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Добірка наукової літератури з теми "Densités des dislocations"

Автор: Grafiati

Опубліковано: 7 серпня 2022

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Статті в журналах з теми "Densités des dislocations"

Li, Yon Gan, Xiang Qian Xiu, Xue Mei Hua, Shi Ying Zhang, Shi Pu Gu, Rong Zhang, Zi Li Xie, et al. "Study of Dislocation Densities of Thick GaN Films." Advanced Materials Research 989-994 (July 2014): 387–90. http://dx.doi.org/10.4028/www.scientific.net/amr.989-994.387.

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The dislocation density of GaN thick films has been measured by high-resolution X-ray diffraction. The results show that both the edge dislocations and the screw dislocation reduce with increasing the GaN thickness. And the edge dislocations have a larger fraction of the total dislocation densities, and the densities for the edge dislocation with increasing thickness reduce less in contrast with those for the screw dislocation.

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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 (November 26, 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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Herring, R. A., P. N. Uppal, S. P. Svensson, and J. S. Ahearn. "TEM characterization of dislocation reduction processes in GaAs/Si." Proceedings, annual meeting, Electron Microscopy Society of America 47 (August 6, 1989): 590–91. http://dx.doi.org/10.1017/s0424820100154925.

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A high density of interfacial dislocations are needed at the GaAs/Si interface to alleviate the 4% lattice mismatch between GaAs and Si. Some remnant dislocations thread through the epilayer and follow the growth interface. Current growth methods are not able to obtain acceptable threading dislocation densities (104 – 105) for devices. Many methods can be used to reduce the number of threading dislocations which include misorienting the substrate to enhance the slip of dislocations on specific [110]{111} planes, annealing during and after growth, and adding strained layer superlattices (SLS's) to block dislocations. Conventional TEM (CTEM), performed using a JEM 100c, has been used to characterize threading dislocations in the epilayer of a GaAs/Si material where in situ thermal annealing and SLS's force dislocation reactions and thereby reduce the threading dislocation density. Using TEM we have viewed dislocations under many two-beam diffraction conditions and with the help of a stereogram have determined their Burgers vectors (b), line directions (u) and habit planes (R).

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Rezvanian, O., M. A. Zikry, and A. M. Rajendran. "Statistically stored, geometrically necessary and grain boundary dislocation densities: microstructural representation and modelling." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463, no. 2087 (August 14, 2007): 2833–53. http://dx.doi.org/10.1098/rspa.2007.0020.

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A unified physically based microstructural representation of f.c.c. crystalline materials has been developed and implemented to investigate the microstructural behaviour of f.c.c. crystalline aggregates under inelastic deformations. The proposed framework is based on coupling a multiple-slip crystal plasticity formulation to three distinct dislocation densities, which pertain to statistically stored dislocations (SSDs), geometrically necessary dislocations (GNDs) and grain boundary dislocations. This interrelated dislocation density formulation is then coupled to a specialized finite element framework to study the evolving heterogeneous microstructure and the localized phenomena that can contribute to failure initiation as a function of inelastic crystalline deformation. The GND densities are used to understand where crystallographic, non-crystallographic and cellular microstructures form and the nature of their dislocation composition. The SSD densities are formulated to represent dislocation cell microstructures to obtain predictions related to the inhomogeneous distribution of SSDs. The effects of the lattice misorientations at the grain boundaries (GBs) have been included by accounting for the densities of the misfit dislocations at the GBs that accommodate these misorientations. By directly accounting for the misfit dislocations, the strength of the boundary regions can be more accurately represented to account for phenomena associated with the effects of the GB strength on intergranular deformation heterogeneities, stress localization and the nucleation of failure surfaces at critical regions, such as triple junctions.

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Trishkina, L. I., T. V. Cherkasova, A. A. Klopotov, and A. I. Potekaev. "Mechanisms of Solid-Solution Hardening of Single-Phase Cu-Al and Cu-Mn Alloys with a Mesh Dislocation Substructure." Izvestiya of Altai State University, no. 4(120) (September 10, 2021): 59–65. http://dx.doi.org/10.14258/izvasu(2021)4-09.

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Анотація:

The dislocation structure and dislocation accumulation during deformation of polycrystalline FCC solid solutions of Cu-Al and Cu-Mn systems are studied by transmission diffraction electron microscopy. The Al content in Cu-Al alloys varies from 0.5 to 14 at.%. The Mn content in Cu-Mn alloys varies in the range of 0.4 ÷ 25 at.%. Alloys with a grain size in the range of 20 ÷ 240 µm are studied. The alloy samples are deformed by stretching at a rate of 2×10-2c-1 to failure at 293 K. The structure of samples deformed to various degrees of deformation is studied on foils using electron microscopes at an accelerating voltage of 125 kV. For each degree of deformation, the scalar dislocation density and its components are measured: statistically stored dislocations ρS and geometrically necessary dislocations ρG and some other parameters of the defective structure. The mechanisms and their contributions due to mesh and mesh-mesh dislocation substructures (DSS) are determined using the example of substructural and solid-solution hardening in polycrystalline Cu-Al and Cu-Mn alloys. The relative role of various mechanisms in the formation of the resistance to deformation of alloys at different grain sizes is determined. The role of the packaging defect energy on the value of solid-solution hardening for different grain sizes is revealed. The average scalar dislocation density is considered and determined along with its components: statistically stored dislocations ρS and geometrically necessary dislocations ρG. The dependences of the flow stress on the square root of the densities of geometrically necessary dislocations and the densities of statistically stored dislocations are found.

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Botros, K. Z., and S. S. Sheinin. "A method for avoiding errors in measurements of dislocation density in specimens with a high dislocation density." Proceedings, annual meeting, Electron Microscopy Society of America 50, no. 2 (August 1992): 1458–59. http://dx.doi.org/10.1017/s0424820100131929.

