La fissuration à chaud de solidification qui est l'un des problèmes majeurs rencontrés dans le cadre du soudage pourrait être préjudiciable à la tenue en service de structures mécano-soudées. Ce phénomène correspond à la formation de fissures en fin de solidification sous l'effet des déformations induites par les contraintes thermiques et le retrait de solidification. Ces travaux de thèse portent sur la modélisation de la fissuration à chaud dans un alliage base nickel en soudage TIG. L'objectif est de proposer une méthodologie permettant d'estimer le risque de fissuration dans l'Inconel 600. Pour cela des essais de soudage instrumentés en température ont été développés de manière à déterminer les conditions d'apparition et de propagation du défaut. Ces essais ont ensuite été modélisés dans l'optique d'établir un critère de fissuration fondé sur la déformation de l'alliage en fin de solidification, déformation qui ne peut être mesurée expérimentalement. La principale valeur ajoutée de cette étude réside dans le fait que le comportement viscoplastique du matériau utilisé lors de la modélisation a été déterminé expérimentalement de la température ambiante à la zone de transition pâteuse au moyen d'essais de caractérisation mécanique spécifiques. Les essais réalisés à l'état semi-solide pour des températures avoisinant 1400 °C ont notamment alimenté un modèle de zone cohésive permettant de modéliser la propagation des fissures. Cette approche couplant expériences et modélisation a ainsi conduit à l'identification d'un critère de fissuration à chaud intrinsèque à l'Inconel 600. / Hot cracking which is one of the major problems in welding may be prejudicial to the safety of welded structures. This phenomenon corresponds to the formation of irreversible cracks at the end of solidification, due to tensile strains associated with solidification shrinkage and thermal contraction. This work focuses on the hot cracking modeling during the welding of a Nickel based alloy. The aim is to propose a methodology which allows estimating the hot cracking risk in the Inconel 600 alloy. To achieve that purpose, self-restrained welding tests with temperature measurements have been developed in order to identify the conditions leading to the defect formation and propagation. These tests have then been modeled to establish a hot cracking criterion based on the strain applied on the alloy at the end of solidification, strain which cannot be experimentally measured. The originality of this study consists in the fact that the viscoplastic behaviour of the studied material (used for thermomechanical modeling) has been determined experimentally from room temperature up to the mushy zone using specific set-ups. Mechanical characterization tests performed in the semi-solid state at temperatures approaching 1400 °C also allowed feeding a cohesive element model leading to crack propagation modeling. This approach coupling experiments with modeling thus led to the identification of a hot cracking criterion intrinsic to Inconel 600.

The thesis is primarily concerned with the design, construction and preliminary commissioning of a novel polarimeter for full three-dimensional analysis of electron spin polarisation. The polarimeter is described in detail, together with the theoretical basis for its operation. Studies of an amorphous ferromagnetic alloy, Co66Fe4Ni1B14Si15, and its application as a secondary standard are presented. Finally, a design study of a GaAs polarised electron source, capable of providing both longitudinal and transverse polarisations, is detailed.

Prof. Dr. Renato Altobelli Antunes / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2016. / Corrosão e desgaste são processos destrutivos que causam enormes prejuízos, comprometendo a segurança de pessoas e das instalações industriais, residenciais e comerciais. Para aumentar a vida útil de elementos de máquinas, por exemplo, revestimentos de níquel obtidos por deposição química são largamente utilizados por sua excelente resistência à corrosão e ao desgaste, boa soldabilidade e brasagem. Por meio do processo de deposição química, a obtenção de ligas e compósitos diversos é possível, visando reforçar e/ou alterar propriedades magnéticas, elétricas, óticas e mecânicas, como dureza, lubricidade, ductilidade, coeficiente de fricção entre outras. A adição de compostos contendo tungstênio nos banhos de deposição química leva à obtenção de revestimentos ternários Ni-W-P, o que afeta o comportamento de corrosão e as características tribológicas dos revestimentos de Ni-P. Neste trabalho realizou-se a incorporação de tungstênio a revestimentos de Ni-P por meio de deposição química, variando-se a concentração de tungstênio por meio da adição de diferentes teores de tungstato de sódio aos banhos. O objetivo foi desenvolver revestimentos ternários de Ni-W-P e investigar o efeito da adição de tungstênio sobre a estrutura, morfologia, resistência à corrosão e propriedades de atrito das camadas. Os revestimentos foram submetidos a um tratamento térmico por uma hora em diferentes temperaturas a fim de promover a formação de fase de fosfeto de níquel (Ni3P), aumentando sua dureza e resistência ao desgaste. Os resultados indicaram que houve a formação de Ni3P com o tratamento térmico realizado. A incorporação de tungstênio levou à formação de uma camada mais compacta e densa, com teor reduzido de fósforo e maior capacidade de proteção contra a corrosão. Além disso, houve um aumento de dureza dos revestimentos, que foi dependente da temperatura na qual ocorreu o tratamento térmico. O coeficiente de atrito apresentou uma variação complexa, a qual não pode ser associada ao teor de tungstênio nos revestimentos. / Corrosion and wear are destructive processes that cause damage and losses affecting the safety of persons, buildings, bridges and facilities for industrial, commercial or residential use. In order to increase the life of machine elements, for example, the use of nickel coatings obtained by chemical reduction is widely used. Electroless nickel coatings are used for functional or decorative purposes or to restore functional properties. In addition to the excellent corrosion and wear resistance, the coating withstands soldering, welding and brazing. The codeposition of one or more elements to binary nickel alloys aims to enhance and/or change the resistance to corrosion, wear, abrasion, magnetic, electrical, optical, or friction properties. By adding tungsten-containing compounds to the electroless deposition bath ternary Ni-W-P are obtained, thus affecting the corrosion behavior and tribological properties of the Ni-P film. In this work, the incorporation of tungsten to Ni-P coatings was carried out using electroless depositon, varying the content of sodium tungstate in the bath. The aim was to develop ternary Ni-W-P coatings and to investigate the effect of tungsten incorporation on the structure, morphology, corrosion behavior and friction properties of the deposited layers. The coatings were annealed for one hour at different temperatures so as to promote the formation of nickel phosphide phases, increasing its hardness and wear resistance. The results showed that Ni3P was formed upon annealing. Tungsten incorporation allowed the formation of a more compact and dense film with reduced phosphorus content and improved corrosion protective ability. Moreover, hardness was increased, but this effect was dependent on the annealing temperature. The coefficient of friction showed a complex variation which does not allow to identify a clear relationship with the tungsten content in the film.

Made available in DSpace on 2014-10-09T12:42:06Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:54Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Made available in DSpace on 2014-10-09T12:42:06Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:54Z (GMT). No. of bitstreams: 0 / As ligas à base de níquel de alta resistência são utilizadas em uma infinidade de sistemas avançados, onde baixo peso e sistemas de transmissão mecânica de alta densidade de energia são necessários. Componentes, tais como, engrenagens, rolamentos e eixos poderiam ser consideravelmente menor e mais durável se uma grande melhoria em propriedades mecânicas de ligas à base de níquel for alcançada. Um refinamento significativo no tamanho de grão (incluindo nível nano) é um método promissor para a obtenção de melhorias fundamentais nas propriedades mecânicas. O tamanho de grão é conhecido por ter um efeito significativo sobre o comportamento mecânico dos materiais. Um dos métodos mais favoráveis de alcançar refinamento de grão extremo é submetendo os materiais à deformação plástica intensa. As principais variáveis microestruturais nas superligas são a quantidade de precipitados e sua morfologia, o tamanho e a forma do grão e a distribuição de carbonetos (Cr7C3 e Cr23C6) que poderão reduzir propriedades mecânicas da liga. Neste trabalho é apresentada análise por microscopia óptica e eletrônica de transmissão e também os dados de dureza após deformação plástica intensa (tensão de cisalhamento puro) e alguns tratamentos térmicos. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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[pt] Oxido de níquel e hematita nanoestruturadas foram sintetizadas a partir da decomposição térmica de nitrato de níquel hexahidratado e nitrato férrico nonahidratado respectivamente, na faixa de temperatura de 350-450°C com variações no tempo reacional. Os tamanhos de cristalito do NiO e Fe2O3 foram estimados a partir dos difractogramas de Difração de Raios-X (XRD) utilizando os software PowderCell e Topas. Foi observado que o tamanho de cristalito varia em função da temperatura de sínteses. O resultado mais significante foi observado nos cristalitos de NiO os quais aumentam de 31 nm (T=350°C, 3hr) a 98 nm (T=450°C, 5hr). Foram realizados estudos cinéticos da redução NiO e Fe2O3 por hidrogênio na faixa de temperatura de 250-600°C. Ligas ferroníquel nanoestruturadas com composições FexNi100-x (x = 25, 50, and 75 w%) têm sido preparadas com sucesso por decomposição térmica de nitratos (formação de óxidos) e posterior redução com hidrogênio a 700ºC (formação das ligas). As ligas Fe-Ni, caracterizadas por difração de raios-X mostraram tamanhos de cristalito da ordem de 25nm. A fase rica em Ni, liga Fe25Ni75, apresentou uma estrutura γ(FCC). A liga Fe50Ni50 apresentou a existência de uma estrutura tetragonal. A fase rica em Fe, liga Fe75Ni25, contém uma mistura de fases α(BCC) e γ(FCC). A coexistência das fases e atribuída à segregação de fases que acontece nestas ligas como resultado da difusão atômica. A partir dos resultados das medições magnéticas efetuadas a 300K, pode-se estabelecer que as ligas Fe-Ni nanoestruturadas tem um comportamento superparamagnético. / [en] Nickel oxide and hematite nanostructured were successfully prepared by thermal decomposition from nickel nitrate hexahydrate and ferric nitrate nonahydrate in the temperature range of 350-450°C with variation of the time. The average crystallite sizes of NiO and Fe2O3 were estimated from X-ray diffraction (XRD) peaks using the PowderCell and Topas software. We observed that the crystallite size changes as a function of synthesis temperature. The significant result was the large size of the resulting NiO crystallites, which increased from 31nm (T=350°C, 3hr) to 98nm (T=450°C, 5hr). Kinetic studies of the reduction of NiO and Fe2O3 by hydrogen in the temperature range 250-600°C have been investigated. Nanostructured Fe-Ni alloys with compositions FexNi100-x (x = 25, 50, and 75 w%) have been successively prepared by thermal decomposition from mixtures of nitrates (formation of oxides) and reduction by hydrogen at 700ºC (formation of alloys). The Fe-Ni alloys, characterized by X-ray diffraction show crystallites sizes about 25nm. The Nirich phase, Fe25Ni75 alloys show the existence of γ(FCC) phase. The Fe50Ni50 alloy show the existence of tetragonal phase. The Fe-rich phase, Fe75Ni25 alloy, contain a mixture of α(BCC) and γ(FCC) phases. The coexistence of these phases is attributed to phase segregation occurring in these alloys as a result of enhanced atomic diffusion. It was inferred from results of magnetic measurements at 300K, that nanostructured Fe-Ni alloys were in a superparamagnetic state.

Nickel-base superalloys have been emerged as materials for gas turbines used for jet propulsion and electricity generation. The strength of the superalloys depends mainly from an ordered precipitates of L12 structure, so called gamma prime (γ’) dispersed within the disorder γ matrix. The Ni-base alloys investigated in this dissertation comprise both model alloy systems based on Ni-Al-Cr and Ni-Al-Co as well as the commercial alloy Rene N5. Classical nucleation and growth mechanism dominates the γ’ precipitation process in slowed-cooled Ni-Al-Cr alloys. The effect of Al and Cr additions on γ’ precipitate size distribution as well as morphological and compositional development of γ’ precipitates were characterized by coupling transmission electron microscopy (TEM) and 3D atom probe (3DAP) techniques. Rapid quenching Ni-Al-Cr alloy experiences a non-classical precipitation mechanism. Structural evolution of the γ’ precipitates formed and subsequent isothermal annealing at 600 °C were investigated by coupling TEM and synchrotron-based high-energy x-ray diffraction (XRD). Compositional evolution of the non-classically formed γ’ precipitates was determined by 3DAP and Langer, Bar-on and Miller (LBM) method. Besides homogeneous nucleation, the mechanism of heterogeneous γ’ precipitation involving a discontinuous precipitation mechanism, as a function of temperature, was the primary focus of study in case of the Ni-Al-Co alloy. This investigation coupled SEM, SEM-EBSD, TEM and 3DAP techniques. Lastly, solute partitioning and enrichment of minor refractory elements across/at the γ/ γ’ interfaces in the commercially used single crystal Rene N5 superalloy was investigated by using an advantage of nano-scale composition investigation of 3DAP technique.

This diploma thesis studies the machining of group S materials. In the theoretical part of this thesis these materials were divided into groups and subsequently analyzed. These materials were also analyzed in terms of their impaired machinability. In the practical part of this thesis experimental tests were conducted to determine tool life, tool wear and in the case of testing titanium alloy surface roughness too.