation can also be determined from its image taken with Lang projection topography. The contribution of a long-range strain field to the section images of edge and screw dislocations normal to the crystal surface is revealed. The experimental contrasts recorded using section topography and Borrmann-effect-based topography are compared. 相似文献
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The free path lengths of ensembles of edge and screw dislocations in the stress field of a concentrated load are studied in γ-irradiated LiF crystals. The relative mobility of edge and screw dislocations is found to depend substantially on the irradiation dose and temperature. The results obtained are discussed in the context of additional retardation of screw dislocations with dislocation debris that appears during double cross slip. 相似文献
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A. S. Dranenko V. A. Makara N. N. Novikov T. M. Perga O. V. Rudenko 《Russian Physics Journal》1973,16(9):1200-1203
The kinetics of the motion and the surmounting of detents by dislocations in sodium chloride and potassium chloride crystals is investigated herein. Special attention is paid to a comparative study of the mean free paths of the screw and edge dislocations. It is established that the mean free paths of the screw dislocations is somewhat less than for edge dislocations under identical test conditions. The kinetic curves obtained were processed within the frame-work of theoretical representations about the motion of dislocations in crystals containing detents of two kinds.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 9, pp. 17–21, September, 1973. 相似文献