It is well known that texture and microstructure play a crucial role in determining properties of metallic materials. The evolution of microstructure and texture during deformation and annealing of copper and some copper base alloys have been investigated to some extent. However, the knowledge about the role of the mode of deformation, particularly different variants of rolling deformation, is still very limited for deformation and annealing texture of two-phase copper alloys. Therefore it appeared important to study the influence of deformation path (in the present case, mode of rolling) on texture and microstructure in two-phase copper alloy Cu-40Zn alloy. Hot rolled bar of Cu-40Zn alloy (as-received material) was subjected to unidirectional and cross rolling ( multi-step cross-rolling) at room temperature with strain per pass (true strain) being constant for each step. In multi-step cross-rolling, the rolling direction was altered (rotated by 90°)after each pass. Strains corresponding to rolling reduction of 50% and 80% were given to as-received material through each of the different mode of rolling. In a second route, the as-received material was solution treated at 800°C for 4 hours first and then subjected to rolling in the same manner as above. A piece was cut from each of the as-rolled materials and was subjected to annealing at 560°C for one hour for recrystallization. The bulk textures were determined by measuring the pole figures at the center of the rolled as well as the annealed specimen using X-ray texture goniometer based on Schultz reflection geometry. Three dimensional texture analyses were carried out using the method of orientation distribution function(ODF). Micro-textures and associated microstructural parameters were determined using a Field Emission Gun Scanning Electron Microscope(FEG-SEM) operated at 20KV, equipped with Electron back scattering detector(EBSD). In the experimental material, texture was examined for both the α (fcc) and the β (ordered cubic) phases. In the present investigation, α phase of unidirectional rolled as-received material had Bs {011}<112> orientation as the strongest component whereas for multi-step cross rolled material P(BND) {011}<111> orientation had the maximum intensity, which could be obtained by rotating the Bs orientation and about ND.The texture development of β phase of as-received unidirectional rolled sample could be understood in terms of relaxed constraints Taylor model. The initial texture had a pronounced effect on texture development of α phase for solution treated alloy during deformation. This material exhibited very strong P(BND) {011}<111> orientation for unidirectional as well as for multi-step cross rolling. For cross rolled alloys, this orientation is promoted by two factors simultaneously, (i) initial texture and (ii) special attributes of cross rolling process. The volume fraction of cube oriented grains was very low for all recrystallized samples because of dominance of Bs orientation in the deformation texture plus formation of shear bands in the microstructure. The texture of β phase for unidirectionally rolled solution treated alloy got sharpened on annealing. However, strength of texture decreased with increasing deformation. Grain boundary (and CSL boundary) analyses were carried out with EBSD data. These analyses indicated that all the recrystallized samples had a high number of Σ3 boundaries. The proportion of Σ3 boundaries was higher in multi-step cross-rolled annealed material. The deformed material had higher number fraction of low angle boundary than any other special boundary. Solution treated material had an average grain size of α phase smaller than the as-received material. Another dimension of the present investigation was to characterize the microstructural features in three dimension(3D) in order to examine the morhphology of constituent phases using serial sectioning. In the present work, 3D studies were carried out on the alloy after post deformation annealing. The alignment of serial section images and generation of 3D image out of the stack of 2D images was carried out through standard software. The same was used to measure the suitable 3D microstructural parameters from the 2D sections. Three dimensional microstructural parameters like mean caliper diameter of β particle, number of β particles per unit volume ‘Nv’, surface to volume ratio for β phase particles (α- β interface) ‘Sv’, were calculated. Number of β particle intercepts per unit area ‘NA’ was determined by measuring number of β phase particle in each section. The volume of a β particle as calculated from the caliper diameter using three-dimensional microstructural analysis, which could not get directly determined with conventional two-dimensional microscopy.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on January 15, 2010). Thesis advisor: Dr. Peter Nabelek. Includes bibliographical references.

The swelling mechanisms of U3Si2 under neutron irradiation in reactor conditions are not unequivocally known. The limited experimental evidence that is available suggests that the main driver of the swelling in this material would be fission gases accumulation at crystalline grain boundaries. The steps that lead to the accumulation of fission gases at these locations are multiple and complex. However, gradually, the gaseous fission products migrate by diffusion. Upon reaching a grain boundary, which acts as a trap, the gaseous fission products start to accumulate, thus leading to formation of bubbles and hence to swelling. Therefore, a quantitative model of swelling requires the incorporation of phenomena that increase the presence of grain boundaries and decrease grain sizes, thus creating sites for bubble formation and growth. It is assumed that grain boundary formation results from the conversion of stored energy from accumulated dislocations into energy for the formation of new grain boundaries.This thesis attempts to develop a quantitative model for grain subdivision in U3Si2 based on the above mentioned phenomena to verify the presence of this mechanism and to use in conjunction with swelling codes to evaluate the total swelling of the pellet in the reactor during its lifetime.

Inconel 738, which is a nickel base superalloy used for hot section components of aircraft and industrial turbines is difficult to fabricate and repair by fusion welding due to its susceptibility to heat affected zone (HAZ) intergranular cracking. Crack-free joining of the difficult-to-weld alloy is currently achieved by using linear friction welding (LFW). Nevertheless, oxidation along the joint during LFW is a major problem. Information about the effect of process parameters on the microstructural evolution of linear friction welded nickel base alloys is very limited. In this work, the effect of forging pressure on the microstructure of linear friction welded Inconel 738 was studied. The results as elucidated in this work showed that increased forging pressure caused strain-induced rapid solidification of metastable liquid, which resulted in complete elimination of deleterious liquid phase oxides in bonded material contrasting the generally accepted view that assumes extrusion of solid state oxides during LFW.

No description available.

Inconel 738, which is a nickel base superalloy used for hot section components of aircraft and industrial turbines is difficult to fabricate and repair by fusion welding due to its susceptibility to heat affected zone (HAZ) intergranular cracking. Crack-free joining of the difficult-to-weld alloy is currently achieved by using linear friction welding (LFW). Nevertheless, oxidation along the joint during LFW is a major problem. Information about the effect of process parameters on the microstructural evolution of linear friction welded nickel base alloys is very limited. In this work, the effect of forging pressure on the microstructure of linear friction welded Inconel 738 was studied. The results as elucidated in this work showed that increased forging pressure caused strain-induced rapid solidification of metastable liquid, which resulted in complete elimination of deleterious liquid phase oxides in bonded material contrasting the generally accepted view that assumes extrusion of solid state oxides during LFW.

En raison d’une combinaison de propriétés physiques, chimiques et mécaniques remarquables, les alliages de titane et de titane sont devenus des candidats prometteurs dans le domaine de l'industrie chimique, de l’aéronautique, de l'aérospatiale et des matériaux biomédicaux. Durant les procédures de fabrication ainsi qu’en service, les composants sont exposés à des environnements tels que la surface de ces composant seront exposées à l’hydrogène. Par conséquent, la compréhension de l’interaction de ces matériaux avec l'hydrogène lors de divers procédés de d’élaboration et de mise en forme est importante afin que leurs propriétés et leurs performances puissent être contrôlées et prédites de manière fiable. Dans le but d'améliorer les propriétés et les performances du titane et de réduire le coût de fabrication des produits en titane, le présent travail se concentre principalement sur les effets de l'hydrogène sur le laminage à froid et le phénomène de recristallisation de deux titanes caractérisés par une structure cristalline différente, c'est-à-dire une structure hexagonale et cubique cubique pour respectivement le titane de pureté commerciale Ti50A et l'alliage de titane β-métastable β-21S. Étant donné que la microstructure du titane et de ses alliages est le facteur contrôlant leurs propriétés et leurs performances, l'évolution microstructurale en présence d'hydrogène introduit par deux méthodes distinctes a été analysée par une combinaison de techniques expérimentales incluant DRX, SEM-EBSD et TEM. L'introduction de l'hydrogène dans le Ti50A par une méthode électrolytique a conduit à la précipitation de deux types d'hydrures (δ-TiHx, ε-TiH2) dans la matrice de phase , et il a été constaté que la fraction volumique de ces hydrures augmentait avec la durée du temps de chargement électrolytique. En raison du mode de formation par précipitation à partir des joints de grains, cinq relations d'orientation (OR) entre la -phase et l'hydrure δ-TiHx ont été déterminées par analyses des projections stéréographiques, et parmi celles-ci trois nouvelles relations d'orientation ont pu être mise en évidence. En outre, la corrélation entre la texture de laminage et la précipitation à l'hydrure a pu être établie. On a constaté