Journal articles: 'Dislocation in metals'

1

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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2

Pande, Chandra S., and Ramasis Goswami. "Dislocation Emission and Crack Dislocation Interactions." Metals 10, no. 4 (2020): 473. http://dx.doi.org/10.3390/met10040473.

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An understanding of the crack initiation and crack growth in metals spanning the entire spectrum of conventional and advanced has long been a major scientific challenge. It is known that dislocations are involved both in the initiation and propagation of cracks in metals and alloys. In this review, we first describe the experimental observations of dislocation emission from cracks under stress. Then the role played by these dislocations in fatigue and fracture is considered at a fundamental level by considering the interactions of crack and dislocations emitted from the crack. We obtain precise expression for the equilibrium positions of dislocations in an array ahead of crack tip. We estimate important parameters, such as plastic zone size, dislocation free zone and dislocation stress intensity factor for the analysis of crack propagation. Finally, we describe very recent novel and significant results, such as residual stresses and relatively large lattice rotations across a number of grains in front of the crack that accompanies fatigue process.

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3

Nakagawa, Koutarou, Momoki Hayashi, Kozue Takano-Satoh, et al. "Characterization of Dislocation Rearrangement in FCC Metals during Work Hardening Using X-ray Diffraction Line-Profile Analysis." Quantum Beam Science 4, no. 4 (2020): 36. http://dx.doi.org/10.3390/qubs4040036.

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Multiplication and rearrangement of dislocations in face-centered cubic (FCC) metals during tensile deformation are affected by grain size, stacking fault energy (SFE), and solute elements. X-ray diffraction (XRD) line-profile analysis can evaluate the dislocation density (ρ) and dislocation arrangement (M) from the strength of the interaction between dislocations. However, the relationship between M and ρ has not been thoroughly addressed. In this study, multiplication and rearrangement of dislocations in FCC metals during tensile deformation was evaluated by XRD line-profile analysis. Furthermore, the effects of grain size, SFE, and solute elements on the extent of dislocation rearrangement were evaluated with varying M values during tensile deformation. M decreased as the dislocation density increased. By contrast, grain size and SFE did not exhibit a significant influence on the obtained M values. The influence of solute species and concentration of solute elements on M changes were also determined. In addition, the relationship between dislocation substructures and M for tensile deformed metals were also explained. Dislocations were loosely distributed at M > 1, and cell walls gradually formed by gathering dislocations at M < 1. While cell walls became thicker with decreasing M in metals with low stacking fault energy, thin cell walls with high dislocation density formed for an M value of 0.3 in metals with high stacking fault energy.

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4

Sato, Eiichi, and Tetsuya Matsunaga. "Grain Boundary Sliding Below Ambient Temperature in H.C.P. Metals." Key Engineering Materials 433 (March 2010): 299–303. http://dx.doi.org/10.4028/www.scientific.net/kem.433.299.

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Hexagonal close-packed metals and alloys show significant creep behavior with extremely low activation energies at and below ambient temperature even below their 0.2% proof stresses. It is caused by straightly-aligned dislocation arrays in a single slip system without any dislocation cuttings. These dislocation arrays should, then, pile up at grain boundary (GB) because of violation of von Mises' condition in H.C.P. structure. The piled-up dislocations have to be accommodated by GB sliding. Electron back scatter diffraction (EBSD) analyses and atomic force microscope (AFM) observations were performed to reveal the mechanism of GB sliding below ambient temperature in H.C.P. metals as an accommodation mechanism of ambient temperature creep. EBSD analyses revealed that crystal lattice rotated near GB, which indicates the pile up of lattice dislocations at GB. AFM observation showed a step caused by GB sliding. GB sliding below ambient temperature in H.C.P. metals are considered to compensate the incompatibility between neighboring grains by dislocation slip, which is called slip induced GB sliding.

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5

Tamura, Manabu. "Relation between Sub-grain Size and Dislocation Density During Steady-State Dislocation Creep of Polycrystalline Cubic Metals." Journal of Materials Science Research 7, no. 4 (2018): 26. http://dx.doi.org/10.5539/jmsr.v7n4p26.

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The sub-grain size, d, during steady-state dislocation creep of polycrystalline metals is theoretically formulated to be inversely proportional to the dislocation density, ρ, which is defined as the number of dislocations swept out of a sub-grain divided by the cross-sectional area of the sub-grain. This dislocation density differs from the typically observed dislocation density inside a sub-grain after unloading, ρ_ob. In the current work, the ρ_ob values inside sub-grains in steadily crept specimens of Al, Cu, Fe, Fe–Mo alloy, austenitic stainless steel, and high-Cr martensitic steel reported in the literature were used to evaluate the relation ρ_ob=ηρ. It was confirmed that η≈1 for pure metals (regardless of the type of metal) crept at high temperatures and low stresses or for long durations and η&gt;1 for Mo-containing alloys and martensitic steel crept at low temperatures and/or high stresses. Moreover, it is suggested that the condition η&gt;1 corresponds to a state of excess immobile dislocations inside the sub-grain. The theoretical relation d_ob (≈d)∝η∙〖ρ_ob〗^(-1), where d_ob is the observed sub-grain size, essentially differs from the well-known empirical relation d_ob∝〖ρ_ob〗^(-0.5).

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6

Portal, Lotan, Iryna Polishchuk, Maria Koifman Khristosov, Alexander Katsman, and Boaz Pokroy. "Self-catalytic growth of one-dimensional materials within dislocations in gold." Proceedings of the National Academy of Sciences 118, no. 39 (2021): e2107930118. http://dx.doi.org/10.1073/pnas.2107930118.

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Dislocations in metals affect their properties on the macro- and the microscales. For example, they increase a metal’s hardness and strength. Dislocation outcrops exist on the surfaces of such metals, and atoms in the proximity of these outcrops are more loosely bonded, facilitating local chemical corrosion and reactivity. In this study, we present a unique autocatalytic mechanism by which a system of inorganic semiconducting gold(I) cyanide nanowires forms within preexisting dislocation lines in a plastically deformed Au-Ag alloy. The formation occurs during the classical selective dealloying process that forms nanoporous Au. Nucleation of the nanowire originates at the surfaces of the catalytic dislocation outcrops. The nanowires are single crystals that spontaneously undergo layer-by-layer one-dimensional growth. The continuous growth of nanowires is achieved when the dislocation density exceeds a critical value evaluated on the basis of a kinetic model that we developed.

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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 (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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8

Muiruri, Amos, Maina Maringa, and Willie du Preez. "Evaluation of Dislocation Densities in Various Microstructures of Additively Manufactured Ti6Al4V (Eli) by the Method of X-ray Diffraction." Materials 13, no. 23 (2020): 5355. http://dx.doi.org/10.3390/ma13235355.

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Dislocations play a central role in determining strength and flow properties of metals and alloys. Diffusionless phase transformation of β→α in Ti6Al4V during the Direct Metal Laser Sintering (DMLS) process produces martensitic microstructures with high dislocation densities. However, heat treatment, such as stress relieving and annealing, can be applied to reduce the volume of these dislocations. In the present study, an analysis of the X-ray diffraction (XRD) profiles of the non-heat-treated and heat-treated microstructures of DMLS Ti6Al4V(ELI) was carried out to determine the level of defects in these microstructures. The modified Williamson–Hall and modified Warren–Averbach methods of analysis were used to evaluate the dislocation densities in these microstructures. The results obtained showed a 73% reduction of dislocation density in DMLS Ti6Al4V(ELI) upon stress relieving heat treatment. The density of dislocations further declined in microstructures that were annealed at elevated temperatures, with the microstructures that were heat-treated just below the β→α recording the lowest dislocation densities.

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9

Bertoni, Mariana I., Clémence Colin, and Tonio Buonassisi. "Dislocation Engineering in Multicrystalline Silicon." Solid State Phenomena 156-158 (October 2009): 11–18. http://dx.doi.org/10.4028/www.scientific.net/ssp.156-158.11.

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Dislocations are known to be among the most deleterious performance-limiting defects in multicrystalline silicon (mc-Si) based solar cells. In this work, we propose a method to remove dislocations based on a high temperature treatment. Dislocation density reductions of >95% are achieved in commercial ribbon silicon with a double-sided silicon nitride coating via high temperature annealing under ambient conditions. The dislocation density reduction follows temperature-dependent and time-dependent models developed by Kuhlmann et al. for the annealing of dislocations in face-centered cubic metals. It is believed that higher annealing temperatures (>1170°C) allow dislocation movement unconstrained by crystallographic glide planes, leading to pairwise dislocation annihilation within minutes.

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10

Filatov, A., A. Pogorelov, D. Kropachev, and O. Dmitrichenko. "Dislocation Mass-Transfer and Electrical Phenomena in Metals under Pulsed Laser Influence." Defect and Diffusion Forum 363 (May 2015): 173–77. http://dx.doi.org/10.4028/www.scientific.net/ddf.363.173.

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The influence of moving dislocations on mass-transfer and the phenomena, accompanying it in pulse-deformed metals is studied in a real-time. Transport of self-interstitial atoms (SIAs) by mobile edge dislocations in crystal with FCC lattice is investigated by molecular dynamics. A strain rate (106s-1) and dislocation density (1010– 1012cm-2) in simulated crystal corresponds to a laser effect in a Q-factor mode. The experimental investigations in a real-time are performed by recording of electrical signal induced by the laser pulse irradiation of metal foils of different crystal structures.

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11

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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12

Sergeev, N. N., S. N. Kutepov, А. Е. Gvozdev, and E. V. Ageev. "DISLOCATION INDUCED MECHANISMS OF HYDROGENE EMBRITTLEMENT OF METALS AND ALLOYES." Proceedings of the Southwest State University 21, no. 2 (2017): 32–47. http://dx.doi.org/10.21869/2223-1560-2017-21-2-32-47.

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The paper discusses some models of hydrogen-stress cracking of metals and alloys. These models are based on hydrogen-dislocation interaction. It is shown that the critical role of dislocation emissions in AIDE mechanism is, in its turn, similar to HELP except for a higher localization of deformations compared with microvoids coalescence that is related with HELP, because that stresses needed for the dislocation propagation are high enough to boost general dislocation activity in deformation zones in front of cracks. This results in the formation of small voids on intersecting deformation bands. It has been observed that a crack is essentially growing due to the emission of dislocations. However the emission of dislocation towards the tip of a crack and the formation of voids in front of a crack contribute a lot to the process. Furthermore, the formation of voids in front of a crack makes for a short radius of the crack tip and low angles of the crack tip opening displacement The paper considers crack growing in inert media in plastic materials. Crack plastic growth takes place mainly due to dislocations that originate from the sources in the deformation zone in front of the crack tip and are propagating backwards along the crack tip plane with a small or zero emission of the dislocations that start from the crack tip. Small number of the dislocations that originate in the sources lying closest to the crack tip will intersect the tip of the crack precisely thus promoting the crack development while the majority of the dislocation will have either blunting effect or contribute to the deformation in front of the crack. Thus to cause a crack growth due to microvoid coalescence and deep cavities with shallow depressions therein on fracture surfaces there must be a large deformation in front of the crack. It is demonstrated that the cracking mechanism resulting from the AIDE mechanism will be either intergranular or transcrystalline depending on the location where the propagation of dislocations and formation of voids run mostly easily. In case of transcrystalline cracking alternative sliding motion along the planes on either side of the crack will tend to minimize the reverse stress caused by previously emitted dislocations. Then the macroscopic transcrystalline cracking plane will divide the angle between the slide planes and the crack front will be located on the intersection line of the crack planes and the slide planes. However, if there is a difference in the number of slides that occur on either crack side because of big differences in shear stresses on different slide planes, there will be deviations from the planes and directions with low refraction index. If the plane index is not low, there still can be deviations in the failure planes depending on the location of nucleus voids in front of the crack. A detailed description of the relationship between hydrogen effect on the behavior of dislocations and voids, sliding motion localization and hydrogen embrittlement is still lacking, moreover, it presents a serious problem that can be solved by describing the kinetics of hydrogen embrittlement process. Thanks to their sophisticated nature HELP and AIDE mechanisms can be embrittlement contributors both in cracking and in the formation of cavities due to ductile fracture.

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13

Li, Juan, G. M. Pharr, and C. Kirchlechner. "Quantitative insights into the dislocation source behavior of twin boundaries suggest a new dislocation source mechanism." Journal of Materials Research 36, no. 10 (2021): 2037–46. http://dx.doi.org/10.1557/s43578-021-00253-y.

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AbstractPop-in statistics from nanoindentation with spherical indenters are used to determine the stress required to activate dislocation sources in twin boundaries (TBs) in copper and its alloys. The TB source activation stress is smaller than that needed for bulk single crystals, irrespective of the indenter size, dislocation density and stacking fault energy. Because an array of pre-existing Frank partial dislocations is present at a TB, we propose that dislocation emission from the TB occurs by the Frank partials splitting into Shockley partials moving along the TB plane and perfect lattice dislocations, both of which are mobile. The proposed mechanism is supported by recent high resolution transmission electron microscopy images in deformed nanotwinned (NT) metals and may help to explain some of the superior properties of nanotwinned metals (e.g. high strength and good ductility), as well as the process of detwinning by the collective formation and motion of Shockley partial dislocations along TBs. Graphic abstract

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14

Poirier, J. P., and G. D. Price. "Dislocation melting of metals." Physics of the Earth and Planetary Interiors 69, no. 3-4 (1992): 153–62. http://dx.doi.org/10.1016/0031-9201(92)90131-e.

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15

Zhang, Meng Qi, and Shan Wu Yang. "Analysis and Calculation of the Strain Field Disturbance Caused by Dislocation Migration." Applied Mechanics and Materials 481 (December 2013): 212–16. http://dx.doi.org/10.4028/www.scientific.net/amm.481.212.

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In order to elucidate the different characters of elastic waves caused respectively by screw and edge dislocation movement, we calculated the stain field disturbance caused by migration of dislocation by elastic theory. Through the calculation, it was found that the strain field disturbance resulted from screw dislocation migration produces a transverse wave radiation while that resulted from edge dislocation migration produces transverse wave and longitudinal wave simultaneously. The result reveals the different energy radiation characters of screw dislocations and edge dislocations and explains the reason that edge dislocation moves faster than screw dislocation in general experiment. It also provides a theoretical basis for determining microcosmic mechanism of plastic deformation of metals by monitoring the changes of elastic waves.

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16

Lu, Yan, Yu-Heng Zhang, En Ma, and Wei-Zhong Han. "Relative mobility of screw versus edge dislocations controls the ductile-to-brittle transition in metals." Proceedings of the National Academy of Sciences 118, no. 37 (2021): e2110596118. http://dx.doi.org/10.1073/pnas.2110596118.

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Body-centered cubic metals including steels and refractory metals suffer from an abrupt ductile-to-brittle transition (DBT) at a critical temperature, hampering their performance and applications. Temperature-dependent dislocation mobility and dislocation nucleation have been proposed as the potential factors responsible for the DBT. However, the origin of this sudden switch from toughness to brittleness still remains a mystery. Here, we discover that the ratio of screw dislocation velocity to edge dislocation velocity is a controlling factor responsible for the DBT. A physical model was conceived to correlate the efficiency of Frank–Read dislocation source with the relative mobility of screw versus edge dislocations. A sufficiently high relative mobility is a prerequisite for the coordinated movement of screw and edge segments to sustain dislocation multiplication. Nanoindentation experiments found that DBT in chromium requires a critical mobility ratio of 0.7, above which the dislocation sources transition from disposable to regeneratable ones. The proposed model is also supported by the experimental results of iron, tungsten, and aluminum.

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Cabibbo, Marcello, and Eleonora Santecchia. "Early Stages of Plastic Deformation in Low and High SFE Pure Metals." Metals 10, no. 6 (2020): 751. http://dx.doi.org/10.3390/met10060751.

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Severe plastic deformation (SPD) techniques are known to promote exceptional mechanical properties due to their ability to induce significant grain and cell size refinement. Cell and grain refinement are driven by continuous newly introduced dislocations and their evolution can be followed at the earliest stages of plastic deformation. Pure metals are the most appropriate to study the early deformation processes as they can only strengthen by dislocation rearrangement and cell-to-grain evolution. However, pure metals harden also depend on texture evolution and on the metal stacking fault energy (SFE). Low SFE metals (i.e., copper) strengthen by plastic deformation not only by dislocation rearrangements but also by twinning formation within the grains. While, high SFE metals, (i.e., aluminium) strengthen predominantly by dislocation accumulation and rearrangement with plastic strain. Thence, in the present study, the early stages of plastic deformation were characterized by transmission electron microscopy on pure low SFE Oxygen-Free High Conductivity (OFHC) 99.99% pure Cu and on a high SFE 6N-Al. To induce an almost continuous rise from very-low to low plastic deformation, the two pure metals were subjected to high-pressure torsion (HPT). The resulting strengthening mechanisms were modelled by microstructure quantitative analyses carried out on TEM and then validated through nanoindentation measurements.

