Dissertations / Theses on the topic 'Recrystallization'
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Tavernier, Philippe. "Modeling of recrystallization textures." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61775.
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Jeniski, Richard A. Jr. "Recrystallization behavior of aluminum alloy 6013." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/19412.
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Halfpenny, Angela. "Recrystallization microstructures and mechanisms in quartzites." Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485942.
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Electron backscatter diffraction (EBSD) has been used to analyse 25 quartz rich rocks. The rock samples represent a range ofcommon microstructures which exhibit variations in the defonnation conditions such as changes in temperature and the amount of strain accumulated. As natural sample's defonnation conditions are poorly constrained, five out of the 25 samples were experimentally defonned samples. EBSD has been used to measure the full crystallographic orientation of all the grains contained within the mapped area The mapped microstructures have been separated out in to original 'parent' grains and recrystallized 'daughter' grains. Neighbour-daughter grains are recrystallized grains which are still in contact with a parent grain (although not necessarily its own). The samples exhibit between 10% and 95% recrystallized microstructures. The samples can be separated into two main groups based upon their microstructural and statistical characteristics. The first group represents samples which have an average subgrain size which is similar in size to the neighbour-daughters. The parent grains show a systematic increase in misorientation from the centre ofthe grain to the edges. These data are consistent with subgrain rotation (SGR) as being the controlling nucleation and recrystallization mechanism The second group ofsamples show an average subgrain size which is much larger than the size of the neighbour-daughter grains. The internal defonnation of the parent grains is randomly arranged and does not gradually increase. These data are inconsistent with SGR The recrystallization was facilitated by bulging at low temperatures or during strain-induced grain boundary migration (SIGBM). All samples studied exhibited angles between the parent and neighbourdaughter grains which had increased after nucleation and recrystallization had taken place. Each sample analysed had at least 50% of the grain boundaries with misorientation angles ofgreater than 30°. Other processes have increased the misorientation angles. The distnbutions of the neighbour-daughter grains have also been redistnbuted from being in contact with the parent they are theorized to have recrystallized from to being located either next to another parent or in the matrix. The microstructures have been modified. Grain boundary sliding (GBS) is interpreted as the controlling modification mechanism which caused the neighbour-switching and further rotations of the recrystallized grains to cause the increased misorientation angles observed.
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Makin, P. L. "Recrystallization in aluminium-lithium based alloys." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356656.
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James, Orin Anthony. "The effects of glycerol on recrystallization." Diss., Online access via UMI:, 2008.
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Svensson, Christoffer. "Recrystallization mapping of Ni-base alloys." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75348.
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Superalloys such as alloy 718 and 925 possesses superior properties at elevated temperatures and corrosive environments. They are commonly found in application such as oil and gas extraction, turbine engines and in the chemistry industry. These alloys were developed during the 1950s but the demand of tubes and pipes of these alloys has rapidly increased. Sandvik has recently started produce these products and faces new challenges within the production.There are several studies within the area of superalloys but the hot working behavior and flow softening mechanism are not fully understood.The goal with this master thesis is to analyze two different steel grades, alloy 718 and 925 and correlate different process parameters that will influence the recrystallization initiation and nucleation.Two ingots manufactured through electric arc furnace, argon oxygen decarburization and refined by vacuum arc remelting were analyzed followed by a homogenization heat treatment. Samples were extracted from three positions, bottom, center, top and from half the radius in the ingot. The chemical composition was analyzed and the mechanical properties was tested trough hot compression testing (Gleeble). From Gleeble testing, the true strain, stress curves were analyzed in order to determine flow softening effects. The microstructure were studied trough light optical microscopy and electron backscatter diffraction.The results reveal that discontinuous dynamic recystallization is the dominant flow softening mechanism. There was no significant difference between the three positioning within the ingot.To maximize the recrystallized area fraction higher strain and temperatures must be provided or lower strain rates.
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Helgeson, Maria Rose. "Fe(II)-catalyzed recrystallization of hematite." Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/1466.
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Hematite (α-Fe2O3) is a common, naturally occurring iron oxide, found throughout the earth's crust and atmosphere. Hematite is of interest to the scientific community because it is able to incite a reaction that produces hydrogen gas (H2), which is a form of clean energy (Bora et al., 2013). The composition of hematite in nature is also used to make inferences about conditions on early earth's surface (Guo et al., 2013). Hematite is useful for clean energy production and as an environmental indicator partly because of its apparent stability. However, some evidence suggests that hematite might not be as stable as previously thought.
Many iron oxides undergo Fe atom exchange when they come into contact with aqueous Fe(II), as often occurs in nature (Pedersen et al., 2005, Jones et al., 2009, Gorski et al., 2012, Handler et al., 2009). This atom exchange can result in elements and nutrients being taken up or released from the iron oxides as they recrystallize (Frierdich & Catalano, 2012, Cwiertny et al., 2008, Boland et al., 2014). Although atom exchange has not been directly shown in hematite, it has been demonstrated that trace metals are released from hematite in the presence of aqueous Fe(II), implying that exchange may be occurring (Frierdich et al., 2011). Here, we directly demonstrate Fe atom exchange between hematite and aqueous Fe(II). This work provides knowledge concerning the surface chemistry of hematite that has important implications for clean energy production and the environment.
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Hopkin, Gareth John. "Modelling anisothermal recrystallization in austenitic stainless steels." Thesis, University of Cambridge, 2002. https://www.repository.cam.ac.uk/handle/1810/221867.
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Ranganathan, Kannan. "Recrystallization resistance in aluminum alloys containing zirconium." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/19560.
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Roucoules, Christine. "Dynamic and metadynamic recrystallization in HSLA steels." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39794.
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A Mo, a Nb and a Ti steel were tested in torsion to study the characteristics of dynamic and postdynamic recrystallization. To characterize dynamic recrystallization, continuous torsion tests were carried out between 850 and 1050$ sp circ$C at strain rates of 0.02, 0.2 and 2s$ sp{-1}.$ Quenches were performed to investigate the grain refinement produced by dynamic recrystallization. Interrupted torsion tests were performed between 850 and 1050$ sp circ$C and at strain rates between 0.02 and 2s$ sp{-1}$ to study the characteristics of postdynamic recrystallization. Quenches were performed after increasing holding times to follow the evolution of the postdynamic microstructure. The evolution of the grain size distribution as a function of holding time shows that the growth of dynamically recrystallized grains is the first change that takes place. Then metadynamically recrystallized grains appear and contribute to the softening of the material. The rate of metadynamic recrystallization increases with strain rate and temperature and is observed to be independent of strain, in contrast to the observations for static recrystallization. The dependence of the metadynamically recrystallized grain size on the Zener-Hollomon parameter was established and is shown to differ from static recrystallization dependence. Simple torsion simulations were carried out using constant interpass times to study the conditions under which dynamic, metadynamic or static recrystallization takes place. Dynamic recrystallization controlled rolling (DRCR) is shown to require such short interpass times that they are not attainable in hot strip mills. A new concept, metadynamic recrystallization controlled rolling (MDRCR), is introduced to describe the case where there is 20 to 80% softening by metadynamic recrystallization. The occurrence of dynamic and metadynamic recrystallization causes the load to increase less rapidly than in the case of pure strain accumulation.
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Hantsoo, Eerik T. (Eerik Torm). "Silicon cast wafer recrystallization for photovoltaic applications." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45954.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references.
