Three aluminium alloys from AA3003 series modified by zirconium were pre- pared by twin-roll casting. The role of composition, heat treatment and deforma- tion by cold-rolling or equal channel angular pressing on evolution of microstruc- ture and mechanical properties were studied. High density of α-Al(Mn,Fe)Si pre- cipitates formed during annealing between 300 ◦ C and 500 ◦ C. Coherent Al3Zr particles precipitated during annealing at 450 ◦ C with slow heating rate. Recrys- tallization resistance of deformed alloys was enhanced by either Al3Zr precipitates formed before deformation or by α-Al(Mn,Fe)Si particles nucleating simultane- ously with recrystallization. 1

Les méthodes conçues pour être incorporées dans des polycristaux de modélisation multi-échelles sont présentées dans ce travail en deux tâches. Ce travail contient des méthodes à moyenne échelle pour capturer les effets des interactions de dislocations de glissement rencontrant des joints de grains maclage et la croissance simultanée de plusieurs fractions de volume de grains maclage sur le durcissement mécanique et l’évolution de la texture. Celles-ci sont mises en œuvre dans un cadre de plasticité cristalline utilisant le code visco-plastic-self consistent de Los Alamos, VPSC-7. Présentés ici, les effets de la croissance simultanée de multiples variantes maclage sur l’évolution de la texture sont suivis à l’aide d’un schéma de transfert de volume double de type Kalidindi. Dans la tâche 1, la mise en œuvre de ce schéma afin de simuler la texture des aciers à plasticité induite par maclage (TWIP) soumis au pressage angulaire à canal égal (ECAP) est résumée. Dans la tâche 2, les effets de durcissement de deux types d’interaction entre les dislocations de glissement et les joints de grain maclage rencontrés, à savoir la transmutation et la dissociation de dislocation, sont capturés au moyen de la modification du modèle de durcissement basé sur la densité de dislocation de [11]. Les interactions du premier type sont présentées dans une relation constitutive calculant la quantité de densité de dislocations attribuée à un système de glissement donné contenu dans la fraction de volume maclage rencontrée à partir de chaque système de glissement en interaction dans la fraction de volume mère. La quantité transmutée à partir de chaque système de glissement en interaction décrit à l’aide de la méthode de correspondance, sur la cartographie des systèmes de glisse- ment d’un grain parent à des systèmes de glissement dans des grains maclage considérés. Des interactions du second type sont ensuite introduites dans cette relation constitutive en tant que paramètre de dissociation, dont la valeur est établie par les observations tirées des résultats des simulations de dynamique moléculaire de [8] et [53]. Ces méthodes sont implantées pour simuler le comportement de durcissement anisotrope du magnésium HCP sous plusieurs chemins de charge / Methods designed for incorporation into multiscale modeling polycrystals are presented in this work in two tasks. This work contains mesoscale methods for capturing the effects of both the interactions of slip dislocations encountering twin grain boundaries and the simultaneous growth of multiple twin grain volume fractions on mechanical hardening and texture evolution. These are implemented in a crystal plasticity framework using the Los Alamos viscoplastic self-consistent code, VPSC-7. Presented here, the effects of simultaneous growth in multiple twin variants on textural evolution is tracked using a Kalidindi-type twin volume transfer scheme. In Task 1, the implementation of this scheme in order to simulate the texture of Twinning Induced Plasticity steels (TWIP) subjected to Equal Channel Angular Pressing (ECAP) are summarized. In Task 2, the hardening effects of two types of interactions between slip dislocations and encountered twin grain boundaries, namely dislocation transmutation and dissociation, are captured by way of modifying the dislocation density based hardening model of [11]. Interactions of the first type are presented in a constitutive relation calculating the amount of dislocation density apportioned to a given slip system contained within the encountered twin volume fraction from each interacting slip system in the parent volume fraction. The amount transmuted from each interacting slip system described using the Correspondence Method, an on to mapping of slip systems in a parent grain to slip systems in considered twin grains. Interactions of the second type are then introduced into this constitutive relation as a disassociation parameter, the value of which is established by observations gleaned from the results of the molecular dynamics simulations of [8] and [53]. These methods are implanted to simulate the anisotropic hardening behavior of HCP magnesium under multiple load paths

Title: Effect of composition and microstructure on mechanical and corrosion properties in magnesium alloys with a potential for medical applications. Author: RNDr. Peter MINÁRIK Department / Institute: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Doc. Dr. rer. nat. Robert Král, PhD., Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Abstract: Doctoral thesis is focused on the effect of thermomechanical processing through ECAP on the microstructure, mechanical properties and corrosion properties. The investigation was performed on the extruded magnesium alloys AE21, AE42 and LAE442, because their potential for medical applications. Microstructure development was characterized in detail by scanning electron microscopy together with detection of back scattered electros, transmission electron microscopy and positron annihilation spectroscopy. Development of mechanical properties was investigated by tensile and compression deformation tests and microhardness measurement. Corrosion resistance was investigated by linear polarization method. Fine-grain structure with grain boundaries with high angle misorientation was achieved by the thermomechanical processing. The resulting...

Title: Magnesium alloys designed for medical applications Author: Mária Zemková Abstract: This Master thesis is focused on the influence of hot extrusion and equal channel angular pressing (ECAP) on the microstructure, mechanical and corrosion properties of magnesium alloys. Investigated materials include three magnesium alloys with the addition of neodymium and/or yttrium elements - N3, W3 and WN43, as a potential material for medical applications. Moreover, the influence of alloying elements in solid solution state was studied. Microstructure development was characterized by scanning electron microscopy together with transmission electron microscopy and X-ray diffraction. Mechanical properties was studied by compression deformation tests in two perpendicular directions and by microhardness tests. The linear polarization method was used to study corrosion resistance. The processing though ECAP resulted in grain refinement in all three alloys. Ultra-fine grained microstructure was achieved in W3 and WN43 alloy. The high degree of recrystallization during ECAP caused the formation of high-angle grain boundaries in all three alloys. Weak texture evolution was maintained during both processings. A different initial fraction of intermetallic phases before extrusion led to significant changes of microstructure...

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This investigated the use of equiangular channel press (ECAP) in samples of pure niobium at room temperature up to 14 passes, using the Bc route, with a matrix with intersection angle between the channels of θ = 90º and 120º, with and curvature angle Ψ = 0°. During ECAP (equal channel angular pressing) deformation a bar is pressed through a rigid matrix consisting of two channels of the same cross-section, which intersect at an angle θ. The microstructure of the deformed samples has been analyzed with the aid of optic microscopy, scanning electron microscopy and Vickers Hardness (HV). With the deformation of pure niobium through ECAP, it was possible to refine the structure and increase the hardness due to the increase of the number of passes and the type of matrix. The results indicated that deformation of the niobium with a pass in the matrices of 90 ° and 120 ° was enough to produce the refinement of the microstructure and practically double the hardness values in relation to the material without deformation. The maximum microstructural refinement, steady state, occurred with 8 passes in the 120 ° matrix and 6 passes in the 90 ° matrix, indicating a higher deformation severity of the last matrix. The microstructures analyzed by scanning electron and optical microscopes revealed the microstructural changes with the increase of the number of passes and the type of matrix. / Este trabalho investigou o uso da prensagem em canais equiangulares (ECAP) em amostras de nióbio puro na temperatura ambiente até 14 passes, utilizando a rota Bc, com matrizes contendo ângulo de intersecção entre os canais de θ = 90º e 120°. Durante a deformação ECAP uma barra é pressionada através de uma matriz rígida consistindo de dois canais de mesma seção transversal, os quais se interceptam a um ângulo θ. A microestrutura das amostras deformadas foi analisada com auxílio de microscopia óptica, microscopia eletrônica de varredura e dureza Vickers (HV). Com a deformação do nióbio puro através do ECAP foi possível refinar a estrutura e aumentar a dureza em função do aumento do número de passes e do tipo de matriz. Os resultados indicaram que deformação do nióbio com um passe, nas matrizes de 90º e 120°, foi suficiente para produzir o refinamento da microestrutura e praticamente dobrar os valores de dureza em relação ao material sem deformação. O refinamento microestrutural máximo, estado estacionário, ocorreu com 8 passes na matriz de 120° e 6 passes na matriz de 90°, indicando maior severidade de deformação da última matriz. As microestruturas analisadas por microscopias ótica e eletrônica de varredura revelaram as mudanças microestruturais com o aumento do número de passes e com o tipo de matriz. / São Cristóvão, SE

Made available in DSpace on 2017-07-21T20:42:44Z (GMT). No. of bitstreams: 1 Marcos Pontes.pdf: 4006153 bytes, checksum: 42b95748e61f5bc3de1b41ca1fbd649b (MD5) Previous issue date: 2012-02-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The processing by equal channel angular extrusion of a duplex stainless steel UNS32205/S31803, with ferritic-austenitic structures, was studied, processing until four passes each sample. The reason of this processing was to promote a grain refinement in the material, to achieve ultrafined grain material by severe plastic deformation. Different number of passes were used in this processing to evaluate how the number of extrusions in the same sample influences the deformation imposed to the material. After processing, some different heat treatments were done in the samples to evaluate the recrystallization process in the processed material. In this study, it was possible to verify the increasing level of deformation in the material after every new processing in the sample, this was verified by the changes in grain orientation and by microstructure evaluation. It was possible to reduce the stress level to values that can avoid the breaking of punctures during processing, this allowed to process the material with a greater number of passes in a material with a high resistance like the duplex stainless steels. Strain bands were found in the structure of the processed material, this indicates high levels of deformation. / Foi realizado o estudo do processamento de um aço inoxidável dúplex SAF2205,com microestrutura ferrítica-austenítica, por extrusão em canal angular por até quatro passes. O objetivo deste processamento foi a obtenção de um refino de grãos no material, atingindo uma estrutura de grãos ultrafinos, a partir da aplicação de deformações plásticas severas. Foram realizados diferentes modos de processamento, variando o número de passes pela matriz e depois foi avaliado como este parâmetro influencia na deformação imposta ao material. Após o processamento por ECA (Extrusão por Canal Angular), foram realizados diferentes tratamentos térmicos para avaliar a cinética de recristalização do material. Foi possível verificar o nível crescente de deformação do material após cada passe, com o acompanhamento da orientação dos grãos e avaliações microestruturais. Foi possível reduzir os níveis de tensões o suficiente para evitar a quebra de punções durante o processamento, permitindo um número maior de passes para um material com a resistência do aço inoxidável dúplex. Foram verificadas bandas de deformação no material processado, indicando níveis elevados de deformação.

La modélisation des efforts de coupe en usinage est nécessaire pour prédire certaines caractéristiques de la pièce usinée comme sa géométrie, son état de surface ou encore l'intégrité de la matière en sub-surface.Les nombreux modèles d'efforts de coupe déjà développés sont souvent appliqués dans le cas d'opérations d'usinage simples, ce qui limite leur diffusion vers le milieu industriel, alors qu'il existe un réel besoin de modélisation d'opérations d'usinage complexes et variées, et prenant en compte d'éventuels changements métallurgiques au niveau du matériau usiné.L'objectif de ces travaux est de proposer un modèle d'efforts de coupe appliqué à toute opération de tournage d'une part et considérant certaines propriétés mécaniques du matériau usiné d'autre part.Concernant l'aspect multi-opérations, un modèle géométrique utilisant des transformations homogènes a été développé et permet de décrire à la fois la trajectoire et la géométrie de l'outil. Les effets de paramètres originaux, tels que le diamètre de la pièce, l'angle de direction d'arête et le rayon de bec, sont étudiés, notamment à l'aide de nouvelles configurations de coupe élémentaires. La prise en compte de ces paramètres dans les relations de coupe locales permet finalement d'améliorer la simulation des efforts de coupe lors d'un contournage.L'approche utilisée pour l'aspect multi-matériaux consiste à modifier progressivement le matériau usiné. Ainsi, le matériau initial, le cuivre pur, a été étudié dans différents états métallurgiques, obtenus par des traitements thermo-mécaniques. En particulier, le procédé d'extrusion coudée à aires égales (ECAE) a été utilisé afin d'écrouir le matériau dans la masse. Ainsi, trois matériaux aux caractéristiques mécaniques différentes mais conservant plusieurs caractéristiques communes (thermiques notamment) ont pu être comparés en termes d'efforts de coupe. Les coefficients des relations de coupe sont finalement mis en regard des propriétés mécaniques obtenues par des essais de traction et de compression à grande vitesse.

Orientador: Ana Paula Rosifini Claro / Resumo: Dentre os materiais utilizados em aplicações biomédicas, o titânio e suas ligas apresentaram destaque devido a suas excelentes propriedades de volume, como por exemplo, resistência mecânica. No entanto, essas propriedades estão diretamente ligadas à microestrutura, que estão diretamente relacionadas com o seu processamento. O objetivo deste trabalho foi avaliar a influência da deformação plástica severa por Equal Channel Angular Presssing (ECAP) na microestrutura e propriedades mecânicas da liga experimental Ti25Ta25Nb3Sn. Os lingotes da liga Ti25Ta25Nb3Sn foram processados em forno de fusão a arco voltaico com atmosfera controlada e submetidos a tratamento térmico de homogeneização para posterior forjamento a frio. Para o processamento por ECAP os lingotes foram previamente tratados por solubilização. Uma matriz com canal de 90º foi utilizada no processamento por ECAP, seguindo a rota Bc, processando o material com 2 e 4 passes. A morfologia, composição e estrutura foram investigadas usando microscopia eletrônica de varredura, microscopia eletrônica de transmissão e análise por EBSD. As análises de microscopia e EBSD mostraram uma estrutura com uma mistura de grãos refinados e grãos grosseiros após 2 passes e uma homogeneidade maior de grãos refinados após 4 passes. A difração de Raios X indicou a formação da fase α'' e β após 2 passes do processamento por ECAP e após 4 passes apenas a fase β estava presente na estrutura. / Doutor

This thesis deals with the influence of grain refinement by ECAP on fatigue properties of magnesium alloy AZ 91. Tensile and fatigue tests were made on the as-cast state samples and samples after ECAP process. Metallographic analysis of the microstructure and fractographic analysis of the fracture surfaces was performed.