Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Th.--Sci. phys.--Grenoble--I.N.P., 1982. N°: DE 130.

Th. 3e cycle--Sci. des matér.--Toulouse--I.N.P., 1982. N°: 125.

Made available in DSpace on 2014-06-11T19:27:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-12-14Bitstream added on 2014-06-13T20:35:17Z : No. of bitstreams: 1 leite_mp_me_guara.pdf: 5697159 bytes, checksum: 3d01e115bf6ba84fde15df65623ceef4 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho foi realizado o estudo da fragilização pelo hidrogênio em um tubo de aço API 5L X65 de alto grau de limpidez para uso em dutos de condução para aplicação em ambientes que contém gás sulfídrico. Ensaios normalizados foram realizados com o objetivo de caracterizar as propriedades do material em estudo, através de análise química, análise microestrutural, ensaios mecânicos - dureza, tração, impacto e drop weight (DWTT), ensaios de corrosão - ensaios de HIC e SSC - e ensaios eletroquímicos - curvas de polarização potenciodinâmica, voltametria cíclica e medições de corrente de permeação de hidrogênio. Os resultados apresentaram: a) microestrutura refinada predominante de ferrita acicular, b) caracterização mecânica com resultados dentro do especificado pela norma de fabricação, c) análise química e ensaios de corrosão com resultados superando os requisitos da norma de fabricação e d) nos ensaios eletroquímicos foi evidenciado que o aço em estudo apresentou uma baixa corrente de permeação e uma maior resistência à corrosão em meio de NaCl 3,5% em relação a um aço padrão. Os resultados indicam que o material em estudo atende os critérios da norma de fabricação do tubo (API 5L), sendo evidenciado que o mesmo é adequado para utilização ao ambiente que lhe é proposto / In this paper, it was carried out a study of a hydrogen embrittlement in a pipe API 5L X65 with high level of cleanness for linepipe used in sour service environment.. It was performed standardized testing in order to perform an assessment of the material properties, through the chemical analysis and microstructural analysis, mechanical tests – hardness, tensile, impact and drop weight tear test (DWTT), corrosion tests - HIC and SSC tests - and electrochemical tests - potentiodynamic polarization curves, cyclic voltammetry and hydrogen permeation current measurements. The results presented: a) refined microstructure predominant of acicular ferrite, b) mechanical characterization with results that fulfilled with the pipe fabrication standard, c) chemical analysis and corrosion tests with results exceeding the requirements of the standard and d) electrochemical tests showing the studied steel presenting a low permeation current and a higher corrosion resistance in a environment of NaCl 3,5% in relation of standard steel. The results indicate that the studied material complies with the acceptance criteria of the pipe fabrication standard (API 5L), and it was evidenced that the material is suitable for use in sour service environment

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Pits have been observed to initiate at certain inclusions in stainless steel, which affect the composition and properties of the passive film in that region. In this thesis, the VG MA500 high resolution scanning Auger microscope associated with Link EDX is used to investigate the surface chemistry of inclusion groups in stainless steel 316 relative to the bulk composition, before and after exposure to sodium chloride solution. The work demonstrates that careful control of experimental conditions allows the progress of initiation of pits to be observed systematically. The role of inclusions as initiators of pitting corrosion has been studied from the very inception of attack. Detailed observation have been taken from separate manganese sulphide as well as mixture of manganese sulphide and multi-element oxide at various pH values of solutions to trace the behaviour of these inclusions during exposures. It is suggested from this investigation that corrosive attack starts on MnS inclusion proper. The dissolution of MnS takes place in sodium chloride solution followed by the acidification in the microarea and dissolution of metal in the region adjacent to the inclusion. The mechanism for the crevice corrosion is of importance after the microcrevice forms. The observations showed that sulphur precipitated on the area surrounding the inclusion group in acidic sodium chloride solution. This is in contrast to the finding in prior studies by electron probe or EDX analyses in which sulphur precipitation was only observed on the inclusion. Because pitting normally occurs on surfacesthat are initially exposed to air before being immersed in the corrosive solution, an understanding of the change of surface film associated with the change of medium is very important. XPS was used in this work to study the air formed and aqueous films, the transformation when the specimens were immersed in solutions. The study of the energy-loss structure of photoelectron peaks has lead to a better understanding of these various films. It has been used to study in greater detail the composition and properties of the films formed on Fe-Cr alloys during oxidation, vacuum annealing, and to find the relationship between the depth distribution of the components in the films and energy loss background of photoelectron peaks. Three features are of particular importance: the background loss tail height, the baseline slope and the post-peak loss structure. These features have been related quantitatively to the relative amounts of the element and the surrounding matrix in the layers which contribute the greatest signal at any given take-off angle. The present work illustrates that the additional depth information available from closer inspection of the inelastic loss background feature may aid an understanding of the change from the air-formed film to the aqueous film as well its effect on the initiation of pits in stainless steel 316. The combination of AES and EDX with high spatial resolution gave an opportunity to re-investigate the initiation of pits at the site of inclusion on stainless steel by offering both bulk and surface information. The use of AES and XPS associated with the energy loss structure of photoelectron peaks facilitates a comprehensive understanding for the whole surface of various films and the local areas which are involved in the formation of pits.

Les aciers inoxydables super martensitiques sont très utilisés dans le secteur pétrochimique, mais ils présentent des ruptures en service en conditions sévères. L'objectif de cette étude est d'apporter une meilleure compréhension du mécanisme de corrosion sous contrainte de ces matériaux en milieu H$_2$S. Pour cela, des coulées laboratoires ont été élaborées avec différentes teneurs en molybdène, élément connu pour améliorer la résistance à la corrosion. Ces ajouts d'éléments d'alliage impliquent alors une caractérisation fine de la microstructure, pour bien appréhender par la suite les mécanismes de rupture. Une attention particulière a été apportée à l'évolution de la fraction d'austénite et de ferrite résiduelle avec les traitements thermiques d'hypertrempe et de revenus qui sont couramment pratiqués sur ces nuances. Puis, par des mesures électrochimiques sans contrainte mécanique, l'ajout de molybdène a été identifiée comme bénéfique pour renforcer la passivité de la nuance dans le milieu H$_2$S. Et pour des teneurs en molybdène inférieures à 2,25%, des produits de corrosion ont été identifiés, principalement des sulfures de nickel, qui sont des inhibiteurs de la recombinaison de l'hydrogène. Par la suite, des essais de corrosion sous contrainte sous charge statique et dynamique couplés à des mesures d'impédance électrochimique montrent un effet bénéfique du molybdène et de l'austénite résiduelle. Le molybdène permet notamment de réduire les défauts du film passif. Un modèle d'éléments finis permet de simuler les essais de traction lente en tenant compte de la fragilisation par hydrogène. Afin de l'alimenter avec des paramètres expérimentaux, une cellule de perméation électrochimique a été montée et a permis de mesurer le coefficient de diffusion de l'hydrogène au sein de nos différentes coulées. Le modèle présente alors une bonne adéquation avec les résultats expérimentaux et une étude paramétrique a été réalisée sur le coefficient de diffusion et sur la concentration interfaciale en hydrogène. Enfin, une synthèse permet la proposition d?un mécanisme de corrosion sous contrainte comportant deux étapes : la résistance du film passif pour limiter l'absorption de l?hydrogène dans la matrice et le piégeage de l'hydrogène par l'austénite résiduelle en fonction de la déformation. / Super martensitic stainless steels are widely used in the oil and gas industry, but failures occurred in service under severe conditions. The aim of this study is to provide a better understanding of the stress corrosion mechanism in H$_2$S medium. For this purpose, laboratory heats have been casted with different molybdenum contents, a component known to improve corrosion resistance. These additions of alloying elements then involve a fine characterization of the microstructure, in order to grasp the mechanisms of rupture. Particular attention has been paid to the evolution of the retained austenite and residual ferrite fraction with the heat treatments of quench and annealing which are commonly practiced on these grades. Then, by electrochemical measurements without mechanical stress, the addition of molybdenum was identified as beneficial for the passivity of the grade in the H$_2$S medium. And for 2.25% molybdenum contents, corrosion products have been identified as mainly nickel sulfides, which are inhibitors of hydrogen recombination. Subsequently, corrosion tests under static and dynamic load coupled to electrochemical impedance measurements show a beneficial effect of molybdenum and residual austenite. In particular, molybdenum reduces the defects of the passive film. A finite elements model simulates the slow strain rate traction tests taking into account the hydrogen embrittlement. In order to use experimental parameters, an electrochemical permeation cell was implemented and used to measure the hydrogen diffusion coefficient within our different heats. A good match with the experimental results was obtained with this model and a parametric study was carried out on the diffusion coefficient and the hydrogen interfacial concentration. Finally, a synthesis provides the proposal of a stress corrosion mechanism divided in two steps: the passive film resistance to limit the hydrogen absorption in the matrix and the trapping of the hydrogen by the residual austenite in function deformation.

Made available in DSpace on 2014-06-11T19:35:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2001Bitstream added on 2014-06-13T18:46:14Z : No. of bitstreams: 1 acciari_ha_dr_araiq.pdf: 3985367 bytes, checksum: 669d0836181f115365689e398ad14653 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Este trabalho consistiu de um estudo da resistência à corrosão relativa de um amálgama dentário comercial e de suas principais fases constituintes, pelo uso de técnicas eletroquímicas, em meio salino e aerado que simula a agressividade do ambiente bucal. Os amálgamas dentários são formados pela reação do mercúrio com uma liga original em pó que contém predominantemente Ag, Sn e Cu, podendo também conter Zn ou outros elementos em menores proporções, resultando numa estrutura metalúrgica complexa e multifásica, com a presença das seguintes fases: γ1-Ag2Hg3 - matriz; γ-Ag3Sn - a segunda fase mais proeminente na microestrutura dos amálgamas dentários; γ2-Sn7-8Hg - a mais suscetível à corrosão dentre todas aquelas que compõem a microestrutura dos amálgamas dentários, de acordo com a literatura especializada; a composição eutética Ag-Cu (72%Ag, 28%Cu) - um componente adicionado às ligas mais modernas com o objetivo de reduzir a quantidade de γ2-Sn7Hg formada durante a reação de amalgamação e, neste sentido, aumentar a resistência à corrosão no meio bucal; e as fases do sistema Cu-Sn, ε-Cu3Sn e η'-Cu6Sn5 presentes em menor quantidade. Dada a natureza multifásica da microestrutura de amálgamas dentários, para este estudo foram elaboradas ligas metálicas binárias com composições químicas correspondentes às fases presentes em sua microestrutura. As ligas que contêem mercúrio, γ1-Ag2Hg3 e γ2- Sn7Hg, foram preparadas de acordo com as normas contidas na Especificação n. 1 para amálgamas dentários, da Associação Dentária Americana (ADA). As demais, correspondentes aos sistemas Ag-Cu, Ag-Sn e Cu-Sn foram preparadas pelos processos metalúrgicos convencionais de fundição, com o propósito de se reproduzir as principais fases que podem estar presentes na estrutura metalúrgica dos amálgamas... / Dental amalgams are formed by the reaction of mercury with a powder alloy containing mainly Ag, Sn, Cu and Zn, and have a complex metallurgical structure which can contain up to six phases. Their observed corrosion is thus a complex process, which involves contributions from each of the phases present as well as intergranular corrosion. It is thus of interest to investigate the corrosion of individual phases present in dental amalgams. Some of the products of the reaction are particles of the original alloy which did not react during the amalgamation process such as, γ-Ag3Sn and the Ag-Cu eutectic. Other products are the γ- phase of the silver-mercury system, designated γ1-Ag2Hg3, the γ-phase of the tin-mercury system, designated γ2-Sn7-8Hg, and intermetallic compounds of the tin-copper system, ε-Cu3Sn and η'-Cu6Sn5. The purpose of this work was to evaluate the corrosion resistance of the phase components of dental amalgams: the matrix phase of the microstructure, γ1-Ag2Hg3; the second more prominent, γ-Ag3Sn; the phase most susceptible to corrosion in the oral cavity, according to the literature, γ2-Sn7Hg; and spherical particles of the Ag-Cu eutectic (72% Ag, 28% Cu), a component of the more modern powder alloys, the objective being to reduce the quantity of γ2-Sn7Hg formed during the amalgam reaction and in this way increase its corrosion resistance. The Ag-Hg and Sn-Hg alloys were made in the correct stoichiometric proportions, taking into account the phase diagrams, by mechanical amalgamation and moulding under high pressure following the criteria adopted by the American Dental Association, Specification No. 1. The commercial dental amalgam employed in this study was Dispersalloy, a copper enriched alloy, type blended. The Ag-Sn, Ag-Cu and Cu-Sn alloys were prepared by heating the components until they were completely melted, and then the melt was poured into a mould...(Complete abstract click electronic access below)

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Made available in DSpace on 2014-10-09T12:37:40Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:21Z (GMT). No. of bitstreams: 1 05333.pdf: 6187094 bytes, checksum: f2e70bb302111d70efab851a434597e9 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP