Journal articles: 'Dislocation structure'

1

Kivambe, Maulid, Gaute Stokkan, Torunn Ervik, Sergio Castellanos, Jasmin Hofstetter, and Tonio Buonassisi. "The Impact of Dislocation Structure on Impurity Decoration of Dislocation Clusters in Multicrystalline Silicon." Solid State Phenomena 205-206 (October 2013): 71–76. http://dx.doi.org/10.4028/www.scientific.net/ssp.205-206.71.

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Light microscopy, electron backscatter diffraction and transmission electron microscopy is employed to investigate dislocation structure and impurity precipitation in commonly occurring dislocation clusters as observed on defect-etched directionally solidified multicrystalline silicon wafers. The investigation shows that poligonised structures consist of parallel mostly similar, straight, well-ordered dislocations, with minimal contact-interaction and no evidence of precipitate decoration. On the other hand, disordered structures consist of various dislocation types, with interactions being common. Decoration of dislocations by second phase particles is observed in some cases. Enhanced recombination activity of dislocations may therefore be a result of dislocation interaction forming tangles, microscopic kinks and jogs, which can serve as heterogeneous nucleation sites that enhance metallic decoration.

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Gan, J., J. S. Vetrano, and M. A. Khaleel. "Microstructure Characterization of Dislocation Wall Structure in Aluminum Using Transmission Electron Microscopy." Journal of Engineering Materials and Technology 124, no. 3 (June 10, 2002): 297–301. http://dx.doi.org/10.1115/1.1479178.

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The configuration of dislocation wall structures and the interactions between dislocations and dislocation walls play a significant role in the understanding of deformation processes in metals. Samples of single-crystal aluminum deformed by tensile-straining (15%) were analyzed using TEM. In tensile-deformed (15%) single crystal aluminum, a cell structure is well developed and dislocations in the cell boundaries consist of either one set of Burgers vector or two sets of Burgers vector. The three-dimensional image of cell wall structure, misorientation angle across the cell boundaries and the Burgers vectors of dislocations in the cell boundaries are characterized.

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Lee, Jae Won, and Marek Skowronski. "Structure of “Star” Defect in 4H-SiC Substrates and Epilayers." Materials Science Forum 527-529 (October 2006): 403–6. http://dx.doi.org/10.4028/www.scientific.net/msf.527-529.403.

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The structure of the “star” defect in 4H-SiC substrates and its effects on the extended defect structures in the epilayers were studied by molten KOH etching and transmission x-ray topography. Star defects consist of a center region with high densities of threading dislocations (both edge and screw types) and six arms of dislocation arrays extending along <11-20> directions. In addition, multiple linear dislocation arrays extending perpendicular to the off-cut direction were observed in the epilayers. Dislocation arrays extending along <11-20> directions are consistent with the slip bands generated by the prismatic slip: a/3<11-20>{1-100}. Bands of linear dislocation arrays extending perpendicular to the off-cut direction correspond to the threading edge dislocations nucleated during epitaxial growth.

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Kaneko, Yoshihisa, M. Ishikawa, and Satoshi Hashimoto. "ECCI Observation of Dislocation Structure Formed around an Intergranular Fatigue Crack in Copper." Advanced Materials Research 26-28 (October 2007): 1317–20. http://dx.doi.org/10.4028/www.scientific.net/amr.26-28.1317.

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A fatigue crack growth test was conducted in a polycrystalline copper. Dislocation structure formed near an intergranular fatigue crack was investigated by electron channelling contrast imaging (ECCI) method. The ECCI method enables us to observe dislocations lying under surface using a scanning electron microscope. The fatigue crack in the copper specimen was grown along both grain boundaries and slip bands inside grain. The ECCI observations revealed that both the vein dislocation structure and the cell structures were formed near the grain boundaries. The formations of different dislocation structures near boundaries could be interpreted in terms of the plastic strain incompatibility.

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Akashi, Naoya, Akinori Seki, Hiroaki Saito, Fumiaki Kawai, and Shinichi Shikata. "Influence of Dislocations to the Diamond SBD Reverse Characteristics." Materials Science Forum 924 (June 2018): 212–16. http://dx.doi.org/10.4028/www.scientific.net/msf.924.212.

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Several studies have been carried out regarding the influence of dislocations on device characteristics; however, most of them had been limited to pseudo-vertical structures using high pressure high temperature (HPHT) insulating material as the substrate. In this study, we have investigated the influence of dislocations to the devices using vertical structure SBD on p+ HPHT substrate. SBDs were selectively fabricated on specific dislocation areas. The SBD fabricated on the threading dislocation area indicated fatal influence of the dislocation on the device characteristics.

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6

Sarafanov, G. F. "INSTABILITY IN A DISLOCATION ENSEMBLE AT PLASTIC DEFORMATION IN METALS." Problems of strenght and plasticity 83, no. 2 (2021): 198–206. http://dx.doi.org/10.32326/1814-9146-2021-83-2-198-206.

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A problem related to the development of instability of a homogeneous state in an ensemble of screw dislocations under plastic deformation of metals is considered . The study of the development of instability and structure formation in the dislocation ensemble is carried out on the basis of the method developed for charged particles in plasma and associated with the correlation interaction of electrons and positively charged ions. Accordingly, the screw dislocation ensemble is represented as a system of dislocations with an opposite Burgers vector, i.e., as a plasma-like medium with opposite dislocation charges. The total dislocation charge of the dislocation ensemble is equal to zero due to the law of conservation of the Burgers vector. In this situation, the elastic field of dislocations is “cut off”. The stress field of a single dislocation is shielded by a uniformly distributed dislocation “background” and is characterized by a certain effective potential. It is found that at long distances it decreases exponentially. Therefore, the value in the argument of the falling potential can be considered as the radius of screening of the elastic field of dislocations. It is shown that the screening radius is equal to the correlation radius, which makes it possible to construct a two-particle correlation function and find the energy of the correlation interaction of dislocations. A system of kinetic equations for a dislocation ensemble is formulated, taking into account the elastic and correlation interaction of dislocations, as well as the processes of their generation and annihilation. The criterion of instability of the homogeneous distribution of dislocations for the formulated system of equations is established. The instability criterion is met under the condition that the dislocation density exceeds a certain critical value that depends on the square of the flow stress and material constants (such as the Burgers vector modulus and shear modulus, as well as indirectly, the packing defect energy). In the framework of linear analysis, it is shown that when one system of sliding screw dislocations is taken into account, a one – dimensional periodic dislocation dissipative structure is formed at the moment of instability occurrence, and when multiple sliding is taken into account, solutions appear in the form of various variants of polyhedral lattices (cellular structures). It is established that the characteristic size of the cellular structure coincides with the experimental dependence both qualitatively and quantitatively ( the cell size is proportional to the square root of the dislocation density, and the proportionality coefficient is about ten). It is shown that the origin of spatially inhomogeneous dislocation structures, based on correlation instability, depends mainly on the features of the elastic interaction of dislocations and is not critical to the choice of the mechanisms of their kinetics (i.e., the mechanisms of generation, annihilation, and runoff of dislocations).

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7

Barry, J. C., and H. Alexander. "Direct structure images of 30° partial dislocation cores in silicon." Proceedings, annual meeting, Electron Microscopy Society of America 45 (August 1987): 242–43. http://dx.doi.org/10.1017/s0424820100126111.

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Dislocations in silicon produced by plastic deformation are generally dissociated into partials. 60° dislocations (Burgers vector type 1/2[101]) are dissociated into 30°(Burgers vector type 1/6[211]) and 90°(Burgers vector type 1/6[112]) dislocations. The 30° partials may be either of “glide” or “shuffle” type. Lattice images of the 30° dislocation have been obtained with a JEM 100B, and with a JEM 200Cx. In the aforementioned experiments a reasonable but imperfect match was obtained with calculated images for the “glide” model. In the present experiment direct structure images of 30° dislocation cores have been obtained with a JEOL 4000EX. It is possible to deduce the 30° dislocation core structure by direct inspection of the images. Dislocations were produced by compression of single crystal Si (sample preparation technique described in Alexander et al.).

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8

Li, Mian, Bo Long Li, Tong Bo Wang, and Zuo Ren Nie. "The Effect of Initial Microstructure on the Dynamic Mechanical Behavior of Titanium Plate at Different Strain Rates." Applied Mechanics and Materials 477-478 (December 2013): 1298–302. http://dx.doi.org/10.4028/www.scientific.net/amm.477-478.1298.

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The dynamic mechanical property and microstructure evolution of commercial pure titanium with initial lamellar dislocation boundary structures were studied at different strain rate compression. The experiments were conducted to the cylindrical specimens using Gleeble-3500 thermal mechanical simulation machine at room temperature. With increasing of the strain rate, strain rate strengthening effect was found in the material. New dislocation boundary structures along impact direction were generated which perpendicular to initial dislocation boundary. Then the S bands boundary structure was formed by interaction between new and initial dislocations. It can be supposed that initial dislocation boundary are sheared and kinked by new dislocation slipping.

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9

Hirth, John P. "Fine-scale structural defects in dislocation cores." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (August 1990): 446–47. http://dx.doi.org/10.1017/s0424820100175363.

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We are now entering what one might consider the third phase of study of dislocations by transmission electron microscopy (TEM). The first phase, in the 1950’s and 1960’s led to classifications of dislocation behavior, concepts of low angle boundaries, equilibrium nodes, and dislocation extension, for example. The second, with the advent of the weak-beam technique, produced improved estimates of stacking fault energy on the basis of dislocation extension, revealed more types of extended dislocation configurations, particularly in ordered intermetallic compounds and inorganic compounds, and revealed finer scale partial dislocations such as misfit dislocations and grain boundary dislocations. With improved resolution for both imaging and direct lattice resolution, we can now be thought to be entering a third phase where information on even finer scale core structure of dislocations might be revealed.The improvement in direct core structure resolution is exciting to those working on the physics of dislocation configurations or on dislocation motion and mechanical properties because of the possibility of direct confirmation of mechanisms and models that have heretofore only been tested by indirect correlations.

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10

Yang, Mino, Chong-Don Kim, Hee-Goo Kim, and Cheol-Woong Yang. "Spatial Distribution of Dislocations in Relation to a Substructure in High-Quality GaN Film." Microscopy and Microanalysis 19, S5 (August 2013): 127–30. http://dx.doi.org/10.1017/s1431927613012488.

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AbstractThe dislocation distribution of high-quality single-crystal gallium nitride (GaN) films grown by the hybrid vapor phase epitaxy was analyzed. This study examined the domain structure of GaN from the dislocation distribution on the macroscale by optical microscopy. The surface structure of GaN consisted of domains with microcolumns as the substructure. The inner domains contained a lower density of dislocations but a large number of these dislocations were observed along the domain boundaries. The existence of a domain boundary structure doubly increased the total dislocation density.

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11

Sarikov, Andrey, Anna Marzegalli, Luca Barbisan, Francesco Montalenti, and Leo Miglio. "Structure and Stability of Partial Dislocation Complexes in 3C-SiC by Molecular Dynamics Simulations." Materials 12, no. 18 (September 18, 2019): 3027. http://dx.doi.org/10.3390/ma12183027.

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In this work, the structure and stability of partial dislocation (PD) complexes terminating double and triple stacking faults in 3C-SiC are studied by molecular dynamics simulations. The stability of PD complexes is demonstrated to depend primarily on the mutual orientations of the Burgers vectors of constituent partial dislocations. The existence of stable complexes consisting of two and three partial dislocations is established. In particular, two types of stable double (or extrinsic) dislocation complexes are revealed formed by two 30° partial dislocations with different orientations of Burgers vectors, or 30° and 90° partial dislocations. Stable triple PD complexes consist of two 30° partial dislocations with different orientations of their Burgers vectors and one 90° partial dislocation, and have a total Burgers vector that is equal to zero. Results of the simulations agree with experimental observations of the stable PD complexes forming incoherent boundaries of twin regions and polytype inclusions in 3C-SiC films.

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12

Cheung, Lawrence Yam-Leung. "Bi-clausal sluicing approach to dislocation copying in Cantonese." International Journal of Chinese Linguistics 2, no. 2 (December 30, 2015): 227–72. http://dx.doi.org/10.1075/ijchl.2.2.03che.

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This article discusses a variant of Cantonese dislocation structures known as “dislocation copying” wherein a (non-)constituent string of the host clause gets copied at the right edge. Unlike some previous proposals, it is argued that the relationship between the host clause and the dislocated string cannot be explained purely on pragmatic grounds. Rather, a syntactic account is necessary to explain the dislocated string’s sensitivity to structure. Adopting bi-clausal analysis, we propose that dislocation copying involves the fronting of a remnant containing an elided XP to the left periphery of the second clause, followed by the sluicing of the remainder of the clause. It is argued that the dislocation string gives rise to contrastive/emphasis interpretation. We have also compared similar dislocations in Dutch, German, Japanese and Korean with Cantonese. The findings suggest that sluicing in a bi-clausal structure is common to all of these dislocation structures. The typological variation arises mainly from the different types of phrasal fronting that feed sluicing.

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13

Medlin, D. L., S. M. Foiles, and C. Barry Carter. "Grain Boundary Dislocation Structure and Motion in an Aluminum Σ=3 Bicrystal." Proceedings, annual meeting, Electron Microscopy Society of America 54 (August 11, 1996): 328–29. http://dx.doi.org/10.1017/s0424820100164106.