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The measurement of dislocation density from electron microscope images of dislocations is an important tool in the hands of the materials scientist. Weak beam images are often chosen for this purpose. In cases where the dislocation density is high, there is a strong possibility that the imaging electrons propagating through the thin foil would encounter several dislocations before emerging from the bottom surface. A question which arises is what effect this may have on image contrast and whether this affects measurements of dislocation density.The authors of this paper have addressed this question by examining the contrast obtained in the case where two dislocations overlap so that the imaging electrons encounter two dislocations before reaching the bottom surface of the specimen. The details of these calculations are presented elsewhere and will not be repeated here. For purposes of this paper, the results can be summarized by stating that, for certain diffraction conditions and dislocation separations, the contrast exhibited by the overlapping dislocation configuration is very weak with the result that the dislocations would not be observed.

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Lauer, Kevin, Martin Herms, Anett Grochocki, and Joachim Bollmann. "Iron Gettering at Slip Dislocations in Czochralski Silicon." Solid State Phenomena 178-179 (August 2011): 211–16. http://dx.doi.org/10.4028/www.scientific.net/ssp.178-179.211.

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The impact of slip dislocations on the interstitial iron distribution in as-grown CZ silicon wafers is investigated by calibrated MWPCD excess charge carrier lifetime measurements, DLTS measurements and measurements of the dislocation density. In regions of high dislocation density low interstitial iron content as well as low lifetime is observed. A linear correlation between dislocation density and interstitial iron content is found. We explain this linear correlation by the thesis that slip dislocations are 60° dislocations, which have adsorbed one iron atom at each dangling bond along the dislocation axis. Interstitial iron is gettered by slip dislocations but iron silicide, which forms along the dislocation axis, is a very strong recombination center for excess charge carriers as well. Hence, gettering of interstitial iron at slip dislocations does not increase the electrical quality of silicon.

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Dalmau, Rafael, Jeffrey Britt, Hao Yang Fang, Balaji Raghothamachar, Michael Dudley, and Raoul Schlesser. "X-Ray Topography Characterization of Large Diameter AlN Single Crystal Substrates." Materials Science Forum 1004 (July 2020): 63–68. http://dx.doi.org/10.4028/www.scientific.net/msf.1004.63.

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Large diameter aluminum nitride (AlN) substrates, up to 50 mm, were manufactured from single crystal boules grown by physical vapor transport (PVT). Synchrotron-based x-ray topography (XRT) was used to characterize the density, distribution, and type of dislocations. White beam topography images acquired in transmission geometry were used to analyze basal plane dislocations (BPDs) and low angle grain boundaries (LAGBs), while monochromatic beam, grazing incidence images were used to analyze threading dislocations. Boule diameter expansion, without the introduction of LAGBs around the periphery, was shown. A 48 mm substrate with a uniform threading dislocation density below 7.0 x 102 cm-2 and a BPD of 0 cm-2, the lowest dislocation densities reported to date for an AlN single crystal this size, was demonstrated.

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Estrin, Y., H. Braasch, and Y. Brechet. "A Dislocation Density Based Constitutive Model for Cyclic Deformation." Journal of Engineering Materials and Technology 118, no. 4 (October 1, 1996): 441–47. http://dx.doi.org/10.1115/1.2805940.

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Анотація:

A new constitutive model describing material response to cyclic loading is presented. The model includes dislocation densities as internal variables characterizing the microstructural state of the material. In the formulation of the constitutive equations, the dislocation density evolution resulting from interactions between dislocations in channel-like dislocation patterns is considered. The capabilities of the model are demonstrated for INCONEL 738 LC and Alloy 800H.

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Yakimov, Eugene B. "EBIC Investigations of Deformation Induced Defects in Si." Solid State Phenomena 131-133 (October 2007): 529–34. http://dx.doi.org/10.4028/www.scientific.net/ssp.131-133.529.

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Calculation of relation between the EBIC contrast and the recombination strength for dislocations and quasi-two-dimensional dislocation trails has been carried out taking into account the real values of depletion region width. Using the relations obtained the linear defect density along dislocations and sheet density in dislocation trails are estimated. The results of EBIC investigations of dislocations and dislocation trails in plastically deformed n- and p-Si are analyzed.

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Більше джерел

Дисертації з теми "Densités des dislocations"

Valdenaire, Pierre-Louis. "Plasticité cristalline : Equations de transport et densités de dislocations." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM002/document.

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Анотація:

Le comportement mécanique des alliages métalliques industriels, notamment ceux utilisés dans le domaine de l’aéronautique, est contrôlé par la présence de différents types de précipités et par la nucléation et propagation de défauts cristallins tels que les dislocations. La compréhension du comportement de ces matériaux nécessite des modèles continus afin d’accéder à l’échelle macroscopique. Cependant, même aujourd’hui, les théories conventionnelles de la plasticité utilisent des variables mésoscopique et des équations d’évolution qui ne reposent pas sur la notion de transport de dislocations. En conséquence, ces théories sont basées sur des lois phénoménologiques qu’il est nécessaire de calibrer pour chaque matériau et chaque application. Il est donc souhaitable d’établir le lien entre les échelles micro et macro afin de générer une théorie continue de la plasticité déduite analytiquement des équations fondamentales de la dynamique des dislocations. L’objet de cette thèse est précisément de contribuer à l’élaboration d’une telle théorie. La première étape a consisté à établir rigoureusement la procédure de changement d’échelle dans une situation simplifiée. Nous avons alors abouti à un système d’équations de transport hyperboliques sur des densités de dislocations contrôlées par des contraintes locales de friction et de backstress qui émergent du changement d’échelle. Nous avons ensuite développé une procédure numérique pour calculer ces termes et analyser leur comportement. Finalement, nous avons développé un schéma numérique efficace pour intégrer les équations de transport ainsi qu’un schéma spectral multi-grille pour résoudre l’équilibre élastique associé à un champ de déformation propre quelconque dans un milieu élastiquement anisotrope et inhomogène
The mechanical behavior of industrial metallic alloys, in particular those used in the aerospace industry, is controlled by the existence of several types of precipitates and by the nucleation and propagation of crystalline defects such as dis- locations. The understanding of this behavior requires continuous models to access the macroscopic scale. However, even today, conventional plasticity theories use mesoscopic variables and evolution equations that are not based on the transport of dislocations. Therefore, these theories are based on phenomenological laws that must be calibrated for each material, or, for each specific applications. It is therefore highly desirable to make link between the micro and macro scales, in order to derive a continuous theory of plasticity from the fundamental equations of the dislocation dynamics. The aim of this thesis is precisely to contribute the elaboration of such a theory. The first step has consisted to rigorously establish a coarse graining procedure in a simplified situation. We have then obtained a set of hyperbolic transport equations on dislocation densities, controlled by a local friction stress and a local back-stress that emerge from the scale change. We have then developed a numerical procedure to compute these local terms and analyze their behavior. Finally, we have developed an efficient numerical scheme to integrate the transport equations as well as a multigrid spectral scheme to solve elastic equilibrium associated to an arbitrary eigenstrain in an elastically heterogeneous and anisotropic medium

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El, Hajj Ahmad. "Analyse théorique et numérique de la dynamique des densités de dislocations." Marne-la-Vallée, 2007. http://www.theses.fr/2007MARN0373.

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Анотація:

Ce travail porte, pour l'essentiel, sur l'analyse théorique et numérique de la dynamique de densités de dislocations. Les dislocations sont des défauts qui se déplacent dans les cristaux, lorsque ceux-ci sont soumis à des contraintes extérieures. D'une façon générale, la dynamique de densités de dislocations est décrite par un système d'équations de transports où les champs de vitesse dépendent de manière non-locale des densités de dislocations. Dans une première partie, nous nous plaçons dans un cadre unidimensionnel. Nous démontrons pour un système 2 x 2 simplifié, des résultats d'existence globale et d'unicité de solution ainsi qu'une estimation d'erreur entre la solution continue et son approximation numérique en utilisant un schéma aux différences finies. Puis, en mettant en œuvre une méthode d'estimation de l'entropie du gradient, développée à la base pour résoudre un modèle bidimensionnel, nous démontrons un résultat d'existence globale et quelques résultats d'unicité pour des systèmes hyperboliques diagonisables en dimension 1. Dans une seconde partie nous nous intéressons à un cadre plus général de la dynamique de densités de dislocations où nous étudions un modèle bidimensionnel. Ce modèle a été introduit par Groma et Balogh (69). Nous démontrons dans ce cadre un résultat d'existence globale via une estimation sur l'entropie du gradient des solutions. Des simulations numériques de ce modèle sont présentées

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Oussaily, Aya. "Étude théorique et numérique des systèmes modélisant la dynamique des densités des dislocations." Thesis, Compiègne, 2021. https://bibliotheque.utc.fr/Default/doc/SYRACUSE/2021COMP2634.

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Анотація:

Dans cette thèse, nous nous intéressons à l’analyse théorique et numérique de la dynamique des densités des dislocations. Les dislocations sont des défauts linéaires qui se déplacent dans les cristaux lorsque ceux-ci sont soumis à des contraintes extérieures. D’une manière générale, la dynamique des densités des dislocations est décrite par un système d’équations de transport, où les champs de vitesse dépendent de manière non-locale des densités des dislocations. Au départ, notre travail se focalise sur l’étude d’un système unidimensionnel (2 × 2) de type Hamilton-Jacobi dérivé d’un système bidimensionnel proposé par Groma et Balogh en 1999. Pour ce modèle, nous montrons un résultat d’existence globale et d’unicité. En addition, nous nous intéressons à l’étude numérique de ce problème, complété par des conditions initiales croissantes, en proposant un schéma aux différences finies implicite dont on prouve la convergence. Ensuite, en s’inspirant du travail effectué pour la résolution de la dynamique des densités des dislocations, nous mettons en œuvre une théorie plus générale permettant d’obtenir un résultat similaire d’existence et d’unicité d’une solution dans le cas des systèmes de type eikonal unidimensionnels. En considérant des conditions initiales croissantes, nous faisons une étude numérique pour ce système. Sous certaines conditions de monotonies sur la vitesse, nous proposons un schéma aux différences finies implicite permettant de calculer la solution discrète et simuler ainsi la dynamique des dislocations à travers ce modèle
In this thesis, we are interested in the theoretical and numerical studies of dislocations densities. Dislocations are linear defects that move in crystals when those are subjected to exterior stress. More generally, the dynamics of dislocations densities are described by a system of transport equations where the velocity field depends non locally on the dislocations densities. First, we are interested in the study of a one dimensional submodel of a (2 × 2) Hamilton-Jacobi system introduced by Groma and Balogh in 1999, proposed in the two dimensional case. For this system, we prove global existence and uniqueness results. Adding to that, considering nondecreasing initial data, we study this problem numerically by proposing a finite difference implicit scheme for which we show the convergence. Then, inspired by the first work, we show a more general theory which allows us to get similar results of existence and uniqueness of solution in the case of one dimensional eikonal systems. By considering nondecreasing initial data, we study this problem numerically. Under certain conditions on the velocity, we propose a finite difference implicit scheme allowing us to calculate the discrete solution and simulate then the dislocations dynamics via this model

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Ibrahim, Hassan. "Analyse de systèmes parabolique/Hamilton-Jacobi modélisant la dynamique de densités de dislocations en domaine borné." Phd thesis, Ecole des Ponts ParisTech, 2008. http://pastel.archives-ouvertes.fr/pastel-00004186.

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Анотація:

Cette thèse porte sur l'étude théorique d'un modèle mathématique provenant de l'étude de la dynamique de densités, de dislocations dans les cristaux de petite taille. Cette dynamique est modélisée par un système non linéaire couplé parabolique/Hamilton-Jacobi. Les dislocations sont des lignes de défauts qui se déplacent dans les cristaux lorsque ceux-ci sont soumis à des contraintes extérieures. De façon indépendante, tout à la fin de la thèse, nous présentons une méthode numérique pour le transport de fronts. Dans le coeur de la thèse, trois types d'équations sont considérées : équations de Hamilton-Jacobi non linéaires, lois de conservation scalaires, et équations paraboliques singulières. Nous traitons un système parabolique/Hamilton-Jacobi singulier où la singularité apparaît par la présence de l'inverse du gradian. Notre système prend en considération l'effet à courte distance entre dislocations ainsi que la formation des couches limites. Nous étudions l'existence, l'unicité et la régularité des solutions du système. cette étude repose en grande partie sur la théorie des solutions de viscosité ; des solutions entropiques et des solutions classiques. Deux cas principaux sont considérés : le cas où les contraintes extérieures sont nulles, et le cas où elles sont constantes (non nécessairement nulles).

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Nguyen, Can Ngon. "Modélisation du comportement en plasticité et à rupture des aciers bainitiques irradiés." Phd thesis, École Nationale Supérieure des Mines de Paris, 2010. http://tel.archives-ouvertes.fr/tel-00469582.

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Анотація:

Les aciers faiblement alliés sont utilisés dans les réacteurs nucléaires pour la réalisation de différents équipements. Soumis à une irradiation neutronique induite par le fonctionnement du réacteur, ces matériaux présentent des évolutions notables de leur microstructure, avec en particulier l'apparition de défauts d'irradiation comme des boucles interstitielles, des amas lacunaires et des précipités, qui conduisent à un durcissement et une fragilisation en relation directe avec la dose reçue et le flux neutronique. Le comportement en plasticité hors irradiation des aciers bainitiques faiblement alliés a fait l'objet de plusieurs modélisations élaborées à partir d'observations expérimentales et de modélisations à l'échelle atomique. Plusieurs thèses ont été supportées par EDF et le CEA dans le passé. Ce travail se place dans leur prolongement, et adopte une démarche classique, en utilisant des éléments expérimentaux connus, mais il se place de façon déterminée à l'échelle de la microstructure, et cherche à intégrer un maximum d'informations de métallurgie physique. C'est dans cet esprit que sont introduites des microstructures réalistes en termes de morphologie et d'orientation cristalline, et qu'on adopte un modèle de plasticité cristalline en grandes déformations basé sur les densités de dislocations. Ce choix permet de prendre en compte dans les lois de plasticité les interactions entre dislocations et défauts d'irradiations pour des conditions de chargements sévères. Ces lois sont introduites dans le code de calcul par éléments finis ZéBuLoN afin de réaliser des calculs d'agrégats polycristallins aux propriétés représentatives d'un élément de volume macroscopique. Les résultats obtenus sur un tel agrégat sont donc considérés comme une donnée élémentaire dans la manipulation des modèles de rupture fragile sur des structures. La nouvelle approche développée a un statut d'approche locale micromécanique".

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Goncalves, Diogo. "Modélisation polycristalline du comportement élasto-viscoplastique des aciers inoxydables austénitiques 316L(N) sur une large gamme de chargements : application à l'étude du comportement cyclique à température élevée." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS089/document.

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Анотація:

L’acier 316L(N) est le matériau de référence pour les structures du circuit primaire des réacteurs nucléaires de quatrième génération, en raison de leur résistance mécanique à la température de fonctionnement, de l’ordre de 550°C. La thèse a permis de développer un modèle polycristallin, capable de prédire le comportement de ces aciers, basé sur la description du glissement viscoplastique des dislocation à haute température, de mise en œuvre simple et avec l’identification d’un nombre de paramètres matériau limité. La démarche de modélisation a été progressive. Lors de la première étape, nous avons proposé et validé une loi d'homogénéisation élasto-viscoplastique à champs moyens, grâce à de nombreux calculs par éléments finis, en considérant des durcissements plastique et des viscosités cristallines. Ensuite, un modèle de viscoplasticité cristalline, reposant sur les lois d’évolution des densités de différents types de dislocations, a été implémenté et les prédictions ont été validés en considérant un très grand nombre de résultats expérimentaux à faible. Le modèle a ensuite été enrichi afin de prendre en compte les mécanismes physiques supplémentaires observés à température élevée, comme la montée des dislocations, le vieillissement dynamique et l’apparition d’une structure de dislocation très hétérogène. Le modèle proposé nécessite uniquement l’ajustement de trois paramètres par identification inverse, utilisant seulement des essais de traction monotone avec saut de vitesse. Les prédictions du comportement mécanique en chargement uniaxial et cyclique sont également en bon accord avec les mesures expérimentales aux températures élevées
The 316L(N) stainless steels is the reference material for the primary circuit structures of fourth-generation nuclear reactors. This alloy present high mechanical resistance at the operation temperature range of these reactors, of the order of 550 °C. This PhD allowed to develop a polycrystalline model based on the description of the viscoplastic dislocation slip at high temperatures, with straightforward implementation and with identification of a limited number of material parameters. The modeling process was progressive. In a first step, we proposed and validated a mean-field elastic-viscoplastic homogenization law, in comparison to numerous finite element calculations, considering crystalline plastic hardening and crystalline viscosity. Then, a model of crystalline viscoplasticity, based on the evolution laws of the different dislocations densities was implemented and the predictions were validated considering a very large number of experimental results at low temperature. The model was then enhanced to take into account the additional physical mechanisms observed at high temperature, such as dislocation climb, dynamic strain aging and the appearance of a very heterogeneous dislocation structure. The proposed model requires the adjustment of only three parameters by inverse identification, using only monotonic tensile tests at different strain rates. The mechanical behavior predictions in uniaxial and cyclic loading are also in good agreement with experimental measurements at high temperature

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Kluender, Rafael. "Mesures en trois dimensions des distorsions cristallines par imagerie en diffraction de Bragg : application aux cristaux de glace." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00635598.

