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Moon, D. P. "Studies of segregation at interfaces." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379916.
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Xu, Lei. "Controlling interfacial reaction in aluminium to steel dissimilar metal welding." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/controlling-interfacial-reaction-in-aluminium-to-steel-dissimilar-metal-welding(721d3009-de49-434c-bd81-b01ff5973706).html.
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Two different aluminium alloys, AA6111 (Al-Mg-Si) and AA7055 (Al-Mg-Zn), were chosen as the aluminium alloys to be welded with DC04, and two welding methods (USW and FSSW) were selected to prepare the welds. Selected pre-welded joints were then annealed at T=400 - 570oC for different times. Kinetics growth data was collected from the microstructure results, and the growth behaviour of the IMC layer was found to fit the parabolic growth law. A grain growth model was built to predict the grain size as a function of annealing time. A double-IMC phase diffusion model was applied, together with grain growth model, to predict the thickness of each phase as a function of annealing time in the diffusion process during heat treatment. In both material combinations and with both welding processes a similar sequence of IMC phase formation was observed during the solid state welding. η-Fe2Al5 was found to be the first IMC phase to nucleate. The IMC islands then spread to form a continuous layer in both material combinations. With longer welding times a second IMC phase, θ-FeAl3, was seen to develop on the aluminium side of the joints. Higher fracture energy was received in the DC04-AA6111 joints than in the DC04-AA7055 joints. Two reasons were claimed according to the microstructure in the two joints. The thicker IMC layers were observed in the DC04-AA7055 joints either before or after heat treatment, due to the faster growth rate of the θ phase. In addition, pores were left in the aluminium side near the interface as a result of the low melting point of AA7055.The modelling results for both the diffusion model and grain growth model fitted very well with the data from the static heat treatment. Grain growth occurred in both phases in the heat treatment significantly, and was found to affect the calculated activation energy by the grain boundary diffusion. At lower temperatures in the phases with a smaller grain size, the grain boundary diffusion had a more significant influence on the growth rate of the IMC phases. The activation energies for the grain boundary diffusion and lattice diffusion were calculated as 240 kJ/mol and 120 kJ/mol for the η phase, and 220 kJ/mol and 110 kJ/mol for the θ phase, respectively. The model was invalid for the growth of the discontinuous IMC layers in USW process. The diffusion model only worked for 1-Dimensional growth of a continuous layer, which was the growth behaviour of the IMC layer during heat treatment. However, due to the highly transient conditions in USW process, the IMC phases were not continuous and uniform even after a welding time of 2 seconds. Therefore, the growth of the island shaped IMC particles in USW was difficult to be predicted, unless the nucleation stage was taken into consideration.
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Garcia, de la Cruz Lucia. "Ultrafine grained nickel processed by powder metallurgy : microstructure, mechanical properties and thermal stability." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMC224.
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La synthèse par métallurgie des poudres de nickel à grains ultrafins (UFG) a été effectuée, et l’effet de l’affinement de la microstructure sur le comportement mécanique et les propriétés physiques a été étudié. La possibilité de coupler le broyage et le frittage flash est étudiée avec des résultats prometteurs. Des échantillons de haute densité avec des tailles de grains d = 0.65 – 4 µm, caractérisés par une fraction élevée des joints de grains Σ3 et un faible niveau de contrainte ont été synthétisés. Les propriétés mécaniques des échantillons UFG montrent une bonne combinaison ductilité-résistance mécanique, avec un impact mineur des porosités présentes. L’étude de l’influence de la taille de grain dans le régime UFG sur les propriétés mécaniques montre une limite d’élasticité supérieure à celle attendue et une capacité d’écrouissage plus faible. Ces observations sont cohérentes avec la microstructure déformée à rupture, étudiée par diffraction d’électrons rétrodiffusés et microscopie électronique en transmission. Une haute diffusivité, mesurée par des expériences de traceurs radioactifs, montrent des profils de pénétration très différents liés aux structures de porosités diverses présents dans les échantillons. Ces différentes structures sont aussi responsables de la densification rétrograde observée, uniquement pour les échantillons frittés à partir de poudres broyéesThe present manuscript concerns the synthesis of ultrafine grained (UFG) Ni by powder metallurgy, and the study of the influence of UFG microstructures on the mechanical behavior and physical properties. The possibilities of coupling ball milling and Spark Plasma Sintering are presented showing promising results. Highly dense homogeneous specimens are obtained, with average grain sizes d = 0.65 - 4 µm, and microstructures highlighted by a high fraction of Σ3 grain boundaries dependent on grain size. The mechanical properties in tensile testing for UFG samples are evaluated showing a good combination of strength and ductility, with little impact from porosities, the major drawback of powder metallurgy. The influence of grain size in the UFG regime on the mechanical properties is investigated, showing strength values that deviate from the expected behavior for grain refinement. Likewise, a reduced strain hardening capacity is depicted which correlates to the microstructural observations performed on the deformed state. High diffusivity measured by means of radiotracer experiments is observed in the sintered samples, displaying different penetration profiles that relate to diverse porosity structures. Such structures are also responsible for retrograde sintering observed exclusively in samples processed from BM powders
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Meredith, Steven L. "CHARACTERIZATION OF A VISCOELASTIC RESPONSE FROM THIN METAL FILMS DEPOSITED ON SILICON FOR MICROSYSTEM APPLICATIONS." DigitalCommons@CalPoly, 2009. https://digitalcommons.calpoly.edu/theses/53.
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Understanding the mechanisms that control the mechanical behavior of microscale actuators is necessary to design an actuator that responds to an applied actuation force with the desired behavior. Micro actuators which employ a diaphragm supported by torsional hinges which deform during actuation are used in many applications where device stability and reliability are critical. The material response to the stress developed within the hinge during actuation controls how the actuator will respond to the actuating force. A fully recoverable non-linear viscoelastic response has been observed in electrostatically driven micro actuators employing torsional hinges of silicon covered with thin metal films. The viscoelastic response occurs over a time period of 50 minutes at an operating temperature of 35°C. This viscoelastic phenomenon is similar to that reported in articles addressing anelastic behavior associated with viscous grain boundary slippage and dislocation bowing. In order to investigate this viscoelastic response as a function of metal film composition and thickness, bi-layer torsional hinge actuators consisting of Si with a deposited metal layer were designed to exhibit similar stress levels as the electrostatically driven micro actuators. The test devices were fabricated using common semiconductor fabrication techniques. The actuators were micromachined by deep etching 100mm diameter, 425µm thick, double side polished, single crystal (100) wafers to create a 4.5µm thick device layer. Subsequent etching of the device layer released the fixed-fixed torsional hinge test actuators. Physical vapor depositions of Au, Al and Al-Ti in two different thicknesses (100nm, and 150nm) were deposited in order to investigate the impact of metal film thickness and composition on the viscoelastic response. Grain sizes of the deposited films were estimated using backscattered electron images. Rotational actuation of the test actuators was achieved by using a modified Ambios XP-1 surface profiler that applies a constant force of 0.28mN while measuring the displacement of the actuator with respect to time. The viscoelastic response was observed in the test devices with Au and Al thin films indicating that this phenomenon is attributable to the stresses induced on the torsional hinge. Results indicate that the viscoelastic response was not observed in AlTi thin films consisting of 0.3at% titanium. Two theoretical models are presented that discuss the mechanism associated with the viscoelastic response as well as a method for inhibiting these mechanisms by the addition of an alloying element to form a second phase precipitate.
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Heiser, Thomas. "Developpement d'une technique d'analyse localisee des defauts electriquement actifs dans les semiconducteurs." Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13136.
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Methode basee sur l'emission thermique de porteurs electriques pieges par les niveaux profonds dans la bande interdite. La modelisation de la technique a permis de determiner l'influence des divers parametres physiques sur la resolution spatiale de la technique et d'etablir les conditions optimales de mesures. L'exploitation numerisee des signaux augmente sensiblement la capacite de detection de la technique. Le phenomene de "gettering" de l'or par les dislocations ainsi que la diffusion acceleree de l'or a travers le joint de grain d'un bicristal de silicium ont ete mis en evidence
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Ihlal, Ahmed. "Analyses quantitatives par sem/ebic des defauts recombinants dans les semiconducteurs polycristallins : influence des traitements thermiques sur l'activite electrique des bicristaux de silicium." Caen, 1988. http://www.theses.fr/1988CAEN2007.
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Etude quantitative , par la methode ebic, de la recombinaison des porteurs minoritaires dans des bicristaux de silicium en fonction des traitements thermiques, entre 450 et 950**(o)c. Un developpement des phenomenes physiques regissant la creation de differentes theories conduisant au traitement quantitatif du signal ebic est presente. Selon le traitement thermique, le contraste des deux types de joints de grains evolue avec la temperature: vitese de recombinaison et longueur de diffusion varient avec la temperature de recuit
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Gryaznov, Denis, Juergen Fleig, and Joachim Maier. "Numerical study of grain boundary diffusion." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-195828.
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Gryaznov, Denis, Juergen Fleig, and Joachim Maier. "Numerical study of grain boundary diffusion: size effects." Diffusion fundamentals 2 (2005) 49, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14382.
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Hiscock, Matthew John. "Importance of grain boundary diffusion : an experimental study." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8882.
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This research is concerned with the mechanisms of diffusion in the Earth and the implications of such an understanding. Specifically, this work is concerned with one particular aspect of diffusion: Grain Boundary Diffusion (GBD). An experimental investigation of GBD has been conducted by considering three specific scenarios; GBD of H in stoichiometric Mg-spinel, GBD of Ti in Quartz and GBD of Li in olivine. By considering the GBD of three very different elements it has been possible to synthesise an understanding of some of the mechanisms involved in the process. GBD is potentially a very important process within the Earth with wide ranging implications. Grain boundaries may provide fast pathways for transportation of a range of compatible and incompatible diffusing species in the Earth’s interior – potentially acting as storage locations and also as efficient pathways between different geological reservoirs. It is also potentially very important in the application of a number of techniques including dating and geothermometry and geobarometry. Here, an experimental study of the GBD of H has been carried out with the overall finding that GBD appears to occur at slightly greater yet broadly similar rates to lattice diffusion. This finding is considered in terms of the mantle properties which are affected by the presence and transport of H. A follow up series of experiments was conducted looking at Li diffusion. Li was chosen due to its volatile nature and larger atomic radius as compared to H. As such, it provided a useful test of the hypothesis that the radius of a diffusant might affect its chosen method of diffusion. A third set of experiments were carried out to investigate the GBD of Ti in quartz with particular reference to the TitaniQ geothermo(baro)meter. This set of experiments provided a very useful comparison to the data which had previously been obtained from lighter elements. This investigation has found that a combination of factors including charge, diffusant diameter and the specific mineralogical characteristics of the host phase will define the dominant diffusive mechanism and the size of the contribution made by that mechanism towards observed bulk diffusivities. A characterisation of the temperature dependency of diffusion within each setting has also been completed. As such, it also makes a useful contribution to the current dataset for GBD.
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Swaroop, Sathya, Martin Kilo, Christos Argirusis, Günter Borchardt, and Atul H. Chokshi. "Lattice and grain boundary diffusion of cations in tetragonal zirconia." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194753.
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Swaroop, Sathya, Martin Kilo, Christos Argirusis, Günter Borchardt, and Atul H. Chokshi. "Lattice and grain boundary diffusion of cations in tetragonal zirconia." Diffusion fundamentals 3 (2005) 13, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A13251.
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Soule, de Bas Benjamin J. "Simulation of Bulk and Grain Boundary Diffusion in B2 NiAl." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/33352.
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Molecular dynamics simulations of the diffusion process in ordered B2 compounds at high temperature were performed using an embedded atom interatomic potential developed to fit NiAl properties. Diffusion in the bulk occurs through a variety of cyclic mechanisms that accomplish the motion of the vacancy through nearest neighbor jumps restoring order to the alloy at the end of the cycle. The traditionally postulated six-jump cycle is only one of the various cycles observed and some of these are quite complex. Diffusion at the grain boundary mainly takes place through sequences of coordinated nearest neighbor jumps yielding to a rearrangement of the grain boundary structure. Two distinct mechanisms resulting in a structural unit migration of the vacancy are also identified. The results are analyzed in terms of the activation and configuration energies calculated using molecular statics simulations.Master of Science
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Iyer, Venkata Subramanian. "Diffusion induced grain boundary motion in the iron-zinc system /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487265143145921.
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Chung, Yong-Chae. "Toward the measurement of reliable grain-boundary diffusion coefficients in oxides." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38105.
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Pan, Zhenguo. "Simulation and analysis of coupled surface and grain boundary motion." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2733.
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At the microscopic level, many materials are made of smaller and randomly oriented grains. These grains are separated by grain boundaries which tend to decrease the electrical and thermal conductivity of the material. The motion of grain boundaries is an important phenomenon controlling the grain growth in materials processing and synthesis.
Mathematical modeling and simulation is a powerful tool for studying the motion of grain boundaries. The research reported in this thesis is focused on the numerical simulation and analysis of a coupled surface and grain boundary motion which models the evolution of grain boundary and the diffusion of the free surface during the process of grain growth.
The “quarter loop” geometry provides a convenient model for the study of this coupled motion. Two types of normal curve velocities are involved in this model: motion by mean curvature and motion by surface diffusion. They are coupled together at a triple junction. A front tracking method is used to simulate the migration. To describe the problem, different formulations are presented and discussed. A new formulation that comprises partial differential equations and algebraic equations is proposed. It preserves arc length parametrization up to scaling and exhibits good numerical performance. This formulation is shown to be well-posed in a reduced, linear setting. Numerical simulations are implemented and compared for all formulations. The new formulation is also applied to some other related problems.
We investigate numerically the linear stability of the travelling wave solutions for the quarter loop problem and a simple grain boundary motion problem for both curves in two dimensions and surfaces in three dimensions. The numerical results give evidence that they are convectively stable.
A class of high order three-phase boundary motion problems are also studied. We consider a region where three phase boundaries meet at a triple junction and evolve with specified normal velocities. A system of partial differential algebraic equations (PDAE) is proposed to describe this class of problems by extending the discussion for the coupled surface and grain boundary motion. The linear well-posedness of the system is analyzed and numerical simulations are performed.
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Osman, Hoch Bachir. "Modelling of hydrogen diffusion in heterogeneous materials : implications of the grain boundary connectivity." Thesis, La Rochelle, 2015. http://www.theses.fr/2015LAROS030/document.
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La diffusion de l’hydrogène dans les métaux est un paramètre clef pour la compréhension des mécanismes de base de la fragilisation par l’hydrogène. Néanmoins, le rôle des joints de grains dans le processus de diffusion de cet élément reste à éclaircir. Avec une approche numérique, nous avons étudié les effets d’un réseau hétérogène de joints de grains sur la diffusivité macroscopique de l’hydrogène. Pour cela, des essais de perméation ont été simulés par la méthode des éléments finis, en modélisant le matériau comme un composite formé d’une phase intra-associée aux grains et deux phases intergranulaires, avec des propriétés de diffusion différentes. Nous avons montré, en caractérisant la topologie et la connectivité du réseau des joints de grains, qu’il existe des fortes corrélations entre les paramètres de connectivité et le coefficient de diffusion effectif. Il a été démontré également que ces corrélations sont plus importantes dans les matériaux nanocristallins. De plus, en utilisant une approche d’homogénéisation, il a été mis en évidence que le coefficient de diffusion effectif est contrôlé par le caractère percolant du réseau des joints de grains, sans pour autant avoir le même seuil de percolation que ces derniers. Une seconde étude, utilisant des microstructures de nickel obtenues par cartographies EBSD, a permis d’évaluer l’écart entre la connectivité des modèles simplifiés et les structures réelles. Cette étude a permis également de confronter les coefficients de diffusion effectifs obtenus par la simulation à des données de la littérature. En parallèle, une étude expérimentale a été conduite sur le nickel pour analyser l’influence des joints de grains sur la distribution locale de l’hydrogène. Les résultats ont montré des corrélations importantes entre la nature du joint de grains et le profil de concentration de l’hydrogène autour de ce joint, qui ne peuvent pas être expliquées uniquement par le processus de diffusionThe diffusion of hydrogen in metals is a key factor for understanding the basic mechanisms of hydrogen embrittlement. However, the contribution of grain boundaries to the hydrogen diffusion is not well established. In this this work, we first investigated the effects of a heterogeneous grain boundary networks on the effective diffusivity in polycrystalline materials, using finite elements modeling. To do so, hydrogen diffusion through heterogeneous materials, modeled by a ternary continuum composite media, was simulated. We showed, by characterizing the grain-boundary connectivity, that there are strong correlations between the grain-boundary connectivity parameters and the effective diffusivity. It was found also that these correlations are more significant for nanocrystalline materials. Moreover, by using a homogenization method, it was evidenced that the percolation behavior of the effective diffusivity is controlled by the grain-boundary network evolution, without exhibiting the same percolation threshold than the latter. A second approach, using EBSD-based microstructures, was conducted to evaluate the effect of microstructural constraints on the grain boundary connectivity and to compare the effective diffusivity numerically obtained with experimental data on polycrystalline nickel from literature. In parallel, experimental analyses were performed to analyze the effects of the grain boundaries on the local hydrogen concentration. This highlighted the significant impact of grain-boundary character on the hydrogen distribution around grain boundaries, which can not be explained by the only diffusion process
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Nissley, Nathan Eugene. "Intermediate temperature grain boundary embrittlement in nickel-base weld metals." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1156949345.