Current industry-standard methods of manufacturing silicon wafers for photovoltaic (PV) cells define the electrical properties of the wafer in a first step, and then the geometry of the wafer in a subsequent step. The geometry is typically defined by a combination of grinding and abrasive wire sawing. While mature, these processes remain slow and wasteful of raw materials. As the PV industry scales to meet increasing global demand for renewable energy, new processes for creating wafers must be explored. This project sets out to enable high-speed casting of individual wafers, by developing a zone recrystallization process to improve rapid-cast wafers of low electrical quality. In the process, individual wafer geometry is defined in an upstream high-speed casting step with little regard to electrical quality. Subsequently, the electrical properties (through grain structure, dislocation density, and segregation of impurities) are optimized by zone recrystallization. The work outlined in this report documents the development of a custom, high- purity zone recrystallization furnace; an encapsulation mechanism for molten wafers; a mechanical fixturing scheme to preserve the planarity of recrystallized samples; and a release layer to prevent adhesion of the wafer to support structures. Further, the results of experiments investigating temperature profile effects on defect density and grain structure are discussed. Specifically, results demonstrating completely redefined grain structure and improved dislocation density are disclosed. Minority carrier lifetime measurements are also disclosed. Although still preliminary, overall results are promising for the successful refinement of small-grained, rapid-cast wafers into large-grained, high-lifetime wafers suitable for use as high-efficiency PV cells.
by Eerik T. Hantsoo.
S.M.
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Charlton, Thomas Aurelio. "Synthesis of Novel Charged Ice Recrystallization Inhibitors." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42333.
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With emerging trends of new cellular therapies, the need for quick access to cellular components is necessary. For most applications genetically compatible biological components are essential to prevent adverse immune responses and graft-versus host disease (GVHD). Since these biological components have a limited window to be used, techniques for long-term storage are needed. Cryopreservation is essential for this in the field of biobanking and regenerative medicine to allow for long-term storage of cell products. During this process, ice recrystallization is the major contributor to cell death and decreased cell viability post-thaw. Due to this, controlling ice growth and recrystallization is imperative to increasing cell survival and function.
The Ben lab is focused on the synthesis of small molecule, carbohydrate-based cryoprotectants that function as ice recrystallization inhibitors (IRIs). Previously, many IRIs have been synthesized showing varying degrees of ice recrystallization inhibition (IRI). Through the structure-function work, a delicate balance between hydrophobic and hydrophilic portions on the same molecule must be met. These compounds are believed to disrupt hydrogen bonding networks present in the formation of ice, and control ice growth. While numerous types of functional groups on carbohydrate derivatives have been explored, many highly solvated functional groups (amines, sulfates, phosphates, etc.) have not been thoroughly investigated. Highly solvated functional groups should disrupt hydrogen bond networks due to their solvation and in theory, should illicit an IRI response.
Sulfate groups have not previously been studied, but are present in several different biological processes, such as immune response and blood coagulation. This suggests that sulfated carbohydrates should be well tolerated biologically. Sulfate groups can also be easily installed on existing IRI active molecules through orthogonal protecting group chemistry. The first part of this thesis is focused on the synthesis and IRI activity of sulfated carbohydrates based upon previously synthesized, IRI active pyranose derivatives. When compared to their parent compounds, most of the sulfated derivatives were less active, but all compounds were incredibly soluble in aqueous media. These derivatives did not show much promise as new IRIs due to the length of their synthesis and reduced IRI activity compared to their parent compounds.
The Ben lab has also developed a new class of IRI active carbohydrates: aldonamide derivatives. These compounds are open-chain carbohydrates with an amide bond, arising from the ring opening of a carbohydrate lactone with a substituted amine. While many of these compounds displayed high degrees of IRI activity, many were incredibly insoluble in aqueous systems (many with solubility limits under 50 mM). Since sulfate groups were able to greatly increase solubility with some derivatives retaining IRI activity, installing sulfate groups on existing aldonamide-based IRIs should increase their solubility. Additionally, since many of these derivatives display high degrees of IRI activity, a reduction in IRI activity can be tolerated. Similarly, to the sulfated pyranose derivatives, the presence of a sulfate group reduced the IRI activity compared to the parent compounds in most derivatives. Though some sulfated derivatives possessed a higher degree of IRI activity, all the derivatives experienced a drastic increase in solubility (over 200 mM in PBS). Some of the sulfated aldonamide derivatives were assessed for their ability to protect red blood cells (RBCs) during freezing with reduced glycerol concentrations (15% glycerol), although none of thew tested derivatives showed an improvement over existing IRIs explored by the Ben lab.
Since the introduction of sulfate groups to existing IRIs drastically increased solubility in aqueous systems, but resulted in reduced IRI activity in most compounds, focus was switched to the addition of different hydrophilic functional groups. Amino functional groups were briefly explored with galactose-based pyranose IRIs, aldonamide derivatives had not been explored. Amino groups are present on many biological carbohydrates and should be well tolerated biologically. The addition of amino groups to aldonamide derivatives should increase solubility, with the amino derivatives ideally retaining some IRI activity. The amino aldonamide derivatives synthesized had high solubilities (>500 mM in PBS), but did possess lower degrees of IRI activity. Due to the high solubility these derivatives were initially assessed in the cryopreservation of RBCs with reduced glycerol concentrations. Initial experiments showed improvements over current IRIs, and the compounds were assessed in a number of other biological cryopreservation scenarios including articular cartilage, platelets, and hematopoietic stem/progenitor cells (HSPCs). While the compounds showed toxicity in these cell types, more studies need to be conducted for the cryopreservation of RBCs.
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Pandey, Rajiv 1967. "Crystal size manipulation of acetaminophen via recrystallization." Thesis, The University of Arizona, 1993. http://hdl.handle.net/10150/278344.
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The crystal size distribution (CSD) of any material determines its end use. Consequently, comminution processes are used to transform material from one size distribution to another. Often, recrystallization from solution is one of the processes used. Recently, a novel recrystallization process named the GAS process was developed to mill compounds that were thermally labile and insoluble in supercritical fluids. CSD could be manipulated using this process. To further illustrate the applicability of this process, size manipulation studies of acetaminophen (a widely available drug) were performed. The aim of this work was to produce crystals in the mass mean size range from 5mum to 50mum, and identify the conditions for producing the desired size distribution. A modified GAS process and a liquid anti-solvent (LAS) process were also investigated. Together with acetaminophen-butanol, other systems studied were aspirin-methanol and benzoic acid-methanol.
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Magee, Kenneth Howard. "The application of the additivity principle to recrystallization." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26311.
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This research is part of an ongoing program at the University of British Columbia to mathematically model industrial annealing processes. To enable one to predict the final mechanical properties of a cold rolled steel sheet after being subjected to an industrial annealing cycle, the progress of recrystallization must be predicted with temperature increase during annealing. This is accomplished by applying the additivity principle to isothermal recrystallization kinetic data.
To determine whether additivity is applicable to recrystallization, isothermal recrystallization kinetic data for a low carbon, rimmed, cold rolled steel sheet, was determined over a temperature range of 440°C-560°C, using molten salt annealing and diamond pyramid microhardness evaluation methods. The data was characterized using the Avrami equation. Continuous heating recrystallization trials were carried out using resistance heated strip specimens. The progress of recrystallization was monitored using an x-ray procedure based on examining the increased Ka doublet peak resolution of the {211} plane, experienced during the formation of recrystallized material. Diamond pyramid microhardness evaluation was also applied to the continuously heated specimens.
Applying the Additivity principle to the isothermal kinetic data resulted in computer predictions which displayed reasonably good agreement with the kinetics obtained experimentally. The difference between the predicted and the experimental recrystallization behaviour was related to recovery effects. The degree of recovery, which is thermal history dependent, determines the amount of stored strain energy available for recrystallization. Once the recovery effect was eliminated by applying suitable heat treatments prior to the continuous heating cycle, the computer predictions displayed excellent correlation with the experimentally obtained continuous heating recrystallization kinetics.