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La déformation visco-plastique de la glace est fortement anisotrope, le plan de glissement préferé étant la plan de base. Le fait que dans un polycristal chaque grain possède sa propre direction de déformation produit des incompatibilités et un champ de contrainte complexe. La déformation à été étudiée expérimentellement en mésurant la dis- tortion des plans cristallins de mono- et polycristaux de glace artificielle. Les expériences ont été réalisées à l'aide d'un faisceau synchrotron. Une nouvelle procédure éxperimental, basée sur les méthodes de l'imagerie en diffraction de Bragg, comme lumière blanche, im- agerie sur la courbe de diffraction et topographie laminaire et ponctuelle, a été dévéloppée. Les désorientations angulaires, les largeurs à mi-hauteur et les intensités intégrées ont été mésurées dans les trois dimensions spatiales de l'échantillon et avec une résolution de 50× 50 × 50µm3. Les algorithmes d'analyse de données ont été écrits pour extraire des données des résultats quantitatifs, et pour calculer les neuf composantes du tenseur de courbure ainsi que la distortion entière des plans cristallins. Les résultats ont permis d'observer les premières étappes de la déformation de la glace. Par example la polygonisation d'un grain à été observée.

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Sandfeld, Stefan. "Evolution of dislocation density in a higher-order continuum theory of dislocation plasticity." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/11367.

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Kerisit, Christophe. "Analyse des mécanismes de recristallisation statique du tantale déformé à froid pour une modélisation en champ moyen." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00873188.

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L'objectif de ce travail est de prédire les évolutions microstructurales se produisant dans le tantale pur lors d'un traitement thermique en fonction de son état microstructural initial. La restauration, la recristallisation et la croissance de grains sont décrites à l'aide d'un modèle en champ moyen qui nécessite une description adéquate de la microstructure, en termes de distributions de tailles de grains et de densités de dislocations équivalentes. La densité de dislocation équivalente moyenne peut être évaluée par une simple mesure de dureté Vickers. L'établissement de la relation dureté-densité de dislocations nécessite l'utilisation d'une loi de comportement basée sur la densité de dislocations équivalente. Les évolutions microstructurales au cours d'un traitement thermique ont été observées et les paramètres pilotant ces phénomènes ont été identifiés à l'aide d'essais originaux comme l'observation in situ de la recristallisation ou l'utilisation d'essais à gradient de déformation pour déterminer le seuil de densité de dislocations équivalente pour déclencher la recristallisation. Des essais plus classiques ont permis d'obtenir des cinétiques de recristallisation dans la gamme 1000°C-1100°C pour différentes microstructures initiales. Les simulations des différents traitements thermiques à l'aide du modèle à champ moyen rendent bien compte des évolutions microstructurales en termes de fraction recristallisée et de taille des grains recristallisés pour des microstructures faiblement déformées ou fortement déformées et fragmentées, en utilisant une description adéquate du type de microstructure initiale. Le modèle devra en revanche être adapté pour traiter le cas de microstructures intermédiaires, en enrichissant non seulement la description de la microstructure initiale mais également celle de l'étape de germination des grains recristallisés. Il deviendra alors capable de prédire les évolutions de microstructures pour tout type de microstructure initiale de tantale.

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Arsenlis, Athanasios 1975. "Modeling dislocation density evolution in continuum crystal plasticity." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/36679.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.
Includes bibliographical references (p. 221-229).
Dislocations are the singly most important material defects in crystal plasticity, and although dislocation mechanics has long been understood as the underlying physical basis for continuum crystal plasticity formulations, explicit consideration of crystallo- graphic dislocation mechanics has been largely absent in working constitutive models. In light of recent theoretical developments in dislocation dynamics, and the introduc- tion of geometrically necessary dislocation (GND) density in continuum formulations through plastic strain gradients, a single crystal plasticity model based on dislocation density state variables is developed. The density state variables evolve from initial conditions according to equations based on fundamental concepts in dislocation me- chanics such as the conservation of Burgers vector in multiplication and annihilation processes. Along with those processes that account for bulk statistical dislocation evolution, the evolving polarity due to dislocation species flux divergences may be in- cluded to detail the length-scale dependence of mechanical properties on the micron level. The full dislocation density description of plasticity allows a simple evaluation of the role of GND density in non-homogeneously deforming bodies. A local version of the constitutive model, which captures the bulk processes of dislocation multiplication and annihilation during plastic deformation, is implemented within a finite element framework to investigate the poly-slip behavior of aluminum single crystals under tension.
(cont.) A non-local version of the constitutive model using an idealized planar double slip system geometry is implemented within a finite element framework to investigate the length-scale dependence observed in the bending of thin single crystal beams. The results not only capture the mechanical stress/strain response of the material, but also detail the development of underlying dislocation structure responsible_ fr: the plistic behavior of the crystal.
by Athanasios Arsenlis.
Ph.D.

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Книги з теми "Densités des dislocations"

Satdarova, Faina. DIFFRACTION ANALYSIS OF DEFORMED METALS: Theory, Methods, Programs. xxu: Academus Publishing, 2019. http://dx.doi.org/10.31519/monography_1598.

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General analysis of the distribution of crystals orientation and dislocation density in the polycrystalline system is presented. Recovered information in diffraction of X-rays adopting is new to structure states of polycrystal. Shear phase transformations in metals — at the macroscopic and microscopic levels — become a clear process. Visualizing the advances is produced by program included in package delivered. Mathematical models developing, experimental design, optimal statistical estimation, simulation the system under study and evolution process on loading serves as instrumentation. To reduce advanced methods to research and studies problem-oriented software will promote when installed. Automation programs passed a testing in the National University of Science and Technology “MISIS” (The Russian Federation, Moscow). You score an advantage in theoretical and experimental research in the field of physics of metals.

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Nelson, David R., and Ariel Amir. Defects on cylinders: superfluid helium films and bacterial cell walls. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198789352.003.0016.

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There is a deep analogy between the physics of crystalline solids and the behaviour of superfluids, dating back to the pioneering work of Phillip Anderson, Paul Martin, and others. The stiffness to shear deformations in a periodic crystal resembles the super-fluid density that controls the behaviour of supercurrents in neutral superfluids such as He4. Dislocations in solids have a close analogy with quantized vortices in superfluids. Remarkable recent experiments on the way rod-shaped bacteria elongate their cell walls have focused attention on the dynamics and interactions of point-like dislocation defects in partially-ordered cylindrical crystalline monolayers. In these lectures, we review the physics of superfluid helium films on cylinders and discuss how confinement in one direction affects vortex interactions with supercurrents. Although there are similarities with the way dislocations respond to strains on cylinders, important differences emerge due to the vector nature of the topological charges characterizing the dislocations.

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The Kohnsham Equation For Deformed Crystals. American Mathematical Society, 2013.

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Wetter, Timothy Scott. The variation of the dislocation density in aluminum deformed to large steady-state creep strains. 1986.

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Частини книг з теми "Densités des dislocations"

Ohmura, Takahito. "Nanomechanical Characterization of Metallic Materials." In The Plaston Concept, 157–95. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-7715-1_8.

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AbstractMechanical behavior of metallic materials on nanoscale is characterized by using Nanoindentation and Transmission Electron Microscope (TEM) to understand the fundamental plasticity mechanisms associated with microstructural factors including dislocations. The advanced characterization techniques enable us to grasp the behavior on the nanoscale in detail. New knowledges are obtained for the plasticity initiation under the extremely high stress close to the theoretical strength in regions with defect-free matrix and pre-existing defects such as grain boundaries, in-solution elements, and dislocations. The grain boundaries act as an effective dislocation source, the in-solution elements retard a nucleation of dislocation, and the pre-existing dislocations assist a plasticity initiation. The deformation behavior associated with microstructures is also described. The dislocation structure with a certain density was observed right after indentation-induced strain burst, which is so-called “pop-in,” suggesting a dislocation avalanche upon the pop-in. It has been directly observed that the lower mobility screw dislocation causes the higher flow stress in a bcc metal. A remarkable strain softening can be understood by an increase in dislocation density based on conventional physical models. Phase stability for indentation-induced transformation depends on a constraint effect by inter-phase boundary and grain boundary.

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Adachi, Hiroki. "Synchrotron X-ray Study on Plaston in Metals." In The Plaston Concept, 197–212. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-7715-1_9.

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AbstractGrain refinement is one of the methods applied to strengthen metallic materials, and various peculiar mechanical properties have been reported to be expressed when the grain size is reduced to less than submicron dimensions. This is considered to be due to a change in the behavior of dislocations that are associated with plastic deformation. In situ synchrotron radiation measurements of microstructural changes during deformation in face-centered cubic (fcc) metals with grain sizes of 20 μm to 5 nm were performed to systematically investigate the effects of grain size on dislocation behavior during plastic deformation. In pure aluminum with grain sizes of 20 to 3 μm, the dislocation density during plastic deformation was approximately 1014 m−2, regardless of the grain size. However, when the grain size was less than 3 μm, the dislocation density increased monotonically in proportion to the grain size to the power of -1. Furthermore, in a nickel alloy with a grain size of less than 10 nm, this relationship was no longer satisfied, and the results suggested that deformation progresses due to partial dislocations. In materials with a grain size of less than 1 μm, the dislocation density after unloading became much smaller than that during loading.

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Nakashima, Koichi, M. Suzuki, Y. Futamura, Toshihiro Tsuchiyama, and Setsuo Takaki. "Limit of Dislocation Density and Dislocation Strengthening in Iron." In Materials Science Forum, 627–32. Stafa: Trans Tech Publications Ltd., 2006. http://dx.doi.org/10.4028/0-87849-985-7.627.

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Rauch, Edgar F., and G. Shigesato. "The Dislocation Patterns in Deformed Metals: Dislocation Densities, Distributions and Related Misorientations." In Materials Science Forum, 193–98. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-434-0.193.

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Beaumont, B., J. P. Faurie, E. Frayssinet, E. Aujol, and P. Gibart. "Low Dislocations Density GaN/Sapphire for Optoelectronic Devices." In UV Solid-State Light Emitters and Detectors, 189–97. Dordrecht: Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-1-4020-2103-9_13.

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Miyazaki, N. "Dislocation Density Simulations for Bulk Single Crystal Growth Process Using Dislocation Kinetics Model." In IUTAM Symposium on Creep in Structures, 115–24. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-015-9628-2_12.

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Gill, J. C. "Dislocations in the Charge Density Wave State of Nbse3." In Physics and Chemistry of Low-Dimensional Inorganic Conductors, 411–19. Boston, MA: Springer US, 1996. http://dx.doi.org/10.1007/978-1-4613-1149-2_26.

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Gill, J. C. "Dislocations in the Charge Density Wave State of NbSe3." In Physics and Chemistry of Low-Dimensional Inorganic Conductors, 421–30. Boston, MA: Springer US, 1996. http://dx.doi.org/10.1007/978-1-4613-1149-2_27.

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Lung, C. W., L. Y. Xiong, and S. Liu. "A dislocation theory based on volume-to-surface ratio: Fracture behavior of metals." In Mechanics and Physics of Energy Density, 179–93. Dordrecht: Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-009-1954-9_12.

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Ameri, A. A. H., N. N. Elewa, M. Ashraf, J. P. Escobedo-Diaz, and P. J. Hazell. "Estimation of Dislocation Density in Metals from Hardness Measurements." In Characterization of Minerals, Metals, and Materials 2017, 441–49. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-51382-9_48.

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Тези доповідей конференцій з теми "Densités des dislocations"

Shao, S., and S. N. Medyanik. "Interaction of Dislocations With Interfaces in Nanoscale Multilayered Metallic Composites." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-67523.

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Atomistic simulation studies of dislocation nucleation and propagation in nanoscale multilayered metallic systems (Cu-Ni and Cu-Nb) are performed. Nanoindentation model is used to generate dislocations at and near the surface. Interaction of the propagating dislocations with two types of interfaces (coherent and incoherent) is analyzed. In the case of coherent interface, Cu(111)-Ni(111), dislocations that initiate in Cu layer propagate through the interface into Ni. However, the interface acts as an obstacle for dislocation propagation and leads to a higher dislocation density near the interface. In the case of incoherent interface, Cu(111)-Nb(110), dislocations that initiate in Cu do not propagate into Nb and tend to accumulate in copper near the interface. In both cases, the interfaces provide mechanisms for strengthening the nanoscale multilayered metallic systems.

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Huang, Haiying, George A. Kadomateas, and Valeria La Saponara. "Mixed Mode Interface Cracks in a Bi-Material Half Plane and a Bi-Material Strip." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0900.

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Abstract This paper presents a method for determining the dislocation solution in a bi-material half plane and a bi-material infinite strip, which is subsequently used to obtain the mixed-mode stress intensity factors for a corresponding bi-material interface crack. First, the dislocation solution in a bi-material infinite plane is summarized. An array of surface dislocations is then distributed along the free boundary of the half plane and the infinite strip. The dislocation densities of the aforementioned surface dislocations are determined by satisfying the traction-free boundary conditions. After the dislocation solution in the finite domain is achieved, the mixed-mode stress intensity factors for interface cracks are calculated based on the continuous dislocation technique. Results are compared with analytical solution for homogeneous anisotropic media.

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Robison, Andrew, Lei Lei, Sowmya Ramarapu, and Marisol Koslowski. "Interface Effects in Strained Thin Films." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-12539.

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Crystalline films grown epitaxially on a substrate consisting of a different crystalline material are of considerable interest in optoelectronic devices and the semiconductor industry. The film and substrate have in general different lattice parameters. This lattice mismatch affects the quality of interfaces and can lead to very high densities of misfit dislocations. Here we study the evolution of these misfit dislocations in a single crystal thin film. In particular, we consider the motion of a dislocation gliding on its slip plane within the film and its interaction with multiple obstacles and sources. Our results show the effect of obstacles such as precipitates and other dislocations on the evolution of a threading dislocation in a metallic thin film. We also show that the material becomes harder as the film thickness decreases in excellent agreement with experiments.

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Abu Al-Rub, Rashid K., and George Z. Voyiadjis. "A Dislocation Based Gradient Plasticity Theory With Applications to Size Effects." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-81384.

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The intent of this work is to derive a physically motivated mathematical form for the gradient plasticity that can be used to interpret the size effects observed experimentally. This paper addresses a possible, yet simple, link between the Taylor’s model of dislocation hardening and the strain gradient plasticity. Evolution equations for the densities of statistically stored dislocations and geometrically necessary dislocations are used to establish this linkage. The dislocation processes of generation, motion, immobilization, recovery, and annihilation are considered in which the geometric obstacles contribute to the storage of statistical dislocations. As a result a physically sound relation for the material length scale parameter is obtained as a function of the course of plastic deformation, grain size, and a set of macroscopic and microscopic physical parameters. The proposed model gives good predictions of the size effect in micro-bending tests of thin films and micro-torsion tests of thin wires.

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Yin, X., and K. Komvopoulos. "A Discrete Dislocation Plasticity Analysis of Plane-Strain Indentation of a Single-Crystal Half-Space by a Smooth and a Rough Rigid Asperity." In STLE/ASME 2010 International Joint Tribology Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ijtc2010-41155.

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A discrete dislocation plasticity analysis of plane-strain indentation of a single-crystal half-space by a smooth or rough (fractal) rigid asperity is presented. The emission, movement, and annihilation of edge dislocations are incorporated in the analysis through a set of constitutive rules [1,2]. It is shown that the initiation of the first dislocation is controlled by the subsurface Hertzian stress field and occurs in the ±45° direction with respect to the normal of the crystal surface, in agreement with the macroscopic yielding behavior of the indented halfspace. For fixed slip-plane direction, the dislocation density increases with the applied normal load and dislocation source density. The dislocation multiplication behavior at a given load is compared with that generated by a rough indenter with a fractal surface profile. The results of the analysis provide insight into yielding and plastic deformation phenomena in indented single-crystal materials.

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Sathyanath, Athul, and Anil Meena. "Influence of Precipitation and Dislocation Density on Flow Stress Characteristics Under Compression Deformation of Heat-Treated 17-4 PH Stainless Steel Alloy." In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-11201.

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Abstract The strengthening mechanism of 17-4 PH stainless steel is mainly due to the precipitation of copper particles in the martensitic lath matrix. The renowned steel grade possesses an exceptional combination of high strength and excellent corrosion resistance and hence is widely employed in high stress environments. In that case, under external loading, the movement and accumulation of dislocations are influenced by the nature of precipitation. Hence, the present study is based on the impact of precipitation on the dislocation induced hardening during compression of the heat-treated 17-4 PH stainless steel. Room temperature uniaxial compression test was used to evaluate the direct effect of precipitates and the dislocation interaction on the flow stress and strain-hardening behavior under the different heat-treated regime. Microstructural evolution during deformation and its influence on the strain-hardening mechanism were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). A semi-empirical model was adopted to quantify the role of precipitate nature on the strain-hardening rate. The evaluated normalized microstrain and dislocation density from the XRD analyses were used to explain the observed variation in the mechanical property. Coarse particle precipitation was found to greatly affect the strain-hardening behavior of the steel alloy during compression deformation.

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Derakhshan, Jaber Fakhimi, Mohammad Habibi Parsa, Vahid Ayati, and Hamidreza Jafarian. "Estimation of dislocations density and distribution of dislocations during ECAP-Conform process." In 6TH INTERNATIONAL BIENNIAL CONFERENCE ON ULTRAFINE GRAINED AND NANOSTRUCTURED MATERIALS: (UFGNSM2017). Author(s), 2018. http://dx.doi.org/10.1063/1.5018957.

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Siopis, Michael S., and Brad L. Kinsey. "Experimental Investigation of Grain and Specimen Size Effects During Electrical-Assisted Forming." In ASME 2009 International Manufacturing Science and Engineering Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/msec2009-84137.

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Alternative manufacturing processes such as hot working and Electrical-Assisted Forming (EAF), which involves passing a high density electrical current through the workpiece during deformation, have been shown to increase the potential strain induced in materials and reduce required forces for deformation. While forming at elevated temperatures is common, the EAF process provides more significant improvements in formability without the undesirable affects associated with forming at elevated temperatures. This research investigates the effect of grain size and current density on annealed pure copper during the EAF process. The flow stress reduction effect of the process was shown to decrease with increasing grain sizes. A threshold current density, required to achieve a significant reduction in the flow stresses, becomes more apparent at larger grain sizes and the value increases with increasing grain size. The effects increase with increasing strain due to dislocations being generated during deformation. Therefore the dislocation density, related in part by the grain size, appears to be a factor in the EAF process.

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Liu, Yi, Kelly Shue, Xin Wu, Zhicheng Li, and Yongbo Xu. "Superplasticity and Microstructural Evolution of a Large-Grained Mg Alloy." In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1818.

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Abstract Commercial Mg-3Al-Zn alloys (AZ31) with initial large grains (∼250μm) has been found superplastic at a strain rate of 0.5×10−2s−1 and at 350–500 C. The maximum elongation to failure of 170% at 500°C was obtained. Scanning electron microscope observations with electron back-scattering diffraction technique (SEM-EBSD) indicate that during deformation significant grain size reduction occurred, the average grain size reduced from about 250μm before deformation to about 50μm after deformation at temperatures from 300 C to 400°C, it reduced to about 100μm if deformed at above 400°C. The observed grain refinement at lower temperature and grain growth at higher temperature during the superplastic deformation is believed to be the result of the competing processes between dynamic recrystallization and dynamic grain growth, which are temperature and strain rate dependent. Transmission electron microscope (TEM) observations indicates that most of the grain boundaries are large-angle grain boundaries, though small amount of small-angle grain boundaries are also observed. The density of dislocations in the grains is very low in these superplasticlly deformed samples. It is evident that grain boundary played a role as the source and sink of the dislocation, being responsible for combined dislocation creep and diffusional creel. Therefore, the very large elongation obtained at the very high strain rates and high temperatures is attributed to dynamic dislocation hardening, recovery and recrystallization.

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Sun, Lei, Zhutian Xu, Linfa Peng, and Xinmin Lai. "Ductile-to-Brittle Fracture Size Effect of Titanium Sheets in Micro/Meso-Scale Plastic Deformation." In ASME 2021 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/imece2021-70083.

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Abstract With a significantly increasing demand for miniaturized titanium thin-walled products, micro forming using sheet metals is a promising approach with high productivity. However, once the sheet thickness is scaled down to a micro-scale, there are many unknowns in terms of size effect and its affected fracture behavior. In this research, the influence of grain size on the fracture behavior of commercially pure titanium sheets with a thickness of 0.1 mm was investigated by the uniaxial tensile tests combined with a digital image correlation measurement system. The ductile-to-brittle transformation of fracture behavior with the grain size increasing from 33.07 to 107.70 μm was revealed. Macroscopically, the elongation and critical fracture stress of CP-Ti samples decrease with the increase of grain size. According to the scanning electron microscopic observations, the number of dimples decreases with grain size increasing, while the cleavage planes and river patterns gradually dominate in the coarse grain fracture surface. To explore the fracture mechanism, the dislocation evolution of various grain sizes is further observed by a transmission electron microscope. The dislocation emission from crack-tips was revealed at different grain sizes. Significant dislocation pile-up at grain boundaries was observed in the specimen with a grain size of 33.07 μm. Those intense dislocations reduce the effective stress at the crack tip resulting in higher crack propagation resistance. Nevertheless, the dislocation density at crack-tip decreases strongly with the increase of grain size leading to high crack-tip effective stress and less crack plasticity. Hence cleavage fracture was dominated in coarse grain CP-Ti sheets.

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Звіти організацій з теми "Densités des dislocations"

Sandra Schujman and Leo Schowalter. GaN-Ready Aluminum Nitride Substrates for Cost-Effective, Very Low Dislocation Density III-Nitride LED's. Office of Scientific and Technical Information (OSTI), October 2010. http://dx.doi.org/10.2172/1014019.

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Brown, Donald W., M. A. Okuniewski, Thomas A. Sisneros, Bjorn Clausen, G. A. Moore, and L. Balogh. Neutron Diffraction Measurement of Residual Stresses, Dislocation Density and Texture in Zr-bonded U-10Mo ''Mini'' Fuel Foils and Plates. Office of Scientific and Technical Information (OSTI), August 2014. http://dx.doi.org/10.2172/1136458.

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