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Liberatore, Michael James. "Secondary-ion mass spectrometric analysis of oxygen-grain boundary diffusion in magnesium-oxide bicrystals." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32163.
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Loginova, Irina. "Phase-field modeling of diffusion controlled phase transformations." Doctoral thesis, KTH, Mechanics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3626.
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Diffusion controlled phase transformations are studied bymeans of the phase-field method. Morphological evolution ofdendrites, grains and Widmanst\"atten plates is modeled andsimulated.
Growth of dendrites into highly supersaturated liquids ismodeled for binary alloy solidification. Phase-field equationsthat involve both temperature and solute redistribution areformulated. It is demonstrated that while at low undercoolingheat diffusion does not affect the growth of dendrites, i.e.solidification is nearly isothermal, at high cooling rates thesupersaturation is replaced by the thermal undercooling as thedriving force for growth.
In experiments many crystals with different orientationsnucleate. The growth of randomly oriented dendrites, theirsubsequent impingement ant formation of grain boundaries arestudied in two dimensions using the FEM on adaptive grids.
The structure of dendrites is determined by growthconditions and physical parameters of the solidifying material.Effects of the undercooling and anisotropic surface energy onthe crystal morphology are investigated. Transition betweenseaweeds, doublons and dendrites solidifying out of puresubstance is studied and compared to experimental data. Two-and three-dimensional simulations are performed in parallel onadaptive and uniform meshes.
A phase-field method based on the Gibbs energy functional isformulated for ferrite to austenite phase transformation inFe-C. In combination with the solute drag model, transitionbetween diffusion controlled and massive transformations as afunction of C concentration and temperature is established byperforming a large number of one dimensional calculations withreal physical parameters. In two dimensions, growth ofWidmanstaetten plates is governed by the highly anisotropicsurface energy. It is found that the plate tip can beapproximated as sharp, in agreement with experiments.
Keywords:heat and solute diffusion, solidification,solid-solid phase transformation, microstructure, crystalgrowth, dendrite, grain boundary, Widmanstaetten plate,phase-field, adaptive mesh generation, FEM.
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Westwood, Chris. "Computer simulation of diffusional creep failure of engineering alloys." Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/843127/.
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A simplified model with only 2 degrees of freedom is developed for cavity growth along a grain-boundary by surface and grain-boundary diffusion following a similar model for a row of grains used by Sun et al, (1996). A variational principle for the coupled diffusion problem is used to follow the cavity growth. The approximate solution can be reduced to the well-established equilibrium cavity growth model at the fast surface diffusion extreme. By comparing the 2 degree of freedom model with the full finite element solution by Pan et al, (1997), a 'Validity Map' is constructed in terms of the relative diffusivity and applied stress relative to the capillarity stress. It is found that the simplified model accurately describes the evolution process, in terms of overall cavity profile and propagation rate for engineering alloys subject to normal levels of applied stresses. The 2 degree of freedom model for a single cavity was then extended to allow the modelling of multiple cavities. These cavities can be either pre-existing or nucleated during the lifetime of the system. The relative rotation between the grains is also considered. The initial 2 degrees of freedom were increased to six, and a cavity element has been derived. The cavity elements are assembled together using the classical finite element approach. This allows the evolution of multiple cavities and their interactions to be modelled under different applied loads and material parameters. This simplified multiple cavity finite element model was compared with a model for cavity evolution based on a 'smeared-out' approach. It was shown that the 'smeared-out' model does not accurately predict the creep damage for realistic engineering materials and conditions and results in an under prediction of creep lifetime. Using the simplified finite element model the effect of surface diffusion on the evolution of the creep damage was investigated. The evolution of a large pre-existing 'crack-like' cavity was modelled and the effects of nucleation, surface diffusion and loading were also investigated. It was shown that in the majority of cases as the surface diffusion was increased the rupture time was also increased. The results from the large 'crack-like' cavity simulations showed that there was very little crack propagation through the material and the smaller cavities tended to grow independently of the large 'crack-like' cavity.
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Li, Jiaqi. "The contribution of the grain boundary engineering to the problem of intergranular hydrogen embrittlement." Thesis, La Rochelle, 2017. http://www.theses.fr/2017LAROS037/document.
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La mobilité de l’hydrogène dans les métaux est un paramètre clef pour la compréhension des mécanismes de base de la fragilisation par l’hydrogène (FPH). Cette problématique est directement associée aux mécanismes de diffusion et de piégeage de l’hydrogène au sein d’un réseau cristallin. Ces derniers dépendent des diverses hétérogénéités microstructurales et en particulier des défauts cristallins présents au sein du matériau. Dans le cadre de nos travaux nous nous sommes restreints à étudier la diffusion et le piégeage de l’hydrogène au sein de deux systèmes élémentaires : des monocristaux et des bi-cristaux de nickel. Nous avons développé une méthodologie associant des outils expérimentaux (Perméation électrochimique/TDS, METHR, EBSD) et numériques (FEM-COMSOL/EAM-LAMMPS). Les résultats obtenus sur monocristaux montrent une dépendance du coefficient de diffusion de l’hydrogène avec l’orientation cristallographique et la teneur en hydrogène. L’analyse thermodynamique du système nickel-hydrogène-lacune démontre une dépendance du potentiel chimique de l’hydrogène à l’état de contrainte induit par la formation d’amas de lacunes associés à la présence de l’hydrogène. Le caractère anisotrope de la diffusion est alors expliqué par l’anisotropie des propriétés d’élasticité du réseau cristallin et la présence de ces amas. D’autre part nous avons caractérisé les processus de diffusion et de piégeage de l’hydrogène pour des bi-cristaux de nickel présentant différents volumes libres. L’énergie de ségrégation de l’hydrogène dépend de la nature du site (volume libre local et énergie mécanique associée à l’incorporation du soluté). La diffusion de l’hydrogène est influencée directement par la nature de joint de grain (excès de volume et distribution des sites). Nos résultats, à l’échelle atomique, montrent une corrélation entre la solubilité et le volume libre du joint de grain. Les joints de grains avec un volume libre important présentent des chemins de diffusion plus favorables pour l'hydrogène que dans le réseau cristallin et dans le même temps un nombre plus important de sites de ségrégationThe mobility of hydrogen in metals is a key parameter for understanding the basic mechanisms of hydrogen embrittlement (HE). This problem is directly related to the mechanisms of diffusion and trapping of hydrogen within a crystal lattice. These mechanisms depend on the various microstructural heterogeneities and in particular the crystalline defects. In our work, we have focused on the diffusion and trapping of hydrogen in two elementary systems: nickel single crystals and bi-crystals. We developed a methodology combining experimental tools (electrochemical permeation / TDS, HRTEM, EBSD) and numerical methods (FEM-COMSOL / EAM-LAMMPS). The results obtained on the single crystals show a dependence of the diffusion coefficient of hydrogen with the crystallographic orientation and the hydrogen content. The thermodynamic analysis of the nickel-hydrogen-vacancy system shows a dependence of the chemical potential of hydrogen with the stress state induced by the formation of clusters of vacancies associated with the presence of hydrogen. The anisotropic character of the diffusion is then explained by the anisotropy of the elastic properties of the crystal lattice and the presence of these clusters. Moreover, we have characterized the processes of diffusion and trapping of hydrogen for nickel bi-crystals with different free volumes. The segregation energy of hydrogen depends on the nature of the site (the local free volume and the mechanical energy associated with the incorporation of solute). The diffusion of hydrogen is directly influenced by the nature of the grain boundary (the free volume and the distribution of the segregation sites). Our results, at the atomic scale, show a correlation between the solubility and the free volume of the grain boundary. The grain boundaries with a higher free volume have more favorable diffusion paths for hydrogen than in the crystal lattice and at the same time more segregation sites
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Ma, Qing. "Effects of grain boundary structure on diffusion along [001] tilt boundaries in the Au/Ag system." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/17283.
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Juden, J. N. "Numerical solution of forced curvature flow for curves and a model for diffusion induced grain boundary motion." Thesis, University of Sussex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388973.
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CARNEIRO, VIVIANE DELVAUX. "RECIPITATION PROCESSES CONTROLLED BY LATTICE AND GRAIN BOUNDARY DIFFUSION IN ALLOY 33 (FE-NI-CR-MO-N)." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=5927@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOREste trabalho é uma investigação da microestrutura e cinética dos fenômenos de precipitação que ocorrem na Liga 33 (Fe-Ni-Cr-Mo-Cu-N), sistema metálico desenvolvido pela Krupp VDM com o intuito de suportar altas temperaturas e ambiente corrosivo. A Liga 33 incorre precipitação contínua e descontínua simultaneamente, como resultado do tratamento de envelhecimento realizado numa faixa de temperatura correspondente àquela que o material atinge quando submetido a um processo de soldagem. A caracterização microestrutural foi realizada por microscopia ótica, microscopia eletrônica de varredura, e microscopia eletrônica de transmissão, incluindo microanálise, devido à ordem de grandeza nanométrica das fases precipitadas. A precipitação descontínua ocasiona uma estrutura lamelar no contorno dos grãos, resultado do crescimento cooperativo entre as lamelas, envolvendo átomos substitucionais (Cr, por exemplo) e intersticiais (N). A precipitação contínua ocorre no interior dos grãos gerando precipitados com diferentes morfologias. A microanálise revela que os produtos gerados em ambas as reações crescem competindo pelo Cr. Uma análise cinética- morfológica aponta para a natureza não estacionária da reação descontínua, que sofre gradativa diminuição de sua taxa de transformação, até ser totalmente paralisada.
This work is an investigation of the microstructure and kinetics of the phenomena occurring inside Alloy 33 (Fe-Ni- Cr-Mo-Cu-N), a metallic system developed by Krupp VDM to endure high temperatures and corrosive environment. Alloy 33 incurs continuous and discontinuous precipitation simultaneously, as a result of the aging treatment induced in a temperature range correspondent to the one of a welding process in the referred material. The microstructural characterization was performed by optical microscopy, scanning electron microscopy and transmission electron microscopy, including microanalysis, due to the nanometric nature of the precipitated phases. Discontinuous precipitation produces a lamellar structure along grain boundaries as a result of a cooperative growth between the lamellae, involving substitucional and interstitial atoms, Cr and N respectively. Continuous precipitation occurs inside grains, generating precipitates with different morphologies. Microanalysis reveals that products of both precipitation reactions grow competing for Cr. A kinetic-morphological analysis points to the non-stationary characteristic of the discontinuous precipitation, where the transformation rate diminishes until it stops completely, as aging occurs.
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Ilin, Dmitrii. "Simulation of hydrogen diffusion in fcc polycrystals. Effect of deformation and grain boundaries : effect of deformation and grain boundaries." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0157/document.
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Une approche couplée prenant en compte l’interaction de la plasticité cristalline et de la diffusion d’hydrogène a été établie et utilisée pour étudier le transport de l’hydrogène dans les agrégats polycristallins synthétiques de l’acier 316L avec des géométries de grains and des orientations cristallographiques différentes. Les champs mécaniques calculés à l’aide du code ZeBuLoN sont transférés dans un code de diffusion développé dans le cadre de ce travail. Une nouvelle formulation associée à un nouveau schéma numérique permet un calcul qui présente une bonne convergence. Les résultats des simulations montrent la redistribution de l’hydrogène dans les polycristaux due à la présence des hétérogénéités des contraintes hydrostatiques à l’échelle intragranulaire. L’effet de la vitesse de déformation a été quantitativement obtenu. Afin d’enrichir l’approche continue, un intérêt particulier est porté sur le rôle des joints de grains. Des simulations numériques d’un modèle atomique plan par plan ont été développées et appliquées aux bicristaux et aux structures de type ”bambou”. Les effets de puits ou de barrière induits par la présence des joints de grains sont clairement démontrés dans le cas du nickel pur. Pour reproduire ces effets dans les simulations de diffusion avec le modèle continue, une approche originale de simulation”multi-échelles” de la diffusion au joint de grain a été développée, et un nouveau régime de diffusion au joint de grain a été modéliséIn the present work, we establish a one-way coupled crystal plasticity – hydrogen diffusion analysis and use this approach to study the hydrogen transport in artificial polycrystalline aggregates of 316L steel with different grain geometries and crystallographic orientation. The data about stress/strain fields computed at the microstructure scaleutilizing the crystal plasticity concept are transferred to the in-house diffusion code which was developed using a new numerical scheme for solving parabolic equations. In the case of initial uniform hydrogen content, the heterogeneity of the mechanical fields is shownto induce a redistribution of hydrogen in the microstructure. The effect of strain rate is clearly revealed. In the second part, hydrogen transport across grain boundaries is investigatedconsidering the specific diffusivity and segregation properties of these interfaces. Using a discrete atomic layer model, the retarding impact of grain boundaries is demonstrated on bicrystals and bamboo type membranes with and without external mechanical loading. To reproduce the effects observed in the atomistic simulations into the crystal plasticity – hydrogen diffusion model, a new physically based multi-scale method is proposed. Using this new approach we study the effect of grain boundary trapping kinetics on hydrogen diffusion and reveal a new grain boundary diffusion regime which has notbeen reported before
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Bhogireddy, Venkata Sai Pavan Kumar [Verfasser], Ingo [Gutachter] Steinbach, and Jörg [Gutachter] Neugebauer. "Liquid metal induced grain boundary embrittlement / Venkata Sai Pavan Kumar Bhogireddy ; Gutachter: Ingo Steinbach, Jörg Neugebauer." Bochum : Ruhr-Universität Bochum, 2016. http://d-nb.info/1121909361/34.
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Zhang, Chaoqun. "Ultrasonic welding of aluminium to titanium : microstructure, properties, and alloying effects." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/ultrasonic-welding-of-aluminium-to-titanium-microstructure-properties-and-alloying-effects(1aaec7d7-19dd-4524-bde4-e6ffef5217a0).html.
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Use of welded titanium alloy to aluminium alloy structures in the aerospace industry has a number of potential benefits for both cost and weight saving by enabling titanium to be used only in the most critical parts, with the cheaper and lighter aluminum alloy making up the rest of the structure. However, due to the formation of brittle intermetallic compounds (IMC) at interface and the enormous gap in melting point, the welding of titanium to aluminium remains a major challenge. Solid state welding processes are most likely to be successful since they do not involve any melting, and so issues associated with the large difference in melting point and the high reaction rate of the liquid phase are avoided. In this study, an emerging low energy input solid state welding process - high-power ultrasonic spot welding (USW) was applied to weld Al and Ti (AA6111-T4/Ti6Al4V and AA2139-T8/Ti6Al4V combinations). No obvious intermetallic reaction layer was observed on the Al/Ti interface even using transmission electron microscopy. As a result, the maximum joint strength measured reached the same level as similar Al-Al (AA6111) welds and greatly exceeded those observed in Al-Fe and Al-Mg joints made using the same technique, in which a brittle reaction layer forms rapidly. However, the Al/Ti welds always failed at the weld interface after natural ageing, which is not desirable due to the low fracture energy associated with interfacial fracture mode. By using high resolution STEM-EDS, residual oxides and Si segregation were detected on the as-welded Al/Ti interface, which are thought to be factors that result in the no reaction layer Al/Ti interface. The Si segregation is predicted to be able to increase the weld interface cohesion through thermodynamic calculation. A series of prolonged heat treatment experiments were performed to understand the Al-Ti reaction layer growth kinetics and to explain the lack of reaction layer in as-welded Al-Ti joint. Al3Ti (D022 structure) was the only Al-Ti intermetallic phase observed in the reaction layer (IMC layer). In pure Al/Ti joints, it is found that the very long slow-growth stage of IMC layer is probably caused by the residual oxides on the interface. Calculations show that grain boundary (GB) diffusion makes the major contribution to the effective diffusion coefficient in the Al3Ti layer. In AA2139/Ti joints, the IMC layer growth is significantly slower than that in pure Al/Ti joints. The effects of alloying elements on the IMC layer growth was studied in detail. Cu was observed to segregate on both the Al3Ti grain boundaries and the Al3Ti/Ti interface. Si also segregated on the the Al3Ti/Ti interface and enriched in the Al3Ti layer. Both Cu and Si are thought to retard IMC layer growth. Interestingly small patches of Al were found trapped in the IMC layer; its formation mechanism is discussed. In pure Al/Ti6Al4V joints, the IMC layer growth rate did not change significantly. The presence of V greatly retarded the Al3Ti grain growth at high annealing temperature (630 °C) and suppressed the anisotropic growth of Al3Ti at 600 °C. Overall this study successfully joined Al/Ti by USW and systematically investigated the grain size effect and alloying effects on the Al3Ti layer growth. The present study for the first time: (a) observed the no-IMC-layer Al/Ti weld interface; (b) observed Cu segeration on Al3Ti GBs; (c) quantitatively studied the grain size effect on Al3Ti layer growth kinetics; (d) observed the orientation relationship between trapped Al islands and the adjacent Al3Ti grains; (e) observed that V greatly retarded the anisotropic growth of Al3Ti grains.
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Thorning, Casper. "Grain Boundary Ridge Formation during High Temperature Oxiditation of Manganese Containing Steels." Doctoral thesis, KTH, Materialvetenskap, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4778.
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Akyildiz, Oncu. "Computer Simulation Of Grain Boundary Grooving By Anisotropic Surface Drift Diffusion Due To Capillary, Electromigration And Elastostatic Forces." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12612034/index.pdf.
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The aim of this study is to develop a theoretical basis and to perform computational experiments for understanding the grain boundary (GB) grooving in polycrystalline thin film metallic conductors (interconnects) by anisotropic surface diffusion due to capillary, electromigration and elastostatic forces.
To this end, irreversible thermo&ndashkinetics of surfaces and interfaces with triple junction singularities is elaborated, and the resulting well-posed moving boundary value problem is solved using the front&ndash
tracking method. To simulate the strain conditions of the interconnects during service, the problem is addressed within the framework of isotropic linear elasticity in two dimensions (plane strain condition). In the formulation of stress induced surface diffusion, not only the contribution due to elastic strain energy density (ESED) but also that of the elastic dipole tensor interactions (EDTI) between the stress field and the mobile atomic species (monovacancies) is considered. In computation of the elastostatic and electrostatic fields the indirect boundary element method (IBEM) with constant and straight boundary elements is utilized. The resulted non&ndash
linear partial differential equation is solved numerically by Euler&rsquo
s method of finite differences. The dynamic computer simulation experiments identify well known GB groove shapes and shed light on their growing kinetics. They also allow generating some scenarios under several conditions regarding to the applied force fields and/or physicochemical parameters. The destruction of groove symmetry, termination of the groove penetration with isotropic surface diffusivity, ridge/slit formations with anisotropic diffusivity and the role played by the wetting parameter are all identified for electromigration conditions. The kinetics of accelerated groove deepening with an applied tensile stress is examined in connection with GB cavity growth models in the literature and a diffusive micro-crack formation is reported at the groove tip for high stresses. On the other hand, the use of EDTI provided a means to dynamically simulate GB ridges under compressive stress fields with surface diffusion. An incubation time for hillock growth and a crossover depth over which GB migration becomes energetically favorable is defined and discussed in this context.
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Akyildiz, Oncu. "Computer Simulation Of Grain Boundary Grooving And Cathode Voiding In Bamboo Interconnects By Surface Diffusion Under Capillary And Electromigration Forces." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605302/index.pdf.
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The processes of grain boundary grooving and cathode voiding which are important in determining the life times of thin films connecting the transistors in an integrated circuit are investigated by introducing a new mathematical model, which flows from the fundamental postulates of irreversible thermodynamics, accounting for the effects of applied electric field and thermal stresses. The extensive computer studies on the triple junction displacement dynamics shows that it obeys the first order reaction kinetics at the transient stage, which is followed by the familiar time law as , in the normalized time and space domain, at the steady state regime in the absence of the electric field (EF). The application of EF doesn&rsquot modify this time law very
but puts only an abrupt upper limit for the groove depth and fixes the total elapse time for that event, which is found to be inversely proportional with the electron wind intensity parameter. The drift in the cathode edge due to the surface diffusion along the side walls is simulated under the constant current regime. An analytical formula is obtained in terms of system parameters, which shows well defined threshold level for the onset of electromigration induced cathode drift, showing an excellent agreement with the reported experimental values in the literature.
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Ozfidan, Asli Isil. "Ab Initio Modeling of Thermal Barrier Coatings: Effects of Dopants and Impurities on Interface Adhesion, Diffusion and Grain Boundary Strength." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19974.
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The aim of this thesis is to investigate the effects of additives, reactive elements and impurities, on the lifetime of thermal barrier coatings. The thesis consists of a number of studies on interface adhesion, impurity diffusion, grain boundary sliding and cleavage processes and their impact on the mechanical behaviour of grain boundaries.
The effects of additives and impurity on interface adhesion were elaborated by using total energy calculations, electron localization and density of states, and by looking into the atomic separations. The results of these calculations allow the assessment of atomic level contributions to changes in the adhesive trend. Formation of new bonds across the interface is determined to improve the adhesion in reactive element(RE)-doped structures. Breaking of the cross interface bonds and sulfur(S)-oxygen(O) repulsion is found responsible for the decreased adhesion after S segregation.
Interstitial and vacancy mediated S diffusion and the effects of Hf and Pt on the diffusion rate of S in bulk NiAl are studied. Hf is shown to reduce the diffusion rate, and the preferred diffusion mechanism of S and the influence of Pt are revealed to be temperature dependent.
Finally, the effects of reactive elements on alumina grain boundary strength are studied. Reactive elements are shown to improve both the sliding and cleavage resistance, and the analysis of atomic separations suggest an increased ductility after the addition of quadrivalent Hf and Zr to the alumina grain boundaries.
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Yang, Fan. "Quantitative Study Of Precipitate Growth In Ti-6al-4v Using The Phase Field Method." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1211902429.
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Mukherjee, Arnab [Verfasser], and B. [Akademischer Betreuer] Nestler. "Electric field-induced directed assembly of diblock copolymers and grain boundary grooving in metal interconnects / Arnab Mukherjee ; Betreuer: B. Nestler." Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1191267334/34.
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Delon, Rémi. "Incorporation et diffusion de l’hélium et de l’argon dans l’olivine polycristalline." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0207/document.
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Les gaz rares sont d’excellents traceurs des hétérogénéités géochimiques et isotopiques présentes dans le manteau terrestre. Cependant, le stockage et le transport de ces éléments dans les minéraux mantelliques restent mal compris. Cette thèse est centrée sur les sites de stockage de l’hélium et l’argon, et leurs mécanismes de diffusion dans les roches mantelliques. Des échantillons d’olivine polycristalline ont été dopés en hélium et argon à haute température (1150 ± 25 and 1050 ± 25 °C) et haute pression (0.30 ± 0.01 GPa), et analysés par chauffage par paliers de température avec un spectromètre de masse. L’influence d’une concentration initiale hétérogène dans l’échantillon sur les diffusivités calculées a également été testée, démontrant la robustesse des paramètres de diffusion obtenus dans cette étude. Les résultats montrent que deux domaines de diffusion sont présents dans l’olivine polycristalline : (i) un domaine à haute température avec une énergie d’activation (Ea) élevée où la diffusion est contrôlée par la diffusion dans la maille cristalline, et (ii) un domaine à plus basse température avec une Ea plus faible où la diffusion est contrôlée par à la fois la diffusion dans la maille cristalline et celle dans les joints de grains. Ces deux domaines sont séparés par une température de transition qui a lieu au moment où les joints de grains ont été vidés. Mes résultats confirment que les joints de grains peuvent représenter un site de stockage significatif pour l’hélium et l’argon. Pour l’hélium, deux populations d’Ea ont été observées dans le domaine de la maille cristalline de l’olivine, interprétées comme correspondant à la diffusion de l’hélium dans les sites interstitiels (Ea = 95 ± 15 kJ.mol-1) et dans les sites vacants du Mg (Ea = 168 ± 19 kJ.mol-1). Pour l’argon, une valeur moyenne des paramètre de diffusion dans la maille cristalline (Ea = 166 ± 44 kJ.mol-1 et logD0 = −7.04 ± 1.13 avec D0 en m2.s-1) a été obtenue à partir des données de la littérature et de notre étude. De plus, les paramètres de diffusion dans les joints de grains ont été déterminés : Ea = 45 ± 12 kJ.mol-1 et D0 = 5.30 ± 1.53 * 10-13 m2.s-1 pour l’hélium, et Ea = 22 ± 5 kJ.mol-1 et log(D0) = -12.33 ± 0.3 pour l’argon avec D0 en m2.s-1. En appliquant ces résultats au manteau supérieur, il s’avère qu’une quantité conséquente d’hélium et d’argon peut être stockée aux joints de grains (~ 22% pour une taille de grain de 1 mm). En conséquence, les diffusivités globales peuvent être significativement plus élevées que celles de la maille cristalline, induisant des implications importantes pour la géochimie et la géodynamique du manteau terrestreNoble gases are key tracers of mantle geochemical and isotopic heterogeneities and can constrain our understanding of mantle geodynamics. Nevertheless, the basic mechanisms of noble gas storage and transport in mantle minerals remain poorly understood. In this PhD thesis, I focused on helium and argon to constrain their storage sites and the diffusive mechanisms, which occur in mantle rocks. Polycrystalline olivine was doped with helium and argon at high temperature (1150 ± 25 and 1050 ± 25 °C) and high pressure (0.30 ± 0.01 GPa), followed by step heating extraction experiments. I also tested the effect of heterogeneous initial concentrations on the extracted diffusivities, and demonstrate the robustness of diffusion parameters obtained in this study. My results show that two diffusion domains are present in polycrystalline olivine: (i) a high temperature domain with high activation energy (Ea) where diffusion is only controlled by lattice diffusion, and (ii) a lower temperature domain with lower Ea where diffusion is controlled by both grain boundary and lattice diffusion. These two domains are separated by a transition temperature that depends on the depletion of helium or argon hosted in grain boundaries, i.e., the amount of helium or argon stored at grain boundaries and the temperature and duration of the step heating sequence. The results confirm that grain boundaries can represent a significant storage site for helium and argon. Moreover, I constrained argon and helium diffusion in olivine lattice. For helium, I report two different populations of Ea in the lattice diffusion domain, which are interpreted as diffusion in interstitials (Ea = 95 ± 15 kJ.mol-1) and Mg vacancies (Ea = 168 ± 19 kJ.mol-1). For argon, a mean value of diffusion parameters in olivine lattice (Ea = 166 ± 44 kJ.mol-1 and logD0 = −7.04 ± 1.13 with D0 in m2.s-1) is obtained for data from literature and this study. Furthermore, I determine grain boundary diffusion parameters: Ea = 45 ± 12 kJ.mol-1 and D0 = 5.30 ± 1.53 * 10-13 m2.s-1 for helium, and Ea = 22 ± 5 kJ.mol-1 and log(D0) = -12.33 ± 0.3 for argon with D0 in m2.s-1. Applying these results to the upper mantle reveals that high content of helium and argon can be stored at grain boundaries. As a consequence, bulk diffusivities can be significantly higher than lattice diffusivities, inducing important implications for mantle geochemistry and geodynamics
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Kidd, Bryce Edwin. "Cation and Anion Transport in a Dicationic Imidazolium-Based Plastic Crystal Ion Conductor." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/23300.
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Here we investigate the organic ionic plastic crystal (OIPC) 1,2-bis[N-(N\'-hexylimidazolium-d2(4,5))]C2H4 2PF6- in one of its solid plastic crystal phases by means of multi-nuclear solid-state (SS) NMR and pulsed-field-gradient (PFG) NMR. We quantify distinct cation and anion diffusion coefficients as well as the diffusion activation energies (Ea) in this dicationic imidazolium-based OIPC. Our studies suggest a change in transport mechanism for the cation upon varying thermal and magnetic treatment (9.4 T), evidenced by changes in cation and anion Ea. Moreover, variable temperature 2H SSNMR lineshapes further support a change in local molecular environment upon slow cooling in B0. Additionally, we quantify the percentage of mobile anions as a function of temperature from variable temperature 19F SSNMR, where two distinct spectral features are present. We also comment on the pre-exponential factor (D0), giving insight into the number of degrees of freedom for both cation and anion as a function of thermal treatment. In conjunction with previously reported conductivity values for this class of OIPCs and the Stokes-Einstein relation, we propose that ion conduction is dominated by anion diffusion between crystallites (i.e., grain boundaries). Using our experimentally determine diffusion coefficient and previously reported PF6- hydrodynamic radius (rH), viscous (" = 4.1 Pa " s) ionic liquid (IL) is present with a cation rH of 0.34 nm. NMR measurements are very powerful in elucidating fundamental OIPC properties and allow a deeper understanding of ion transport within such materials.Master of Science
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Zhao, Hongwei. "Local tunneling characteristics near a grain boundary of a d-wave superconductor as probed by a normal-metal or a low-Tc-superconductor STM tip." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2373.
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We studied the local single-particle tunneling characteristics [as observed with scanning
tunnel microscopy (STM)] for N D and S D tunneling, where N is a normal
metal, S is a s-wave superconductor, and D is a d-wave superconductor with
a {100} | {110} grain boundary. The tunneling Hamiltonian method was used. The
self-consistent order parameter is first determined using the quasiclassical Green'sfunction
method, and then the tunneling characteristics at various distances from
the interface, reectivity of the interface, and temperature are studied. For N D
tunneling, a zero-bias conductance peak (ZBCP) occurs near the interface with diminishing
magnitude away from it. For S D tunneling, the ZBCP splits to exhibit
the gap of the s-wave low-Tc superconducting tunneling tip and there is a range of
negative conductance just outside the peaks when the tunneling point is near the
grain boundary. The results are compared with those obtained by using a constant
order parameter in each grain.
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Kuper, Michael W. "Investigations Near the Fusion Boundary of Grade 91 Steel Dissimilar Metal Welds with Nickel Based Filler Metals." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1543505600533312.
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Hashim, Leïla. "Unraveling the grain size evolution in the Earth’s upper mantle : experimental observations and theoretical modeling." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2025/document.
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La taille de grains dans le manteau terrestre a des implications cruciales sur les processus à grande échelle, telles que la propagation des ondes sismiques, la perméabilité et la rhéologie des roches. Cependant, la taille de grains évolue constamment avec le temps, car la croissance de grains statique induit une augmentation de la taille moyenne tandis que la recristallisation dynamique contribue à sa décroissance. La croissance d’olivine au sein d’agrégats mantelliques dans un milieu inter-granulaire sec, en présence de liquide magmatique ou dans des conditions sursaturées en eau a été modélisée dans le cadre de cette thèse. En s’appuyant sur la théorie de croissance cristalline ainsi que sur des expériences à 1-atmosphère et hautes températures précédemment publiées, la loi de croissance d’olivine sèche a été déterminée. Le facteur limitant est, dans ce cas, la diffusion du silicium aux joints de grains à travers une épaisseur effective de 30 nm. La croissance d’agrégats en présence de liquide magmatique et fluide aqueux a été contrainte par de nouvelles expériences haute pression/haute température. Ces données indiquent que les taux de croissance sont significativement plus importants que dans des conditions sèches et sont limités par des réactions aux interfaces cristal/liquide. Nous proposons une loi de croissance générale régulée par une combinaison de joints de grains secs et mouillés, grâce aux paramètres de contiguité et de mouillabilité. Cette loi de croissance unifiée est fondamentale pour extrapoler les tailles de grains expérimentales à des échelles de temps, des profondeurs et des quantités de liquides relatives au manteau supérieurGrain size in the Earth’s mantle is a fundamental parameter that has crucial implications on large-scale processes, such as seismic wave propagation, the permeability and the rheology of rocks. However, grain size is constantly evolving with time, where static grain growth implies an increase of the average grain size whereas dynamic recrystallization contributes to its decrease. Static grain growth of olivine-rich mantle aggregates in an intergranular medium being dry, melt-bearing and water-oversaturated has been here modeled. By using the appropriate theoretical background, the dry olivine grain growth law has been established from previously published experimental grain growth data at 1-atmosphere and high-temperature conditions. Grain growth rates for these samples are limited by silicon diffusion at grain boundaries through an effective width of 30 nm. Grain growth for melt- and water-bearing aggregates was, however, constrained by new high-pressure and high-temperature experiments. This data indicates that grain growth rates for liquid-bearing samples are significantly faster than for dry samples and are limited by precipitation reactions at the crystal/liquid interface rather by diffusion through the liquid phase. We propose a general grain growth law, which takes into account dry grain boundaries as well as wetted grain-grain interfaces, through the contiguity and wetness parameters. This unified law is fundamental to extrapolate experimental grain sizes to time scales, depths and liquid contents that are relevant of the upper mantle
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Hamm, Magnus Verfasser], Astrid [Akademischer Betreuer] Pundt, Astrid [Gutachter] Pundt, Reiner [Gutachter] [Kirchheim, Cynthia A. [Gutachter] Volkert, Vasily [Gutachter] Moshnyaga, Hans Christian [Gutachter] Hofsäss, and Michael [Gutachter] Seibt. "Hydrogen diffusion and hydride formation in grain boundary rich magnesium / Magnus Hamm ; Gutachter: Astrid Pundt, Reiner Kirchheim, Cynthia Volkert, Vasily Moshnyaga, Hans Christian Hofsäss, Michael Seibt ; Betreuer: Astrid Pundt." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2019. http://d-nb.info/118575749X/34.
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Hamm, Magnus [Verfasser], Astrid Akademischer Betreuer] Pundt, Astrid [Gutachter] Pundt, Reiner [Gutachter] [Kirchheim, Cynthia A. [Gutachter] Volkert, Vasily [Gutachter] Moshnyaga, Hans Christian [Gutachter] Hofsäss, and Michael [Gutachter] Seibt. "Hydrogen diffusion and hydride formation in grain boundary rich magnesium / Magnus Hamm ; Gutachter: Astrid Pundt, Reiner Kirchheim, Cynthia Volkert, Vasily Moshnyaga, Hans Christian Hofsäss, Michael Seibt ; Betreuer: Astrid Pundt." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2019. http://d-nb.info/118575749X/34.
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Bertali, Giacomo. "Mechanistic understanding of Alloy 600 preferential intergranular oxidation : 'precursor events of stress corrosion cracking'." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/mechanistic-understanding-of-alloy-600-preferential-intergranular-oxidation-precursor-events-of-stress-corrosion-cracking(db6c7668-7cf5-4d50-a6bf-34eacf5b1216).html.
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Primary Water Stress Corrosion Cracking (PWSCC) of Alloy 600 and similar Ni-Cr-Fe alloys is regarded as one of the most important challenges to nuclear power plant operation. During the past decades the majority of research has focused on PWSCC crack growth rate measurements in order to assess the lifetime of real components and to develop empirical models for crack propagation. However, the incubation and initiation stages of PWSCC have the same or even greater importance than the propagation stage, particularly because SCC can be undetected for more than 20 years before the occurrence of a rapid and catastrophic failure. There is, therefore, the scientific need to understand the mechanisms playing a fundamental role in the formation and development of intergranular cracks embryo, the so-called SCC initiation "precursor events", in order to be able to predict and mitigate the occurrence of PWSCC. Amongst all the models proposed for SCC initiation, the internal oxidation mechanism proposed by Scott and Le Calvar in 1992 appears to be the most comprehensive. Although the internal oxidation mechanism is widely accepted, it still requires further elucidation, especially in terms of enhanced grain boundary diffusivity and the role of intergranular carbides on the oxidation mechanism. The present work has focused on the initial stages of intergranular oxidation of solution-annealed (SA) and thermally-treated (TT) Alloy 600 with the aim of understanding the active mechanism responsible for the enhanced intergranular oxide penetration kinetics. The material was tested in simulated PWR primary water at 320°C, high-pressure hydrogenated-steam at 400°C and low-pressure H2-steam environment at 480°C at potential more reducing than the Ni/NiO equilibrium. The detailed microstructural characterization was conducted using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and analytical transmission electron microscopy (ATEM) and demonstrated that Alloy 600SA is susceptible to diffusion-induced grain boundary migration (DIGM), preferential intergranular oxidation (PIO) and localised Cr and Fe depletions at the grain boundaries. The similar analyses performed on Alloy 600TT demonstrated reduced susceptibility to PIO and grain boundary migration. Further, detailed analyses confirmed that intergranular carbides were readily oxidized/consumed in all 3 environments and acted as Cr reservoir/O trap. These results shed additional light on the "precursor events" for PWSCC of Alloy 600, especially on the mechanism responsible for the enhanced Cr and O diffusivity and on the mechanism responsible for the enhanced Alloy 600TT SCC initiation resistance. Moreover, the strong similarities in the Alloy 600 oxidation behaviour observed for the 3 different environments and at the 3 different temperatures suggested that the same PIO mechanism is active in both steam and water and at temperatures between 320°C and 480°C. These results strongly support the possibility of using the low-pressure H2-steam environment as a substitute environment to accelerate PWSCC initiation without changing the mechanism.
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Breitwieser, Matthias, Friedemann D. Heinz, Andreas Büchler, Martin Kasemann, Jonas Schön, Wilhelm Warta, and Martin C. Schubert. "Analysis of solar cell cross sections with micro-light beam induced current (µLBIC)." Elsevier, 2014. https://publish.fid-move.qucosa.de/id/qucosa%3A72456.
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A highly resolving micro-light beam-induced current (µLBIC)-system is presented in this work. Based on the laser excitation via an optical microscope, current values can be measured with sub-micron precision. We show, that this non-destructive, light-based approach delivers superior results to a reference electron microscope based electron beam induced current method concerning contrast and robustness towards reflection differences, whereas no vacuum is needed, no charging effects can occur and equal resolution is achieved. µLBIC allows therefore mapping of pn-junctions at silicon solar cell cross sections. By combination of µLBIC with other measurement methods in the same setup, such as micro-Raman spectroscopy, complementary microscopic information about material stress or crystallinity and electronic properties at the same region of interest on the sample is revealed. By applying µLBIC for analyzing silicon solar cross sections, two characterization examples of current technological relevance are presented: enhanced dopant diffusion along grain boundaries between grains with different orientations is quantified and the impact of a nickel silicide spike on local charge collection quality is studied.
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Fliegans, Jérôme. "Coercivity of NdFeB-based sintered permanent magnets : experimental and numerical approaches." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY071.
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Les aimants permanents Nd-Fe-B sont actuellement les plus puissants du marché. Ils sont indispensables pour des applications telles que les moteurs des véhicules électriques ou les générateurs des éoliennes. Leurs propriétés exceptionnelles viennent des propriétés magnétiques intrinsèques de la phase Nd2Fe14B et de leur microstructure. Cependant, les machines électriques fonctionnent entre 120 et 180°C et les propriétés magnétiques extrinsèques telles que la coercitivité et la rémanence diminuent avec la température. Un moyen d’améliorer la coercitivité des aimants frittés Nd-Fe-B est la substitution du Nd par des terres rares lourdes comme le Dy, afin d’augmenter l’anisotropie magnétocristalline. Néanmoins, le Dy est un matériau critique et un objectif majeur de la recherche est actuellement de développer des aimants possédant d’excellentes propriétés magnétiques extrinsèques et contenant peu de Dy. Cela nécessite une meilleure compréhension du lien entre microstructure et coercitivité. Dans les aimants frittés Nd-Fe-B, un des points-clés est le contrôle de la taille de grain et de la répartition des phases secondaires aux joints de grains de façon à limiter la nucléation du retournement de l’aimantation et à garantir un bon découplage magnétique des grains. La première partie de la thèse est une étude comparative des caractérisations magnétiques en circuit ouvert et fermé réalisées sur des aimants frittés Nd-Fe-B. Les différences de coercitivité observées sont expliquées par les phénomènes de viscosité magnétique et d’effets de champ démagnétisant. La deuxième partie traite du procédé de diffusion aux joints de grains appliqué aux aimants frittés Nd-Fe-B et utilisant des alliages Dy-Co. Des caractérisations microstructurales ont été réalisées en complément de mesures magnétiques afin de déterminer les profils de diffusion et de coercitivité, et ainsi d’établir le lien entre les variations locales de composition chimique et le champ coercitif. De plus, des simulations micromagnétiques ont permis de décrire le retournement de l’aimantation à l’échelle nanométrique dans un modèle simplifié cœur-coquille. Enfin, la dernière partie de la thèse constitue une discussion sur la coercitivité des aimants diffusés au Dy-Co (à gradient de champ coercitif) à l’aide d’un modèle de diffusion et de simulations sur un modèle polycristallinNd-Fe-B permanent magnets are the most powerful among all commercially available magnets. They play a significant role in energy applications, such as motors of electric vehicles and generators of windmills. Their outstanding properties come from the excellent intrinsic magnetic properties of the Nd2Fe14B phase and from their microstructure. However, electrical machines operate at about 120-180°C and extrinsic magnetic properties such as coercivity and remanence decrease rapidly with temperature. One way of improving coercivity of Nd-Fe-B sintered magnets is to substitute Nd with a heavy rare earth such as Dy, so as to increase the magnetocrystalline anisotropy. However, Dy is a strategic element and a major objective of the research community is therefore to develop Nd-Fe-B magnets that possess excellent extrinsic magnetic properties with a reduced content of Dy. This requires a better understanding of the link between microstructure and coercivity. The key point is the control of the grain size and the distribution of secondary phases at grain boundaries to prevent magnetization reversal and magnetic coupling. The first part of this thesis concerns a comparison of open-circuit and closed-circuit magnetization measurements carried out on Nd-Fe-B sintered magnets. The observed differences in coercivity values are discussed in terms of magnetic viscosity and demagnetizing field effects. The second part deals with the grain boundary diffusion process performed on Nd-Fe-B sintered magnets using Dy-Co alloys. Microstructural observations and magnetic measurements have been carried out to characterize the diffusion and coercivity profiles and to establish the link between local variations in composition and coercivity. Moreover, micromagnetic simulations have been performed to describe magnetization reversal at the nanoscale in a simple core-shell model. The last part constitutes a discussion about coercivity in graded magnets via a diffusion model and further simulations on a polycrystalline model
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Kajbaji, Mohamed El. "Etude du joint de grain [SIGMA] = 9 dans le silicium parfait, déformé et recuit par microscopie électronique à haute résolution." Grenoble 1, 1986. http://www.theses.fr/1986GRE10102.
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Etude des mecanismes d'interaction joint de grain dislocations lors de la deformation du bicristal, mettant en evidence la dissociation des dislocations entrant dans le joint, leur perte d'identite et l'interaction entre eux des residus. Determination des structures des dislocations residuelles. Apparition de precipites lors du recuit du bicristal deforme
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Riet, Adriaan Anthony. "INVESTIGATION OF DEFECT-ASSISTED MATERIAL TRANSPORT IN MAGNESIUM OXIDE BY MOLECULAR SIMULATIONS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1592306263843628.
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Rouvière, Jean-Luc. "Structure atomique des joints de grains de flexion d'axe <001> dans le silicium et le germanium." Grenoble 1, 1989. http://www.theses.fr/1989GRE10010.
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Etude de cinq joints de grains de flexion d'axe 001, de grande coincidence (sigma=5, 65, 13, 25 et 41) par microscopie electronique haute resolution et relaxation numerique. Presentation d'une analyse en termes d'unites structurales-dislocation
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Hagège, Serge. "Contribution a l'etude des joints de grains en coincidence dans la symetrie hexagonale." Caen, 1985. http://www.theses.fr/1985CAEN2019.
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Les joints de grains peuvent etre decrits comme des joints en relation d'orientations de coincidence. Cette description necessite l'introduction d'une serie de parametres necessaires et suffisants pour caracteriser completement la relation d'orientation. Le rapport c/a de la symetrie hexagonale introduit une difficulte supplementaire qui conduit a discuter de la dimension de la coincidence et a envisager la notion de coincidence approchee. Applications aux macles de deformation des metaux hexagonaux compacts que l'on peut decrire comme des joints de coincidence. La notion de symetrie permet de choisir entre les differentes configurations atomiques possibles d'une relation d'orientation donnee. Pour le macle (1012), une configuration de symetrie maximale permet de proposer une description simple du processus de maclage. On confirme par microscopie electronique le role des dislocations dans la structrure des macles de deformation
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Nguejio, Nguimatsia Josiane. "Processus diffusionnels à l'origine de l'évolution de la composition d’un alliage au cours de l'oxydation sélective en pointe de fissures intergranulaires. Application à la CSC de l'Alliage 600 en milieu primaire des REP." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM054/document.
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La corrosion sous contrainte (CSC) des alliages à base nickel est un des principaux phénomènes de dégradation des composants du circuit primaire des Réacteurs à Eau Pressurisée (REP). La compréhension de ce mécanisme de fissuration est un élément essentiel pour la prolongation de la durée d’exploitation des réacteurs.Des études antérieures ont permis d’établir un modèle de propagation de la CSC basé sur une oxydation sélective et dissymétrique du joint de grains en pointe de fissure qui s’accompagne d’une zone appauvrie en chrome. La cinétique de diffusion du chrome étant plus lente que celle de l’oxygène, il est supposé que la diffusion du chrome est une étape limitante de la propagation de la fissure. Si ces observations ont été validées dans la littérature, les hypothèses proposées sur l’origine de l’appauvrissement en chrome dans le grain sont encore sujettes à discussion. Comme la diffusion du chrome en volume dans les alliages base nickel à 350°C ne permet pas d’expliquer les ordres de grandeur des appauvrissements en chrome mesurés dans la littérature, il est supposé qu’il existerait un élément accélérateur de la diffusion du chrome dans l’alliage en pointe de fissure. Ainsi, deux hypothèses sont proposées dans ces travaux : la diffusion du chrome accélérée sous l’effet de la plasticité et la migration des joints de grains induite par la diffusion.L’objectif principal de la thèse a été de confronter les deux hypothèses énoncées au moyen d’essais expérimentaux et de modélisation afin de déterminer le mécanisme de formation de la zone appauvrie en chrome et d’identifier les paramètres favorisant cet appauvrissement.A cet effet, des essais de diffusion sous charge ont été réalisés dans le but d’étudier l’effet de la déformation plastique sur la diffusion du chrome. Les résultats ont permis d’établir une relation entre le coefficient de diffusion et la vitesse de déformation. Ainsi, une accélération de la diffusion en volume de l’ordre de 106 est observée à 350°C sous l’effet de plasticité. De même, des traitements thermiques visant à mettre en évidence la migration des joints de grains induite par la diffusion (DIGM) sont présentés dans ces travaux. Les caractérisations chimiques et microstructurales montrent que la DIGM est bien associée à la formation d’une zone appauvrie en chrome observée dans le sillage du joint de grains migrant. Pour finir, une discussion est proposée afin de relier ces hypothèses au modèle de propagation de la CSCStress Corrosion Cracking (SCC) of nickel base alloys is one of the major degradation phenomena in the primary circuit of Pressurized Water Reactors (PWR). Understanding the SCC mechanism is a key issue for the extension of reactor lifetime.A SCC model based on a selective and asymmetrical oxidation of the grain boundary ahead of the crack tip has been proposed in previous studies. Adjacent to this oxide, a chromium-depleted area is observed exclusively in one of the two grains adjacent to the grain boundary. As oxygen transport is found to be faster than chromium diffusion in the alloy, the latter is assumed to be the rate-limiting step of crack propagation. Nevertheless, the mechanism responsible for chromium depletion is still under debate. Indeed, the lattice and the grain boundary diffusion coefficients of chromium in nickel-based alloys at 350°C are not high enough to explain the chromium depletion magnitudes measured in the literature. Accordingly, factors accelerating chromium diffusion in the alloy ahead of the SCC crack tip should exist. Thus, two assumptions have been proposed in this work: plasticity-enhanced chromium diffusion and diffusion-induced grain boundary migration (DIGM).The aim of this study is to confront these two assumptions by combining both experiments and modeling in order to explain chromium depleted areas observed at the SCC crack tip.Thus, diffusion tests under loading were performed in order to study the effect of plastic deformation on chromium diffusion. Plasticity-enhanced diffusion is evidenced. A relationship between the diffusion coefficient and strain rate has been established leading to a 106-fold increase of the diffusion coefficient at 350°C. In addition, thermal treatments and oxidation tests have shown that diffusion-induced grain boundary migration occurs in Ni-Cr alloys. DIGM leads to dissymmetric Cr-depleted areas, observed in the wake of the moving grain boundary
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Tao, Liang. "Atomic-scale calculations of interfacial structures and their properties in electronic materials." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1127163029.
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Spirig, John Vincent. "A new generation of high temperature oxygen sensors." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1188570727.
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