The x-ray procedure used to monitor recrystallization was found to be effective. However, modifications to the procedure will be necessary to enable it's use for the insitu monitoring of specimens subjected to the high heating rates typical of continuous annealing conditions.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Colyer, Lorna Marie. "Recrystallization processes in transition metal exchanged zeolite-A." Thesis, Keele University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297204.
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Janabi, Joseph. "Investigating Small Amine Molecules as Ice Recrystallization Inhibitors." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37779.
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Cryopreservation is a technique used to store cells and tissues for long time. It requires the addition of a cryoprotectant, which prevents damage to cells caused by the formation of large ice crystals. Few compounds have been classified as cryprotectants, and some of them are very toxic like DMSO. Our lab is interested in the synthesis of small, non-toxic cryoprotectants that possess ice recrystallization inhibition (IRI) activity. Much attention has been drawn towards small molecules that contain an amine group because they have some activity towards inhibiting ice recrystallization. Herein we have examined few monoamine and diamine molecules as well as PAMAM dendrimer for IRI activity. Some of the small molecules tested contain an aryl ring, and we found that changing the position of groups around the ring can have some impact in the IRI activity. We have also found that increasing the number of amines in a molecule can have little effect of the IRI activity. It is hoped that these findings can open new doors for further investigation in small amino molecules and the development of novel cryoprotectants.
Corticosteroids were first identified and isolated from both teleost and elasmobranch fish. Corticosterone and cortisol were measurable in the plasma of elasmobranchs and 1α-hydroxycorticosterone (1α-OH-B) was the dominant corticosteroid produced by the internal tissue. Limited amount of 1α-OH-B was synthesized because available supplies were exhausted in the early 1990s. Synthetic 1α-OH-B was used in steroid receptor studies to examine the evolution of the corticosteroid receptor system and measure stress levels.
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Ha, Yoosung. "Recrystallization Behavior of Oxide Dispersion Strengthened Ferritic Steels." Kyoto University, 2014. http://hdl.handle.net/2433/192210.
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Sterling, Elizabeth. "Precipitation and recrystallization in a binary magnesium-neodymium alloy." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54396.
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The influence of precipitate state and annealing temperature on the recrystallization of a Mg-2.8wt.%Nd alloy has been investigated. Precipitation kinetics at 190°C, 350°C and 400°C were studied in order to understand precipitate evolution during recrystallization. Precipitation was studied primarily through electrical resistivity measurements, and modelled using a mean radius model. It was found that predicting the kinetics required the spatial distribution of solute to be considered. Pre-aging conditions were selected in order to study the influence of either pre-existing or concurrently formed precipitates during recrystallization. After aging, the samples were cold rolled to a strain of 20%. The microstructures were characterized primarily through EBSD, and also through hardness measurements. Pre-aging the samples at 400°C for three hours resulted in a dispersion of stable β precipitates during annealing. This led to a recrystallized microstructure with recrystallization nucleation sites similar to those previously reported in the literature. Pre-aging the sample at 190°C for 24 hours lead to the formation of metastable β'' precipitates which strengthened the sample, but dissolved rapidly upon annealing at higher recrystallization temperatures. When samples previously solutionized at 545°C or aged at 190°C were subsequently annealed at 350°C, recrystallization stagnated. This was attributed to concurrent precipitation pinning grain boundaries. In all samples, irrespective of aging condition, recrystallization was observed primarily in twins and shear bands. The twins which recrystallized were found to be {10-11} contraction twins and {10-11}{10-12} contraction-extension twins. As the nuclei forming within these regions were not randomly oriented, recrystallization in these alloys did not randomize the texture. The work presented in this thesis increases understanding of recrystallization in Mg-Nd alloys. In particular, the means by which Nd interacts with and affects the recrystallizing microstructure have never been studied in detail. Furthermore, this work points to possible ways in which new magnesium alloys and thermomechanical processes could be designed to improve final material properties.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Martin, Étienne. "A microtexture characterization of recrystallization and twinning in magnesium." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=95140.
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The evolution of texture and microstructure during the deformation of two Mg-based (+Al, Mn, Zn) alloys has been studied under various conditions of temperature and strain rate. The tested materials were taken from AZ31 and AM30 extruded tubes. The mechanism of recrystallization was investigated by using uniaxial compression, while twinning was studied under uniaxial tension testing. Optical metallography, X-ray analysis and EBSD techniques were employed to study the texture and grain scale development. The first part of the investigation focused on the misorientations that apply to the different mechanisms of new grain formation during the hot compression of magnesium alloy AM30. This approach led to the identification of three types of microstructural features produced during deformation at high temperature (350°C at a strain rate of 0.001s-1). In the first, microbands were produced in grain interiors due to the accumulation of basal dislocations. Their orientation changes involve rotations of the basal planes to a more favorable orientation for glide, leading to geometric softening. In the second, two different types of DRX nuclei were observed, i.e. those formed i) by bulging and ii) by continuous dynamic recrystallization. Although visually distinct, the two mechanisms are formed as a result of dislocation-based processes that produce c-axis rotations toward the loading axis. For low misorientation angles, the boundary character is consistent with the accumulation of basal dislocations. Once nuclei of the latter two types have formed, however, only those orientations belonging to the RD-TD fibre are able to grow. In this way, recrystallization leads to the retention of the main characteristics of the initial RD-TD texture. The second part focused on the mechanisms associated with variant selection during contraction and double twinning. These twins are of practical interest since they have a high potential for texture randomization. For this purpose, magnL'évolution des orientations cristallographiques préférentielles et de la microstructure de deux alliages de magnésium, soit AZ31 et AM30, a été étudiée à des températures et à des vitesses de déformation différentes. Les échantillons des deux alliages utilisés ont été prélevés sur des tubes extrudés. Des essais de traction et de compression uniaxiales ont été effectués dans le but de comprendre les mécanismes à l'origine de la formation des macles et des grains recristallisés. L'effet de la recristallisation sur les macles primaires (ou de contraction) et secondaires (ou d'extension) a finalement été étudié. La première partie de l'étude porte sur les relations de désorientation qui sont associées aux joints de grain qui se forment durant la compression de l'alliage de magnésium AM30 à haute température (soit 350 °C, et à une vitesse de déformation de 0.001s-1). Cette méthode de caractérisation a permis l'identification de trois types de composantes structurales. Premièrement, des microbandes se forment au centre des grains par l'accumulation de dislocations basales. Ces bandes produisent des rotations qui positionnent les plans de glissement basal de façon à faciliter le glissement des dislocations. Ainsi, un adoucissement géométrique est généré, ce qui a pour effet de diminuer la contrainte d'écoulement. Deuxièmement, la recristallisation engendre la formation de nouveaux grains aux joints des grains initiaux. Deux mécanismes de recristallisation sont observés : les nouveaux grains sont créés soit par la migration des joints de grain ou par recristallisation continue. Bien que visuellement distincts, ces deux mécanismes sont tout deux initiés par une accumulation de dislocations. Les résultats ont démontré que les nouveaux grains ayant une orientation similaire à celle des grains initiaux sont avantagés au niveau de la croissance. Ainsi, la recristallisation a tendance à retenir les orientations
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Wang, Ganlin. "Static recrystallization and precipitation in Nb-Al HSLA steels." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74566.
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Constant true strain rate (2 s$ sp{-1})$ compression tests with one or two interruptions were carried out on a series of steels over the temperature range 900-1050$ sp circ$C. Based on a 0.07% C, 1.25% Mn and 0.006% N reference steel, the three microalloyed steels contained the following: (i) 0.08% Al, (ii) 0.04% Nb, or (iii) 0.045% Nb and 0.08% Al. The degree of fractional softening during the interpass was used to assess recrystallization start (R$ sb{ rm s})$ and finish (R$ sb{ rm f})$ times as well as those for the onset (P$ sb{ rm s})$ and termination (P$ sb{ rm f})$ of precipitation.Relative to a plain C steel, the static recrystallization kinetics show that the single solute retarding effect of Al is small but measurable while that of Nb is substantially larger. The influence of each element is enhanced when they are present jointly. The retardation effects observed at 1000$ sp circ$C are due solely to the presence of these elements in solution. Additional delays observed at or below 950$ sp circ$C in the two Nb bearing steels are ascribed to strain induced precipitation of Nb(CN).
The P$ sb{ rm s}$ times were estimated from the fractional softening data as well as from stress relaxation type tests. The presence of high levels of Al retarded the onset of Nb(CN) precipitation while it accelerated its progress. The Nb precipitates were cube shaped and heterogeneously distributed, suggesting that they were formed on dislocation networks.
A thermodynamic model was developed for the alloy system studied. The calculations indicated that there is a higher chemical driving force for precipitation in the Nb steel than in the Nb-Al steel at a given temperature. Consequently, this produces a higher equilibrium mole fraction of Nb(CN) in the former. The P$ sb{ rm s}$ times calculated based on the classical nucleation theory are in good agreement with the values observed.
Three hit test results further showed that increased hold times between the first two hits decrease the rate of softening between the second and third hits. Residual strain in the partially recrystallized structure is more effectively accumulated at lower temperature due to slower softening rates. These data enabled the development of a model for calculation of residual strains following a hold in a partially recrystallized structure. (Abstract shortened by UMI.)
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鍾志源 and Chi-yuen Chung. "Recrystallization of cold rolled, direct-chill cast copper alloys." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1992. http://hub.hku.hk/bib/B31232565.
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Chung, Chi-yuen. "Recrystallization of cold rolled, direct-chill cast copper alloys /." [Hong Kong : University of Hong Kong], 1992. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13212497.
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Poisson, Jessica. "Synthesis and In Vitro Applications of Ice Recrystallization Inhibitors." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39466.
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Recent advances in the clinical diagnosis and treatment of diseases using cell transplantation have emphasized the urgent need to cryopreserve many types of cells. In transfusion medicine, red blood cell (RBC) transfusions are used to treat anemia and inherited blood disorders, replace blood lost during or after surgery and treat accident victims and mass casualty events. In regenerative medicine, mesenchymal stem cell (MSC) therapy offers promising treatment for tissue injury and immune disorders. Current cryoprotective agents (CPAs) utilized for RBCs and MSCs are 40% glycerol and 10% dimethyl sulfoxide (DMSO), respectively. Although glycerol is required for successful cryopreservation of RBCs, it must be removed from RBCs post-thaw using costly and time-consuming deglycerolization procedures to avoid intravascular hemolysis. Unfortunately, while DMSO prevents cell damage and increases post-thaw MSC viability and recovery, recent reports have suggested that MSCs cryopreserved in DMSO display compromised function post-thaw. As a result, improvements to the current cryopreservation protocols such as reducing post-thaw RBC processing times and improving MSC function post-thaw are necessary in order to meet the increasing demands of emerging cellular therapies. Ice recrystallization has been identified as a significant contributor to cellular injury and death during cryopreservation. Consequently, the ability to inhibit ice recrystallization is a very desirable property for an effective CPA, unlike the conventional CPAs such as DMSO and glycerol that function via a different mechanism and do not control or inhibit ice recrystallization. Over the past few years, our laboratory has reported several different classes of small molecules capable of inhibiting ice recrystallization such as lysine-based surfactants, non-ionic carbohydrate-based amphiphiles (alkyl and aryl aldonamides) and O-linked alkyl and aryl glycosides. The use of these small molecule ice recrystallization inhibitors (IRIs) as novel CPAs has become an important strategy to improve cell viability and function post-thaw. With the overall goal to identify highly effective inhibitors of ice recrystallization, the first part of this thesis examines the IRI activity of three diverse classes of small molecules including carbohydrate-based surfactants bearing an azobenzene moiety, fluorinated aryl glycosides and phosphate sugars. While the majority of the carbohydrate-based surfactants and fluorinated aryl glycosides were not effective inhibitors of ice recrystallization, this work revealed that monosaccharides possessing a phosphate group could be effective IRIs. Our laboratory has previously demonstrated that small molecule IRIs β-PMP-Glc and β-pBrPh-Glc can protect human RBCs from cellular injury during freezing using reduced concentrations of glycerol (15% w/v). This was significant as reducing the concentration of glycerol can drastically decrease deglycerolization times. Consequently, structure- function studies were conducted on β-PMP-Glc and β-pBrPh-Glc to elucidate key structural features that further enhance their IRI activity and may increase their cryoprotective ability. In particular, the influence of an azido moiety on the IRI activity of β-PMP-Glc and β-pBrPh-Glc was investigated and it was determined that the position of the azide substituent on the pyranose ring is crucial for effective inhibition of ice recrystallization. Furthermore, the presence of an azido group at C-3 was found to increase the IRI activity of β-PMP-Glc and β-pBrPh-Glc. Despite the discovery that β-PMP-Glc and β-pBrPh-Glc are beneficial additives for the freezing of RBCs, a significant amount of cellular damage occurred during deglycerolization, resulting in very low cell recoveries. Thus, IRI active azido aryl glucosides were explored for their cryopreservation potential in RBCs to determine whether they could function as effective additives that reduce cellular damage post-thaw and improve cell recovery. One of the most significant results of this thesis is the discovery that azido aryl glucosides can successfully cryopreserve RBCs in the presence of 15% glycerol with significantly improved cell recovery. This thesis also explores the use of small molecule IRIs to improve the cryopreservation of MSCs. In particular, the addition of an N-aryl-aldonamide (2FA) to the standard 10% DMSO solution was found to enhance the proliferative capacity of MSCs post-thaw. Lastly, the ability of small molecule IRIs to cross the cell membrane and behave as permeating CPAs was evaluated in two different cell models, RBCs and human umbilical vein endothelial cells (HUVECs). These studies demonstrated that small molecule IRIs are capable of permeating the cell membrane and controlling intracellular ice recrystallization.
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Tonelli, Devin L. "Small Molecule Ice Recrystallization Inhibitors and Their Use in Methane Clathrate Inhibition." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/23994.
Full textAbstract:
Inhibiting the formation of ice is an essential process commercially, industrially, and medically. Compounds that work to stop the formation of ice have historically possessed drawbacks such as toxicity or prohibitively high active concentrations. One class of molecules, ice recrystallization inhibitors, work to reduce the damage caused by the combination of small ice crystals into larger ones. Recent advances made by the Ben lab have identified small molecule carbohydrate analogues that are highly active in the field of ice recrystallization and have potential in the cryopreservation of living tissue.
A similar class of molecules, kinetic hydrate inhibitors, work to prevent the formation of another type of ice – gas hydrate. Gas hydrates are formed by the encapsulation of a molecule of a hydrocarbon inside a growing ice crystal. These compounds become problematic in high pressure and low temperature areas where methane is present - such as an oil pipeline.
A recent study has highlighted the effects of antifreeze glycoprotein, a biological ice recrystallization inhibitor, in the inhibition of methane clathrates. Connecting these two fields through the synthesis and testing of small molecule ice recrystallization inhibitors in the inhibition of methane hydrates is unprecedented and may lead to a novel class of compounds.
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Go, Johnson. "Modelling the interaction between recovery, recrystallization and precipitation in AA6111." Thesis, University of British Columbia, 2006. http://hdl.handle.net/2429/30874.
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The present work investigates the evolution of microstructure during the annealing of an
industrial precipitation hardened aluminum alloy AA6111. Special emphasis is placed on
understanding the interaction between recovery, recrystallization and precipitation through a
combination of experimental and modelling approaches. Experimentally, extensive heat
treatments were carried out to study the effect of varying initial precipitate conditions on the
isothermal annealing behaviour of the alloy in the temperature range of 250-445°C. A total of
four prior aging conditions were considered: naturally aged (T4), peak aged (PA), overaged
(OA) and severely overaged (SOA). It was found that recrystallization was severely retarded
at the annealing temperature of 325°C irrespective of prior precipitate conditions. Microscopic
evidence confirmed that the growth of recrystallizing grains is directly related to the non-uniform
spatial distribution of precipitates. Subsequently, a new microstructure model was
developed to link the changes in the microstructure to the mechanical properties of the alloys.
The model which was developed based on the internal state variable approach is capable of
translating quantitatively the interaction between recovery, subgrain growth, recrystallization
and precipitation into a yield stress vs. time relationship. The effect of non-uniform
distribution of precipitates was considered explicitly by using a simple rule of mixtures. The
validity of the model was verified by comparing the model calculations to the experimental
data obtained from overaged 40% cold rolled AA6111.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Kieliba, Thomas. "Zone-melting recrystallization for crystalline silicon thin-film solar cells." Berlin dissertation.de, 2006. http://deposit.d-nb.de/cgi-bin/dokserv?id=2898611&prov=M&dok_var=1&dok_ext=htm.
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Favre, Julien. "Recrystallization of L-605 cobalt superalloy during hot-working process." Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00876664.
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Co-20Cr-15W-10Ni alloy (L-605) is a cobalt-based superalloy combining high strength with keeping high ductility, biocompatible and corrosion resistant. It has been used successfully for heart valves for its chemical inertia, and this alloy is a good candidate for stent elaboration. Control of grain size distribution can lead to significant improvement of mechanical properties: in one hand grain refinement enhance the material strength, and on the other hand large grains provide the ductility necessary to avoid the rupture in use. Therefore, tailoring the grain size distribution is a promising way to adapt the mechanical properties to the targeted applications. The grain size can be properly controlled by dynamic recrystallization during the forging process. Therefore, the comprehension of the recrystallization mechanism and its dependence on forging parameters is a key point of microstructure design approach. The optimal conditions for the occurrence of dynamic recrystallization are determined, and correlation between microstructure evolution and mechanical behavior is investigated. Compression tests are carried out at high-temperature on Thermec-master Z and Gleeble forging devices, followed by gas or water quench. Mechanical behavior of the material at high temperature is analyzed in detail, and innovative methods are proposed to determine the metallurgical mechanisms at stake during the deformation process. Mechanical properties of the material after hot-working and annealing treatments are investigated. The grain growth kinetics of L-605 alloy is determined, and experimental results are compared with the static recrystallization process. Microstructures after hot deformation are evaluated using SEM-EBSD and TEM. Significant grain refinement occurs by dynamic recrystallization for high temperature and low strain rate (T≥1100 ◦ C, strain rate < 0.1s−1), and at high strain rate (strain rate > 10s−1). Dynamic recrystallization is discontinuous and takes place from the grain boundaries, leading to a necklace structure. The nucleation mechanism is most likely to be bulging from grain boundaries and twin boundaries. A new insight of the modeling of dynamic recrystallization taking as a starting point the experimental data is proposed. By combining the results from the mechanical behavior study and microstructure observation, the recrystallization at steady-state is thoroughly analyzed and provides the mobility of grain boundaries. The nucleation criterion for the bulging from grain boundaries is reformulated to a more general expression suitable for any initial grain size. Nucleation frequency can be deduced from experimental data at steady-state through modeling, and is extrapolated to any deformation condition. From this point, a complete analytical model of the dynamic recrystallization is established, and provides a fair prediction on the mechanical behavior and the microstructure evolution during the hot-working process.
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Kaale, Lilian Daniel. "Modelling and ice crystallization/recrystallization of foods in superchilling technology." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-24202.
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The superchilling process is defined as a method of preserving food by partial ice-crystallization. The product quality of superchilled food is very promising, and has nearly the same sensorial attributes and nutritional value as the original product. However, more research is required to make the technology more suitable to the preservation of food. The optimal degree of superchilling and information on the development of the ice crystals during the superchilling process and storage are needed because of their large influence on the quality of the final superchilled food. The main objective of this thesis was modelling and studying of ice crystallization/recrystallization of food during the superchilling process and storage. In order to fulfil the objective the following research activities have been carried out: A one-dimensional model for predicting partial freezing time necessary to achieve an optimal degree of superchilling in foods was developed. The degree of superchilling is the amount of free water frozen (5 -30%) inside the food and is among the most important parameters which influence the quality of superchilled product. The study of the ice crystallization/recrystallization of food in superchilling technology was studied based on the superchilling rate, and the state of food muscle. The relationship between the development of ice crystals in salmon and quality parameters during the superchilled storage was also studied. The final research activity in this thesis was to study differences in the superchilling storage methods, shell freezing and non- shell freezing. The developed model was sufficient to study the thermal behaviour of food, and had the advantage that it was simple, very fast and detailed enough to estimate the superchilling time and behaviour of food. The model was validated experimentally using salmon, and there was good agreement between the numerical and experimental results. Further study to quantify the model using other food products is recommended. The characteristics of ice crystals have a large influence on the quality of the final superchilled food. At a high superchilling rate (227 W/m2.K, -30 ℃ and 2.1 min), smaller and well distributed ice crystals within and outside the cell were formed compared to a slow superchilling rate (153 W/m2.K, - 20 ℃ and 4.2 min), where larger and extra-cellular ice crystals were formed. The state of muscle also has an influence on the characteristics of ice crystals. In pre-rigor muscle, the ice crystals were formed inside the cells regardless of the superchilling rate. However, at a slow superchilling rate the ice crystal size was larger than at a high superchilling rate. The formation of the ice crystals inside the cells, regardless of the superchilling rates, is the most important factor for reducing the damage of food muscles and hence maintaining the quality. New information was discovered in this work on the development of ice crystals during the superchilling process and storage of salmon. There was a significant increase in ice crystal size between the superchilling process (day 0) and superchilled storage (after 1 day of storage). The ice crystals formed in the surface layer were 4 times larger after only 1 day of storage than those formed at day 0. Prior to temperature equalisation, ice crystals growth progressed from the surface to the centre of the superchilled food. Different layers with different sizes of ice crystals within the superchilled salmon were also observed. This was due to thermal behaviour within the superchilled sample, and because we have both ice at the surface and water at the centre, the diffusion process should occur. The recrystallization at this time (between day 0 and 1) is unavoidable however, after temperature equalization (after 1 day of storage) and control of temperature during storage there was no significant growth of ice crystals for the entire storage time. The development of ice crystals in red salmon muscle was also studied during the superchilling process and storage. The size of the ice crystals formed in the red salmon muscle was smaller than those formed in the white salmon muscle. In addition, the ice crystals formed in the pre-rigor red muscle was smaller than that formed in the post-rigor red salmon muscle. These findings are significant for the industry because small ice crystals indicate better quality. Quality changes have been studied with a focus on physical measurements, water holding capacity (WHC) and drip loss. The disappearance of liquid water is a major factor affecting the protein changes during superchilled storage. It was observed that the drip loss was lower in superchilled salmon compared to conventional chilled salmon, and frozen salmon between 1 and 14 days of storage. No significant differences were found in WHC and drip loss between 1 and 14 days of storage in superchilled salmon. The two superchilling storage methods showed differences in the development of ice crystals within the superchilled salmon. In non-shell frozen samples, the ice crystals were mainly formed in the extracellular spaces. Fine and well distributed ice crystals were formed in both the intracellular and extracellular spaces in shell frozen samples. Generally, the results found in this study have given more information in the superchilling area. The developed model which can be scaled-up to the industrial level, together with information on the development of the ice crystals, which has a large influence on the quality of the final superchilled food are useful for the industry in estimating the refrigeration requirements for a superchilling system and designing the necessary equipment. In addition, the quality study revealed that the superchilling is practicable if the product is partially freezing fast, with an optimal degree of superchilling (5 - 30 %), good packaging and a strict control of the temperature during superchilled storage.
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Nilsson, Robin. "Experimental Methodologies for Analyzing Austenite Recrystallization in Martensitic Tool Steels." Thesis, KTH, Materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176091.
Full textAbstract:
Revealing the prior austenite grain boundaries from a martensitic structure is well known to be very difficult and dependent on the chemical composition and the thermomechanical processing of the steel. In the present study, four different chemical etching reagents and additional thermal etching have been conducted for thermomechanical simulated tool steels Orvar Supreme and Stavax ESR. The etching results have been characterized using light optical microscopy and electron backscattered diffraction. The obtained results show that saturated aqueous picric acid, oxalic and sodium bisulfite based acid reveals prior austenite grain boundaries well for Orvar Supreme. For Stavax ESR, only aqueous CrO3-NaOH-picric acid provides good results in revealing the prior austenite grain boundaries. Thermal etching shows good potential and if conducted properly, thermal etching is a good alternative to the chemical reagents from a health- and environmental perspective.
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Deller, Robert C. "The investigation and application of ice recrystallization inhibitors as cryoprotectants." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/61919/.
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There is a continuing need for improvements in the cryopreservation of clinically relevant cells, tissues and organs as advances in transplantation science and regenerative medicine rise alongside an aging populace that intensifies demand. Antifreeze (glyco)proteins (AF(G)Ps) and antifreeze proteins (AFPs) are classes of proteins found in cold acclimatized species. Ice recrystallization is a highly damaging process that occurs upon the thawing of frozen specimens with AF(G)Ps and AFPs limiting this effect in a process termed ice recrystallization inhibition (IRI). However AF(G)Ps and AFPs largely fail to improve in vitro and ex vivo cryopreservation due to their secondary property of dynamic ice shaping. The biocompatible and synthetically accessible polymer poly(vinyl alcohol) (PVA) has been shown to process a strong IRI activity. The IRI property of PVA along with numerous other polymers and polyols is investigated to highlight the uniqueness of PVA (Chapter 2). PVA is then explored as a cryoprotectant with red blood cells (Chapter 3), immortalized mammalian cell lines (Chapter 4) and primary cells (Chapter 5) with a significant advantageous effect observed with each cell type in terms of the number of cells recovered post thaw. However, this is despite the use of proportionately low concentrations of PVA compared to traditional membrane permeable cryoprotectants. The application of PVA as a cryoadjuvant could therefore improve the cryopreservation of cells, tissues and organs resulting in widespread clinical benefits.
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Clinch, Michael. "The thermomechanical processing of aluminium alloys for high pressure gas cylinders." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326551.
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Lam, Kai-tung George. "A novel thermomechanical treatment process for enhancing gamma fibre texture recrystallisation components." Click to view the E-thesis via HKUTO, 2002. http://sunzi.lib.hku.hk/hkuto/record/B42576507.
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Lissel, Linda. "Modeling the microstructural evolution during hot working of C-Mn and Nb microalloyed steels using a physically based model." Licentiate thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4118.
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Bäcke, Linda. "Modeling the Microstructural Evolution during Hot Deformation of Microalloyed Steels." Doctoral thesis, KTH, Materialvetenskap, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10390.
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This thesis contains the development of a physically-based model describing the microstructural evolution during hot deformation of microalloyed steels. The work is mainly focused on the recrystallization kinetics. During hot rolling, the repeated deformation and recrystallization provides progressively refined recrystallized grains. Also, recrystallization enables the material to be deformed more easily and knowledge of the recrystallization kinetics is important in order to predict the required roll forces. Hot strip rolling is generally conducted in a reversing roughing mill followed by a continuous finishing mill. During rolling in the roughing mill the temperature is high and complete recrystallization should occur between passes. In the finishing mill the temperature is lower which means slower recrystallization kinetics and partial or no recrystallization often occurs. If microalloying elements such as Nb, Ti or V are present, the recrystallization can be further retarded by either solute drag or particle pinning. When recrystallization is completely retarded and strain is accumulated between passes, the austenite grains will be severely deformed, i.e. pancaking occurs. Pancaking of the grains provides larger amount of nucleation sites for ferrite grains upon transformation and hence a finer ferrite grain size is achieved. In this work a physically-based model has been used to describe the microstructural evolution of austenite. The model is built-up by several sub-models describing dislocation density evolution, recrystallization, grain growth and precipitation. It is based on dislocation density theory where the generated dislocations during deformation provide the driving force for recrystallization. In the model, subgrains act as nuclei for recrystallization and the condition for recrystallization to start is that the subgrains reach a critical size and configuration. The retarding effect due to elements in solution and as precipitated particles is accounted for in the model. To verify and validate the model axisymmetric compression tests combined with relaxation were modeled and the results were compared with experimental data. The precipitation sub-model was verified by the use of literature data. In addition, rolling in the hot strip mill was modeled using process data from the hot strip mill at SSAB Strip Products Division. The materials investigated were plain C-Mn steels and Nb microalloyed steels. The results from the model show good agreement with measured data.QC 20100706
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Li, Jian. "Near-surface microtextural evolution during deformation and its effect on recrystallization." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq20570.pdf.
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Bocher, Philippe. "Dynamic recrystallization in a 304 stainless steel : microtexture measurements and models." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0027/NQ50116.pdf.
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Riddle, Yancy Willard. "Control of recrystallization in Al-Mg alloys using Sc and Zr." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/20127.
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Wang, Ganlin. "Effect of aluminum on recrystallization and precipitation of Nb HSLA steels." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65336.
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Simielli, Eider Alberto. "Deformation and recrystallization kinetics of microalloyed steels in the intercritical region." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74539.
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Three microalloyed steels were tested under continuous and interrupted loading conditions. These materials consisted of a base steel containing 0.06%C and 1.31%Mn and two further alloys containing single additions of 0.29%Mo and 0.04%Nb.Double hit compression tests were performed on cylindrical specimens of the three steels at 820, 780 and 740$ sp circ$C within the $ alpha$ + $ gamma$ field. A softening curve was determined at each temperature using the offset method. It was observed that, in the base steel, $ alpha$ recrystallizes more slowly than $ gamma$. The addition of Mo steel retards the recrystallization of the base material; it has a greater influence on $ gamma$ than on $ alpha$ recrystallization. Nb addition has an even greater effect on the recrystallization of the two phases. In this steel, the recrystallization of ferrite was incomplete at the three intercritical temperatures. Furthermore, the austenite remained completely unrecrystallized up to the maximum time involved in the experiments (1 hr).
The progress of ferrite recrystallization was followed on quenched specimens of the three steels by means of quantitative metallography. Most of the data fit an Avrami equation with exponents in the range 2 to 2.5. A departure from this equation was observed for the final stages of the recrystallization process. Growth rate analysis showed that the average growth rate decreased with time for all the experimental materials, this decrease being greatest for the base steel and least for the Nb-containing grade. The nucleation of recrystallization was observed to occur heterogeneously in the microstructure. The interface between ferrite and austenite was the preferred site for nucleation. Measurement of the number and size of recrystallized ferrite grains showed that some grains begin to recrystallize very early, growing to a large size by the end of the process. The total number of grains increased continuously until almost 80% of the volume fraction was recrystallized. After that, due to coalescence, the number of recrystallized grains decreased very rapidly. (Abstract shortened by UMI.)
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Zissis, Nikolaos. "Design and study of an electron beam system for silicon recrystallization." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241194.
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Sallez, Nicolas. "Recrystallization, abnormal grain growth and ultrafine microstructure of ODS ferritic steels." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI075/document.
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Les alliages ODS (Oxides Dispersion Strengthened), sont principalement étudiés pour leur capacité à répondre favorablement au cahier des charges de la fonction de gainage combustible pour les réacteurs nucléaire de type RNR-Na (Réacteur à Neutrons Rapides à caloporteur sodium). Elaborés par métallurgie des poudres, mécanosynthèse puis extrusion, ils affichent des propriétés mécaniques, et notamment en fluage, extrêmement intéressantes. Néanmoins, la voie élaboration utilisée induit une forte anisotropie microstructurale. Cette anisotropie se retrouve au niveau de leurs propriétés mécaniques et conduit à une fragilité dans le sens de sollicitation transverse. Le but de cette thèse est d'étudier l'évolution microstructurale de ces matériaux. Les aciers ODS présentent des microstructures ultra fines en termes de grains, de précipités, et de formation d'amas qui conduisent à de grandes difficultés pour en obtenir la recristallisation. De plus, les microstructures obtenues présentent souvent une recristallisation avec croissance anormale. De telles évolutions demandent des investigations à très fine échelle et ont été relativement peu examinées dans le domaine des alliages ODS. Il faut en effet être capable d'une étude structurale la plus quantitative possible de la microstructure des nanograins, ainsi que de la précipitation afin d'étudier les mécanismes d'interaction précipitation / joints de grain. Ceci n'est possible que par un couplage de différentes méthodes : la microscopie électronique en transmission (en particulier avec l'utilisation des outils récemment développés pour l'étude de la nanotexturation, i.e. ACOM-TEM); la diffusion centrale des neutrons ou des rayons X; et enfin la sonde atomique tomographique, à la fois pour apporter les informations sur la morphologie et la chimie des amas et nanoprécipités mais surtout sur la composition chimique aux joints de grains. A partir de l'identification des mécanismes contrôlant la croissance anormale, une modélisation permettant de prédire son apparition dans la microstructure est confrontée à cette caractérisation microstructurale poussée. Cette modélisation prête une attention particulière à la migration des joints de grains couplée à la diffusion et effets d'ancrage préférentiel des joints triples par les précipités ainsi qu'à l'énergie motrice stockée sous forme de densité de dislocationOxide Dispersion Steels (ODS) alloys are mainly studied for their ability to fulfil the technical specifications required for Sodium Fast Reactor (SFR) fuel cladding application. Their processing involves powder metallurgy, mechanical alloying and extrusion. Therefore, despite their interesting mechanical creep properties, the extrusion processing involves a high microstructural anisotropy. These particular feature leads to poor mechanical properties in the transverse direction which are worsen by the occurrence of abnormal grain growth. Unfortunately, since internal pressure increases in the tube with the accumulation of gas fission products, the major stress component is precisely applied in the transverse direction. As a result, the material faces a critical risk of failure and control of the microstructure is a key issue. The aim of this thesis is to study the microstructural evolution of ODS ferritic steels. ODS ferritic steels show ultrafine microstructures in terms both grains and precipitates which made the recrystallization very difficult and allow for abnormal grain growth. To observe such evolutions, fine scale microstructure characterization are necessary. This is only possible by coupling different characterization methods: transmission electronic microscopy (in particular with the new developed tools for nanotexturation studies, i.e. ACOM-TEM); neutron and X-ray small angle scattering; and atomic probe tomography. Based on the mechanisms that lead to and control the abnormal grain growth, a model to predict the occurrence of abnormal grain growth is confronted to the experimental results. This model that takes a particular attention to the dislocation stored energy effect to adequately reproduce the observed characterization results
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Lienshöft, Laura, Paul Chekhonin, Dana Zöllner, Juliane Scharnweber, Tom Marr, Tina Krauter, Heinz Werner Hoeppel, and Werner Skrotzki. "Static recrystallization and grain growth of accumulative roll bonded aluminum laminates." Cambridge University Press, 2017. https://tud.qucosa.de/id/qucosa%3A70745.
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Aluminum laminates of high and technical purity layers were produced by accumulative roll bonding (ARB) at room temperature. To study the thermal stability, the laminates after 2 to 9 ARB cycles were annealed between 100 and 400 °C for one hour. Changes of the microstructure were analyzed by electron backscatter diffraction. For low ARB cycle numbers (4 or below) and 300 °C annealing temperature, the deformed technical pure layers start to recrystallize while the high-purity coarse recrystallized layers experience intralayer grain growth. For higher ARB cycle numbers (6 and 8) and an annealing temperature of 300 °C or above, the ultra-fine grained layers of technical purity are consumed by the layer overlapping growth of high-purity grains producing a banded grain structure. For 9 ARB cycles and at an annealing temperature of 400 °C, a globular grain structure develops with grain sizes larger than twice the layer thickness. The effect of impurities on recrystallization and grain growth of ARB laminates is discussed with regard to tailoring its microstructure by heat treatment. For further analyses, the results are compared with Potts model simulations finding a rather good qualitative agreement with the experimental data albeit some simplified model assumptions.
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Huhmann, Brittany. "Influence of As(V) on Fe(II)-catalyzed Fe oxide recrystallization." Thesis, University of Iowa, 2013. https://ir.uiowa.edu/etd/2525.
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Human exposure to arsenic in groundwater is a global concern, and arsenic mobility in groundwater is often controlled by Fe mineral dissolution and precipitation. Additionally, Fe(II)-catalyzed recrystallization of Fe oxides has been shown to enable trace element release from and incorporation into Fe oxides. However, the effect of As(V) on the Fe(II)-catalyzed recrystallization of Fe oxides such as goethite, magnetite, and ferrihydrite remains unclear. Here, we measured the extent of Fe atom exchange between aqueous Fe(II) and magnetite, goethite, or ferrihydrite in the presence of As(V) by reacting isotopically "normal" Fe oxides with 57Fe-enriched aqueous Fe(II). At lower levels of adsorption (≤13.3 μM), As(V) had little influence on the rate or extent of Fe(II)-catalyzed Fe atom exchange in goethite or magnetite. However, Fe atom exchange was increasingly inhibited as As(V) concentration increased above 100 μM. Additionally, adsorbed As(V) may be incorporated into magnetite over time in the presence and absence of added aqueous Fe(II) as indicated by X-ray absorption spectroscopy (XAS) and chemical extraction data, with more rapid incorporation in the absence of added Fe(II). XAS and chemical extraction data are also consistent with the incorporation of As(V) during goethite and magnetite precipitation. Additionally, atom exchange data indicated that low levels of As(V) coprecipitation (As:Fe = 0.0005-0.0155) had little influence on the rate or extent of Fe(II)-catalyzed Fe atom exchange in goethite or magnetite. Atom exchange data indicated that ferrihydrite likely transforms via a dissolution-reprecipitation mechanism both to lepidocrocite at 0.2 mM Fe(II) and to magnetite at 5 mM Fe(II). The presence of 206 μM As(V) slowed the transformation of ferrihydrite to more crystalline iron minerals and slowed the rate of atom exchange between aqueous Fe(II) and ferrihydrite. However, the degree of atom exchange did not directly correlate with the amount of ferrihydrite transformed. In summary, Fe oxide recrystallization processes may affect As(V) uptake and release in the environment, and As(V) may inhibit Fe(II)-catalyzed Fe oxide recrystallization.
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ALMEIDA, FILHO AMERICO de. "Elaboração e estudos de recristalização de ligas alumínio-magnésio-tório e alumínio-magnésio-nióbio." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11345.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Chang, Sin-ting Cynthia. "Randomization of recrystallization textures in an experimental Al-5%Mg alloy and AA6111." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36375561.
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Balcerzak, Anna. "Elucidating the Key Structural Features of Carbohydrates and Surfactants Necessary for Inhibiting Ice Recrystallization." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31768.
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Ice recrystallization during thawing after cryopreservation results in extensive cellular damage that ultimately leads to cell death and decreased cell viabilities. This is a significant problem particularly with cryopreserved cells utilized in various regenerative medicine therapies. Given the success of these therapies to treat spinal cord injury, cartilage lesions, and cardiacdisease, the development of new and improved cryprotectants that minimize cell damageduring freeze-thawing and improve cell viability post-cryopreservation are urgently required. The current cryopreservative dimethyl sulfoxide, DMSO, is associated with cytotoxicity in clinical settings and is not an optimal cryopreservative.
Our laboratory is interested in synthesizing small molecules that possess the property of ice recrystallization inhibition (IRI) activity that can be utilized as cryopreservatives without the cytotoxic effects associated with DMSO. This thesis focuses on the development of small molecule ice recrystallization inhibitors and elucidating the structural features of disaccharides and surfactants that are responsible for potent IRI activity.
The first part of this study examines simple disaccharide derivatives mimicking those found in the native AFGP to determine whether disaccharide structure influences IRI activity. Towards this end, the (1,6)-linked AFGP disaccharide analogue was synthesized, assessed for IRI activity using a splat-cooling assay, and compared to the native (1,3)- and (1,4)-linked AFGP disaccharide analogues. The change in linkage was found to have a profound affect on IRI activity.
The second part of the study focuses on surfactants and gelators as ice recrystallization inhibitors. Our laboratory has demonstrated that carbohydrate-based hydrogelators can be potent inhibitors of ice recrystallization. While our studies have indicated that a delicate balance between hydrophobic and hydrophilic interactions is crucial for ice recrystallization inhibition (IRI) activity, the essential structural features necessary for potent IRI activity remain unknown. To address this issue, structurally diverse amino acid-based surfactants/gelators, anti-ice nucleating agents, and glycoconjugates were synthesized and assessed for IRI activity. The results indicate that long alkyl chains and increased hydrophobicity are important for potent IRI activity and
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that the position of these alkyl chains is essential. Also, the counterion of these compounds affects the IRI activity and is related to the counterion degree of hydration. These compounds were assessed for their ability to cryopreserve human liver cells (Hep G2) and human bone marrow cells (Tf-1α) in cell-based assays. Additionally, the best IRI assay solution was determined, which involved studying how the salts of the phosphate buffered saline (PBS) solution modulated IRI activity.
Finally, small molecule ice recrystallization inhibitors were assessed for their ability to protect the viral vectors vaccinia virus, vesicular stomatitis virus, and herpes simplex-1 virus at various storage conditions. This will aid in developing improved preservation protocols for vaccines and viruses utilized in cancer therapy (oncolytic viruses).
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Briard, Jennie Grace. "The Rational Design and Use of Novel Small-Molecule Ice Recrystallization Inhibitors for the Cryopreservation of Hematopoietic Stem Cells and Red Blood Cells." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35005.
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Over the past few decades, there has been an increase in the development of new cellular therapies used for the treatment of various conditions. Thus, the rapid development of therapies requiring transfusion and transplantation of cells has resulted in a need to preserve these cellular therapy products. Cryopreservation is the only currently used method for the long-term storage of cells. The most commonly used cryoprotectants are 10% dimethyl sulfoxide (DMSO) for hematopoietic stem cells (HSCs) and 40% glycerol for red blood cells (RBCs). DMSO fails to protect the functionality of HSCs after cryopreservation and therefore, up to 20% of HSC transplantations fail to engraft. The glycerol in thawed RBC units must be removed to <1% to prevent intravascular hemolysis which is time-consuming. Thus, there is an urgent need to develop improved cryoprotectants for HSCs and RBCs.
DMSO and glycerol are unable to control ice recrystallization which is a major source of cellular injury during cryopreservation. Therefore, compounds with the ability to inhibit ice recrystallization could represent a new class of cryoprotectant with a novel mechanism of action.
This thesis focuses on the rational design of small-molecule ice recrystallization inhibitors. The key structural attributes required for ice recrystallization inhibition (IRI) activity are investigated. The amphiphilic balance required for IRI activity is explored. Furthermore, two new classes of small-molecule IRIs containing aromatic rings were rationally designed. As a result, several very highly IRI active molecules were discovered.
The use of IRIs to improve the cryopreservation of HSCs and RBCs was explored. A number of IRIs improved the post-thaw functionality of HSCs. Supplementation of the current cryoprotectant solution with IRIs resulted in an increase in CFU recovery and frequency of multipotent progenitors. This would reduce the percentage of engraftment failure and allow for a larger proportion of cord blood banks’ inventory to provide an adequate dose for patients requiring transplants. Several IRIs were found to be effective cryoprotectants for RBCs with reduced amounts of glycerol. This could reduce the deglycerolization time for RBCs. These results demonstrate the potential of small-molecule IRIs to improve the current cryopreservation procedures for important cellular therapy products.
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Timans, P. J. "Time resolved reflectivity studies of electron beam processing of semiconductors." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234108.
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This work describes methods for making dynamic observations of the effects of electron beam heating, in a range of applications to semiconductors. The studies were based on the use of the time resolved reflectivity (TRR) method, in which the reflectivity of the specimens surface is measured during the heating cycle. The best experimental conditions for this technique have been identified and several applications are described in detail. Studies were made of epitaxial regrowth of amorphous layers created by ion implantation into silicon. The TRR method was applied using red and infra-red wavelengths, to characterize the regrowth kinetics, paying special attention to the influence of electrically active dopants. The results demonstrate that doping has a large effect on the regrowth process, for reasons which are related to both electrical and structural factors. The use of isothermal electron beam heating for annealing silicon-on-sapphire (SOS) specimens was investigated. In these studies, the TRR technique was applied to measurement of the temperature of the specimens and to observation of epitaxial recrystallization of amorphous layers created by self-implantation. In SOS films the amorphous layers could be at the surface or buried beneath a thin single crystal layer, and these cases resulted in different regrowth behaviour. TRR methods using green and red probe wavelengths proved to be sensitive to the type of crystallization, as well as the rate at which it occurs. They should also help to identify the best conditions for improvement of the crystal quality of SOS films. TRR was also used to examine heating of silicon-on-insulator materials by swept line electron beams. Temperature distributions were evaluated by measuring the reflectivity of a small area as the electron beam passed through it and the effects of various changes in the heating conditions were explored. Studies were made of zone melting recrystallization by observing the abrupt reflectivity changes which occur when silicon melts or freezes. In future work, TRR techniques could be developed to allow detailed investigation of the recrystallization process in structures intended for seeded recrystallization.
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Chang, Sin-ting Cynthia, and 張倩婷. "Randomization of recrystallization textures in an experimental Al-5%Mgalloy and AA6111." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36375561.
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林繼棟 and Kai-tung George Lam. "A novel thermomechanical treatment process for enhancing gamma fibre texture recrystallisation components." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B42576507.
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