que l'existence de la texture de de laminage facilitait la précipitation d'hydrure δ suivant l'orientation d’orientation de type OR2. Les analyses de rayons X révélaient un élargissement des pics de diffraction de la phase , ce qui indiquait une augmentation de la densité de dislocation, ces dislocations étant nécessaires pour tenir compte de l'inadéquation du réseau entre les hydrures et la matrice. Sur la surface d’échantillons déformés en compression, l'observation des traces de glissement et de macle de tension de type TT1 {10 2} < 011> dans les -grains contenant des hydrures a suggéré que les hydrures avaient une certaine capacité à supporter une déformation de cisaillement, en fonction des relations d'orientation entre la matrice et les hydrures mais aussi de leur épaisseur. Bien qu'aucune corrélation directe entre la nucléation des macles et la présence des hydrures n’ait été établie dans cette étude, l'effet des hydrures sur le développement des macles a été constaté. En étudiant l’effet de l'hydrogène sur le comportement au laminage à froid dans Ti50A, il a été possible de montrer que la formation de macle de type TT1 peut être facilitée par l'augmentation du rapport c/a de la maille hexagonale résultant de l’addition de l'hydrogène et de l'existence de contraintes locales générées par la précipitation des hydrures. Un raffinement de la microstructure a également été observé dans le Ti50A hydrogéné, ce qui suggère que la présence d'hydrures a tendance à générer de nouveaux grains de fortes désorientations (HAB). En outre, de nombreuses dislocations géométriquement nécessaires (GND) permettant de tenir compte de l'incompatibilité de contrainte entre l'hydrure et [...] / Due to an attractive combination of physical, chemical and mechanical properties, titanium and titanium alloys have become promising candidates in the field of chemical industry, aerospace and biomedical materials. During manufacturing procedures and applications, components are exposed to environments that can act as sources of hydrogen. Therefore, understanding their interaction with hydrogen upon various mechanical/thermal processing is important so that their properties and performance can be controlled and reliably predicted. With the aim of enhancing the properties and performance of titanium and reducing the cost of manufacturing products, the present work is primarily focusing on the effect of hydrogen on the cold rolling behavior and the subsequent annealing of titanium and titanium alloy characterized by different crystalline structure, i.e. hexagonal and body cubic centered (bcc) structure for the commercial pure titanium Ti50A and metastable β-titanium alloy β-21S, respectively. Since the microstructure of titanium and its alloys is the governing factor that determines their properties and performance, the microstructural evolution in the presence of hydrogen upon various procedures was analyzed by combination of XRD, SEM-EBSD and TEM. The introduction of hydrogen in Ti50A by electrolytic method induced the precipitation of two types of hydrides (δ-TiHx, ε-TiH2) in the  phase matrix, and it was found that the volume fraction of these hydrides increased as the charging time increased. Five orientation relationships (ORs), three of them being new orientation relationships ever reported, between the -phase and the hydride δ-TiHx were determined. Moreover, the correlation between the rolling texture and the hydride precipitation was also established. It was found that the existence of the rolling texture facilitated the precipitation of δ-hydride following the OR2-type orientation relationship. X-ray analyses revealed a broadening of the diffraction peaks corresponding to the  phase, indicating a increase of the dislocation density, these dislocations being necessary to accommodate the lattice misfit between hydrides and the matrix. Under compression loading, the observation of slip traces and tension twin {10 2}< 011> TT1 in the -grains containing hydrides, suggested that the hydrides had a certain ability to accommodate the imposed shear strain, depending on the orientation relationships between the matrix and the hydrides as well as on their thickness. Although no correlation between the nucleation of twinning and the hydride could be established in this study, the hydrides seemed to play an important role on the development of twinning deformation. The effects of hydrogen on the cold rolling behavior in Ti50A showed that, the formation of TT1tension twins can be facilitated due to the increase of the c/a ratio owing to the hydrogen addition and the existence of local stresses generated by the precipitation of hydrides. The refinement of the microstructure was also observed in the hydrogenated Ti50A-H suggesting that the presence of hydrides can enhance the generation of high angle boundaries (HABs). In addition, the formation of numerous geometrically necessary dislocations (GND) allowing the accommodation of the strain incompatibility between the hydride and matrix could be worked out by SEM-EBSD, which also confirmed analyses of the X-ray traces. In the case of β-21S alloy, with bcc structure that can accommodate a larger concentration of interstitial atoms, hydrogen was introduced by gas method. The effect of hydrogen on the microstructure was found to be closely related to the hydrogen concentration. In the range of hydrogen/metal ratio 0.052 < H/M < 0.300, the microstructure consisting of the single β-phase showed that the dissolved hydrogen atoms expanded the bcc β-lattice and suppressed the decomposition of the β phase upon cooling [...]

Este trabalho foi desenvolvido como parte das atividades relacionadas ao projeto de cooperação internacional Brasil-Alemanha intitulado "Bulk metal formed parts for power plants" pertencente ao BRAGECRIM (Iniciativa Brasil-Alemanha para Pesquisa Colaborativa em Tecnologia de Manufatura), realizado em parceria entre o Laboratório de Transformação Mecânica (LdTM) da Universidade Federal do Rio Grande do Sul e o Instituto de Conformação Mecânica (IBF) da Universidade Técnica de Aachen (RWTH), Alemanha. Este projeto visa o desenvolvimento do processo de forjamento a quente em matriz aberta para a produção de um eixo vazado para aplicação em aerogeradores de energia, em substituição à eixos maciços usualmente obtidos por fundição, visando aumento de desempenho mecânico e redução de peso da estrutura. Neste trabalho buscou-se analisar, por meio de simulação numérica computacional empregando o método de elementos finitos, diferentes parâmetros de forjamento, de modo a indicar a configuração operacional que se mostra mais adequada para a produção de um eixo vazado para a aplicação pretendida. Para isto, foram realizados cinco experimentos numéricos, avaliando a influência de parâmetros de forjamento na qualidade do produto forjado. Alguns parâmetros analisados foram: a sequência operacional de forjamento, geometrias e combinações de matrizes utilizadas industrialmente, razão de mordida, etc. Para as simulações termomecânicas foi utilizado o software de Elementos Finitos PEP/Larstran acoplado ao módulo de simulação de microestrutura Strucsim. O material utilizado nas simulações foi o aço DIN 42CrMo4 (AISI 4140). Os resultados mostraram que, dentre as diferentes combinações e geometrias de matrizes analisadas, o emprego de um par de matrizes côncavas, aplicando a sequência operacional-A analisada, tende a propiciar um produto de mais alta qualidade, promovendo maior uniformidade de deformação e microestrutura mais homogênea. Também, a razão de mordida influencia diretamente na qualidade do produto, sendo que uma razão de mordida na ordem de 0,6 induz graus de deformação maiores e mais profundos na peça forjada, ao mesmo tempo em que exige maiores cargas de conformação. Comparativos entre resultados da simulação e resultados experimentais de ensaios de compressão a quente de corpos de prova cilíndricos foram realizados para validação do software de simulação numérica. Os resultados experimentais mostraram que o software de simulação numérica pode prever com boa aproximação o fluxo de material e a evolução microestrutural durante o forjamento a quente do aço DIN 42CrMo4. / This work was developed as a part of the activities related to the international cooperation project between Brazil and Germany titled "Bulk formed metal parts for power plants" belonging to BRAGECRIM (Brazil-Germany Initiative for Collaborative Research in Manufacturing Technology). This project is in partnership between the Metal Forming Laboratory (LdTM) from the Federal University of Rio Grande do Sul (UFRGS) and the Institute of Metal Forming (IBF), from Technical University of Aachen (RWTH), Germany. The project aims the development of an open die forging process to produce a hollow shaft for application in wind turbines, replacing the solid shafts usually obtained by casting, in order to increase the mechanical performance and providing weight reduction to wind turbines. The present work aimed to analyze different forging parameters, using Finite Element Method, in order to indicate most suitable forging configuration to the production of a hollow shaft. Five numerical experiments were performed, evaluating the influence of various forging parameters on the quality of the forged product, such as the forging sequence, tool geometries and tool combinations and bite ratio. For thermomechanical simulations the Finite Element software PEP/Larstran was used, coupled to the microstructure simulation module Strucsim. The material used for the numerical simulations was the DIN 42CrMo4 steel (AISI 4140). The results showed that, among the different parameters analyzed, the use of concave dies, applying the operational sequence-A, tends to provide a forged with higher quality, promoting uniform strain distribution and homogeneous microstructure. Also, results showed that a bite ratio around 0,6 provides higher and deeper strain degrees, but requires higher forming loads. Hot compression tests using cylindrical specimens were performed to validate the numerical simulation software, including microstructure evolution. Comparison between simulation and experimental results showed that the numerical simulation software can predict with good approximation the material flow and microstructure evolution during hot forging for DIN 42CrMo4 steel.

