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1
Liu, Juan. "Influence of grain size, morphology and aggregation on galena dissolution." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/26202.
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The acidic, non-oxidative dissolution of galena nanocrystals has been studied using both microscopic and wet-chemical methods. The effects of particle size, shape, aggregation state, and grain proximity on dissolution rates were investigated. Nearly monodisperse galena nanocrystals with an average diameter of 14.4 nm and a truncated cubic shape were synthesized. In the dissolution experiments of dispersed nanocrystals, galena nanocrystals attached on the surface of a TEM grid were exposed to deoxygenated HCl solutions (pH 3) at 25 °C. Capping groups on nanocrystals were removed via a washing process, and chemistry of nanocrystals was examined using X-ray photoelectron spectroscopy (XPS). The evolution of the size and shape of the pre- and post-dissolution nanocrystals were studied using transmission electron microscopy (TEM), and the dissolution rate was calculated directly according to the size shrinking of galena nanocrystals. To assess the size effect, galena microcrystals (~ 3 μm) were synthesized and dissolved under similar conditions to the dispersed nanocrystals. The results showed that the nanocrystals dissolved at a surface area normalized rate of one order of magnitude faster than the microcrystals. In addition, dissolution rate is orientationdependent on a single nanocrystal. High-resolution TEM (HRTEM) images indicated the {111} and {110} faces dissolve faster than {100} faces on galena nanocrystals,
rationalized by the average coordination number of ions on each of these faces. To assess the aggregation effect, dissolution experiments of aggregated galena nanocrystals were conducted using a wet-chemical method, and the results were compared with the rates of microcrystals and dispersed nanocrystals. These experiments showed that the rate of aggregated nanocrystals is in the same order of magnitude as the rate of microcrystals, but one order of magnitude smaller than that of dispersed nanocrystals. Finally, the effect of the close proximity between nanocrystals on dissolution was observed by HRTEM.
Dissolution was greatly inhibited on nanocrystal surfaces that were closely adjacent (1-2nm, or less) to other nanocrystals, which is probably relevant to the slow dissolution of aggregated nanocrystals. The dissolution phenomena of galena nanocrystals observed in this study is likely important for understanding the environmental fate and behavior of nanoparticles in aquatic systems.Ph. D.
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Moiz, Muhammad. "The influence of grain size on mechanical properties of Inconel 718." Thesis, Linköpings universitet, Konstruktionsmaterial, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-113148.
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The thesis work discuss about how the materials mechanical properties are influenced by the microstructure. The most common way of altering the microstructure of the material is by heat treatment.The mechanical properties that are of interest are strength, toughness, ductility, creep and fatigue. The material under consideration iswidely used superalloy In718. Two different sets of specimens areheat treated at different temperatures and influence of heat treatmenton the grain size is analyzed. In order to get better understanding ofthe grain size on mechanical properties, microstructural investigation was done using SEM. Efforts are made to understand the influence of different elements on the overall characteristic of the material. The tensile, creep and stress relaxation tests were conducted and the results were discussed.Master Thesis
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Gullberg, Daniel. "Influence of composition, grain size and manufacture process on the anisotropy of tube materials." Thesis, Uppsala University, Department of Engineering Sciences, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-125336.
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A problem with cold pilgered tubes for OCTG applications is that they can get anisotropic properties with regard to yield strength. One source of anisotropy is texture that is developed during the cold deformation. EBSD measurements have been made on several austenitic stainless steels with different deformations to see what influence the composition has on the texture formation. The same measurements were used to study the influence of grain size on texture formation. The conclusion was that the composition can have an impact on the texture and hence has potential to also affect the anisotropy. The differences in texture cannot be associated with a specific alloying element, but is rather a synergetic effect. It was also concluded that grain structure has no strong influence on texture formation. An evaluation of three different tool designs used for cold pilgering was made. The designs evaluated are referred to as design A, B and C. EBSD measurements showed large deviations in texture in the middle of the wall compared to close to the surface of pilgered OCTG. However, the measurements showed no large differences between the three designs and the texture could not be coupled to the anisotropy.
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Cain, Victoria. "Influence of grain size and niobium content on the creep resistance of ferritic stainless steels." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/5563.
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Includes abstract.Includes bibliographical references (leaves 98-102).
Type 441 ferritic stainless steel is used for the production of catalytic converter housings. As the housing is subjected to high temperatures it is necessary that the material offers creep resistance. Type 441 is dual stabilised with Ti and Nb to provide improved weldability; however, Nb addition also enhances the hot strength and creep resistance by means of precipitation and solid solution strengthening. Notwithstanding the Nb strengthening effect, the strong dependence of creep resistance on grain size also means that the relationship between creep resistance and Nb content may be complicated by grain growth inhibition that arises from aspects of solute drag and grain boundary pinning. Thus it may not be simple to predict the relative creep resistance of standard production heats on the basis of Nb level alone and other factors affecting solid solution and grain size also need to be taken into account. Consequently, it is pertinent to evaluate more closely the sensitivity of these parameters in influencing creep resistance by choosing two alloy heats with different Nb contents and subjecting them to a range in heat treatments that will modify solute level and grain size. This thesis reports on the examination of the dependence of creep resistance on Nb level by eliminating the influence of grain size. The latter was achieved by manipulating the post-cold roll recrystallisation temperature in such a way that equivalent grain sizes were produced in two alloy heats with Nb levels of 0.46 and 0.74 wt.% respectively. Although the grain size was essentially stabilised by recrystallisation between 1050-1100 C for 30 minutes, the solution treatment prior to creep testing was varied for each heat to evaluate not only the influence of bulk Nb level on creep resistance, but also to consider the influence of the distribution of Nb in the microstructure. Consequently, the total heat treatment cycle prior to constant load creep testing at 850 C involved recrystallisation, ageing at 700 C, and final solution treatment at 950, 1000 or 1050 C for 200 seconds. The microstructure after the different heat treatments was investigated using light microscopy, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The latter was particularly useful in accurately measuring grain size. The microstructural evolution of both alloys during creep testing was also monitored. This was done in order to examine the microstructural changes that occur during the prolonged creep testing period. Not surprisingly, the creep tests at initial stresses of 5, 10 and 15 MPa all revealed greater creep resistance for the higher Nb-containing alloy heat. However, the correlation with solution treatment practice was much less obvious, particularly for the alloy with the lower Nb content. Detailed analysis of the precipitate distribution after the various heat treatments is presented to illustrate the difference in microstructure that can arise and consequently consideration is given to the influence of precipitation on creep behaviour.
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Waganaar, Spencer. "Influence of median grain size ratio on the strength and liquefaction potential of loose granular fills." Thesis, Florida Atlantic University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10172612.
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The characterization of silty soils is usually designated by the percentage of silt contained within the soil matrix, along with the soil’s void ratio, which is used to describe the soil’s current state. The use of these parameters to assess a soil’s strength and undrained behavior is limited when finer material is contained within the soil. Therefore, additional parameters must be considered in order to correctly assess the strength and liquefaction potential of silty soils. These additional parameters include the skeleton void ratio, equivalent void ratio and granulometric factors. The current research investigates the influence of granulometric parameters, specifically the Median Grain Size Ratio (D50/ d50), denoted as μDR (or MDR within graphs and charts), on the strength and liquefaction potential of loose silty sands. A series of undrained monotonic triaxial compression tests (σ3’= 69, 83, and 103 kPa) are performed on reconstituted soil samples, using three different base sand samples and a constant silt material. As a result, three distinct median grain size ratios (μDR = 4.2, 6.75, and 9) were tested with fines content ranging from 0-30% for each μDR. The undrained shear strength at all confining pressures tends to increase with in μDR; beyond 10% fines content there was no noticeable influence of μDR. At any μDR the excess PWP is higher than that of clean sand, when fines content is larger than 5% fines content. The slope of the instability line and phase transformation line are directly affected by the μDR and fines content, with an increase in the instability line and decrease in the phase transformation line with a growing μ DR. The results indicate loose granular fills can be designed to be stronger and more resilient under extreme conditions by careful choice of materials in which the μDR>6.75 and the fines content does not exceed 10%.
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Saadi, Yusron. "The influence of different time varying antecedent flows on the stability of mixed grain size deposits." Thesis, University of Sheffield, 2002. http://etheses.whiterose.ac.uk/12833/.
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The objective of this work was to examine the impact of unsteady flows on the erosion and movement of mixed grain size sediment. Time varying flows were examined as flowrates in natural rivers are rarely constant. There are very few reported studies on the movement of sediment in unsteady open channel flow and most of those used single sized sediment. River reach has its own sedimentological character and non-uniform beds exhibit very different behaviour from that of single sized material. Therefore it was thought important to examine the impact of time varying flow on the stability of water worked mixed grain size sediment beds. The thesis reports on a series of laboratory experiments in which a bimodal sediment bed was exposed to different flow hydrographs. The flow hydrographs consisted of constant flowrate with different duration and time varying flows with different rising and falling limb but had the same peak flowrate. Each experiment was followed by a stability test in which a standard "triangular shaped hydrograph" was used to assess the stability of each water worked deposit. The stability observation demonstrated that grain size fractions have different thresholds of motion when beds are formed by different antecedent flow patterns. The bed stability increased as the antecedent constant flow hydrograph progressed. The rising and falling limbs of the flowrate hydrographs were found to have a significant effect on the bed stabilisation process. It revealed that the shortest rising limb of flow hydrograph formed the weakest bed while the longest recession limb of flow hydro graph formed the most stable bed. It is believed that the short period of flowrate acceleration did not allow the coarse grains to stabilise with numerous exposed large grains spread on the bed. In a longer duration of recession limb of hydrograph, the coarse grains moved and eventually deposited over a length of time. As the flowrate declined the finer grains also rolled and then deposited forming a strong bond with the coarse grams. These experiments also provided important information on the flow structures and the changes in the bed topography as the tests progressed. There is strong evidence that only upward interactions (ejections) with high momentum magnitude were able to transport coarser grains. The lack of change in the distribution of downward looking-bed interactions (sweeps) in all tests indicated that these features are not important in determining transport. Changes in bed topography were also measured and characteristics of the distribution of bed surface elevation were linked to the observed changes in bed stability.
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Elsenbeck, James R. "Influence of grain size evolution and water content on the seismic structure of the oceanic upper mantle." Thesis, Online version of original thesis, 2007. http://hdl.handle.net/1912/1821.
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Zhemchuzhnikova, Daria. "Influence of the extreme grain size reduction on plastic deformation instability in an AlMg and AlMgScZr alloys." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0324/document.
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L'élaboration de nouveaux alliages maintient un fort intérêt pour le phénomène d’instabilité plastique, ou l'effet Portevin-Le Chatelier (PLC), provoqué par l'interaction des dislocations avec des atomes de soluté. Par ailleurs, l'effet PLC attire l'intérêt comme un exemple remarquable d'auto-organisation dans les systèmes dynamiques. Il est associé à des motifs complexes de séries de chutes de contrainte liées à la nucléation et au mouvement des bandes de déformation dans le matériau déformé, et nécessite une compréhension de l'auto-organisation des dislocations. La déformation plastique des alliages Al-Mg est sujette à l'instabilité dans une large gamme de conditions expérimentales. Pour cette raison, les alliages Al-Mg binaires ont longtemps servi d'objets modèles pour l'étude de l'effet PLC. En même temps, l'utilisation pratique des alliages binaires Al-Mg est limitée en raison d’une faible résistance mécanique. Une amélioration significative de leurs propriétés peut être atteinte en ajoutant des solutés supplémentaires, conduisant en particulier à la formation de précipités. En outre, une forte réduction de la taille de grains du polycristal pourrait être une technique clé pour produire des matériaux à haute résistance et ténacité. Cependant, il existe très peu d'information, souvent contradictoire, sur l'instabilité PLC dans les alliages Al-Mg à grains fins et contenant des précipités. Le but de l'étude de cette thèse a été d'étudier les caractéristiques spécifiques de l'effet PLC dans les alliages à base AlMg, avec et sans nanoparticules, à gros grains et à grains fins, ces derniers obtenus par une méthode de déformation plastique sévère. Grâce à l’application de méthodes d’extensométrie locale, notamment de la technique de corrélation d’images, ces études ont révélé une persistance non habituelle de la propagation des bandes de déformation dans les alliages comprenant des précipités et/ou des grains fins. Ce mode dynamique est observé dans un large intervalle de vitesses de déformation, tandis qu’il n’apparait qu’à haute vitesse dans des alliages modèles AlMg. Par ailleurs, l’analyse des distributions statistiques des amplitudes des chutes de contrainte a révélé une tendance vers une statistique en loi puissance, caractéristique du mode de propagation. Ce phénomène est attribué à une modification du couplage spatial entre les dislocations, due à la concentration de contraintes internes. La combinaison de ces études avec l’analyse de l’émission acoustique a mis en évidence une influence de la microstructure sur la compétition entre un facteur aléatoire et la synchronisation des dislocations. Enfin, l’étude par corrélation d’images a permis d’observer une interrelation entre l’instabilité PLC et la formation de la strictionThe elaboration of new alloys sustains a strong interest to the phenomenon of unstable plastic flow, or the Portevin–Le Chatelier (PLC) effect, caused by interaction of dislocations with solute atoms. Moreover, this effect attracts interest as a rich example of self-organization in dynamical systems. It is associated with complex patterns of stress serrations related to nucleation and motion of deformation bands in the deforming material, and requires understanding of self-organization of dislocations. Plastic deformation of Al-Mg alloys is prone to instability in a wide range of experimental conditions. For this reason, binary Al-Mg alloys served for a long time as model objects for investigation of the PLC effect. At the same time, the practical use of binary Al-Mg alloys is limited because of their low strength. A significant improvement of their properties can be achieved by additional alloying, in particular, leading to precipitation. Further, extensive grain refinement could be a key technique used to produce tough and high- strength materials. However, there exists very limited and often contradictory information on the PLC instability in fine-grained Al-Mg alloys containing precipitates. The objective of the present thesis was to investigate specific features of the PLC effect in AlMg-based alloys with and without nanoscale particles, both in coarse-grained and fine-grained states, the latter obtained by severe plastic deformation. Using local extensometry methods, particularly the image correlation technique, these studies revealed an unusual persistence of the propagation of deformation bands in alloys with precipitates and/or fine grains. This dynamic mode is observed in a wide range of strain rates, whereas it only appears at high strain rate in model Al-Mg alloys. Moreover, the analysis of statistical distributions of stress drop amplitudes revealed a tendency to power law statistics characteristic of the propagation mode. This phenomenon was attributed to a modification of the spatial coupling between dislocations due to the concentration of internal stresses. The combination of these studies with the acoustic emission analysis uncovered an influence of the microstructure on the competition between a random factor and the dislocation synchronization. Finally, the study by the image correlation made it possible to observe an interrelation between the PLC instability and the neck formation
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Härtel, Sebastian, Birgit Awiszus, Marcel Graf, Alexander Nitsche, Marcus Böhme, Martin F. X. Wagner, Hana Jirkova, and Bohuslav Masek. "Influence of Austenite Grain Size on Mechanical Properties after Quench and Partitioning Treatment of a 42SiCr Steel." MDPI AG, 2019. https://monarch.qucosa.de/id/qucosa%3A34779.
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This paper examines how the initial austenite grain size in quench and partitioning (Q-P) processes influences the final mechanical properties of Q-P steels. Differences in austenite grain size distribution may result, for example, from uneven heating rates of semi-finished products prior to a forging process. In order to quantify this influence, a carefully defined heat treatment of a cylindrical specimen made of the Q-P-capable 42SiCr steel was performed in a dilatometer. Different austenite grain sizes were adjusted by a pre-treatment before the actual Q-P process. The resulting mechanical properties were determined using the upsetting test and the corresponding microstructures were analyzed by scanning electron microscopy (SEM). These investigations show that a larger austenite grain size prior to Q-P processing leads to a slightly lower strength as well as to a coarser martensitic microstructure in the Q-P-treated material.
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Gaspar, Blake T. "Influence of Grain Size and Widmanstätten Colonies on Variability of Tensile Properties of Forged Ti-6Al-4V." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1196.
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When testing forgings for specifications, it was found that some parts did not meet the requirements for mechanical properties. This triggered an investigation into two of the parts from the lot that did not meet specification. The ultimate reason for failure was due to lower than necessary yield strength and ultimate tensile strength values, as well as unwanted variability between regions of the part. Therefore, samples of the regions were tensile tested to determine the differences that existed in yield strength, ultimate tensile strength, and elongation. After tensile testing, quantitative metallography and fractography were conducted to identify aspects of the microstructure and fracture surfaces that may have caused the variability. Three aspects of the microstructure that were identified as characteristics that may affect the mechanical properties were: grain size, Widmanstätten colony size, and volume fraction of the β phase. Based on measurements it was determined that a smaller Widmanstätten colony size found to be roughly 120 microns/colony was associated with a larger yield strength and UTS than larger colony sizes of roughly 170 microns/ colony. Grain size also played a role with smaller grain sizes of roughly 1550 microns/grain being associated with a higher yield strength and UTS than the larger grains of roughly 2000 microns/grain. Fractography also suggested that the presence of interlamellar decohesion and trans-lamellar failure may have created sites of further crack initiation, resulting in a lower ultimate tensile strength. These differences were theorized to be caused by a temperature gradient created during the heat treatment that created non-uniform cooling rates, resulting in the differences in microstructural characteristics.
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Witharamage, Chathuranga Sandamal. "The Influence of Ball Milling Time on Solid Solubility, Grain Size and Hardness of Al-V Alloys." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1596808089058447.
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Xu, Su. "The influence of grain size on creep and creep crack growth in Udimet 520, a forged nickel-base superalloy." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq33036.pdf.
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Fritz, Cortney M. "The Influence of Language Preference on Bilingual Children's Expressive and Receptive Vocabulary and Reading Ability." Digital Archive @ GSU, 2011. http://digitalarchive.gsu.edu/psych_theses/87.
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Given the increase of Spanish- and English-speaking bilingual students in US schools, identifying the predictors of reading in this group of students is of significant importance to developing appropriate screening measures and intervention strategies. Thus, the current study evaluated the pattern of language preference in an elementary school bilingual (Spanish-English) population and its relationship with expressive and receptive vocabulary, and broad reading ability in English and Spanish. Participants were 58 Latino students ranging in age from 7 years, 5 months to 11 years, 1 month (M = 8.98, SD = .98) with 48% born in the United States. Results indicated that English expressive vocabulary partially mediated the relationship between outside language preference and English broad reading ability. In contrast, neither Spanish expressive nor receptive vocabulary mediated the relationship between outside language preference and Spanish broad reading ability.
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Desnain, Philippe. "Influence de la convection sur la taille de grains de solidification d'alliages industriels d'aluminium." Grenoble INPG, 1989. https://hal.archives-ouvertes.fr/tel-01338778.
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Etude de la formation de la structure de grains lors de la solidification d'alliages industriels d'aluminium. Enregistrement des courbes de refroidissement et examen des phenomenes de recalescence lors de la solidification dans une lingotiere rectangulaire verticale munie d'un brasseur electromangetiques a champ glissant. Caracterisation des lingots et mesures de la taille des grains equiaxes. Modelisation de la nucleation et de la croissance des cristaux equiaxes. Influence du brassage et de la composition. Prevision a partir du modele etabli de l'affinement des grains resultant du brassage
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Ferry, Mark Peter. "An evaluation of the sedimentology and the influence of grain size and facies on permeability for the White Rose A-17 cored interval, White Rose Oilfield, offshore eastern Newfoundland /." Internet access available to MUN users only, 2005. http://collections.mun.ca/u?/theses,16593.
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SILVA, MARIA R. O. de O. da. "Influencia da microestrutura e composicao de alumina na termoluminescencia visando sua aplicacao em dosimetria." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10974.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Soares, Marcus [Verfasser], Günter [Akademischer Betreuer] Gunkel, Thomas [Akademischer Betreuer] Grischek, Martin [Akademischer Betreuer] Jekel, and Gunnar [Akademischer Betreuer] Nützmann. "The influence of high infiltration rates, suspended sediment concentration and sediment grain size on river and lake bed clogging / Marcus Soares. Gutachter: Martin Jekel ; Günter Gunkel ; Gunnar Nützmann ; Thomas Grischek. Betreuer: Günter Gunkel ; Thomas Grischek." Berlin : Technische Universität Berlin, 2015. http://d-nb.info/1070284408/34.
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Le, Marion. "Influence des liserés de carbures induits par la nitruration gazeuse sur les mécanismes de fissuration de fatigue de contacts roulants." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0102/document.
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La nitruration gazeuse est utilisée par les fabricants d’engrenages pour traiter la surface des dentures. En effet, l’augmentation de la dureté et l’introduction de contraintes résiduelles de compression contribuent à retarder voire inhiber l’initiation et la propagation des fissures superficielles de fatigue de contact. Cependant la majorité des aciers alliés présentent des réseaux de précipités de carbures dans la couche nitrurée. Ceux-ci ont la particularité de se retrouver aux joints de grains relativement parallèles à la surface, ce qui leurs ont attribué les surnoms de «liserés de carbures». Associés à une phase dure et fragile, ces carbures constituent des zones d’hétérogénéités. Par ailleurs, la norme pour la qualité des matériaux d’engrenages autorise une large gamme de tailles de grains, conduisant à diverses microstructures pour les couches nitrurées des aciers alliés. En effet, la morphologie des réseaux de carbures après nitruration dépend entre autres de la taille de grain de l’acier. De par le manque de travaux sur l’impact réel de ces précipités sur la fatigue de contact, la présente étude propose des analyses d’essais. Les essais consistent à reproduire de l’écaillage initié en surface sur des éprouvettes dont les couches nitrurées, issues d’un seul traitement thermochimique, présentent les mêmes propriétés mécaniques (dureté et contraintes résiduelles) mais différentes propriétés microstructurales (tailles de grains et morphologies de carbures). Les analyses ont permis de proposer des mécanismes d’initiation de micro-fissures induites en proche surface sous les conditions d’essai appliquées. Les sites d’initiation dépendent de la taille de grain de l’acier et peuvent en particulier s’établir au niveau des carbures intergranulaires. L’étude des réseaux de fissures couplée à l’analyse des contraintes résiduelles a permis d’établir des scénarii de propagation des fissures dans les couches nitrurées. Sous les conditions de contact appliquées, l’apparition de déformation plastique entraîne, par accommodation des variations de volume, la relaxation des contraintes résiduelles compressives initialement présentes dans le matériau, aux profondeurs les moins sollicitées. Ces contraintes étant moins compressives, elles libèrent les micro-fissures déjà présentes en proche surface. Dès lors, la propagation au travers des carbures qui s’apparentent à des sites privilégiés pour la croissance des fissures en cours de fatigue est possible. En particulier, ces précipités entraînent les fissures vers le cœur lorsqu’ils sont en forte densité dans les couches nitrurées, tandis que l’endommagement reste superficiel lorsque l’éloignement entre les précipités est trop important. Enfin, la continuité et la longueur des carbures augmentent localement la vitesse de propagation des fissures. Ceci se traduit par l’apparition plus rapide de l’écaillage initié en surface pour les couches nitrurées de microstructures grossièresGas nitriding is a thermochemical surface treatment widely used by gear manufacturers to improve the rolling contact fatigue endurance of their components. Indeed, increasing the hardness and introducing compressive residual stresses to the geartooth surfaces inhibit or delay crack initiation and propagation. However, most of the alloyed steel nitrided layers show the presence of intergranular carbide networks. The precipitation of these carbides specifically occurs at parallel grain boundaries during the treatment and, being a carbon-rich phase, they are associated to tough and fragile heterogeneities. Besides, standards for gear material quality recommend a broad range of steel grain sizes which lead to various possible microstructures on gear components after nitriding. Indeed, the intergranular carbide network morphology depends on the steel grain size. Since there is no evidence regarding the real effect of the carbides on rolling contact fatigue, this work presents experimental investigations carried out on a twin-disc machine. The tests consist in reproducing surface-initiated pitting on specimens whose nitrided layers, obtained by a unique thermochemical surface treatment, display similar mechanical properties (hardness and compressive residual stresses) but different microstructures (grain sizes and carbide network morphologies). The first analysis resulted in suggesting the micro-crack nucleation mechanisms. In this study, the test conditions were chosen to induce these micro-cracks near the disc surfaces. For a given contact stress field, nucleation sites depend on the steel grain size and can take place at intergranular carbides. Investigations of crack networks led on cross sections and 3D observations by means of high energy X-ray computed tomography, coupled with compressive residual stress evolution analysis, help the authors proposing the rolling contact fatigue crack propagation scenarios in nitrided layers. When contact shear stresses locally exceed the material micro-yield shear stress limit, micro-deformations arise and add compressive residual stresses to the treated layers. To accommodate these volume variations the compressive residual stresses, initially induced by nitriding, release at depths where contact stresses are lower. The pre-existing residual stresses being less compressive, micro-cracks near the surface can propagate through the carbides that act as preferential crack growth sites. When the nitrided layers display high carbide density, the intergranular precipitates drag the cracks toward the core, whereas rolling contact fatigue failures are limited to the near surface when the distance between the precipitates is too important. Finally, the length and the continuity of the carbides, linked to the steel grain size, locally increase the crack propagation speed. This gives rise to a lower endurance to surface-initiated pitting in coarse microstructures
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Hazan, Jérôme. "Etude de la durée de vie et de l'endommagement intergranulaire par fatigue des métaux cubiques à faces centrées : influence de la taille de grains et de l'épaisseur d'éprouvette." Thesis, Sorbonne université, 2019. https://accesdistant.sorbonne-universite.fr/login?url=http://theses-intra.upmc.fr/modules/resources/download/theses/2019SORUS564.pdf.
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La compréhension et la prédiction de l’endommagement par fatigue est un enjeu majeur dans la conception de l’échangeur de chaleur sodium-gaz de la prochaine génération de réacteurs nucléaire. Des essais cycliques à rupture ont été réalisés sur des éprouvettes en acier 316L à différentes épaisseurs, pour deux tailles de grains très différentes afin de quantifier l’influence de ces paramètres sur la durée de vie. Ensuite, des essais cycliques interrompus par des séances de microscopie (MEB) ont permis la compréhension des stades précoces de l'endommagement par fatigue induits par une forte taille de grains.Des simulations numériques par éléments finis de la déformation cyclique d’agrégats cristallins ont été réalisées avec le logiciel Cast3M. La localisation de la plasticité sous forme de bandes de glissement persistantes (BGPs) est considérée. L’accroissement de la concentration des lacunes au sein des BGPs induisant une dilatation de ces dernières est introduit. Des prédictions de l’évolution des extrusions formées au travers des joints impactés par les BGPs ainsi que les champs de contraintes associés ont été étudiées. L’ensemble de ces prédictions couplées à deux modèles d’endommagement ont permis la prédiction du nombre de cycles à initiation de microfissures intergranulaires. Finalement, des comparaisons entre mesures expérimentales et prédictions (i) des extrusions des BGPs au travers des joints de grains et (ii) du nombre de cycles à initiation des fissures sont réalisées. Les effets de matériau, de nature des joints de grains et de chargement sur les mécanismes d’initiation de fissures de fatigue sont finalement discutésUnderstanding and predicting the fatigue damage is a major issue in the design of the sodium-gas heat exchanger of the next generation of nuclear reactors.Cyclic tests were carried out on 316L SS specimens with different thicknesses, for two very different grain sizes, in order to quantify the influence of these parameters on the fatigue lifetime. Then, cyclic tests interrupted by microscopy observations (SEM) allowed the understanding of the early stages of fatigue damage induced by a large grain size specimen. Finite element simulations of the cyclic deformation of crystalline aggregates were performed with the Cast3M software. The localization of plasticity in the form of persistent slip bands (PSBs) is considered. The increase of the vacancy concentration in the PSBs, leading to their dilatation is introduced. Predictions of the PSB extrusion through impinged GBs and of the associated stress fields were studied. All these predictions, coupled with two damage models, made possible to predict the number of cycles to intergranular microcrack initiation. Finally, comparisons between experimental measurements and predictions of (i) the PSB extrusion through GBs and (ii) the number of cycles to microcrack initiation are made. The effects of material, nature of GBs and loading conditions on fatigue crack initiation mechanisms are finally discussed
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Hadj, Romdhane Youssef. "Hydrogenolyse du n-butane sur des catalyseurs modeles au nickel : influence du facteur electronique." Paris 6, 1986. http://www.theses.fr/1986PA066556.
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Benmessaoud, Fatna. "Influence de la microstructure sur le comportement mécanique de l'alliage de titane Ti-6Al-4V : étude expérimentale et modélisation numérique multi-échelle Role of grain size and crystallographic texture on tensile behavior induced by sliding mechanism in Ti-6Al-4V alloy An optimization of the local hall-petch relationship using slip trace analysis technique and scale transition rules: application in equiaxed Ti-6Al-4V titanium alloy." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2020. http://www.theses.fr/2020EMAC0005.
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L’amélioration des performances mécaniques des matériaux utilisés dans l’aéronautique repose généralement sur la compréhension de la relation entre les paramètres microstructuraux et le comportement mécanique macroscopique. De plus, le caractère hétérogène et anisotrope de la plupart des matériaux métalliques, notamment l’alliage de titane Ti-6Al-4V, implique une étude assez approfondie à l’échelle locale. Ce travail constitue une contribution dans ce domaine. Il a pour but d’analyser le comportement mécanique de l’alliage Ti-6Al-4V soumis à des sollicitations monotones et cycliques en lien avec la microstructure. Des caractérisations microstructurales ont été tout d’abord effectuées sur des microstructures nodulaires de Ti-6Al-4V possédant la même texture cristallographique mais avec trois tailles de grain différentes : ultra fine, fine et standard, puis sur des microstructures possédant la même taille de grain mais avec deux textures différentes : forte et faible. Dans une deuxième étape, des essais mécaniques monotones et cycliques ont été réalisés. Les résultats de cette partie ont permis le développement d’un modèle à l’échelle macroscopique. Par la suite, une technique d’analyse des traces de glissement a été développée dont l’objectif est d’identifier la contribution de différents systèmes de glissement dans l’accommodation de la déformation plastique. La dernière partie de cette thèse a été consacrée au développement d’un modèle de plasticité cristalline couplé à la méthode des éléments finis (Crystal Plasticity Finite Element Method (CPFEM)) permettant d’analyser l’effet couplé de la taille moyenne des grains, leur dispersion relative et leur texture cristallographique sur le comportement obtenu aux échelles microscopique, mésoscopique et macroscopique. Les paramètres du modèle ont été identifiés en utilisant des techniques appropriées de transition d’échelles en champs moyens. Les Volumes Élémentaires Représentatifs (VER) utilisés dans le modèle ont été optimisés en considérant deux contraintes majeures : un nombre de grains représentatif et un maillage adéquat. Les simulations numériques ont été réalisées par le biais du code de calcul éléments finis Abaqus/Standard interfacé par la librairie ZMATImproving the mechanical performances of materials used in aeronautics industry is generally based on the understanding of the relationships between their microstructural features and their mechanical behavior observed at the macroscopic scale. In addition, the heterogeneous and the anisotropic nature of many materials, in particular Ti-6Al-4V titanium alloy, implies a rather detailed investigation of the mechanical behavior at the local scale. This PhD work is a contribution to analyze the mechanical behavior of the Ti-6Al-4V alloy submitted to monotonic and cyclic loadings by considering relationship with the microstructure features. Microstructural characterizations were first performed on nodular Ti-6Al-4V microstructures with identical crystallographic texture and three different grain sizes (ultra fine, fine and standard), then on microstructures with the same grain size but two texturing degrees (strong texturing and weak) were assessed. In a second step, mechanical tensile and cyclic experiences were carried out. The results were used in development of a model with a macroscopic approach. Subsequently, a sliding trace analysis technique was developed in order to identify the contribution of different sliding systems on the accommodation of plastic deformation during the tensile or cyclic loadings. The final part of PhD work was dedicated to the development of a Crystal Plasticity-Finite Element model (CPFEM) to analyze the coupled effect of the average grain sizes, their relative scattering and crystallographic textures on the mechanical behavior at different scales: microscopic (sliding mechanism), mesoscopic (grains) and macroscopic scales. The model parameters were identified using appropriate techniques for the scale transitions. The Representative Volume Element (RVE) necessary for such modeling has been optimized with two constraints: a representative number of grains and an adequate meshing in terms of numbers and type of elements. The numerical simulations were performed using Abaqus/ Standard finite element calculation code interfaced by ZMAT library
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Cassiano, Gaspar Stefania. "Mise en forme par extrusion de supports de catalyseurs à base d'alumine et à microstructure multi-échelles : Effet de la composition granulaire et du liant sur les propriétés des matériaux." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0056/document.
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L'empilement maîtrisé de granules de différentes tailles est un concept utilisé dans la plupart de procédés de mise en forme de matériau. Cette organisation hiérarchique est connue pour améliorer les propriétés d'écoulement à l'étape de mise en forme et les caractéristiques mécaniques du matériau final. Il est apparu intéressant d'appliquer ce concept à la mise en forme par extrusion de supports de catalyseurs avec des petites (2 µm) et grosses (19 µm) granules d'alumine poreuse dont l'assemblage est assurée par un liant traditionnel, la boehmite peptisée et neutralisée, ou par un liant plus original, le phosphate d'aluminium. L'étude vise ainsi à évaluer l'effet du liant et de la microstructure multi-échelles apportée par l'organisation hiérarchique des granules, sur les propriétés texturales et mécaniques des supports. Le contrôle des conditions de mise en forme et l'optimisation de la formulation des deux liants ont permis d'obtenir des extrudés à microstructure comparable entre la boehmite et le phosphate d'aluminium et variable en fonction de la proportion de petites. Cette population remplit les espaces entre les grosses granules de manière optimale entre 40 et 60% pds et les desserre aux plus fortes teneurs. La rétraction du liant au cours des traitements thermiques génère un volume de macropores qui est minimisé lorsque les petites granules comblent les espaces formés par les grosses. La macroporosité minimale conduit à de meilleures résistances à la rupture (par tests d'écrasement de type brésilien) et les matériaux les plus résistants sont ceux mis en forme avec le phosphate d'aluminium. Ce résultat est expliqué par la nature très cohésive de ce liant formée in situ par réaction de l'acide phosphorique avec la boehmite et la périphérie des granules d'alumine. Dans ce cas, la rupture a lieu au sein des granules différemment des supports mis en forme avec la boehmite peptisée à l'acide nitrique qui présentent une rupture à l'interface granule-liant. Les matériaux à microstructure multi-échelles présentent également une meilleure ténacité déterminée par des essais de flexion trois points. Le phosphate d'aluminium étant un liant non-poreux conduit à des supports avec une mésoporosité plus faible. Les nouveaux supports à microstructure multi-échelles semblent prometteurs pour des nombreuses applications catalytiques sensibles aux propriétés diffusionnelles et mécaniquesThe controlled packing of different sized-granules is a concept widely used in most of the shaping material processes. This hierarchical organization is known to improve the flow properties during shaping and the mechanical characteristics of the finished material. It seemed interesting to apply this concept in order to prepare catalyst supports by extrusion containing small (2 µm) and large (19 µm) porous alumina granules assembled by a traditional binder, the peptized and neutralized boehmite, or by a more original, an aluminum phosphate binder. This study aims to investigate the effect of binder type and of the multiscale microstructure achieved by the packing of different granules size on textural and mechanical support properties. The control of kneading and extrusion conditions associated with the optimized binder formulation, conducted to similar microstructures with both binders according to the amount of each granular population. Small granules fills better the residual spaces between the larges between 40 and 60 wt.% and loosens them with strongest contents. Binder shrinkage during heat treatment generates a macroporosity which is minimized when small granules fills the voids formed by the larger ones. Minimal macroporosity leads to better crushing resistance (by Brazilian test) and the most resistant materials are the ones shaped with the aluminum phosphate. This result is explained by the high cohesive capacity of this binder obtained in situ by reaction of the phosphoric acid with the boehmite and the border of the alumina granules. In this case, the breakage takes place inside the granules differently from the supports shaped with the peptized boehmite by nitric acid which present a breakage at the granule-binder interface. Also, the multiscale microstructure materials present a better tenacity determined by three point bending. Aluminum phosphate being a non-porous binder, leads to supports with a weaker mesoporosity. The new multiscale microstructure supports seem interesting for several catalytic applications that are sensitive to diffusivity and mechanical properties
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Klemm, Robert. "Zyklische Plastizität von mikro- und submikrokristallinem Nickel." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1085403884093-17423.
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Im Rahmen der vorliegenden Arbeit wurde der Einfluss der Korngröße und der Gefügestabilität auf die zyklische Plastizität von mikro- und submikrokristallinem Nickel, hergestellt durch ECAP und PED, untersucht. Zur Gefügecharakterisierung kamen verschiedene elektronenmikroskopische und röntgenographische Methoden zum Einsatz. Die Untersuchungen zur Gefügestabilität zeigten, dass (i) die Stabilität der Korn- und Substruktur bei der zyklischen Verformung empfindlich vom Gefüge im Ausgangszustand abhängt, (ii) generell die Tendenz zur Umwandlung der vorhandenen Substruktur in eine universelle ermüdungstypische Substruktur besteht, diese Transformation jedoch durch die lokale Gefügebeschaffenheit be- bzw. verhindert sein kann und (iii) zur Erklärung des Entfestigungsverhaltens der ECAP-Materialien sowohl die Transformation der Substruktur als auch die Vergröberung der Kornstruktur berücksichtigt werden müssen. Auf der Basis der Ergebnisse der vorliegenden Arbeit und unter Hinzunahme von Resultaten aus der Literatur lassen sich Schlussfolgerungen zum Einfluss der Korngröße auf die zyklische Plastizität in einem vier Größenordnungen umfassenden Korngrößenbereich ziehen. In grob- und feinkörnigem Nickel bilden sich bei der zyklischen Verformung ermüdungstypische Versetzungsstrukturen, deren Abmessungen kaum von der Korngröße abhängen. Der Versetzungslaufweg in diesen Materialien ist wesentlich kleiner als die Kornabmessungen. Dementsprechend besteht höchstens ein schwacher Einfluss der Korngröße auf das sich bei der Wechselverformung einstellende Spannungsniveau. Bei mikro- und submikrokristallinem Nickel, wo der Versetzungslaufweg in der Größenordung der Kornabmessungen liegt, wird ein deutlicher Umschlag bei der Versetzungsmusterbildung und dem zyklischen Verformungsverhalten beobachtet. In diesem Korngrößenbereich entstehen entweder qualitativ andere (D<DS1=5µm) oder keine Versetzungsstrukturen (D<DS2=1µm) und das Spannungsniveau steigt mit sinkender Korngröße entsprechend einer HALL-PETCH-Beziehung.
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Klemm, Robert. "Zyklische Plastizität von mikro- und submikrokristallinem Nickel." Doctoral thesis, Technische Universität Dresden, 2003. https://tud.qucosa.de/id/qucosa%3A23831.
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Im Rahmen der vorliegenden Arbeit wurde der Einfluss der Korngröße und der Gefügestabilität auf die zyklische Plastizität von mikro- und submikrokristallinem Nickel, hergestellt durch ECAP und PED, untersucht. Zur Gefügecharakterisierung kamen verschiedene elektronenmikroskopische und röntgenographische Methoden zum Einsatz. Die Untersuchungen zur Gefügestabilität zeigten, dass (i) die Stabilität der Korn- und Substruktur bei der zyklischen Verformung empfindlich vom Gefüge im Ausgangszustand abhängt, (ii) generell die Tendenz zur Umwandlung der vorhandenen Substruktur in eine universelle ermüdungstypische Substruktur besteht, diese Transformation jedoch durch die lokale Gefügebeschaffenheit be- bzw. verhindert sein kann und (iii) zur Erklärung des Entfestigungsverhaltens der ECAP-Materialien sowohl die Transformation der Substruktur als auch die Vergröberung der Kornstruktur berücksichtigt werden müssen. Auf der Basis der Ergebnisse der vorliegenden Arbeit und unter Hinzunahme von Resultaten aus der Literatur lassen sich Schlussfolgerungen zum Einfluss der Korngröße auf die zyklische Plastizität in einem vier Größenordnungen umfassenden Korngrößenbereich ziehen. In grob- und feinkörnigem Nickel bilden sich bei der zyklischen Verformung ermüdungstypische Versetzungsstrukturen, deren Abmessungen kaum von der Korngröße abhängen. Der Versetzungslaufweg in diesen Materialien ist wesentlich kleiner als die Kornabmessungen. Dementsprechend besteht höchstens ein schwacher Einfluss der Korngröße auf das sich bei der Wechselverformung einstellende Spannungsniveau. Bei mikro- und submikrokristallinem Nickel, wo der Versetzungslaufweg in der Größenordung der Kornabmessungen liegt, wird ein deutlicher Umschlag bei der Versetzungsmusterbildung und dem zyklischen Verformungsverhalten beobachtet. In diesem Korngrößenbereich entstehen entweder qualitativ andere (D<DS1=5µm) oder keine Versetzungsstrukturen (D<DS2=1µm) und das Spannungsniveau steigt mit sinkender Korngröße entsprechend einer HALL-PETCH-Beziehung.
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Morris, Billy Ray. "Grain size estimation in anisotropic materials." Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/20042.
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Leguen, Claire. "Prior Austenite Grain Size Controlled by Precipitates." Phd thesis, INSA de Lyon, 2010. http://tel.archives-ouvertes.fr/tel-00511322.
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During this study, the correlation between the evolution of the prior austenitic grain size and of the precipitation state during thermal treatment performed on steels is presented. To do this, the precipitation state has been finely characterized. Precipitate volume fractions were measured by plasma spectroscopy. Transmission Electron Microscopy (TEM) was used to determine the precipitate size distributions (HAADF images) and the precipitate chemical composition (EDX, EELS for carbon and nitrogen). In order to treat ELLS spectra obtained on complex carbonitrides (V,Nb,Ti)(C,N), a routine based on the Least Mean square Fitting have been developed. Results obtained with this method are in gopd agreement with those obtained by EDX analysis for metallic elements (Nb, V, Ti, ...). Then, grain size distributions were determined using a special etching called "Bechet-Beaujard", which reveals the prior austenite grain boundaries. Two alloys have been characterized in this study. (i) A model alloy, the FeVNbCN, which presents two precipitate types, NbC and VCN. This alloy was chosen to study the role of nitrogen on the precipitation state during reversion treatments. A model predicting the precipitation kinetics, coupled with a model for grain growth, give a good agreement with experimental results on grain sizes, precipitate sizes and on precipitate volume fraction. (ii) An industrial steel, the 16MnCr5+Nb was also studied. This alloy exhibits the presence of AlN and NbC precipitates. The correlation obtained between the Prior Austenite Grain Size and the evolution of the precipitation state shows that a large volume fraction of small precipitates allows a great pinning of grain boundaries. Finally, during thermo-mechanical treatments performed in the industry, some large grains may grow faster than smaller grains, leading to the so-called abnormal grain growth. This kind of growth can lead to undesirable mechanical instabilities. We have developed a criterium for abnormal grain growth which predicts the risk of such growth for a given precipitation state. This model presents a good agreement with all experimental results for both studied alloys.
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Fry, Taylor D. "Metallophthalocyanine Optical Properties Dependence on Grain Size." Thesis, California State University, Long Beach, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10838499.
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Vacuum sublimated thin films of metallophthalocyanines (where metal = Cu, Fe, Zn, and Mn) and metal-free phthalocyanine were prepared at different deposition temperatures. The optical properties have been studied in the wavelength range of 340 nm to 2500 nm for samples deposited at room temperature up to 250 °C. Atomic force microscopy was used to obtain images of the surface morphology. Absorption coefficient spectra obtained verify the π to π* transition in the region 526 nm to 735 nm for the Q band, throughout all samples studied. The independence of deposition temperature or grain size in peak positions in absorption coefficient throughout all samples has been shown. The ratio of intensity of the two absorption coefficient peaks in the Q band has been calculated, showing a change in MnPc intensity ratio with changing deposition temperature. The intensity of the highest peak in the Q band has been compared for different metallophthalocyanines and across different deposition temperatures. CuPc deposited at 250 °C has been shown to have the highest peak magnitude of absorption coefficient, with a value of 3.9×10 5 cm–1.
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Chandrasekaran, Dilip. "Grain Size and Solid Solution Strengthening in Metals." Doctoral thesis, KTH, Materials Science and Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3641.
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The understanding of the strengthening mechanisms is crucialboth in the development of new materials with improvedmechanical properties and in the development of better materialmodels in the simulation of industrial processes. The aim ofthis work has been to study different strengthening mechanismsfrom a fundamental point of view that enables the developmentof a general model for the flow stress. Two differentmechanisms namely, solid solution strengthening and grain sizestrengthening have been examined in detail. Analytical modelsproposed in the literature have been critically evaluated withrespect to experimental data from the literature. Two differentexperimental surface techniques, atomic force microscopy (AFM)and electron backscattered diffraction (EBSD) were used tocharacterize the evolving deformation structure at grainboundaries, in an ultra low-carbon (ULC) steel. A numericalmodel was also developed to describe experimental featuresobserved locally at grain boundaries.
For the case of solid solution strengthening, it is shownthat existing models for solid solution strengthening cannotexplain the observed experimental features in a satisfactoryway. In the case of grain size strengthening it is shown that asimple model seems to give a relatively good description of theexperimental data. Further, the strain hardening in materialsshowing a homogenous yielding, is controlled by grainboundaries at relatively small strains. The experimentalresults from AFM and EBSD, indicate more inhomogenousdeformation behaviour, when the grain size is larger. Bothtechniques, AFM and EBSD, correlate well with each other andcan be used to describe the deformation behaviour both on alocal and global scale. The results from the numerical modelshowed a good qualitative agreement with experimentalresults.
Another part of this project was directed towards thedevelopment of continuum models that include relevantmicrostructural features. One of the results was the inclusionof the pearlite lamellae spacing in a micromechanically basedFEM-model for the flow stress of ferriticperlitic steels.Moreover a good agreement was achieved between experimentalresults from AFM and FEM calculations using a non-local crystalplasticity theory that incorporates strain gradients in thehardening moduli.
The main philosophy behind this research has been to combinean evaluation of existing strengthening models, with newexperiments focused on studying the fundamental behaviour ofthe evolving dislocation structure. This combination can thenbe used to draw general conclusions on modelling thestrengthening mechanisms in metals.
Keywords:strengthening mechanisms, flow stress, solidsolution strengthening, grain size strengthening,micromechanical modelling, AFM, EBSD
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Fromm, Bradley S. "Incorporating grain size effects in Taylor crystal plasticity /." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2261.pdf.
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Fromm, Bradley S. "Incorporating Grain Size Effects in Taylor Crystal Plasticity." BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/1275.
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A method to incorporate grain size effects into crystal plasticity is presented. The classical Hall-Petch equation inaccurately predicts the macroscopic yield strength for materials with non-equiaxed grains or materials that contain unequal grain size distributions. These deficiencies can be overcome by incorporating both grain size and orientation characteristics into crystal plasticity theory. Homogenization relationships based on a viscoplastic Taylor-like approach are introduced along with a new function, the grain size and orientation distribution function (GSODF). Estimates of the GSODF for high purity α-titanium are recovered through orientation imaging microscopy coupled with the chord length distribution. A comparison between the new method and the traditional viscoplastic Taylor approach is made by evaluating yield surface plots.
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Alvarado, Blohm Fernando Jose. "Determination of Hydraulic Conductivities through Grain-Size Analysis." Thesis, Boston College, 2016. http://hdl.handle.net/2345/bc-ir:106982.
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Thesis advisor: Alfredo UrzuaThesis advisor: John Ebel
Nine empirical equations that estimate saturated hydraulic conductivity as a func- tion of grain size in well-graded sands with gravels having large uniformity coecients (U > 50) are evaluated by comparing their accuracy when predicting observed conduc- tivities in constant head permeability tests. According to the ndings of this thesis, in decreasing order of accuracy these equations are: USBR (Vukovic and Soro, 1992; USBR, 1978), Hazen (Hazen, 1892), Slichter (Slichter, 1898), Kozeny-Carman (Carrier, 2003), Fair and Hatch (Fair and Hatch, 1933), Terzaghi (Vukovic and Soro, 1992), Beyer (Beyer, 1966), Kruger (Vukovic and Soro, 1992), and Zunker (Zunker, 1932). These re- sults are based on multiple constant head permeability tests on two samples of granular material corresponding to well-graded sands with gravels. Using the USBR equation sat- urated hydraulic conductivities for a statistical population of 874 samples of well-graded sands with gravels forming 29 loads from a heap leaching mine in northern Chile are calculated. Results indicate that, using the USBR equation, on average the hydraulic conductivity of the leaching heaps has a two standard deviation range between 0.18 and 0.15 cm/s. Permeability tests on the actual material used in the heaps provided by the mine shows that the results presented in this thesis are consistent with actual observa- tions and represent saturated conductivities in heaps up to 3 m high under a pressures of up to 62 Kpa. In future work hydraulic conductivities can be combined with water retention curves, discharge rates, irrigation rates, porosities, and consolidation so as to evaluate the relationship between copper yields and the hydraulic conductivities of the heap
Thesis (MS) — Boston College, 2016
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Geology and Geophysics
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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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Leguen, Claire. "Precipitation controlled prior austenite grain size in steels." Lyon, INSA, 2010. http://theses.insa-lyon.fr/publication/2010ISAL0018/these.pdf.
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Au cours de cette étude nous présentons la corrélation existant entre l’évolution de la croissance des grains austénitiques et celle de l’état de précipitation au cours de traitements thermiques d’aciers. Pour cela, nous avons, dans un premier temps, caractérisé l’état de précipitation expérimentalement. Les fractions volumiques précipitées sont mesurées par dissolution électrolytique. La Microscopie Electronique en Transmission (MET) permet d’obtenir les distributions de taille (imagerie HAADF) et la composition chimique des précipités (EDX, EELS pour le carbone et l’azote). Afin de traiter les spectres EELS obtenus sur des carbonitrures complexes du type (V,Nb,Ti)(C,N), nous avons mis en place une approche basée sur la méthode du ‘Least Mean Square Fitting’ (LMSF). Les résultats obtenus par cette routine sont en accord avec ceux obtenus par EDX sur les éléments lourds (Nb,V,Ti,…), ce qui crédibilise les résultats obtenus pour le carbone et l’azote. Dans un second temps, des distributions de taille de grains austénitiques ont été obtenues par observation métallographique après une attaque chimique spécifique (dite de "Bechet-Beaujard"). Dans le cadre de cette étude deux alliages ont été étudiés. (i) Un alliage modèle, le FeVNbCN, présentant des précipités NbCet VCN. La raison du choix de cet alliage est d’étudier l’influence de l’azote sur l’évolution de l’état de précipitation au cours de traitements d’austénitisation. Des modèles thermodynamiques combinés de prédiction des cinétiques de précipitation et de croissance des grains conduisent à des prédictions en bon accord avec les résultats expérimentaux de taille de grains, de tailles de précipités, de composition chimique et de fraction volumique. (ii) Un alliage industriel, le 16MnCr5+Nb a également été étudié. Cet alliage contient des précipités de NbC et de AlN. La corrélation obtenue entre la taille de grains austénitiques et l’évolution de l’état de précipitation montre que la composition chimique des précipités n’entre pas en jeu, mais plus leur taille est petite et plus leur fraction volumique est grande, plus le contrôle des grains par les précipités est efficace. Enfin, nous nous sommes intéressés au phénomène de croissance anormale (lors de traitements thermomécaniques comme ceux réalisés dans l’industrie notamment, la taille de grain austénitique peut croître de façon hétérogène). Ce type de croissance entraîne des instabilités mécaniques indésirables. Nous avons donc développé un modèle de prédiction du risque de croissance anormale pour un état de précipitation donné. Ce modèle présente un très bon accord avec les résultats expérimentaux des deux alliages étudiésDuring this study, the correlation between the evolution of the prior austenitic grain size and of the precipitation state during thermal treatment performed on steels is presented. To do this, the precipitation state has been finely characterized. Precipitate volume fractions were measured by plasma spectroscopy. Transmission Electron Microscopy (TEM) was used to determine the precipitate size distributions (HAADF images) and the precipitate chemical composition (EDX, EELS for carbon and nitrogen). In order to treat ELLS spectra obtained on complex carbonitrides (V,Nb,Ti)(C,N), a routine based on the Least Mean square Fitting have been developed. Results obtained with this method are in good agreement with those obtained by EDX analysis for metallic elements (Nb, V, Ti, …). Then, grain size distributions were determined using a special etching called "Bechet-Beaujard", which reveals the prior austenite grain boundaries. Two alloys have been characterized in this study. (i) A model alloy, the FeVNbCN, which presents two precipitate types, NbC and VCN. This alloy was chosen to study the role of nitrogen on the precipitation state during reversion treatments. A model predicting the precipitation kinetics, coupled with a model for grain growth, give a good agreement with experimental results on grain sizes, precipitate sizes and on precipitate volume fraction. (ii) An industrial steel, the 16MnCr5+Nb was also studied. This alloy exhibits the presence of AlN and NbC precipitates. The correlation obtained between the Prior Austenite Grain Size and the evolution of the precipitation state shows that a large volume fraction of small precipitates allows a great pinning of grain boundaries. Finally, during thermo-mechanical treatments performed in the industry, some large grains may grow faster than smaller grains, leading to the so-called abnormal grain growth. This kind of growth can lead to undesirable mechanical instabilities. We have developed a criterium for abnormal grain growth which predicts the risk of such growth for a given precipitation state. This model presents a good agreement with all experimental results for both studied alloys
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Vallejo, Fernandez Gonzalo. "Grain size effects in polycrystalline exchange biased systems." Thesis, University of York, 2006. http://etheses.whiterose.ac.uk/14090/.
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The capability of a novel sputtering technology known as HiTUS to produce thin films with controlled grain size and distribution has been evaluated. This has been achieved for different materials chosen due to their importance in industrial applications. The grain size of the deposited films was measured from TEM images in bright field mode. All the distributions were lognormal and over five hundred particles were measured to recompose each lognormal function. For a range of materials close control of grain size between 4nm and 30nm was achieved. The grain size was controlled through the deposition rate. This has allowed the investigation of the effect of the antiferromagnetic grain size on exchange bias without the use of underlayers, additives or substrate heating. It was found that the magnitude of the loop shift strongly correlated to the distribution of grain volumes in the antiferromagnetic layer. Using detailed measurements of the grain size distribution the features of exchange bias in these systems can be explained on the basis of a grain volume model with coherent rotation. For example using measurement protocols that ensure reproducibility of data has allowed the development of a new measurement technique for the anisotropy constant of metallic antiferromagnets. This is a key result since the anisotropy is used in all theoretical models of exchange bias as a fitting parameter. The anisotropy was determined only from experimental features and only its temperature dependence had to be assumed to be of the form K(OK)(1-T/TN)3 in order to calculate the values. For IrMn K(293K) =4.14xlO6erg/cc and for FeMn K(293K) = 1.36x106erg.
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Persson, Erik. "Austenite grain growth in bearing steels : An investigation on steel grades 100Cr6 and 100 CRMnMoSi8-4-6." Thesis, KTH, Materialvetenskap, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-140433.
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An investigation of austenite grain growth of two bearing steel grades; 100Cr6 and100CrMnMoSi8-4-6 is performed. Austenitization treatments were performed between 860°C and 1200 °C for 5 minutes to 5 hours and the grain size was determined for each sample.Grain boundary etching was carried out using a water based, picric-acid etchant. Generally,100CrMnMoSi8-4-6 was harder to etch than 100Cr6. Therefore, a precipitation heattreatment was performed in order to facilitate etching of prior austenite grain boundaries in100CrMnMoSi8-4-6. The precipitation treatment was found to be effective. However, theprecipitation heat treatment was not suitable for 100Cr6 as the grain size increased duringthe precipitation heat treatment.Light optical microscope equipped with a camera was utilized to take micrographs for grainsize evaluation. Jeffries' standard procedure according to ASTM E112-96 was used tomeasure the grain size. The results shows that the austenite grain size increases withtemperature and time as expected. The experimental data was fitted to a well-known graingrowth model. The model only worked for the temperatures investigated and could not bemade to fit different temperatures.Local grain size variation was studied and its influence on fatigue properties was evaluated.The result showed that variation in local grain size can significantly alter the fatigueproperties. The findings are only theoretical and have not been tested practically.Two different spheroidization heat treatments and one homogenization heat treatmentwere performed. Both spheroidization heat treatments investigated exhibited similar grainsize. The homogenization heat treatment reduced the local grain size variation.Homogenization treatment prior to the spheroidization treatments did not increase ordecrease the grain size. The long heating, holding and cooling times in the secondspheroidization heat treatment is probably the reason for the lack of grain refinementcompared to the first spheroidization heat treatment. The grains had time to grow to theinitial austenite grain size during each cycle.
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Austin, Nicholas James. "Grain size evolution and strain localization in deformed marbles." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45604.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references.
In the lithosphere, strain is frequently accommodated along localized shear zones, the rheology of which are inextricably linked to their microstructural characteristics. Shear zones in orogenic belts frequently form in calcite-rich lithologies due to the relatively low strength of these rocks, especially when compared to quartz- and feldspar-rich lithologies. This dissertation addresses the kinetics of microstructural evolution during deformation of calcite-rich rocks, and the coupling between the rheological properties of deforming rocks and such microstructural characteristics as grain size and crystallographic preferred orientation (CPO) by combining laboratory studies with field based observations. In Chapter 2, a scaling relationship for recrystallized grain size is derived based on a balance between the rate that mechanical work is done during deformation and the rate that this energy can be dissipated. This suggests that recrystallized grain size reflects the product of stress and strain rate rather than stress alone. When this scaling relationship is applied to measured calcite grain sizes from the Morcles nappe, in the Swiss Helveitc Alps, where the microstructure is unaffected by second phases, the geologically estimated regional strain rates are successfully reproduced, and when it is applied to samples collected along a transect perpendicular to the thrust contact, the results suggest strain became progressively localized (Chapter 3). This calculation is consistent with the increased CPO intensity which is observed in the finest grained mylonites closest to the thrust contact. In Chapter 4, laboratory deformation experiments are used gain insight into the kinetics of microstructural evolution in calcite-rich rocks. The grain size evolution rates measured in experiments correlate well with the product of the measured stresses and strain rates, consistent with the scaling relationship presented in Chapter 2. These experiments also suggest that, with increasing strain, strain rates will increase at constant stress, and there is a correlation between this weakening and the formation and intensification of CPO, consistent with the observations in the Morcles nappe. Rocks are seldom composed of a single mineral phase.
(cont.) The influence of rigid second phases on the strength, CPO, and grain size of deforming marbles is investigated through a combination of hydrostatic, compression, and torsion experiments performed in the laboratory, which are presented in Chapters 5&6. Both the volume fraction and geometry of rigid second phases have a dramatic effect on the mechanical strength, the CPO, and the grain size. In samples deformed to high strains in torsion, where the recrystallized grain size resulting from deformation is finer than the grain size due to pinning of grain boundaries by the rigid inclusions, the scaling relationship derived in Chapter 2 successfully predicts the measured recrystallized grain size. Thus, this scaling relationship is consistent with both grain size evolution rates and stabilized grain sizes measured in the laboratory, and with field constraints on the strain rates in the Morcles nappe.
by Nicholas James Austin.
Ph.D.
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Richardson, Mark. "Errors in predicting snow's near-infrared optical grain size." Thesis, University of Reading, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.625443.
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Knowledge of snow's spatial distribution in terms of snow water equivalent (SWE) is important for hydrological forecasting, but current SWE products commonly disagree on regional scales. Assimilating passive microwave observations into a forecast from a physically-based snow model has been suggested to reduce or remove this disagreement, in which case the snow model must produce properties that are relevant to radiative transfer in snow. Here, the SNOWCAN model produces profiles of grain size for comparison with field measurements using contact probe spectroscopy and the impact of considering grain shape or conglomeration type (chain or cluster) is estimated. Prediction error in near-infrared optical grain size is estimated to be ±0.094 mm for all grains, or a possible best-case of ±0.083 mm if grain shape is included. The Helsinki University of Technology microwave radiative transfer model is used with the Cold Land Processes Experiment field data to make a preliminary estimate of the associated errors in simulated microwave brightness temperature difference, which is commonly used in SWE products such as Globsnow. Grain size error is associated with a ±5.1 K error and including grain shape, at best, reduces this error to ±4.5 K. Increasing stratigraphic detail by simulating more layers is an alternative method to reduce error, and layering error is found to increase linearly with snow depth. A single-layer simulation of 100 cm depth is associated with a ±8.7 K error relative to a pack described at the measurement resolution, whereas a 2-layer model is associated with a ±3.9 K error. Further work is required to determine the impact of grain: shape in the microwave regime, rather than the near infrared, but these results suggest that increased stratigraphic detail is a higher priority than including grain shape in order to improve the assimilation of passive microwave observations.
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Teague, Eleanor. "Evaluating methods for detrital grain-size analysis of lake sediments." Thesis, University of Manchester, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516796.
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Ivanov, Maksim. "Grain size effect on dielectric properties of ferroelectrics and relaxors." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20141230_153112-03380.
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The aim of doctoral dissertation „Grain Size Effect on Dielectric Properties of Ferroelectrics and Relaxors“ by Maksim Ivanov is to investigate, how grain size of ceramics and powders of a few ferroelectrics and relaxors influences macroscopic dielectric properties. The studied materials are powders of a relaxor PbMg⅓Nb⅔O3 (PMN), ceramics of a relaxor with a spontaneous phase transition PbSc½Nb½O3 (PSN), ceramics of a ferroelectric 0.36BiScO3-0.64PbTiO3, and ceramics of Ba2SnO4, which were compared to a better investigated BaSnO3. Investigations were performed in broad frequency (100 Hz – 55 GHz) and temperature (30 K – 1000 K) ranges. Experimental investigations and modelling showed, that bulk properties of relaxor materials are heavily influenced by polar nanoregions, but they do not fully determine them. Morphology of the material (i.e. grain size of ceramics) determines growth and interactions of the nanoregions, thus influencing bulk properties. Moreover, effective medium approximation can explain evolution of dielectric properties of ferroelectrics and relaxors only if dependence of bulk properties on grain size is known. The most interesting result is, that there exist polar entities in ferroelectrics, which are different from ferroelectric domains and are similar to polar nanoregions in relaxors. Their contribution to dielectric permittivity can be comparable to all other contributions. Dimensions of these entities depend on grain size in accordance with Kittel's law.Maksimo Ivanovo daktaro disertacijos tema yra “Grūdų dydžio įtaka dielektrinėms feroelektrikų ir relaksorių savybėms”. Šio darbo tikslas yra ištirti, kaip keramikų ar miltelių grūdų dydis įtakoja makroskopiškai stebimas kelių feroelektrikų bei feroelektrinių relaksorių dielektrines savybes. Tirtos medžiagos yra klasikinio relaksoriuas PbMg⅓Nb⅔O3 (PMN) milteliai, relaksoriaus su savaiminiu feroelektriniu faziniu virsmu PbSc½Nb½O3 (PSN) keramikos, feroelektriko 0.36BiScO3-0.64PbTiO3 keramikos, bei Ba2SnO4 keramiką, kuri buvo palyginta su kiek labiau žinoma BaSnO3 keramika. Tyrimai buvo atlikti plačiame dažnių (100 Hz – 55 GHz) bei temperatūrų (30 K – 1000 K) intervaluose. Eksperimentiniai tyrimai bei modeliavimai parodė, kad polinės nanosritys labai stipriai įtakoja tūrines relaksorių savybes, tačiau jų neapsprendžia. Medžiagos morfologija (antai keramikų grūdų dydis) lemia nanosričių augimą bei tarpusavio sąveikas, tokiu būdų įtakojamos tūrinės savybės. Be to, efektyvios terpės aproksimacija gali paaiškinti feroelektrikų ir relaksorių dielektrinių savybių priklausomybę nuo grūdų dydžio tik, jei žinomas sąryšis tarp dydžio ir tūrinių savybių. Įdomiausia yra tai, kad feroelektrikuose yra objektų, kurie nėra feroelektriniai domenai ir yra panašūs į relaksorių polines nanosritis. Jų indėlis į dielektrinę skvarbą gali būti palyginamas su visų kitų procesų (pvz. domenų sienelių ir polinių modų) indėliais. Šių objektų dydis priklauso nuo grūdų dydžio pagal Kittel'io dėsnį.
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Lamborn, Ellen. "The evolution of pollen grain size variation in Mimulus (Scrophulariaceae)." Thesis, University of Exeter, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269837.
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Ueland, Stian Melhus. "Grain constraint and size effects in shape memory alloy microwires." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/80893.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 142-147).
Shape memory alloys exhibit interesting and useful properties, such as the shape memory effect and superelasticity. Among the many alloy families that have been shown to exhibit shape memory properties the ones based on copper are interesting because they are relatively inexpensive and show excellent properties when made as single crystals. However, the performance of these alloys is severely compromised by the introduction of grain boundaries, to the point where they are too poor for commercial applications. This thesis studies the mechanical properties of fine Cubased wires with a bamboo microstructure, i.e., where triple junctions are absent and grain boundaries run perpendicular to the wire axis. These microwires are not single crystals, but their microstructure is not as complex as that of polycrystals either: we call this new class of shape memory alloys oligocrystals. This thesis seeks to better understand the relationship between microstructure and properties in these alloys through a combination of mechanical testing, in situ experiments and modeling. First, in situ scanning electron microscopy, together with finite element modeling, is used to understand the role of grain constraint on the martensitic transformation. Grain constraints are observed to be much less severe in oligocrystalline wires as compared to polycrystals. Oligocrystalline microwires are then thermomechanically tested and shown to exhibit excellent properties that approach those of single crystals. Next, property evolution during cycling is investigated, revealing training effects as well as fatigue life and fracture. Finally, size effects in damping and transformation morphology are studied and it is shown that a transition from a many-domain to a single domain martensite morphology takes place when the wire diameter is decreased.
by Stian Melhus Ueland.
Ph.D.
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Hanlon, Timothy 1977. "Grain size effects on the fatigue response of nanocrystalline materials." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16635.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.Includes bibliographical references (p. 151-158).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
The resistance of metals and alloys to fatigue crack initiation and propagation is known to be influenced significantly by grain size. Based on a wealth of experimental results obtained from microcrystalline metals, where the grain size is typically greater than 1 um, it is widely recognized that an increase in grain size generally results in a reduction in the fatigue endurance limit. On the other hand, a coarser grain structure can lead to an increased fatigue threshold stress intensity factor range, as well as a decrease in the rate of fatigue crack propagation. The relevance of these trends to ultra-fine-crystalline metals (grain size between 100 nm and 1000 nm) and nanocrystalline metals (grain size less than 100 nm) is relatively unknown. Such lack of understanding is primarily a consequence of the paucity of experimental data on the fatigue response of metals with very fine grains. In this work, the fatigue behavior of electrodeposited, fully dense, nanocrystalline pure Ni, with average and total range of grain sizes well below 100 nm, was examined. The fatigue response of nanocrystalline Ni was also compared with that of ultra-fine-crystalline and microcrystalline Ni wherever appropriate. It was found that grain refinement to the nanocrystalline regime generally leads to an increase in resistance to failure under stress-controlled fatigue whereas a deleterious effect was seen on the resistance to fatigue crack growth. To explore the generality of the above trends, similar experiments were performed on additional ultra-fine-crystalline material systems, produced using alternate processing techniques such as cryomilling and equal channel angular pressing.
(cont.) Contact fatigue behavior was also examined down to the nanocrystalline grain size regime. Friction and damage evolution was monitored as a function of the number of unidirectional sliding contact fatigue cycles introduced at the surface of several material systems. Critical experiments were performed to isolate the effects of grain size and material strength. Over the range of materials investigated, strength rather than grain size dominated the contact fatigue response, with substantial improvements in strength resulting in reduced damage accumulation, and a lower steady state friction coefficient. Conversely, grain size was found to govern the rate of crack growth under mechanical fatigue, with all other structural factors approximately held fixed. In addition, the cyclic deformation behavior of nanocrystalline materials was also investigated. Experiments designed to extract the strain response at a constant range of imposed cyclic stresses provided the first evidence of cyclic hardening in a nanocrystalline material. This behavior was observed over a broad range of loading conditions and fatigue frequencies.
by Timothy Hanlon.
Ph.D.
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Mastera, Lawrence. "Estimating Permeability from the Grain-Size Distributions of Natural Sediment." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1278618761.
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Onur, Emine Mercan. "PREDICTING THE PERMEABILITY OF SANDY SOILS FROM GRAIN SIZE DISTRIBUTIONS." Kent State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=kent1389550812.
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Abbott, Patrick Roland. "The Effect of Average Grain Size on Polycrystalline Diamond Films." Thesis, University of North Texas, 2002. https://digital.library.unt.edu/ark:/67531/metadc3164/.
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The work function of hydrogen-terminated, polycrystalline diamond was studied using ultraviolet photoelectron spectroscopy. Polycrystalline diamond films were deposited onto molybdenum substrates by electrophoresis for grain sizes ranging from 0.3 to 108 microns. The work function and electron affinity were measured using 21.2 eV photons from a helium plasma source. The films were characterized by x-ray photoelectron spectroscopy to determine elemental composition and the sp2/sp3 carbon fraction. The percentage of (111) diamond was determined by x-ray diffraction, and scanning electron microscopy was performed to determine average grain size. The measured work function has a maximum of 5.1 eV at 0.3 microns, and decreases to 3.2 eV at approximately 4 microns. Then the work function increases with increasing grain size to 4.0 eV at 15 microns and then asymptotically approaches the 4.8 eV work function of single crystal diamond at 108 microns. These results are consistent with a 3-component model in which the work function is controlled by single-crystal (111) diamond at larger grain sizes, graphitic carbon at smaller grain sizes, and by the electron affinity for the intervening grain sizes.
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Siafakas, Dimitrios. "On deoxidation practice and grain size of austenitic manganese steel." Licentiate thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Material och tillverkning – Gjutning, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-37788.
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The exceptional wear resistance and work hardenability, place Hadfield steel as one of themost important materials for manufacturing cast components used in the mining, crashing,drilling, and excavation industries. In all metallic alloys used for component casting, themechanical properties are highly influenced by the microstructure of the material. Castcomponents with finer microstructural characteristics are known to present bettermechanical properties and reduced risk of defects when compared with components witha coarser microstructure. A reduced grain size in Hadfield steel can increase the strengthof the material up to 30% and reduce the risk of porosity formation during solidification.The practice of adding selected compounds or alloying elements in a metal melt to modifyand refine the microstructure is called inoculation. It is currently one of the trendingmethods utilized in light-metal alloys and cast-iron components production but has not,yet, gained adequate acceptance in the steel casting industry because researchers have notbeen able to find proper inoculants.The main objective of this work is to investigate the qualitative and quantitativecharacteristics of the by-products of deoxidation of Hadfield steel that remain in thematerial after solidification and their positive or negative effect on the coarseness of thefinal as-cast microstructure. This type of research can help to identify the type of particlesor alloying elements that are most effective for refining the microstructure of austeniticsteels and pave the way for developing new or improving conventional deoxidation andinoculation processes that will, in turn, result in the improvement of the properties of thecomponent.The precipitation of particles and the as-cast grain size are studied in aluminum andtitanium deoxidized Hadfield steel samples acquired under pilot scale experimentalconditions. In the first part of this work, the qualitative and quantitative characteristics ofparticles such as type, morphology, composition amount and size are identified. Thesequence of precipitation is established. A model for predicting particle size and growth isdeveloped. The experimental results are compared against thermodynamic equilibriumcalculations and the precipitation mechanisms for each type of particles are described. Inthe second part, the as-cast grain size of samples with varying deoxidation treatments ismeasured. Then, the grain-size is correlated with certain particle characteristic and theparticles are ranked according to their ability to refine the microstructure. The particledisregistry with austenite is calculated and compared to the experimentally acquiredranking.Hadfieldstålen exceptionella slitstyrkan och deformationshårdnande har gjort dessa till ettav de viktigaste materialen för tillverkning av gjutna komponenter som används inomgruv-, kross-, borr-och gruvindustrin. I alla metallegeringar som används för tillverkningav gjutna komponenter styrs de mekaniska egenskaperna av materialets mikrostruktur.Gjutna komponenter med fin mikrostruktur presentera bättre mekaniska egenskaper ochminskad risk för defekter jämfört med komponenter med grov mikrostruktur. En minskadkornstorlek i Hadfieldstål kan öka materialets hållfasthet upp till 30% och minska riskenför porositetsbildning vid stelning.Tillsatsning av spårämnen eller legeringselement i en metallsmälta för att modifiera ochförbättra mikrostrukturen kallas ympning. Denna metod används i lättmetaller och vidtillverkning av gjutjärnskomponenter, men har ännu inte fått acceptans i stålindustrineftersom forskningen inte har funnit effektiva kärnbildare att användas som ympmedel.Huvudsyftet med detta arbete är att undersöka kvalitativa och kvantitativa egenskaper hosde desoxideringsprodukter som skapas under tillverkningen av Hadfield stål och hur deunder och efter stelning påverkar mikrostrukturens grovlek. Arbetet syftar till att identifierapartikeltyper och legeringselement som är effektiva för att förfina den austenitiskamikrostrukturen och bana väg för utveckling nya och förbättra desoxiderings- ochympningsprocesser som i sin tur kommer att resultera i en förbättring av den gjutnakomponentens egenskaper.Partiklarnas utskiljning och materialet resulterande kornstorlek studerades i aluminiumochtitan-desoxidiserade Hadfieldstål, tillverkade i pilotskala. Den första delen av dettaarbete var att identifiera kvalitativa och kvantitativa egenskaper hosdesoxidationspartiklar, som typ, morfologi, sammansättning och storlek.Utskiljningssekvensen fastställdes. En modell för att förutsäga partikelstorlek och derastillväxt utvecklades. De experimentella resultaten jämfördes med termodynamiskajämviktberäkningar och utskiljningen för varje typ av partikel beskrevs. I den andra delenstuderades kornstorleken och hur denna varierade desoxideringsbehandlingen. Därefterkorrelerades kornstorleken med partikeltyp och dess karaktäristika och rangordnades efterderas förmåga att förfina mikrostrukturen. Partiklarnas kristallografiska missanpassningmot austenitens kristallstruktur beräknades och jämfördes med experimentellt fastställdarangordningen.
InDeGrainS I
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Cox, Melissa Reiko Brooke. "The Influence of Grain Shape on Dilatancy." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/195563.
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Grain shape is a key factor affecting the mechanical properties of granular materials. However, grain shape quantification techniques to distinguish one granular material from another have not reached a stage of development for inclusion in modeling the behavior of granular materials. Part of the problem is the equipment of choice for grain shape measurement is the scanning electron microscope. This is a relatively expensive and complex device. In this research, a practical approach using light microscopy to quantify grain shape and to identify the key shape parameters that can distinguish grains was investigated. A light microscope was found to produce grain images with sufficient quality for the purpose of observing the grain shape profile. Several grain shape parameters were determined for eight different sands - four sands chosen for this study and four sands from an outside source. Six of these - Circularity, Roundness, Sphericity, Aspect Ratio, Compactness and ModRatio - are shown to be the key shape parameters that differentiate these sand grains.Relationships between the six key grain shape parameters and dilatancy were developed to enable a better understanding of the mechanics of granular materials and for potential use in practice. Data to build the relationships were obtained using a light microscope, digital image processing software (ImageJ), and direct shear tests on four uniform sands composed of grains with varying, somewhat-homogeneous, shape profiles - ranging from very rounded grains in one granular conglomerate to very angular shaped grains in another.A Weighted Single Sand Shape Factor (WSSSF) was derived from all of the six key shape parameters was developed using Weighted Factor Analysis. A good correlation was found to exist between dilatancy and WSSSF. The correlation also incorporates normal effective stress, relative density and the critical state friction angle. Verification was conducted through the introduction of a subangular to subrounded sand that was not used in building the correlation. The correlation proved to provide a good estimate of the dilatancy of sands based on the physical properties of grains and the applied loading.
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Jennerholm, Hammar Filip. "Dust driven winds of cool giant stars : dependency on grain size." Thesis, Uppsala universitet, Teoretisk astrofysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-156814.
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Aim. In this project, theoretical models of dust driven winds of asymptotic giant branch (AGB) stars with effective temperatures within a range of 2400 − 3200 [K] and relative carbon-to-oxygen abundance C/O > 1 are studied. The aim is to understand if and how a detailed description of the grain size in winds of carbon rich AGB stars affects the wind formation and wind driving processes. Method. The computations were performed with a well tested FORTRAN code by calculating a grid of 60 models with different stellar parameters using grain size-dependent opacities. The results were then compared with models where the small particle approximation (SPA) had been used. Conclusions. The results indicate a certain dependency on grain size of the wind properties. The results from the computations of the majority of the models show no significant diferences however, especially not for the mass loss rates. Thus earlier computations performed using the SPA need not necessarily to be rejected.
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Negelspach, Greg L. "Grain size management in repetitive task graphs for multiprocessor computer scheduling." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA288575.
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Deffenbaugh, Kristen Lynn. "Grain size control in AA5083 : thermomechanical processing and particle stimulated nucelation /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://handle.dtic.mil/100.2/ADA430595.
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