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A lattice dislocation may interact with a grain boundary leaving either a residual dislocation or a step or both. These products may then contribute to further deformation by themselves moving along the interfaces. For instance, Pond1 observed the dissociation of a perfect lattice dislocation in an aluminum Σ=3 (211) incoherent twin boundary by a reaction of the type:Furthermore, the a/3[111] dislocation was observed to dissociate into two partial grain boundary dislocations (GBD), with Burgers vectors of approximately 2a/9[111] and a/9[111], separating structurally degenerate regions of opposite rigid body displacement.

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14

Mao, Zhigang, Stuart McKeraan, C. Barry Carter, Wei Yang, and Scott A. McPherson. "Weak-Beam Thickness-Fringe Contrast Analysis of Defects in GaN Pyramids." Microscopy and Microanalysis 5, S2 (August 1999): 736–37. http://dx.doi.org/10.1017/s1431927600017001.

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The possible dislocations and slip systems in the wurtzite structure are the same as in hcp structure [1]. The Burgers vectors of these dislocations are . The dislocations can lie on either the (0001) basal plane or prism planes. The dislocations lie on pyramidal planes. TEM studies have revealed that there are predominately three types of dislocations in a wurtzite GaN epilayer which has not been grown by selective overgrowth (e. g. [2, 3]). The majority of the dislocations are threading dislocations with Burgers vector which appear randomly in the epilayer, they result from the growth errors during the growth process. The other two types of dislocation are halflpops with a [0001] or Burgers vector. The [0001] dislocation half-loop lies on the prism plane and the dislocation half-loop lies on the (0001) basal plane which usually appears near the epilayer/substrate interface.

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15

Pichaud, Bernard, N. Burle, Michael Texier, C. Fontaine, and V. I. Vdovin. "Dislocation Nucleation in Heteroepitaxial Semiconducting Films." Solid State Phenomena 156-158 (October 2009): 251–59. http://dx.doi.org/10.4028/www.scientific.net/ssp.156-158.251.

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The nucleation of dislocation in semiconductors is still a matter of debate and especially in heteroepitaxial films. To understand this nucleation process the classical models of dislocation nucleation are presented and discussed. Two main points are then developed: emission of dislocations from surface steps and the role of point defects agglomeration on dislocation nucleation. Recent atomic simulation of half loops emission from surface steps and experimental evidences of anisotropic relaxation of GaInAs films deposited on vicinal (111) GaAs substrates strongly support surface steps as preferential sites for nucleation. In low temperature buffer layer structures (SiGe/Si) an original dislocation structure is observed which corresponds to the dislocation emission in different glide systems by a unique nucleation centre.

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16

Wu, X. F. "Weak beam image of a superlattice dislocation in deformed Ni3 (AlHfB)." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (August 1990): 476–77. http://dx.doi.org/10.1017/s042482010017551x.

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A number of intermetallic compounds with the L12 structure exhibit a strange increase in the flow stress and work-hardening rate with increasing temperature. Despite the success of some model in explaining macroscopic properties, the detailed dislocation processes of model that are assumed to take place have not been observed in microscope. This work is an attempt to determine how the dislocation fine structure is related to the deformation behaviour of L12.Single crystal Ni-23Al-1Hf-0.1B(at%) was used in the present study. direction was chosen as compression axis. Samples were deformed to plastic strain of 6%, specimens were cut parallel to by spark erosion. Fined electropolishing was donein solution of 1% perchloric acid in methanol at −50°c and 30V. The g/3g diffraction condition used in weak beam observation.Fig1 shows the dislocation structure in foil. Long fairly straight screw dislocations with b=a[011] are imaged. The formation of dipoles is regarded as a characteristic and unusual feature of the dislocation structure. This indicates that annihilation is difficult at room temperature deformation. Weak beam images of superlattice dislocations are shown in fig.2 by using different reflections. The dislocation CC is long straight screw dislocation.

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Merriman, C. C., and David P. Field. "Observations of Dislocation Structure in AA 7050 by EBSD." Materials Science Forum 702-703 (December 2011): 493–98. http://dx.doi.org/10.4028/www.scientific.net/msf.702-703.493.

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During and after plastic deformation of metals, dislocations tend to evolve into generally well-defined structures that may include tangles, bands, cell walls, and various additional features. Observation of these structures by electron backscatter diffraction is only accomplished by analysis of changes in orientation from one position to the next. Excess (or geometrically necessary) dislocation densities can be inferred from 2D measurements or obtained directly from 3D measurements as indicated by Nye’s dislocation density tensor. Evolution of excess dislocation densities was measured for a split channel die specimen of aluminum alloy 7050 in the T7451 temper. Densities evolved by a factor or 1.6 for compressive deformations of 15%.

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Caillard, Daniel. "Dislocation Mechanisms and Plasticity of Quasicrystals: TEM Observations in Icosahedral AlPdMn." Materials Science Forum 509 (March 2006): 49–56. http://dx.doi.org/10.4028/www.scientific.net/msf.509.49.

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Quasicrystals can deform Plastically at high temperatures by the movement of dislocations like in crystals. Little is known, however, on the mechanisms that control dislocation movements in these structures. In a first part, the crystallography of quasicrystals is introduced as the projection, in the physical space, of a periodic structure in a hyperspace with more than three dimensions (6 in the case of icosahedral structures). The main properties of dislocations are defined in the physical space and in the six-dimensional space. New results are then presented, showing that dislocation movements may have a large component of climb, in contrast with all existing models that are based on glide processes only. Dislocation movements in two-fold and five-fold planes are compared and discussed in connection with macroscopic mechanical properties.

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19

Emelyanov, V. V., V. A. Emelyanov, V. V. Baranov, and V. V. Busliuk. "Formation of a stable defects structure in silicon noise diodes." Proceedings of the National Academy of Sciences of Belarus, Physical-Technical Series 66, no. 2 (July 16, 2021): 145–53. http://dx.doi.org/10.29235/1561-8358-2021-66-2-145-153.

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vThe possibilities and methods of creating a stable defective structure, including dislocation structure near the zones of p–n-transitions of silicon diodes of noise generators on plates with crystallographic orientations (111) and (001) have been investigated. The effective distribution control of uncontrolled impurities in monocrystalline silicon is achieved by forming a stable dislocation structure in its volume. In order to obtain the reproducible characteristics of noise generator diodes, it is necessary that the dislocation density be homogeneous throughout the plate area. Since the density of dislocations is slightly lower at the edge of the dislocation trail than in the middle, this means that the dislocation traces formed by the adjacent melting zones with the help of a laser beam should overlap. On the basis of experimental studies, it has been established that the necessary degree of uniformity of the density of defects generated is achieved by compliance with the condition of a = (1.5–5.0)d, where a is a step, d is a width of the laser spot on the wafer. The melting process was carried out in a nitrogen environment using a laser hettering unit. The real width of the melting zone turns out to be slightly larger than the diameter of the laser spot due to the thermal conductivity of the silicon and is about 10 μm. Increased dislocation generation on the Si3N4 inclusions, as opposed to dislocations on the Si–SiO2 border, leads to an additional expansion of the dislocation track at the work surface of the plate of noise diodes. The presence of the stable dislocation structure, as well as the presence of impurities and secondary metal atoms in the noise diodes ND 103L structure are confirmed by the secondary ion mass spectroscopy (SIMS) method. The results of the study have been tested at Corporation “INTEGRAL” (Belarus) and can be used in the manufacture of silicon noise diodes.

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Tani, Komomo, Tatsuo Fujimoto, Kazuhito Kamei, Kazuhiko Kusunoki, Kazuaki Seki, and Takayuki Yano. "Evolution of Threading Edge Dislocations at Earlier Stages of PVT Growth for 4H-SiC Single Crystals." Materials Science Forum 858 (May 2016): 73–76. http://dx.doi.org/10.4028/www.scientific.net/msf.858.73.

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Dislocation structures at the seed/grown-crystal interface in PVT-grown 4H-SiC crystals are investigated. The dislocation density is found to show a sharp increase at the interface and its main contribution is probably ascribable to TEDs which stem from BPDs generating at the interface through the structural transformation. Intense TEM observations reveal an intriguing in-plane distribution structure of the interface BPDs; the BPDs form a two-dimensional dislocation network comprising of {-1100} partial dislocations associated with expanded areas of stacking faults at the nodes of the network.

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Petrenec, Martin, Karel Obrtlík, Jaroslav Polák, and Jiří Man. "Dislocation Structures in Nickel Based Superalloy Inconel 792-5A Fatigued at Room Temperature and 700°C." Materials Science Forum 567-568 (December 2007): 429–32. http://dx.doi.org/10.4028/www.scientific.net/msf.567-568.429.

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Dislocations structures were studied using transmission electron microscopy in specimens of cast polycrystalline nickel based superalloy Inconel 792-5A cyclically strained up to failure with constant total strain amplitudes at temperatures 23 and 700 °C. Spatial arrangement of dislocations in individual grains was determined using the technique of oriented foils. Planar dislocation arrangements in the form of bands parallel to the {111} planes were observed in specimens cycled at both temperatures. The bands showed up as thin slabs of high dislocation density cutting both the γ channels and γ´ precipitates. They correspond to areas of cyclic slip localization. Experimental results concerning the dislocation structure are used to discuss the effect of temperature on the cyclic stress-strain response and fatigue life.

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Huang, X., Q. H. Lu, M. L. Sui, D. X. Li, and Niels Hansen. "Structural Change during Cold Rolling of Electrodeposited Copper." Materials Science Forum 539-543 (March 2007): 5013–18. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.5013.

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Copper sheet samples composed of nanometer scale lamellar twins was produced by electrodeposition. The coherent lamellar twin boundaries were within 20˚ of being parallel to the sheet plane in more than 60% of the grains. The electrodeposited sample was cold rolled to 30 and 85% reductions in thickness and the structural evolution during cold rolling was examined by transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Extensive activity of partial dislocations along twin boundaries and of perfect dislocations within twins (in particular in coarse twins >100nm) were identified. Moreover, it was found that shear banding occurred, which locally destroyed the lamellar twin structure. A dislocation structure developed within the shear bands, and such a structure evolved with strain and gradually replaced the lamellar twin structure. After 85% deformation, a large volume fraction of the lamellar twin structure was replaced by a lamellar dislocation structure characteristic of high strain rolling where the lamellar dislocation boundaries are almost parallel to the rolling plane. It was also found that the structural scales are coarser in the lamellar dislocation structure than in the initial lamellar twin structure.

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Trushin, Maxim, O. F. Vyvenko, Teimuraz Mchedlidze, Oleg Kononchuk, and Martin Kittler. "Electronic States of Oxygen-Free Dislocation Networks Produced by Direct Bonding of Silicon Wafers." Solid State Phenomena 156-158 (October 2009): 283–88. http://dx.doi.org/10.4028/www.scientific.net/ssp.156-158.283.

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The results of experimental investigations of the dislocation-related DLTS-peaks originated from the dislocation networks (DN) are presented. Samples with DNs were produced by direct bonding of p-type silicon wafers and no enhancement of oxygen concentration was detected near the DN plane. Origins of the DLTS peaks were proposed and a correlation with the dislocation-related photoluminescence data was established based on known dislocation structure of the samples. Two types of shallow DLTS peaks exhibited Pool-Frenkel effect, which could be linked to the dislocation deformation potential. One of the shallow DLTS peaks was related to straight parts of screw dislocations and another - to the intersections of the dislocations.

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Li, Miao Miao, Xiao Ping Su, De Shen Feng, Jian Long Zuo, Nan Li, and Xue Wu Wang. "The Study of Flower-Shaped Structure Dislocation in 4 Inch <100> Germanium Single Crystal." Materials Science Forum 685 (June 2011): 141–46. http://dx.doi.org/10.4028/www.scientific.net/msf.685.141.

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As the key component of single junction GaAs/Ge solar cells and GaAs/Ge solar cells, the quality of germanium single crystal affects the properties of space solar cell directly. The dislocation of germanium single crystals is the main impact factor on solar cells efficiency. Through measuring dislocation densities in the different positions of 4 inch <100> germanium single crystals produced by Czochralski method, we found that flower-shaped structure dislocations pattern was mainly caused by the inclusions. This paper briefly analyzed dislocations produced by inclusions, chemical etching pits method. SEM and EDS measurement methods were also employed to study the flower-shaped structure defects. A germanium single crystal with low dislocation density was obtained and the special defects were almost eliminated. The germanium single crystal with low dislocation density (PV) was obtained, which could meet the requirement of the GaAs/Ge solar cells.

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Kiguchi, Takanori, Kenta Aoyagi, Yoshitaka Ehara, Hiroshi Funakubo, Tomoaki Yamada, Noritaka Usami, and Toyohiko J. Konno. "Nano-Structure around 90° Domain Wall and Elastic Interaction with Misfit Dislocation in PbTiO₃ Thin Film." Key Engineering Materials 566 (July 2013): 167–70. http://dx.doi.org/10.4028/www.scientific.net/kem.566.167.

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We have elucidated the elastic interaction between the 90° domains and misfit dislocations in PbTiO3/SrTiO3 (001) epitaxial thin films by the local strain mapping based on high-resolution transmission electron microscopy. The novel mechanism of the nucleation and growth of 90 ̊ domain has been proposed based on the results, including the introduction of the additional dislocation perpendicular to the misfit dislocation and the dissociation of these dislocations into two pairs of partial dislocations with an anti-phase boundary.

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Zhou, M., T. F. Kelly, and J. E. Flinn. "A study of the dislocation core structure in high nitrogen austenitic stainless steel by weak beam EM." Proceedings, annual meeting, Electron Microscopy Society of America 53 (August 13, 1995): 536–37. http://dx.doi.org/10.1017/s0424820100139056.

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The large strengthening effect of nitrogen interstitials and its strong influence on the dislocation distribution of Fe-Cr-Ni austenite have been rationalized by Owen et al. using a short-range-order-based model. However, the model cannot explain the high population of screw dislocations resulted from a small amount of plastic deformation. Grujicic suggested that nitrogen addition to Fe-Cr-Ni austenitic stainless steels causes spreading of the screw dislocation core into two or more non-parallel planes which results in low dislocation mobility. Higher stress and higher temperature are thus required to overcome the energy barrier for the movement of dislocations. The core structure of dislocations in nitrogen-containing stainless steels is of fundamental importance for understanding the strengthening mechanism of this material. The weak beam dark field imaging technique allows the direct observation of partial dislocations and stacking faults bonded by the partials. When the optimum imaging condition is satisfied, relatively intense, narrow images of less than 2 nm wide can be obtained.

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27

Mogilevsky, M. A., and L. S. Bushnev. "Investigation of shock-wave deformation history from recovered structure." Proceedings, annual meeting, Electron Microscopy Society of America 44 (August 1986): 434–35. http://dx.doi.org/10.1017/s0424820100143754.

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Single crystals of Al were loaded by 15 to 40 GPa shock waves at 77 K with a pulse duration of 1.0 to 0.5 μs and a residual deformation of ∼1%. The analysis of deformation structure peculiarities allows the deformation history to be re-established.After a 20 to 40 GPa loading the dislocation density in the recovered samples was about 1010 cm-2. By measuring the thickness of the 40 GPa shock front in Al, a plastic deformation velocity of 1.07 x 108 s-1 is obtained, from where the moving dislocation density at the front is 7 x 1010 cm-2. A very small part of dislocations moves during the whole time of compression, i.e. a total dislocation density at the front must be in excess of this value by one or two orders. Consequently, due to extremely high stresses, at the front there exists a very unstable structure which is rearranged later with a noticeable decrease in dislocation density.

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Starenchenko, Vladimir A., Dmitry N. Cherepanov, Olga V. Selivanikova, and Elena A. Barbakova. "Formation of Shear Zone's Defect Structure in F.C.C. Metals." Advanced Materials Research 1084 (January 2015): 26–29. http://dx.doi.org/10.4028/www.scientific.net/amr.1084.26.

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As a result of the work of Frank-Read dislocation source the shear zone is formed. It is filled with deformation defects forming as a consequence of the dynamic features of the motion of dislocation loops and due to the interaction of shear forming dislocations with dislocations of non-coplanar slip systems. The accumulation of jogs on screw segments leads to the fact that the edge segments are moving faster than the screw segments so the shear zone is swept out generally by screw segments. The expressions of the intensities of the deformation defects accumulation in shear zones are given in the article. The point defects plays special role in the formation and evolution of misorientation substructures into deformed monocrystals, polycrystals and nanocrystals.

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Ebrahimi, Alireza, and Thomas Hochrainer. "Three-Dimensional Continuum Dislocation Dynamics Simulations of Dislocation Structure Evolution in Bending of a Micro-Beam." MRS Advances 1, no. 24 (2016): 1791–96. http://dx.doi.org/10.1557/adv.2016.75.

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ABSTRACTA persistent challenge in multi-scale modeling of materials is the prediction of plastic materials behavior based on the evolution of the dislocation state. An important step towards a dislocation based continuum description was recently achieved with the so called continuum dislocation dynamics (CDD). CDD captures the kinematics of moving curved dislocations in flux-type evolution equations for dislocation density variables, coupled to the stress field via average dislocation velocity-laws based on the Peach-Koehler force. The lowest order closure of CDD employs three internal variables per slip system, namely the total dislocation density, the classical dislocation density tensor and a so called curvature density.In the current work we present a three-dimensional implementation of the lowest order CDD theory as a materials sub-routine for Abaqus®in conjunction with the crystal plasticity framework DAMASK. We simulate bending of a micro-beam and qualitatively compare the plastic shear and the dislocation distribution on a given slip system to results from the literature. The CDD simulations reproduce a zone of reduced plastic shear close to the surfaces and dislocation pile-ups towards the center of the beam, which have been similarly observed in discrete dislocation simulations.

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Bernstock-Kopaczyńska, Ewelina, and Magdalena Jabłońska. "Study of Defects Structure in Fe-Al Alloys." Solid State Phenomena 203-204 (June 2013): 411–16. http://dx.doi.org/10.4028/www.scientific.net/ssp.203-204.411.

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In the literature it is proven that thermal vacancies have a great influence on the mechanism of hardening of Fe-Al alloys. Moreover, in these alloys, we observed a long-range ordering, which can significantly affect the mechanical and physical properties and their stability. In this paper, influence of low-temperature annealing on elimination of excess vacancies was investigated. TEM observation of annealed specimens for the alloys with 28 and 38 at.% aluminum have helped elucidate the phenomena responsible for vacancies elimination due to the occurrence of particular interactions between point and linear structure defects. It was shown that the aluminum content influences significantly changes in defects structure. The alloy with 28 at.% aluminum has mainly superdislocations in the structure, while in alloy with 38 at.% aluminum, mainly unit dislocations and high-energy dislocation configurations, like dislocation loops, dislocation dipoles, and dislocation jogs, were observed. The results suggest that different defect types may control the diffusion process during low-temperature annealing and that it is affected by alloy composition.

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Reiche, Manfred, Martin Kittler, Eckhard Pippel, Hans Kosina, Alois Lugstein, and Hartmut Uebensee. "Electronic Properties of Dislocations." Solid State Phenomena 242 (October 2015): 141–46. http://dx.doi.org/10.4028/www.scientific.net/ssp.242.141.

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Dislocations are one-dimensional crystal defects. Their dimension characterize the defects as nanostructures (nanowires). Measurements on defined dislocation arrays proved numerous exceptional electronic properties. A model of dislocations as quantum wires is proposed. The formation of the quantum wire is a consequence of the high strain level on the dislocation core modi-fying locally the band structure.

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Mastorakos, Ioannis N., Firas E. Akasheh, and Hussein M. Zbib. "Treating internal surfaces and interfaces in discrete dislocation dynamics." Journal of the Mechanical Behaviour of Materials 20, no. 1-3 (December 1, 2011): 13–20. http://dx.doi.org/10.1515/jmbm.2011.002.

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AbstractThe treatment of coherent interfaces and cracks is discussed in the framework of dislocation dynamics (DD). In the case of interfaces, we use DD to study dislocation interactions in nanoscale bimetallic laminates, and to predict their structure after relaxation and during loading. In agreement with experimental observations, our discrete dynamics simulations show that dislocation structure develops only at the interface between coherent layers leaving layers’ interior dislocation-free. The main dislocation mechanism at this length scale is Oworan bowing of threading dislocations confined to their respective layers by the sign-alternating coherency stress field in the layers. Slip transmission across the interfaces marks the end of the confined slip regime, hence, the breakdown of the interfaces and macroscopic yielding of these structures. In the case of crack, its long-range and singular stress field is determined by modeling the crack as continuous distribution of dislocation loops. The traction boundary condition to be satisfied at the crack surface, results into a singular integral equation of the first kind that is solved numerically. The model is integrated with the DD technique to investigate the behavior of a specimen containing cracks of different shapes under fatigue. The results are compared with the behavior of an uncracked specimen and conclusions are extracted. Extension of this crack treatment methodology to account for their presence at interfaces, all within the frame dislocations dynamics, opens the door for a more realistic approach to a wide range of interfaces-related problems.

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Orlová, Alena, and Ferdinand Dobeš. "Contributions to Internal Stress from Free Dislocations and from Substructure Boundaries in Dislocation Structure Formed in High Temperature Creep." Materials Science Forum 567-568 (December 2007): 173–76. http://dx.doi.org/10.4028/www.scientific.net/msf.567-568.173.

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The relation of the internal stress and the parameters of the heterogeneous dislocation structure was suggested in the form of the classical Taylor formula relating the internal stress to the total dislocation density stored in the subgrain interior and in the subgrain boundaries. The other formula combines linearly the stress contribution generated by network dislocations and the stress contribution of the subgrain structure semiempirically related to the subgrain size. The formulas can evaluate the ratio of internal stress components due to sub-boundaries and free dislocations.

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34

Sato, Michihiro, Tetsuya Ohashi, Takuya Maruizumi, and Isao Kitagawa. "Crystal Plasticity Analysis of Thermal Deformation and Dislocation Accumulation in ULSI Cells." Key Engineering Materials 324-325 (November 2006): 1035–38. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.1035.

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Thermal stress, plastic slip deformation and accumulation of dislocations in shallow trench isolation (STI) type ULSI devices when the temperature drops from 1000 し to room temperature are analyzed by a crystal plasticity analysis cord. The results show that dislocation accumulation takes place at the temperature range over 800 し, and the difference of 6 MPa in the lattice friction stress at 1000 し!causes increase of dislocation density more than 1.6 times. Dislocations generate and accumulate at the shoulder part of the device area and bottom corners of the trench. Dislocations are categorized into two groups. In one group, dislocation lines are mostly straight and parallel to the trench direction, and in the other group, dislocations make half loop type structure. Possibilities for the suppression of dislocation accumulation through control of lattice friction stress at high temperature region are discussed.

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35

Lane Rohrer, C. "Cluster/dislocation interactions in dilute aluminum-based solid solutions." Journal of Materials Research 10, no. 3 (March 1995): 578–90. http://dx.doi.org/10.1557/jmr.1995.0578.

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The influence of single solute atoms and solute clusters on an extended edge dislocation dipole in Al was studied by atomistic simulation. Single Cu and Ag solute/dislocation interaction energy calculations showed that Cu interacts strongly with an Al extended dislocation and prefers sites in the compressive region, in agreement with elasticity theory predictions. Single Ag atoms, however, are strongly repelled by an Al extended dislocation, in contrast with elasticity theory predictions. Monte Carlo simulations of Al: 1% Cu, Al: 2% Cu, Al: 1% Ag, Al: 0.5% Cu, 0.5% Ag, and Al: 0.75% Cu, 0.25% Ag were carried out in the presence of an extended dislocation dipole at 600 K allowing for solute segregation. Cu atoms in the binary alloys were observed to segregate to the compressive regions of the extended dislocation dipole, forming widespread “atmospheres” over the width of both extended dislocations which did not affect the partial dislocation spacing. Ag in the binary alloy formed small Ag zones which also had little influence on the spacing between the partials. The ternary systems, however, exhibited highly localized solute clusters that had a large impact on the extended dislocation dipole structure, increasing the separation between the partial dislocations. The resulting cluster structures are discussed along with their influence on the apparent stacking fault energy of the alloy systems.

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36

Kornilov, D. A., V. M. Kosenkov, and P. P. Silantev. "INFLUENCE OF INITIAL DISLOCATION STRUCTURE ON POINT AND MICROSCOPIC DEFECTS KINETIC UNDER IRRADIATION." Vestnik of Samara University. Natural Science Series 22, no. 1-2 (April 24, 2017): 69–84. http://dx.doi.org/10.18287/2541-7525-2016-22-1-2-69-84.

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This work is aimed for justification of quantitative effect of radiation defect concentration decreasing in materials depending on density of edge dislocation which are their outlet. The results of defect kinetics modeling with taking into account their recombination on dislocation loops, edge dislocations and pores are given. The summery of this work is useful in the frame of solving problem of decreasing radiation swelling and material properties degradation during neutron irradiation.

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37

Oktyabrsky, S., R. Kalyanaraman, K. Jagannadham, and J. Narayan. "Dislocation structure of low-angle grain boundaries in YBa2Cu3O7−δ/MgO films." Journal of Materials Research 14, no. 7 (July 1999): 2764–72. http://dx.doi.org/10.1557/jmr.1999.0369.

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Grain boundaries in laser-deposited YBa2Cu3O7−δ (YBCO)/MgO thin films have been investigated by high-resolution transmission electron microscopy. The films exhibit perfect texturing with YBCO(001)/MgO(001) giving rise to low-angle [001] tilt grain boundaries resulting from the grains with the c axis normal to the substrate surface and with misorientation in the a-b plane. The atomic structure of the grain boundaries was analyzed by using a dislocation model. Low-angle grain boundaries have been found to be aligned along (100) and (110) interface planes. For the (110) boundary plane, the low-energy dislocation configuration was found to consist of an array of alternating [100] and [010] dislocations. We have calculated the energy of various configurations and shown that the energy of the (110) boundary with dissociated dislocations is comparable to that of the (100) boundary, which explains the coexistence of (100) and (110) interface facets along the boundary. We have also modeled critical current transport through grain boundaries with various structures and found that the low-energy (110) grain boundary with dissociated dislocation array is expected to transport a lower superconducting current (by 25% for 6° misorientation) than (100) boundaries.

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38

Uazyrkhanova, Gulzhaz, Bauyrzhan K. Rakhadilov, Alexandr Myakinin, and Zhuldyz Uazyrkhanova. "The Change in the Thin Structure and Mechanical Properties of Aluminum Alloys at Intensive Plastic Deformation." Materials Science Forum 906 (September 2017): 114–20. http://dx.doi.org/10.4028/www.scientific.net/msf.906.114.

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Electron microscopy and x-ray analysis and mechanical testing have been investigated the influence of severe plastic deformation on structure and mechanical properties of aluminum alloys. It is established that in the initial state in the alloy AMC has a high density of chaotically distributed dislocations with a density of 5-10*109 сm-2. It is shown that microdiffraction paintings in alloy AMC in the bulk of grains are observed uniformly distributed particles of the second phase. It is established that in the initial state in the alloy AMG6 there is a high density of chaotically distributed dislocations with a density of 2-6 *1010 сm-2. Determined that after ECAP the dislocation structure of alloys AMG6, AMC and changes: formed dislocation networks inside the fragments of the dislocation is practically not observed. Determined that after ECAP-12 increase the tensile strength and yield strength of alloys AMG6 and AMC.

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39

Sakwe, Sakwe Aloysius, and Peter J. Wellmann. "Influence of Growth Temperature on the Evolution of Dislocations during PVT Growth of Bulk SiC Single Crystals." Materials Science Forum 556-557 (September 2007): 263–66. http://dx.doi.org/10.4028/www.scientific.net/msf.556-557.263.

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In this paper we report, based on analysis of dislocation statistics, on the influence of growth temperature on the nucleation, propagation and annihilation mechanisms of dislocations. Using KOH defect etching and optical microscopy we have conducted dislocation tracking along lengths of crystals grown under various process temperature regimes to study their evolution and propagation mechanisms statistically. We further present the influence of growth temperature on the step structure of the growth front using AFM measurements. From the analysis of dislocation statistics and step structure in relation to temperature we derive the role of surface kinetics of the SiC gas species on the growth surface in dislocation evolution during PVT growth of bulk SiC.

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Baitsch, M., K. C. Le, and T. M. Tran. "Dislocation structure during microindentation." International Journal of Engineering Science 94 (September 2015): 195–211. http://dx.doi.org/10.1016/j.ijengsci.2015.05.005.

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41

Bassim, N. D., Mark E. Twigg, Michael A. Mastro, Philip G. Neudeck, Charles R. Eddy, R. L. Henry, R. N. Holm, J. Anthony Powell, and Andrew J. Trunek. "Electron Microscopy Investigation of the Role of Surface Steps in the Generation of Dislocations during MOCVD Growth of GaN on 4H-SiC." Materials Science Forum 527-529 (October 2006): 1509–12. http://dx.doi.org/10.4028/www.scientific.net/msf.527-529.1509.

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Through the use of specially-prepared on-axis SiC substrates with patterned mesa tops completely free of atomic-scale surface steps, we have previously reported the growth of highquality GaN heteroepitaxial films with greatly reduced threading dislocation densities on the order of 107/cm2. In these films, we reported a defect substructure in which lateral a-type dislocations are present in the nucleation layer but do not bow into threading dislocations during the subsequent GaN growth. This study focuses further on the role of SiC substrate surface steps in the generation of misfit, a-type, and threading dislocations at the heteroepitaxial interface. By using weak-beam imaging (both to eliminate Moiré effects and to observe narrow dislocation images) from plan-view transmission electron microscopy (TEM), we identify dislocations generated on stepped and unstepped mesas and compare their geometries. We observe that misfit dislocations nucleated on an unstepped SiC mesa are confined to one set of a-type Burgers vectors of the form g=1/3 [2110] _ _ , straight and well-ordered so that they are less likely to interact with each other. On the other hand, misfit dislocation structures on a stepped SiC mesa surface are not nearly as well-ordered, having bowed structure with threading dislocations that appear to nucleate at SiC surface steps.

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42

Oktyabrsky, S., R. Kalyanaraman, K. Jagannadham, and J. Narayan. "Structure of Low- And High-Angle Grain Boundaries In YBCO/MgO Films." Microscopy and Microanalysis 4, S2 (July 1998): 676–77. http://dx.doi.org/10.1017/s1431927600023503.

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Grain boundaries (GBs) in laser deposited YB2Cu3O7-δ/MgO(001) thin films have been investigated by high-resolution transmission electron microscopy (TEM) and scanning TEM (STEM). We report both statistics and atomic structure of low-angle and high-angle [001] tilt grain boundaries resulting from almost perfect c-axis textured YBCO films.Atomic structure of low-angle GBs was analyzed using a dislocation model. These boundaries have been found to be aligned primarily along (100) and (110) interface planes. For (100) boundary plane, the GB consists of a periodic array of [100] dislocations (Fig.l). For (110) boundary plane, the array is also periodic but every [110] dislocation is split by ∼ 1.5 nm into two [100] and [010] dislocations (Fig.2). We have calculated energy of various configurations and shown that the energy of the (110) boundary with dissociated dislocations is comparable to that of (100) boundary, which explains the coexistence of (100) and (110) interface facets along the boundary.

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43

Ino, Yuji, Satoru Matsumoto, Suzuka Nishimura, and Kazutaka Terashima. "Effect of Si Doping on the Crystal Structure of HVPE Grown Boron Phosphide." Materials Science Forum 725 (July 2012): 285–88. http://dx.doi.org/10.4028/www.scientific.net/msf.725.285.

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Boron Phosphide (BP) layers have been grown on Si (100) as a substrate for cubic GaN heteroepitaxy. Si heavy doping was attempted to reduce the threading dislocation density in the BP. To observe the effect on dislocations in BP by Si doping, we used cross-sectional transmission electron microscopy (XTEM). Also, Glow Discharge-Optical Emission Spectroscopy (GDOES) were used to evaluate the effect of Si doping. For the samples under the conditions (a) and (e), we found the formation of pits at BP surface and an increasing in the proportion of threading dislocations with an angle of 90 ° to the surface. We could not see a significant change in the threading dislocation density by Si doping under the conditions used in this paper.

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44

Bak, Sang Hwan, Sung Soo Kim, and Dong Bok Lee. "Effect of hydrogen on dislocation structure and strain-induced martensite transformation in 316L stainless steel." RSC Advances 7, no. 45 (2017): 27840–45. http://dx.doi.org/10.1039/c7ra01053b.

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Hydrogen forced that SIM distributed locally in a α′/γ laminated structure. Hydrogen changed dislocation structure from only cellular to planar dislocations. Hydrogen promoted strain-induced ordering and suppressed the formation of SIM.

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45

Breuer, D., P. Klimanek, and W. Pantleon. "X-ray determination of dislocation density and arrangement in plastically deformed copper." Journal of Applied Crystallography 33, no. 5 (October 1, 2000): 1284–94. http://dx.doi.org/10.1107/s0021889800008256.

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Using the kinematical theory of X-ray scattering by crystals with dislocations as developed by Krivoglazet al.and Wilkens, the dislocation content of compressed copper single and polycrystals was investigated by means of profile analysis of selected diffraction peaks. Measurements of radial intensity distributionsI(2θ) were performed with a double-crystal spectrometer in the case of the single crystals and with conventional polycrystal diffractometers in the case of the polycrystals. Additionally, the misorientations Θ occurring within the dislocation cell structure because of the accumulation of excess dislocations of one sign were investigated by means of rocking curves of the single-crystal reflections and by evaluation of electron backscattering patterns (EBSPs). Within a wide deformation range, the mean total dislocation density ρdcan be related well to the flow stressviathe Taylor relationship. Assuming a random distribution of the misorientations Θ between adjacent dislocation cells, the evaluation of the rocking curves gives mean values 〈|Θ|〉 much smaller than those determined by EBSP analysis. For this reason, a model of a dislocation cell structure with restrictedly correlated misorientations, which leads to better agreement of the X-ray and the EBSP data, is proposed.

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46

Lu, P., R. W. Glaisher, and David J. Smith. "Atomic structure of CdTe dislocations studied by HREM." Proceedings, annual meeting, Electron Microscopy Society of America 47 (August 6, 1989): 576–77. http://dx.doi.org/10.1017/s0424820100154858.

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The determination of the atomic core of dislocations in semiconductors is a challenging problem for high-resolution electron microscopy(HREM). In previous studies, various defects in elemental semiconductors, III-V and II-VI compound semiconductors have been reported. In particular, the core structure of the 30° partial dislocations in silicon, which are dissociated from a perfect 60° dislocation, have been deduced. present study, various CdTe dislocations have been imaged at 400keV. and their core structures have been analyzed with assistance from multi-slice image simulations. Sections of CdTe single crystal were cut normal to the [110] direction, followed by mechanically polishing to a thickness of ˜ 20 microns and finally argon ion-beam milling to perforation for electron microscopy. The crystals were examined with a JEM-4000EX. having a structure resolution limit of ˜ 1.7Å at 400keV.

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47

Nakamura, Atsutomo, E. Tochigi, Naoya Shibata, Takahisa Yamamoto, and Yuichi Ikuhara. "Dislocation Structure Analysis of Low Angle Tilt Grain Boundaries in Alumina by Elastic Theory." Materials Science Forum 561-565 (October 2007): 2465–68. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.2465.

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Structure and configuration of boundary dislocations on the low angle tilt grain boundaries in alumina were considered based on the ideas that the boundary is composed of regularly arrayed edge dislocations and that the dislocations could dissociate into partial dislocations as well as glide dislocations in bulk. Moreover, the structure of the dissociated boundary dislocations were evaluated by the calculations based on an elastic theory. The calculations indicated that the largeness of the stacking fault region between partial dislocations formed by the dissociation will decrease with increasing tilt angles. It can be said that the idea and calculations used here will be powerful in considering the dislocation structure of low angle tilt grain boundaries that are not or are difficult to be identified.

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48

Zhang, Yudong, Shiying Wang, Claude Esling, Jean-Sébastien Lecomte, Christophe Schuman, Xiang Zhao, and Liang Zuo. "A method to identify dislocations in a known crystal structure by transmission electron microscopy." Journal of Applied Crystallography 44, no. 6 (October 29, 2011): 1164–68. http://dx.doi.org/10.1107/s0021889811041173.

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This paper proposes a method to identify the type and the Burgers vector of dislocations visualizedviatransmission electron microscopy (TEM). The first step is to determine experimentally the orientation, with respect to the sample holder, of a grain of known crystal structure whose dislocation slip systems have been previously reported. With this determined orientation of the grain, the method calculates the orientation of the projections of the possible dislocation line vectors in the transmission electron microscope screen coordinate system and then compares them with the observed dislocations to identify their type and the Burgers vector. The coordinate transformations underlying the method are outlined, and its validity is demonstrated using TEM measurements on a titanium sample. The method is expected to simplify the related TEM determination work.

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Moriarty, John A., Wei Xu, Per So¨derlind, James Belak, Lin H. Yang, and Jing Zhu. "Atomistic Simulations for Multiscale Modeling in bcc Metals." Journal of Engineering Materials and Technology 121, no. 2 (April 1, 1999): 120–25. http://dx.doi.org/10.1115/1.2812355.

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Quantum-based atomistic simulations are being used to study fundamental deformation and defect properties relevant to the multiscale modeling of plasticity in bcc metals at both ambient and extreme conditions. Ab initio electronic-structure calculations on the elastic and ideal-strength properties of Ta and Mo help constrain and validate many-body interatomic potentials used to study grain boundaries and dislocations. The predicted Σ5 (310) [100] grain boundary structure for Mo has recently been confirmed in HREM measurements. The core structure, γ surfaces, Peierls stress, and kink-pair formation energies associated with the motion of a/2〈111〉 screw dislocations in Ta and Mo have also been calculated. Dislocation mobility and dislocation junction formation and breaking are currently under investigation.

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Seyed Salehi, Majid, Nozar Anjabin, and Hyoung S. Kim. "Study of Geometrically Necessary Dislocations of a Partially Recrystallized Aluminum Alloy Using 2D EBSD." Microscopy and Microanalysis 25, no. 3 (April 10, 2019): 656–63. http://dx.doi.org/10.1017/s1431927619000382.

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AbstractDuring recrystallization, the growth of fresh grains initiated within a deformed microstructure causes dramatic changes in the dislocation structure and density of a heavily deformed matrix. In this paper, the microstructure of a cold rolled and partially recrystallized Al-Mg alloy (AA5052) was studied via electron backscattered diffraction (EBSD) analysis. The structure and density of the geometrically necessary dislocations (GNDs) were predicted using a combination of continuum mechanics and dislocation theory. Accordingly, the Nye dislocation tensor, which determines the GND structure, was estimated by calculation of the lattice curvature. To do so, five components of the Nye dislocation tensor were directly calculated from the local orientation of surface points of the specimen, which was determined by two-dimensional EBSD. The remaining components of GNDs were determined by minimizing a normalized Hamiltonian equation based on dislocation energy. The results show the elimination of low angle boundaries, lattice curvature, and GNDs in recrystallized regions and the formation of low angle boundaries with orientation discontinuities in deformed grains, which may be due to static recovery.

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Journal articles on the topic 'Dislocation structure'

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