Made available in DSpace on 2014-06-11T19:32:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-08-15Bitstream added on 2014-06-13T20:23:37Z : No. of bitstreams: 1 almeida_hl_dr_rcla.pdf: 806140 bytes, checksum: 7940276ecd62a931d89c15464ccc97db (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A zona de cisalhamento Itapetim (ZCI) desenvolveu foliação e lineação nos diferentes tipos de rochas, milonitos a ultramilonitos. Muitos dos tipos de microestruturas observadas na ZCI preservam evidências de condições metamórficas de alto grau e baixo grau de temperatura. O padrão das orientações preferenciais dos eixos [c] de quartzo, obtida a partir de agregados policristalinos deformados, mostra dois diferentes tipos de simetrias, guirlandas do tipo I e simples. A análise da textura sugere partição da deformação com cisalhamento coaxial e não coaxial na ZCI. Um veio de quartzo mineralizado em ouro encaixado em rocha ultramilonítica, constitui a zona de precipitação hidrotermal. O veio é bandado por segmentos de turmalina, o qual inclui agregados de grãos de quartzo maciço entre as bandas. Os grãos de quartzo mostram contatos poligonais e restritos limites intumescentes. O último sugere recristalização dinâmica por migração de limite de grão e os grãos poligonais (microestrutra em espuma) são melhor explicados por annealing. Os padrões de eixos [c] de quartzo obtido no veio aurífero é idêntico ao observado nos ultramilonitos da ZCI. Este padrão é interpretado como uma textura preservada formada durante o cisalhamento não coaxial. A estrutura bandada é interpretada como o resultado de variações da pressão de fluidos e a formação microfraturas, associadas a eventos de crack-seal. Mecanismos de crack-seal foram ativos antes ou durante a deformação da ZCI. As feições microestruturais suportam evidências para a última possibilidade. / The Itapetim shear zone(ISZ) developed both foliation and lineation in the different rock types, from mylonites to ultramylonites. Most of the microstructure types observed in the ISZ preserve evidence of high temperature metamorphic conditions. The quartz [c]-axis, of deformed polycrystalline aggregates, show two distinct symmetries, type I crossed girdles and single girdles. The geometrical analysis of texture, suggest non-coaxial shear for deformation in ISZ. A gold mineralized quartz vein hosted in ultramylonitic rocks, constitutes the hydrothermal precipitation zone. The vein is banded by tourmiline segments, which include massive quartz grains aggregates between the bands. The quartz grains show polygonal contacts and minor intumescent limits. These latter suggest grain boundary migration recrystallization and the polygonal grains seem to be best explained by the annealing after stopping the shear deformation. The quartz [c]-axis obtained in the auriferous vein shows the same single girdle pattern observed in the ultramylonites of the ISZ. This pattern is interpreted as a preserved texture formed during the shear deformation. The banded structure is interpreted as the result of variations of the fluid pressure and the formation of microfractures, associated the crack-seal events. Crack-seal mechanisms can have been active previous or during the deformation of the IZS. The microstructurals features supports evidences for the last possibility.

Made available in DSpace on 2014-10-09T12:34:12Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:46Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP