Made available in DSpace on 2014-10-09T12:41:19Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:03Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:26:44Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:15Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:41:19Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:03Z (GMT). No. of bitstreams: 0 / O titânio e suas ligas são biomateriais metálicos extensamente utilizados em aplicações médicas e odontológicas, apesar de não formarem ligação química com o osso circundante. Por isto é desejável técnicas que proporcionem a bioatividade na superfície desses metais. A proposta deste estudo foi avaliar e comparar, por testes in vitro e in vivo o comportamento de Ticp e da liga Ti-13Nb-13Zr utilizando diferentes tratamentos de superfície frente à formação do recobrimento biomimético e ao processo de osteointegração. Foram utilizadas placas comerciais de Ti e amostras da liga e de Ticp, obtidas por M/P. As amostras foram submetidas a quatro diferentes tratamentos de superfície (padrão - tratamento alcalino; 1°- tratamento alcalino e térmico; 2°- tratamento ácido e alcalino; 3º- tratamento alcalino, CaCl2, térmico e água quente), analisadas quanto à formação de apatita em SBF em períodos de 1 a 21 dias. Os recobrimentos obtidos foram caracterizado por MEV e DRIFT. Para a avaliação in vivo dos implantes, obtidos por M/P, de Ticp e da liga, com e sem tratamentos superficiais, foram utilizados coelhos adultos machos. A avaliação teve duração de 7 semanas em que foram aplicados marcadores celulares ósseos em tempos e sequência específicos do pós-operatório. Na avaliação in vitro, os recobrimentos de maior espessura foram nas amostras obtidas por M/P, comparativamente à amostra laminada. Todos os tratamentos foram efetivos na promoção da bioatividade. O 2º tratamento obteve recobrimento com maior espessura nos períodos avaliados para todas as superfícies. Na avaliação in vivo, ocorreu crescimento ósseo com osteointegração em todos os implantes com e sem tratamentos superficiais. O crescimento ósseo na interface osso/implante ocorreu de forma contínua em todo o período de reparação para o Ticp, o Ticp com tratamento padrão, o Ticp com o 2º tratamento e a liga com o 1° tratamento; e ocorreu de forma mais intensa no primeiro e terceiro período de reparação para os demais implantes. Os resultados dos testes in vitro e in vivo não são passíveis de analogia direta neste estudo, pois forneceram informações importantes sobre a formação, morfologia e taxa de aposição do recobrimento aos diferentes tratamentos de superfície e a efetividade da osteointegração destes tratamentos de superfície em modelo animal. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:26:44Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:15Z (GMT). No. of bitstreams: 0 / O hidrogênio vem sendo muito utilizado como agente pulverizador de ligas à base de terras raras e metais de transição devido à sua taxa de difusão ser extremamente alta mesmo em baixas temperaturas. Tais materiais são utilizados em dispositivos de estocagem de hidrogênio, geração de eletricidade ou de campos magnéticos, que são produzidos através de um processo cuja primeira etapa é a transformação das ligas em um pó fino através de moagem. Além destas, o hidrogênio também está sendo utilizado para a obtenção de ligas à base de titânio nióbio zircônio para sua pulverização. Para a fabricação destas ligas a metalurgia do pó é utilizada, pois com ela é possível obter como resultado peças com superfície porosa, requisito para sua aplicação como biomateriais. Outras vantagens da utilização da metalurgia do pó na fabricação dessas ligas são melhor acabamento superficial e melhor homogeneidade microestrutural. Neste trabalho foram preparadas amostras na composição Ti-13Nb-13Zr. A hidrogenação foi realizada a 700°C, 600°C e a 500°C para o titânio, nióbio e zircônio, respectivamente. Após a hidrogenação, foram realizadas moagens em moinho do tipo planetário de alta energia utilizando velocidade de 200rpm durante 90 minutos, e moinho convencional de bolas durante 30h. As amostras foram prensadas em prensa uniaxial e em seguida em prensa isostática e então sinterizadas a 1150°C com tempo de patamar de 7 a 13h. As amostras foram caracterizadas microestruturalmente por microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva (EDS) e difração de raios X. As propriedades estruturais e mecânicas determinadas foram de densidade, microdureza e módulo de elasticidade. A amostra sinterizada a 1150°C por 7h, hidrogenada com pressão de 10.000 mbar e produzida por moagem em moinho planetário de alta energia apresentou melhores propriedades mecânicas e boa homogeneidade microestrutural, obtendo a composição final da liga Ti-13Nb- 13Zr. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Durant un scénario d'Accident par Perte de Réfrigérant Primaire (APRP), les gainages combustible en alliage de zirconium fluent sous pression interne et s'oxydent en présence de vapeur à haute température (HT). La gaine devient un matériau stratifié : des couches de zircone et de phase alpha fortement enrichie en oxygène, dite alpha(O), se forment à la surface externe de la gaine, qui est alors en phase beta. L'effet durcissant de l'oxydation sur le comportement en fluage des gaines sous pression interne a été mis en évidence dans des essais de laboratoire. Pour modéliser cet effet, le comportement mécanique de chacune des couches doit être déterminé. En particulier, cette étude a porté sur la caractérisation expérimentale du comportement en fluage de la phase alpha(O). Via un procédé original, des matériaux « modèles » contenant de 2 à 7 % en masse d'oxygène et représentatifs de la phase alpha(O) ont été produits puis testés en fluage axial sous vide. Pour la première fois, deux régimes de fluage ont été observés, pour lesquels les mécanismes et paramètres microstructuraux influents sont discutés. L'effet durcissant de l'oxygène sur le comportement en fluage de la phase alpha(O) a été quantifié et des lois d'écoulement viscoplastique, intégrant cet effet, ont été identifiées. Une fragilisation progressive par l'oxygène a également été mise en évidence. Une transition ductile/fragile, fonction de la température et de la teneur en oxygène, est proposée. Après avoir discuté leur pertinence, les lois de fluage pour chacune des couches, identifiées dans cette étude ou tirées de la littérature, ont été implémentées dans un modèle par éléments finis, décrivant la gaine comme un matériau stratifié. Ce modèle permet de reproduire une partie du durcissement observé expérimentalement. / During hypothetical Loss-Of-Coolant-Accident (LOCA) scenarii, zirconium alloy fuel cladding tubes creep under internal pressure and are oxidized at high temperature (HT). Claddings become stratified materials: zirconia and oxygen-stabilized alpha phase, called alpha(O), are formed on the outer surface of the cladding in beta phase.The strengthening effect of the oxidation on the cladding creep behavior under internal pressure was highlighted at HT. In order to model this effect, the creep behavior of each layer must be known.This study focused on the characterization of the creep behavior of the alpha(O) phase at HT, through axial creep tests performed under vacuum on model materials containing from 2 to 7 wt.% of oxygen, representative of the alpha(O) phase. The strengthening effect and the embrittlement due to oxygen on the alpha(O) phase creep behavior at HT was quantified and creep laws were identified.Relevance of the creep laws for each layer, identified in this study or from the literature, is discussed. Then, a finite elements model, describing the oxidized cladding as a stratified material, is built. Based on this model, a fraction of the experimental strengthening during creep is predicted.

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No description available.

During loss-of-coolant accidents (LOCA) and reactivity-initiated accidents (RIA), nuclear fuel rods experience high heating rates that change the microstructure and properties of zirconium cladding materials, which are in forms of stress-relieved, like cold-worked (CW) or recrystallised (RX) microstructure. The present study aimed to determine how different fast heating rates and starting microstructures affect the kinetics of phase transformation, the transformation textures and eventually the mechanical response in the dual-phase region. The LOCA/RIA cycles from heating at 8 to 100C/s to alpha+beta or above beta transus temperature were achieved via resistive heating in an electro-thermal-mechanical tester. Synchrotron X-ray diffraction (SXRD) and electrical resistivity measurements showed that the approach curves of CW Zircaloy-4 shift to higher temperature at faster constant heating rates and change to a new approach curve when changing rates. 2-second holding at two-phase temperature produces identical phase fractions as equilibrium. These observations are consistent with the diffusional character of the phase trans- formation. Heated at 100oCs1, RX samples transform with 2D beta-growth while CW ones show simultaneous beta-nucleation and growth. The difference arises because the fast heating rate helps preserve low-angle grain boundaries (GB) in the CW microstructure up to phase transformation temperature, increasing beta nucleation sites and prevent beta-growth. This gives rise to different textures of RX and CW materials before transformation, producing different textures, which are weak in both cases. However, this difference is enhanced during grain growth and transformation on cooling. Thus, the RX material shows strong final alpha texture with 0002 maxima aligned in TD and tilted 20deg from ND towards TD while the CW reveals an essentially random one. In both RX and CW materials, variant selection does not occur during transformation on heating. During beta-grain growth, although there is variability in beta-textures measured by SXRD and EBSD beta reconstruction, it is clear that variant selection occurs, leading to strengthening of the beta texture. During transformation on cooling, variant selection occurs early in nucleation of the alpha phase from the shared 110 beta GB in the RX condition. The flow stresses of CW Zircaloy-4 in the two-phase regime at a given temperature depend on the heating rates, despite having the same phase fractions. Heated at a slower rate, the material shows an upper yield stress followed by softening behaviour while that heated faster has a smaller yield stress followed by a high work-hardening rate and then stable flowing stresses. The evolution of diffraction elastic strains and intensity suggest the upper yield stress and softening are due to stress-induced transformation of the harder alpha grains into large and isolated softer beta grains. In contrast, the sample heated faster develops an almost continuous film of beta grains along the GB of unrecrystallised alpha-grains which results in early beta-yielding and coherent deformation of the two phases, leading to constant flow stresses. The findings will improve the accuracy of inputs from phase fractions, microstructure and texture of zirconium claddings when modelling LOCA/RIA. A crystal plasticity model should consider the effects of heating rates and cold-work, which are often ignored. The link between deformation, fast heating rates and microstructure evolution might be relevant to other processes like additive layer manufacturing and even forging in the two-phase region.

Ce travail de thèse a pour objet de contribuer à la compréhension de la déformation des assemblages combustibles REP équipés de composants en alliages de zirconium (Zy-4 ou M5). En particulier, nous nous sommes intéressés à l’accélération de croissance, corrélée à l’apparition d’un type de défaut d’irradiation : les boucles à composante <c>. Des irradiations aux particules chargées nous ont permis de reproduire ces évolutions microstructurales et d’étudier leur représentativité. La morphologie du dommage primaire n’a ainsi que peu d’impact sur la microstructure de boucles <c> tandis que le taux de création de dommage (tout comme la température) semble jouer un rôle majeur. Par ailleurs, la dose seuil pour la nucléation des boucles <c> apparaît étroitement liée à la cinétique de croissance des amas lacunaires et des germes de boucles. Cette cinétique peut être influencée par le taux de création de dommage, les éléments d’alliages, mais également la contrainte ou la présence d’hydrogène (introduit dans le matériau lors de l’oxydation en réacteur). Ce travail a ainsi exploré de manière approfondie l’effet d’une contrainte appliquée dans les domaines d’élasticité et de plasticité ainsi que l’impact de l’hydrogène absorbé sur la nucléation et la croissance des boucles <c>. Conformément au mécanisme SIPA proposé dans la littérature, nous avons observé un effet de la contrainte sur les boucles <c>. Par ailleurs, cette étude met en évidence que l’hydrogène en solution et / ou sous forme d’hydrures influence significativement la nucléation et la croissance des boucles <c>. / The aim of this PhD work is to have a better understanding of axial elongation of the PWR fuel assemblies manufactured in zirconium alloys (Zy-4 or M5). More specifically, we focused on the growth acceleration of these assemblies, clearly correlated to the nucleation of specific irradiation defects: the c-loops. Irradiations by charged particles were performed in order to reproduce the microstructure evolution and to study its representativeness. Thus, primary damage morphology has no impact on the c-loop microstructures where as the damage creation rate (like the temperature) seems to play a major role. Moreover, the nucleation dose for c-loops appears clearly correlated to the nuclei and vacancy clusters growth kinetics. This kinetics could be influenced by the damage creation rate, the alloying elements, but also by an applied stress or the hydrogen content (which can be introduced during oxidation in reactor). Thus, this work has explored the effect of an applied stress (in the elasticity or plasticity domain) and the impact of the hydrogen pick-up on the nucleation and growth of c-loops. In accordance with the SIPA mechanism described in the literature, we observed an effect of the applied stress on the c-loop microstructures. Moreover, this study clearly shows an impact of hydrogen in solid solution and as precipitated hydrides on the nucleation and growth of c-loops.

Theoretical studies of point defect interactions and structural stability of compounds have been performed using density functional theory. The defect-related properties, such as activation energy of diffusion, electronic and magnetic structure of selected materials have been studied. The major part of the present work is devoted to a very important material for semiconductor industry, GaAs. The formation energies of intrinsic point defects and the solution energies of 3d transitions in GaAs have been calculated from first principles. Based on the calculated energies, we analysed the site preference of defects in the crystal. The tendency of defects to form clusters has been investigated for the intrinsic defects as well as for impurities in GaAs. The magnetic moment of 3d impurities has been calculated as a function of the chemical environment. The possibility of increasing the Curie temperature in (Ga,Mn)As by co-doping it with Cr impurities has been examined on the basis of calculated total energy difference between the disordered local moment and the ferromagnetically ordered spin configurations. We found that, in order to reach the highest critical temperature, GaAs should be separately doped with either Cr or Mn impurities. Also, we have shown that diffusion barrier of interstitial Mn depends on the charge state of this impurity in (Ga, Mn)As. The formation of defect complexes between interstitial and substitutional Mn atoms, and their influence on the value of diffusion barrier for interstitial Mn, has been studied. The pair interactions energies between interstitial oxygen atoms in hcp Zr, Hf and Ti have been calculated using first principles. Based on the calculated energies, the oxygen ordering structures in IVB transition metal solid solutions have been explained. A prediction of nitrogen ordering in Hf-N solid solution has been made. The thermodynamic description of intermetallic compounds in the Zr-Sn binary system has been obtained. The conclusion has been made that Zr substitution on the Sn sites takes place in the Zr4Sn phase, which accounts for the unusual stoichiometry of this Cr3Si structure type compound. The influence of pressure on the phase stability in the Fe-Si system has been investigated. We have found instability of the hcp Fe0.9Si0.1 random alloy with respect to the decomposition onto the Si-poor hcp Fe alloy and the B2 FeSi under high pressure. The tendency of this decomposition becomes stronger with increasing the applied pressure. / QC 20100624