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18

Sato, A. "Dislocation structures and dislocation sources in deformed metals." Radiation Effects and Defects in Solids 148, no. 1-4 (1999): 345–60. http://dx.doi.org/10.1080/10420159908229100.

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19

Rauch, Edgar F., and G. Shigesato. "The Dislocation Patterns in Deformed Metals: Dislocation Densities, Distributions and Related Misorientations." Materials Science Forum 550 (July 2007): 193–98. http://dx.doi.org/10.4028/www.scientific.net/msf.550.193.

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The dislocation substructure that appears in deformed metals and alloys have been extensively investigated in the past by transmission electron microscopy (TEM). They are known to form a broad variety of microstructures. These substructures are characterized by three main parameters, namely the density of the dislocations that are trapped in the tangles, their degree of patterning and the misorientation between the cells. The aim of the present work is to investigate the relationship between these features and the mechanical properties of the material.

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Pang, Wei Wei, Guang Cai Zhang, Ai Guo Xu, and Ping Zhang. "Dynamic Fracture of Ductile Metals at High Strain Rate." Advanced Materials Research 790 (September 2013): 65–68. http://dx.doi.org/10.4028/www.scientific.net/amr.790.65.

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Dynamic fracture of ductile metals at different strain rates and temperatures is studied via molecular dynamic simulations. The results show that both increase of temperature and decrease of strain rate reduce the yield strength, but the stress-strain curves separate prior to yield point at different temperatures. Both increase of temperature and strain rate shorten the duration of the stage of dislocation nucleation and slip. The stress-strain curves for various materials indicate that void nucleation needs not only lower yield strength but also lower fault energy. After the yield point, initially some defect clusters form along the loading direction. With the increasing of strain, small dislocation loops nucleate from some larger defect clusters, then quickly multiply and move on slip plane. When the stress exceeds a critical value, some voids nucleate in dislocation aggregation regions. The incipient void shapes are clavate and void distributions predominantly are along the perpendicular directions of tensile loading. Nucleated voids gradually grow into spherical-like shapes via emitting dislocations.

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21

Morrison, S. Roy. "1/f Noise from levels in a linear or planar array: Dislocations in metals." Canadian Journal of Physics 71, no. 3-4 (1993): 147–51. http://dx.doi.org/10.1139/p93-022.

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This report compares the double-layer noise expected for metal dislocations with the earlier analysis of semiconductor dislocations. In both cases we describe the asymmetric trapping of charge over an electrical double layer at the dislocation. The earlier reports describe how a 1/f spectrum should be observed, in the form of a truncated Lorentzian, if the double-layer voltage shows fluctuations greater than kT/q. This report describes the origin of a double layer at metal dislocations that fulfills the requirements. It shows why, despite the substantial difference in parameters, the noise predicted for metals is of the same magnitude (in terms of the Hooge parameter) as that predicted for semiconductors.

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Zhang, Hong Wang, X. Huang, Niels Hansen, Reinhard Pippan, and Michael Zehetbauer. "Strengthening of Nickel Deformed by High Pressure Torsion." Materials Science Forum 584-586 (June 2008): 417–21. http://dx.doi.org/10.4028/www.scientific.net/msf.584-586.417.

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The strength of a deformed metal depends on the content of high angle boundaries, low angle dislocation boundaries and the dislocations between the boundaries. High angle boundaries contribute by Hall-Petch strengthening, whereas for the low angle dislocation boundaries and dislocations between boundaries the strengthening is proportional to the square root of the dislocation density. Based on an assumption of additivity of these contributions, the flow stresses of metals deformed by cold rolling have been calculated successfully. In the present investigation pure Ni (99.9%) has been deformed by high pressure torsion (HPT) to von Mises strains of 0.9, 1.7, 8.7 and 12. The strength of the HPT Ni has been determined by Vickers microhardness (HV) measurements and the microstructural parameters have been determined by transmission electron microscope (TEM) in the longitudinal section. HPT has been compared with deformation by cold rolling and torsion based on the structural evolution with strain and the stress-structure relationship. Based on an assumption of a linear additivity of boundary strengthening and dislocation strengthening, good agreement has been found between the calculated and the experimental flow stress.

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Kang, Keonwook, Vasily V. Bulatov, and Wei Cai. "Singular orientations and faceted motion of dislocations in body-centered cubic crystals." Proceedings of the National Academy of Sciences 109, no. 38 (2012): 15174–78. http://dx.doi.org/10.1073/pnas.1206079109.

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Dislocation mobility is a fundamental material property that controls strength and ductility of crystals. An important measure of dislocation mobility is its Peierls stress, i.e., the minimal stress required to move a dislocation at zero temperature. Here we report that, in the body-centered cubic metal tantalum, the Peierls stress as a function of dislocation orientation exhibits fine structure with several singular orientations of high Peierls stress—stress spikes—surrounded by vicinal plateau regions. While the classical Peierls-Nabarro model captures the high Peierls stress of singular orientations, an extension that allows dislocations to bend is necessary to account for the plateau regions. Our results clarify the notion of dislocation kinks as meaningful only for orientations within the plateau regions vicinal to the Peierls stress spikes. These observations lead us to propose a Read-Shockley type classification of dislocation orientations into three distinct classes—special, vicinal, and general—with respect to their Peierls stress and motion mechanisms. We predict that dislocation loops expanding under stress at sufficiently low temperatures, should develop well defined facets corresponding to two special orientations of highest Peierls stress, the screw and the M111 orientations, both moving by kink mechanism. We propose that both the screw and the M111 dislocations are jointly responsible for the yield behavior of BCC metals at low temperatures.

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Takaki, Setsuo, Y. Fujimura, Koichi Nakashima, and Toshihiro Tsuchiyama. "Effect of Dislocation Distribution on the Yielding of Highly Dislocated Iron." Materials Science Forum 539-543 (March 2007): 228–33. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.228.

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Yield strength of highly dislocated metals is known to be directly proportional to the square root of dislocation density (ρ), so called Bailey-Hirsch relationship. In general, the microstructure of heavily cold worked iron is characterized by cellar tangled dislocations. On the other hand, the dislocation substructure of martensite is characterized by randomly distributed dislocations although it has almost same or higher dislocation density in comparison with heavily cold worked iron. In this paper, yielding behavior of ultra low carbon martensite (Fe-18%Ni alloy) was discussed in connection with microstructural change during cold working. Originally, the elastic proportional limit and 0.2% proof stress is low in as-quenched martensite in spite of its high dislocation density. Small amount of cold rolling results in the decrease of dislocation density from 6.8x1015/m-2 to 3.4x1015/m-2 but both the elastic proportional limit and 0.2% proof stress are markedly increased by contraries. 0.2% proof stress of cold-rolled martensite could be plotted on the extended line of the Bailey-Hirsch equation obtained in cold-rolled iron. It was also confirmed that small amount of cold rolling causes a clear microstructural change from randomly distributed dislocations to cellar tangled dislocations. Martensite contains two types of dislocations; statistically stored dislocation (SS-dislocation) and geometrically necessary dislocation (GN-dislocation). In the early deformation stage, SS-dislocations easily disappear through the dislocation interaction and movement to grain boundaries or surface. This process produces a plastic strain and lowers the elastic proportional limit and 0.2% proof stress in the ultra low carbon martensite.

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Wang, Zhang-Jie, Qing-Jie Li, Yi-Nan Cui, et al. "Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals." Proceedings of the National Academy of Sciences 112, no. 44 (2015): 13502–7. http://dx.doi.org/10.1073/pnas.1518200112.

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When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. Here we demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. This “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising from increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. These results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen.

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Arechabaleta, Zaloa, Peter van Liempt, and Jilt Sietsma. "Unravelling dislocation networks in metals." Materials Science and Engineering: A 710 (January 2018): 329–33. http://dx.doi.org/10.1016/j.msea.2017.10.099.

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Kratochvil, J. "Dislocation pattern formation in metals." Revue de Physique Appliquée 23, no. 4 (1988): 419–29. http://dx.doi.org/10.1051/rphysap:01988002304041900.

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Burbery, Nathaniel, Raj Das, W. George Ferguson, Giacomo Po, and Nasr Ghoniem. "Atomistic Activation Energy Criteria for Multi-Scale Modeling of Dislocation Nucleation in FCC Metals." International Journal of Computational Methods 13, no. 04 (2016): 1641006. http://dx.doi.org/10.1142/s0219876216410061.

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This study contributes to the development of a ‘fundamental, atomistic basis’ to inform macro-scale models that can provide significant insights about the effect of dislocation microstructure evolution during plastic deformation. Within a mesoscale model, multi-dislocation interactions can be studied which are capable of driving high-stress effects such as dislocation nucleation under low applied stresses, due to stress-concentration in dislocation pile-ups at interfaces. This study establishes a methodology to evaluate a phenomenological model for atomic-scale crystal defect interactions from molecular dynamics simulations, which is a critical step for mesoscale studies of plastic deformation in metals. Dislocations are affected by thermally activated processes that become energetically favorable as the stress approaches a threshold value. The nudged elastic band technique is ideal for evaluating the energetic activation parameters from atomic simulations. With this method, the activation energy and volume were obtained for the process of homogeneous nucleation of a full dislocation loop in pure FCC aluminum. Using the (atomistic) activation parameters, a constitutive mathematical model is developed for simulations at the mesoscale, to evaluate the critical (local) shear stress threshold. The constitutive model is effective for extrapolating from an atomistic timeframe of femtoseconds to experimentally accessible timespans of seconds.

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Kameda, Toshihiro, and Bao Rong Zhang. "Molecular Dynamics Based Observations of Grain Boundaries and Lattice Defects Functions in Fine Grained Metal." Materials Science Forum 654-656 (June 2010): 1582–85. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.1582.

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In order to study the characteristics of fine grained polycrystalline metals, it is important to recognize the function of grain boundaries (GB), crystal defects such as dislocation and/or nanoscale voids, since the fraction of GB increases as grain sizes decreases, the deformation process of these metals could be different from those in larger size grains. In this study, we first evaluate the hypothesis that GB behaves as dislocation source and sink during the deformation of fine grained metal, then compare the behavior between GB and a tiny defect from the view point of dislocation source and sink phenomena. Since continuous dislocation supplies could be considered as the key issue to improve the toughness of fine grained metals, this concept could be helpful to design next generation polycrystalline metals.

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Yokobori, A. Toshimitsu. "Holistic Approach on the Research of Yielding, Creep and Fatigue Crack Growth Rate of Metals Based on Simplified Model of Dislocation Group Dynamics." Metals 10, no. 8 (2020): 1048. http://dx.doi.org/10.3390/met10081048.

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The simplified model of numerical analyses of discrete dislocation motion and emission from a stressed source was applied to predict the yield stress, dislocation creep, and fatigue crack growth rate of metals dominated by dislocation motion. The results obtained by these numerical analyses enabled us to link various dynamical effects on the yield stress, dislocation creep, and fatigue crack growth rate with the experimental results of macroscopic phenomena, as well as to link them with theoretical results obtained by the concept of static, continuously distributed infinitesimal dislocations for the equilibrium state under low strain or stress rate conditions. This will be useful to holistic research approaches with concern for time and space scales, that is, in a time scale ranging from results under high strain rate condition to those under static or low strain rate condition, and in a space scale ranging from meso-scale to macro-scale mechanics. The originality of results obtained by these analyses were found by deriving the analytical formulations of number of dislocation emitted from a stressed source and a local dynamic stress intensity factor at the pile-up site of dislocations as a function of applied stress or stress rate and temperature material constants. This enabled us to develop the predictive law of yield stress, creep deformation rate, and fatigue crack growth rate of metals dominated by dislocation motion. Especially, yielding phenomena such as the stress rate and grain size dependence of yield stress and the delayed time of yielding were clarified as a holistic phenomenon composed of sequential processes of dislocation release from a solute atom, dislocation group moving, and stress concentration by pile-up at the grain boundary.

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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 (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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Nikonov, Anton Y., Andrey I. Dmitriev, Dmitry V. Lychagin, Lilia L. Lychagina, Artem A. Bibko, and Olga S. Novitskaya. "Numerical Study and Experimental Validation of Deformation of <111> FCC CuAl Single Crystal Obtained by Additive Manufacturing." Metals 11, no. 4 (2021): 582. http://dx.doi.org/10.3390/met11040582.

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The importance of taking into account directional solidification of grains formed during 3D printing is determined by a substantial influence of their crystallographic orientation on the mechanical properties of a loaded material. This issue is studied in the present study using molecular dynamics simulations. The compression of an FCC single crystal of aluminum bronze was performed along the <111> axis. A Ni single crystal, which is characterized by higher stacking fault energy (SFE) than aluminum bronze, was also considered. It was found that the first dislocations started to move earlier in the material with lower SFE, in which the slip of two Shockley partials was observed. In the case of the material with higher SFE, the slip of a full dislocation occurred via successive splitting of its segments into partial dislocations. Regardless of the SFE value, the deformation was primarily occurred by means of the formation of dislocation complexes involved stair-rod dislocations and partial dislocations on adjacent slip planes. Hardening and softening segments of the calculated stress–strain curve were shown to correspond to the periods of hindering of dislocations at dislocation pileups and dislocation movement between them. The simulation results well agree with the experimental findings.

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Sheinerman, A. G., and S. V. Bobylev. "A Model of Enhanced Strain Rate Sensitivity in Nanocrystalline and Ultrafine-Grained Metals." REVIEWS ON ADVANCED MATERIALS SCIENCE 57, no. 1 (2018): 1–10. http://dx.doi.org/10.1515/rams-2018-0042.

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Abstract A model is suggested that describes enhanced strain rate sensitivity of nanocrystalline and ultrafine-grained metals. Within the model, plastic deformation of such metals incorporates dislocation transmission across grain boundaries (GBs) in the stress fields of dislocation pileups, the emission of individual dislocations from GBs as well as GB sliding accommodated by GB dislocation climb and/or Coble creep. The model predicts a strong increase in the strain rate sensitivity and a decrease in the activation volume with decreasing grain size, in accord with experimental data.We also considered the effect of GB sliding and Coble creep on the anomalous dependence of the activation volume on temperature observed in nanocrystalline Ni. It is demonstrated that although an account for GB sliding and Coble creep leads to the appearance of cusps in the temperature dependence of the activation volume, these mechanisms alone cannot be responsible for the observed anomalous dependence of the activation volume on temperature.

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34

Ferreira, Paulo. "Are Dislocations Possible in Nanoparticles?" Acta Crystallographica Section A Foundations and Advances 70, a1 (2014): C226. http://dx.doi.org/10.1107/s2053273314097733.

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The deformation behavior of nanoscale metals continues to be an exciting area for materials research. However, in the case of single crystal 0-D nanoscale metals, no deformation experiments, to our knowledge, have been performed at the nanoscale. The one experiment closest to the nanoscale was an in-situ TEM compression of ~200 nm Si nanoparticles. However, the particle tested was too large to extract relevant information at the nanoscale and the mechanical deformation of Si is also expected to be different from that of metals. For nanoparticles it is claimed there is a conspicuous lack of dislocations, regardless of the materials processing history, even after significant deformation. Therefore, it has been suggested that dislocations cannot exist or/ do not play a role on the deformation of 0-D nanomaterials. To address this issue of the role played by dislocations in the deformation of 0-D nanomaterials, nanoparticles with diameters <20nm were compressed in-situ under phase-contrast in a transmission electron microscope (TEM). Two phase-contrast TEM experiments were done, one in a conventional TEM and the other in an aberration corrected TEM. Evidence for nucleation of dislocations and dislocation motion was observed during in-situ TEM nanoindentation, but upon unloading dislocations were no longer visible. A new model for explaining dislocation instability is introduced. In this model we consider the change in Gibbs free energy of an edge dislocation, as it moves through the nanoparticle, towards the surface. The nanoindentation experiments seem to confirm the model proposed.

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35

Hansen, Niels. "Metal Working and Dislocation Structures." Key Engineering Materials 353-358 (September 2007): 9–16. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.9.

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Microstructural observations are presented for different metals deformed from low to high strain by both traditional and new metal working processes. It is shown that deformation induced dislocation structures can be interpreted and analyzed within a common framework of grain subdivision on a finer and finer scale down to the nanometer dimension, which can be reached at ultrahigh strains. It is demonstrated that classical materials science and engineering principles apply from the largest to the smallest structural scale but also that new and unexpected structures and properties characterize metals with structures on the scale from about 10 nm to 1 μm.

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Wirth, B. D., V. V. Bulatov, and T. Diaz de la Rubia. "Dislocation-Stacking Fault Tetrahedron Interactions in Cu." Journal of Engineering Materials and Technology 124, no. 3 (2002): 329–34. http://dx.doi.org/10.1115/1.1479692.

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In copper and other face centered cubic metals, high-energy particle irradiation produces hardening and shear localization. Post-irradiation microstructural examination in Cu reveals that irradiation has produced a high number density of nanometer sized stacking fault tetrahedra. The resultant irradiation hardening and shear localization is commonly attributed to the interaction between stacking fault tetrahedra and mobile dislocations, although the mechanism of this interaction is unknown. In this work, we present results from a molecular dynamics simulation study to characterize the motion and velocity of edge dislocations at high strain rate and the interaction and fate of the moving edge dislocation with stacking fault tetrahedra in Cu using an EAM interatomic potential. The results show that a perfect SFT acts as a hard obstacle for dislocation motion and, although the SFT is sheared by the dislocation passage, it remains largely intact. However, our simulations show that an overlapping, truncated SFT is absorbed by the passage of an edge dislocation, resulting in dislocation climb and the formation of a pair of less mobile super-jogs on the dislocation.

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37

Rong, Z., V. Mohles, D. J. Bacon *, and Yu N. Osetsky. "Dislocation dynamics modelling of dislocation–loop interactions in irradiated metals." Philosophical Magazine 85, no. 2-3 (2005): 171–88. http://dx.doi.org/10.1080/14786430412331315644.

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38

Petelina, Yulia, Svetlana Kolupaeva, Anna Kayuda, Anna Shmidt, Olesya Vorobyeva, and Aleksander Petelin. "The Impact of the Dislocation Density, Lattice and Impurity Friction on the Dynamics of Expansion of a Dislocation Loop in FCC Metals." Key Engineering Materials 712 (September 2016): 390–93. http://dx.doi.org/10.4028/www.scientific.net/kem.712.390.

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The study of the role of various factors in plastic behavior of materials is carried out using a mathematical model that takes into account fundamental properties of deformation defects in a crystal lattice based on the continuum theory of dislocations. Calculations were performed for copper, nickel, aluminum, and lead using a specialized software system Dislocation Dynamics of Crystallographic Slip. It has been shown that a decrease in the density of dislocations from 1012 m-2 to 1011 m-2 leads to an increase in the dislocation path in 10−16 times, and the maximum velocity in 1.5−2 times in copper and nickel, by nearly 20% in aluminum, and practically remains unchanged in lead. A decrease in the lattice and impurity friction from 2 MPa to 0.1 MPa leads to a linear increase in the path and the maximum velocity of the dislocation by 10−25%.

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39

Петухов, Б. В. "Механизм обусловленного динамической примесной подсистемой аномального поведения пластического течения материалов с высоким кристаллическим рельефом". Физика твердого тела 63, № 12 (2021): 2126. http://dx.doi.org/10.21883/ftt.2021.12.51674.157.

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A model of dynamic interaction of dislocations with an impurity subsystem of crystals with a high potential relief of the crystal lattice (Peierls barriers) is developed. Such materials include metals with body-centered cubic structure, semiconductors, ceramics, and many others. It is shown that the modification of impurity migration barriers near the dislocation core significantly affects the segregation of impurities on the moving dislocation. The presence of a substantially nonequilibrium initial stage of segregation kinetics leading to anomalies of dislocation dynamics and yield strength of materials is substantiated.

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40

Champion, Yannick, and Sophie Nowak. "Activation Volume in Fine Grained Metals from Stress Relaxation and Nano-Indentation." Materials Science Forum 584-586 (June 2008): 399–404. http://dx.doi.org/10.4028/www.scientific.net/msf.584-586.399.

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Fine grained copper was studied using the stress relaxation technique and creep testing in nano-indentation, to determine the activation volume involved in the micro-mechanism of the deformation. This material exhibits a near-perfect elasto-plastic deformation, featured by a steep work-hardening, after the elastic domain, followed by flow at a constant stress. Measurements of the activation volumes in the various domains reveal the role of the dislocations and the variation in the dislocation density in the deformation mechanism. This emphasizes the importance, in the determination of the activation volume, of the deformation domain investigated as well as the testing technique used and whether in both cases, the measurement is carried out in a transient domain or condition where variation in dislocation density occurs.

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41

Shimokawa, Tomotsugu, Masaki Tanaka та Kenji Higashida. "Effect of Grain Boundaries on Fracture Toughness in Ultraﬁne-Grained Metals by Atomic-Scale Computational Experiments". Materials Science Forum 706-709 (січень 2012): 1841–46. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.1841.

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In order to investigate roles of grain boundaries on the improved fracture tough-ness in ultraﬁne-grained metals, interactions between crack tips, dislocations, and disclinationdipoles at grain boundaries are performed to aluminium bicrystal models containing a crackand h112i tilt grain boundaries using molecular dynamics simulations. A proposed mechanismto express the improved fracture toughness in ultraﬁne-grained metals is the disclination shield-ing eﬀect on the crack tip mechanical ﬁeld. The disclination shielding can be activated whena transition of dislocation sources from crack tips to grain boundaries and a transition of thegrain boundary structure into a neighbouring energetically stable boundary by emitting dis-locations from the grain boundary occur. The disclination shielding eﬀect becomes large asdislocations are continuously emitted from the grain boundary without dislocation emissionsfrom crack tips. This mechanism can further shield the mechanical ﬁeld around the crack tipand obtain the plastic deformation by dislocation emissions from grain boundaries, hence itcan be expected that the disclination shielding eﬀect can improve the fracture toughness inultraﬁne-grained metals

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42

Bertin, Nicolas, Ryan B. Sills, and Wei Cai. "Frontiers in the Simulation of Dislocations." Annual Review of Materials Research 50, no. 1 (2020): 437–64. http://dx.doi.org/10.1146/annurev-matsci-091819-015500.

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Dislocations play a vital role in the mechanical behavior of crystalline materials during deformation. To capture dislocation phenomena across all relevant scales, a multiscale modeling framework of plasticity has emerged, with the goal of reaching a quantitative understanding of microstructure–property relations, for instance, to predict the strength and toughness of metals and alloys for engineering applications. This review describes the state of the art of the major dislocation modeling techniques, and then discusses how recent progress can be leveraged to advance the frontiers in simulations of dislocations. The frontiers of dislocation modeling include opportunities to establish quantitative connections between the scales, validate models against experiments, and use data science methods (e.g., machine learning) to gain an understanding of and enhance the current predictive capabilities.

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43

Argani, Luca, Davide Bigoni, and Gennady Mishuris. "Dislocations and inclusions in prestressed metals." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 469, no. 2154 (2013): 20120752. http://dx.doi.org/10.1098/rspa.2012.0752.

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The effect of prestress on dislocation (and inclusion) fields in nonlinear elastic solids is analysed by extending previous solutions by Eshelby and Willis. Using a plane-strain constitutive model (for incompressible incremental nonlinear elasticity) to describe the behaviour of ductile metals ( J 2 -deformation theory of plasticity), we show that when the level of prestress is high enough that shear band formation is approached, strongly localized strain patterns emerge, when a dislocation dipole is emitted by a source. These may explain cascade activation of dislocation clustering along slip band directions.

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44

Kramer, I. R., C. R. Feng, and B. Wu. "Dislocation-depth distribution in fatigued metals." Materials Science and Engineering 80, no. 1 (1986): 37–48. http://dx.doi.org/10.1016/0025-5416(86)90300-9.

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45

Wolfer, W. G., and B. B. Glasgow. "Dislocation evolution in metals during irradiation." Acta Metallurgica 33, no. 11 (1985): 1997–2004. http://dx.doi.org/10.1016/0001-6160(85)90122-1.

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46

Kaschner, George C., and Jeffrey C. Gibeling. "A Study of Fatigue (Cyclic Deformation) Behavior in FCC Metals Using Strain Rate Change Tests." Key Engineering Materials 378-379 (March 2008): 371–84. http://dx.doi.org/10.4028/www.scientific.net/kem.378-379.371.

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Strain rate jump tests were performed during low cycle fatigue using plastic strain rate as the real time computed control variable. Test materials included OFE polycrystalline copper, AA7075-T6 aluminum, and 304 stainless steel. The evolution of dislocation interactions was observed by evaluating the activation area and true stress as a function of cumulative plastic strain. Activation area values for each of the three materials were evaluated from an initial state to saturation. All three materials exhibit a deviation from Cottrell-Stokes law during cyclic deformation. Tests performed on each of the three materials at saturation reveal a dependence of activation area on plastic strain amplitude for copper and aluminum but no such relationship for stainless steel. These results reflect a contrast between wavy slip for pure copper and 7075 aluminum versus planar slip for 304 stainless steel tested at room temperature. Dislocation motion in copper transitions from forest dislocation cutting [1-6] to increasing contributions of cross slip. Dislocation motion in 7075 aluminum and 304 stainless steel is controlled by obstacles that are characteristically more thermal than forest dislocations: obstacles in 7075-T6 aluminum are identified as solutes from re-dissolved particles; obstacles in 304 stainless steel are also solutes.

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47

Unga´r, T., G. Riba´rik, J. Gubicza, and P. Hana´k. "Dislocation Structure and Crystallite Size Distribution in Plastically Deformed Metals Determined by Diffraction Peak Profile Analysis." Journal of Engineering Materials and Technology 124, no. 1 (2001): 2–6. http://dx.doi.org/10.1115/1.1418364.

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The dislocation densities and arrangement parameters and the crystallite size and size-distributions are determined in tensile or cyclically deformed polycrystalline copper specimens by X-ray diffraction peak profile analysis. The Fourier coefficients of profiles measured by a special high resolution X-ray diffractometer with negligible instrumental broadening have been fitted by the Fourier transforms of ab-initio size and strain profiles. It is found that in the fatigued samples the dislocations are mainly of edge type with strong dipole character. In the fatigued specimens the dislocation densities are found to be larger than in the tensile deformed samples when the saturation and flow stress levels are the same.

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48

Clark, W. A. T. "Quantitative measurements of stresses at grain boundaries in polycrystalline metals." Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988): 620–21. http://dx.doi.org/10.1017/s0424820100105163.

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It has long been recognized that the deformation of polycrystalline metals proceeds by the movement of individual dislocations both within the grains and across the grain boundaries which separate them. It is known, for example, that the yield stress is directly affected by the density of grain boundaries in a metal; in the familiar Hall-Petch relationship it is inversely proportional to the grain diameter. Various models have been proposed to account for this behaviour, all of which involve the interaction between dislocations and grain boundaries (for a review see e.g. ref. 1). Microscopically, these interactions can be accomplished by several different mechanisms, which include the nucleation of new dislocations, direct transmission of dislocations across the interface, the absorption and desorption of dislocations into and out of the interface.The TEM can be used for both static and in-situ dynamic studies of these interactions. In the static mode, a TEM is used to analyze fully the crystallography of dislocation pile-up/grain boundary interactions; one such pile-up is shown in Fig. 1.

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VAN MEURS, P., A. MUNTEAN, and M. A. PELETIER. "Upscaling of dislocation walls in finite domains." European Journal of Applied Mathematics 25, no. 6 (2014): 749–81. http://dx.doi.org/10.1017/s0956792514000254.

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We wish to understand the macroscopic plastic behaviour of metals by upscaling the micro-mechanics of dislocations. We consider a highly simplified dislocation network, which allows our discrete model to be a one dimensional particle system, in which the interactions between the particles (dislocation walls) are singular and non-local. As a first step towards treating realistic geometries, we focus on finite-size effects rather than considering an infinite domain as typically discussed in the literature. We derive effective equations for the dislocation density by means of Γ-convergence on the space of probability measures. Our analysis yields a classification of macroscopic models, in which the size of the domain plays a key role.

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Takahashi, A., and K. Kurata. "Dislocation dynamics based modelling of dislocation-precipitate interactions in bcc metals." IOP Conference Series: Materials Science and Engineering 10 (June 1, 2010): 012081. http://dx.doi.org/10.1088/1757-899x/10/1/012081.

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Journal articles on the topic 'Dislocation in metals'

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