Orientador: Amauri Garcia / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-04T03:17:22Z (GMT). No. of bitstreams: 1 Peres_ManoelDiniz_D.pdf: 9910066 bytes, checksum: 05cb5fd7d671ae9a511052bdddd2835e (MD5) Previous issue date: 2005 / Resumo: Foi desenvolvida no presente trabalho uma seqüência de experimentos para analisar a solidificação unidirecional vertical em condições transitórias de fluxo de calor de ligas AI-Si hipoeutéticas. Abordagens teóricas e experimentais são desenvolvidas para a determinação quantitativa de variáveis térmicas de solidificação tais como: coeficientes transitórios de transferência de calor metal/molde; velocidades de deslocamento das isotermas liquidus; taxas de resmamento à frente das isotermas liquidus e tempos locais de solidificação. A análise das macroestruturas obtidas mostra que a transição colunar/equiaxial (TCE) ocorre essencialmente à mesma posição a partir da superficie dos lingotes para todas as ligas examinadas experimentalmente. As variáveis térmicas de solidificação são muito similares na TCE, não sendo possível identificar um critério de transição macroestrutural baseado em apenas uma variável em particular. O trabalho analisa também a dependência dos espaçamentos interdendríticos em relação às variáveis térmicas de solidificação e ao teor de soluto da liga. Estes parâmetros dendríticos experimentais referentes à solidificação das ligas AI 3, 5, 7, 9 % Si, são comparados com os principais modelos teóricos de crescimento dendrítico da literatura / Abstract: Experiments were conducted to analyze the upward unsteady state directional solidification of AI-Si hypoeutectic alloys. A combined theoretical and experimental approach is developed to quantitatively determine solidification thermal variables such as: transient metal/mold heat transfer coefficients, tip growth rates, thermal gradients, tip cooling rates and local solidification time. The observation of the macrostructures has shown that the columnar to equiaxed transition (CET) occurred essentially at the same position from the casting surface for any alloy experimentally examined. The solidification thennal variables are very similar at the CET and it is not possible to identify a structural transition criterion based on a particular variable. The work also focuses on the dependence of dendrite ann spacings on the solidification thermal variables and on alloy solute content. The experimental data concerning the solidification of AI 3, 5, 7 and 9 wt % Si alloys are compared with the main predictive dendritic models from the literature / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Nickel and iron-based alloys are important structure and cladding materials for modern nuclear reactors due to their high mechanical properties and high corrosion resistance. To understand the radiative and corrosive environment influence on the mechanical strength, computer simulation works are conducted. In particular, this dissertation is focused on multiscale modeling of the effects of radiation-induced solute segregation and oxidation on grain boundary (GB) strength in nickel-based and iron-based alloys. Besides the atomistic scale density functional theory (DFT) based calculations of GB strength, continuum-scale cohesive zone model (CZM) is also used to simulate intergranular fracture at the microstructure scale. First, the effects of solute or impurity segregation at GBs on the GB strength are studied. Thermal annealing or radiation induced segregation of solute and impurity elements to GBs in metallic alloys changes GB chemistry and thus can alter the GB cohesive strength. To understand the underlying mechanisms, first principles based DFT calculations are conducted to study how the segregation of substitutional solute and impurity elements (Al, C, Cr, Cu, P, Si, Ti, Fe, which are present in Ni-based X-750 alloys) influences the cohesive strength of Σ3(111),Σ3(112),Σ5(210) and Σ5(310) GBs in Ni. It is found that C and P show strong embrittlement potencies while Cr and Ti can strengthen GBs in most cases. Other solute elements, including Si, have mixed but insignificant effects on GB strength. In terms of GB character effect, these solute and impurity elements modify the GB strength of the Σ5(210) GB most and that of the Σ3(111) least. Detailed analyses of solute-GB chemical interactions are conducted using electron localization function, charge density map, partial density of states, and Bader charge analysis. The results suggest that the bond type and charge transfer between solutes and Ni atoms at GBs may play important roles on affecting the GB strength. For non-metallic solute elements (C, P, Si), their interstitial forms are also studied but the effects are weaker than their substitutional counterparts. Nickel-base alloys are also susceptible to stress corrosion cracking (SCC), in which the fracture mainly propagates along oxidized grain boundaries (GBs). To understand how oxidation degrades GB strength, the next step is to use density functional theory (DFT) calculations to study three types of oxidized interfaces: partially oxidized GBs, fully oxidized GBs, and oxide/metal interface, using Ni as a model system. For partially oxidized GBs, both substitutional and interstitial oxygen atoms of different concentrations are inserted at three Ni GBs: Σ3(111) coherent twin, Σ3(112) incoherent twin, and Σ5(210). Simulation results show that the GB strength decreases almost linearly with the increasing oxygen coverage at all GBs. Typically, substitutional oxygen causes a stronger embrittlement effect than interstitial oxygen, except at the Σ3(111). In addition, the oxygen-induced mechanical distortion has a much smaller contribution to the embrittlement than its chemical effect, except for oxygen interstitials at the Σ3(111). For the fully oxidized GBs, three NiO GBs of the same types are studied. Although the strengths of Σ3(112) and Σ5(210) NiO GBs are much weaker than the Ni counterparts, the Σ3(111) NiO GB has a higher strength than that in Ni, indicating that Σ3(111) GB may be difficult to fracture during SCC. Finally, the strength of a Ni/NiO interface is found to be the weakest among all interfaces studied, suggesting the metal/oxide interface could be a favorable crack initiation site when the tensile stress is low. Furthermore, the effects of co-segregation of oxygen and solute/impurity elements on GB strength are studied by DFT, using the 5(210) GB in an face-centered-cubic (FCC) Fe as a model system. Four elements (Cr, Ni, P, Si) that are commonly present in stainless steels are selected. Regarding the effects of single elements on GB strength, Ni and Cr are found to the increase the GB strength, while both P and Si have embrittlement effects. When each of them is combined with oxygen at the GB, the synergetic effect can be different from the linear sum of individual contributions. The synergetic effect also depends on the spatial arrangement of solute elements and oxygen. If they are aligned on the same plane at the GB, the synergetic effect is similar to the linear sum, although P and Si show stronger embrittlement potencies when they combine with both interstitial and substitutional oxygen. When they are arranged on a trans-plane structure, only nickel combined with oxygen show larger embrittlement potencies than the linear sum in all cases. Crystal Orbital Hamilton Populations analysis of bonding and anti-bonding states is conducted to interpret how the interaction between solutes and oxygen impacts GB strength. Finally, the continuum-scale CZM method, which is based on the bilinear mixed mode traction separation law, is used to model SCC-induced intergranular fracture in polycrystalline Ni and Fe based alloys in the MOOSE framework. The previous DFT results are used to justify the input parameters for the oxidation-induced GB strength degradation. In this study, it is found that the crack path does not always propagate along the weak GBs. As expected, the fracture prefers to occur at the GB orientations perpendicular to the loading direction. In addition, triple junctions can arrest or deflect fracture propagation, which is consistent with experimental observations. Simulation results also indicate that percolated weak GBs will lead to a much lower fracture stress compared to the discontinuous ones. / Doctor of Philosophy / Iron and Nickel based alloys are important structural materials for nuclear reactors due to their good mechanical properties, corrosion resistance, and radiation resistance. Under radiation and corrosive conditions, those alloys are susceptible to radiation induced segregation (RIS) and stress corrosion cracking (SCC). This dissertation is mainly focused on understanding the influence of the two effects on grain boundary (GB) strength. Systematic atomistic scale density functional theory (DFT) simulations are applied for the nickel and iron systems. Based on the DFT results, cohesive zone model is utilized for the continuum scale fracture simulation in nickel and iron polycrystal. First, DFT calculations are conducted for studying the RIS effect on the GB strength in nickel. Al, Cr, Cu, C, Si, P, Fe, and Ti are chosen as segregated element. Σ3(111), Σ3(112), Σ5(210), Σ5(310) four types of GBs are built for GB strength calculations. It is found that substitutional C and P always embrittle the GB, while substitutional Ti and Cr can strengthen the GB in most cases. Partial density of states (PDOS) analysis indicates the formation of C-Ni and P-Ni covalent bonds is the possible reason for their embrittlement effects. Bader charge analysis shows negatively charged elements likely reduce the GB strength. Interstitial element segregation is applied for non-metal elements (C, P, and Si). The results indicate interstitial elements have weaker effects than substitution ones. On the next stage to study the SCC effect, DFT calculations are performed for nickel Σ3(111), Σ3(112), and Σ5(210) GBs with difference oxygen concentration and oxygen incorporation types. Besides partially oxidized GBs, fully oxidized GBs (NiO GBs) and metal-oxide interface are also constructed for comparison. Simulation results show that the GB strength decreases nearly monotonically as oxygen concentration goes up. Typically, substitution oxygen causes a larger embrittlement effect than interstitial oxygen except at Σ3(111). It is found that the large mechanical distortion in this coherent twin GB contributes significantly to the GB strength drop. NiO GBs can be weak (Σ3(112),Σ5(210)) or strong (Σ3(111)). NiO/Ni interface shows lowest strength compared with partially and fully oxidized GBs, indicating the importance of the metal-oxide interface in the SCC process. Furthermore, the combined effects between segregated elements and oxygen are studied in face center cubic (FCC) iron system. In this part only Σ5(210) GB is selected with substitutional Cr, Ni, P, and Si as segregated elements. The results of single element effects show Cr can strength the GB while P has an opposite effect. Other two elements show little effect. For the co-segregation effects, the trans-plane structures have larger embrittlement potencies than in-plane ones for Ni, suggesting the GB strength can also be affected by the spatial arrangement of segregated elements. Finally, cohesive zone model is applied for fracture simulations in polycrystalline nickel and iron under tensile loading condition. It is found that intergranular fracture depends on both GB strength and orientation. GBs perpendicular to the loading direction have higher chances to crack. It is also found the percolated weak GBs induce larger strength drop than the discontinuous ones.

Amalgamations are a promising replacement for electronic solders, thermal interface materials, and other conductive joining materials. Amalgams are mechanically alloyed materials of a liquid constituent with a solid powder. Unlike traditional solders, these materials are processed at room temperature or slightly above, and can often operate at temperatures near, or beyond, their processing temperatures. Existing bonding processes require an excessive amount of heat, which may cause thermal stress to the electronic components and delaminate the attachment. Amalgams have promising characteristics for thermal interface materials (TIMs) due to being fully metallic, relatively easy of handling, and possessing metallic strength similar to solder or braze. Non-toxic gallium (Ga) based room temperature liquid metal alloys are a favorable material for structural amalgamations over conventional mercury (Hg). Unlike Hg amalgamations, Ga-based amalgamations have not been widely studied in the literature. In this work, the authors investigate a novel Ga-based amalgamation, further detailing the fabrication process and characterize the physical structure, chemistry, and mechanical strength. Different packing ratios are examined, by weight, 2:1, 1:1, 4:3, and 4:1 of Galinstan, which is composed of 68wt% Ga, 22wt% indium (In), 10wt% tin (Sn), to copper (Cu) powder. These ratios are molded into three-dimensional (3D) printed tensile bars of the American Society of Testing and Materials (ASTM) standard dimensions of a model that is per D638 TypeIV. The tensile bars are cured for 24-hours at three different temperatures (room temperature, 100°C, 200°C). The 4:1 ratio was the only specimen that failed to solidify. After allowing 24-hours of undisturbed curing, the samples that solidified were tested for their ultimate tensile strength. The optimal strength was achieved with the 2:1 ratio cured at 100°C, reaching an average tensile strength of 32.0 MPa. A scanning electron microscope (SEM), equipped with energy dispersive spectroscopy (EDS), was then utilized to perform microstructural characterization and local chemical composition mapping of fractured and polished sample surfaces. It is concluded that, of the packing ratios that set, there is no statistically significant correlation between packing ratio and tensile strength. Further, the phases formed during curing at room temperature are the same for all packing ratios but are present at different dispersions. However, it is found that the tensile strength decreases with statistical significance as the cure temperature is increased to 200°C. This change can be attributed to the presence of new phases that occur when the sample is heated to 200°C vs. when cured at room temperature. In the room temperature sample, x-ray diffraction (XRD) revealed the existence of pure Cu, CuGa2, and In3Sn. At 200°C, XRD shows a decrease in pure Cu, the presence of CuGa2 and In3Sn, and the emergence of a new Cu2Ga phase. These different phases form different interfaces with different bond energies, resulting in a change in tensile strength.

Les alliages métalliques complexes (CMAs) sont des intermétalliques dont la structure est basée sur une maille unitaire géante pouvant contenir jusqu’à plusieurs milliers d’atomes. La maille unitaire est décorée par des clusters de haute symétrie, qui gouvernent les propriétés physiques de ces matériaux mais, jusqu’à présent, la réactivité chimique de ces matériaux a été peu étudiée. Le but de cette thèse était de comprendre l’influence de la complexité structurale et de la nature du métal de transition sur les premiers stades d’oxydation des alliages complexes Al-TM (TM= Co, Cu). L’influence de la complexité structurale a été examinée en étudiant des intermétalliques appartenant à la même famille (Al-Co) mais présentant une complexité structurale différente (Al9Co2, 22 atomes/maille unitaire et Al13Co4, 102 atomes/maille unitaire). L’influence du métal de transition a été étudiée en comparant les résultats obtenus sur Al9Co2, Al13Co4 et Al4Cu9 (52 atomes/maille unitaire). Les premiers stades d’adsorption, sous ultravide, d’oxygène moléculaire sur des surfaces propres Al4Cu9(110), Al9Co2(001) et Al13Co4(100) à différentes températures et dans une gamme de pression 10-8-10-7 mbar ont été suivis par LEED, XPS et STM.Pour les trois surfaces étudiées, seul l’aluminium est oxydé dans les conditions expérimentales utilisées. A température ambiante une couche désordonnée d’oxyde d’aluminium d’environ 1,34 nm est formée sur Al4Cu9, qui cristallise après chauffage à 650 °C pour former un film d’oxyde de structure sixton. Sur les surfaces d’alliages Al-Co, la couche désordonnée formée à température ambiante est plus fine (0,54 à 0,43 nm) et ne cristallise pas après recuit. Par contre, un oxyde de structure sixton est formé après oxydation de la surface de Al9Co2 à 500 °C. La formation de cette phase oxydée cristallisée est gouvernée par la compétition entre la ségrégation de l’aluminium et la diffusion de l’oxygène. Lorsque la ségrégation d’aluminium est insuffisante ou la diffusion d’oxygène trop rapide, cet oxyde n’est pas observé. La mobilité des atomes d’aluminium, liée au degré de covalence des liaisons intermétalliques, est donc le facteur prépondérant pour la structure du film d’oxyde formé. / Complex metallic alloys (CMAs) are intermetallics having a crystalline structure based on a giant unit cell which can contain up to several thousands of atoms. The cell structure is usually decorated with highly symmetric clusters which can affect the alloy physical properties. So far, very few studies of the chemical reactivity of these materials have been published. The aim of the thesis was to understand the influence of the structural complexity and of the nature of the transition metal on the oxidation of Al-TM (TM=Co, Cu). The influence of structural complexity was examined by studying intermetallics belonging to the same Al-Co family but showing different structural complexity (Al9Co2, 22 atoms/unit mesh and Al13Co4, 102 atoms/unit mesh). The effect of the transition metal was studied by comparing the results obtained on Al9Co2, Al13Co4 and Al4Cu9 (52 atoms/unit mesh) surfaces. The early stages of molecular oxygen adsorption on clean Al4Cu9(110), Al9Co2(001) and Al13Co4(100) surfaces at different temperatures and in the pressure range 10-8-10-7 mbar was followed using LEED, XPS and STM.For all surfaces studied, aluminum is the only element oxidised in our experimental conditions. At room temperature, a thin layer (1.34 nm thick) of disordered aluminium oxide is formed on Al4Cu9, which crystallises following annealing at 650 °C to form a sixton structure. On the Al-Co surfaces, the disordered oxide layer formed at room temperature is thinner (0.53 to 0.43 nm) and remains disordered after annealing at various temperatures. However, an ordered oxide with the sixton structure is formed after oxidation of the Al9Co2 surface at 500 °C. The formation of the ordered oxide layer is governed by the competition between aluminium segregation and oxygen diffusion. When aluminium segregation is too low or oxygen diffusion too fast, the ordered phase is not observed. Therefore, the aluminium atoms mobility, hence the degree of covalency of the intermetallic bonds, is the main parameter governing surface oxidation of these materials.

Made available in DSpace on 2016-06-02T19:10:27Z (GMT). No. of bitstreams: 1 6459.pdf: 4283564 bytes, checksum: 527069b2b33732466b82a6f78943d62f (MD5) Previous issue date: 2014-02-21 / Financiadora de Estudos e Projetos / This thesis presents the development of a new criterion which can indicate new compositions for amorphous metallic alloys. This new criterion was based on dense packing of spheres combined with the lambda criterion through the coordination number. The mathematical development is presented and a software was developed with the purpose of indicating alloys with best glass forming ability (GFA). This software includes and concatenates several other criteria. For this purpose, we performed a mathematical analysis of the criteria, which included: (i) (λmin) criterion which uses the minimum topological instability parameter and it is used as an indication of phase competition during the solidification. (ii) the γ parameter, which reflects the relative GFA between bulky metallic glasses (BMG) and it is based on characteristic temperatures, such as: the glass transition temperature - Tg, the crystallization onset temperature - Tx and the liquidus temperature - Tl. (iii) the parameter Zc that is the critical thickness for bulky glass formation, which corresponds to the maximum dimension in which the molten can be formed without any crystals precipitation and (iv) the parameter Rc that is the critical cooling rate for glass formation, which decreases inversely to the Zc values. Through a mathematical formalism combining all the parameters, the software can decide the most suitable composition range to produce a new alloy. The results are presented and compared with the ones available on the literature. Also, for comparison, new alloys were developed by using the new criterion. These results indicate good agreement with the literature and with the experimental data since it is not a general theory, but intends to meet some specific cases with a reasonable convergence and which still need to be better studied. / Esta tese apresenta o desenvolvimento de um novo critério para indicar novas composições de ligas metálicas amorfas. Este novo critério foi baseado no empacotamento denso de esferas combinado com o critério lambda através do número de coordenação. O desenvolvimento matemático é apresentado e um software que engloba e concatena diversos outros critérios foi desenvolvido com o propósito de indicar as melhores ligas metálicas com alta tendência à formação de vidros (GFA). Para tal, houve uma análise matemática dos critérios, entre eles: (i) o critério λmin, que usa o parâmetro de mínima instabilidade topológica, usado como indicativo da competição de fases durante a solidificação; (ii) o parâmetro γ, que reflete a GFA relativa entre vidros metálicos volumosos (BMG) com base nas temperaturas características como a temperatura de transição vítrea - Tg; temperatura de início de cristalização - Tx e a temperatura liquidus - Tl; (iii) o parâmetro Zc, que é a espessura crítica para a formação do vidro volumoso e que corresponde à máxima dimensão com que o fundido pode ser formado sem que haja precipitação de cristais e (iv) o parâmetro Rc, que é a taxa de resfriamento crítico para a formação de vidro a qual decresce inversamente aos valores de Zc. Através de formalismo matemático para combinar todos os parâmetros, o software pode decidir qual a faixa de composição mais adequada para a produção de uma nova liga. Os resultados são apresentados e comparados com a bibliografia existente, além de terem sido desenvolvidas ligas experimentais para comparação. Estes resultados indicam uma boa concordância com a literatura e com os dados experimentais, uma vez que não se trata de uma teoria geral, mas que pretende atender a alguns casos específicos com razoável convergência e que ainda precisam ser melhor estudados.

Orientador: Amauri Garcia / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-06T06:42:40Z (GMT). No. of bitstreams: 1 Goulart_PedroRoberto_M.pdf: 16218050 bytes, checksum: 1cc723921f7b1426050c06e4bcedea4d (MD5) Previous issue date: 2005 / Resumo: No presente trabalho, é realizada uma seqüência de experimentos com ligas hipoeutéticas de AIlSi para analisar a solidificação unidirecional horizontal em condições transitórias de fluxo de calor. Abordagens teóricas e experimentais são desenvolvidas para a determinação quantitativa de variáveis térmicas de solidificação, tais como: coeficientes transitórios de transferência de calor metal/molde; velocidades de deslocamento das isotermas liquidus; taxas de resfriamento à frente das isotermas liquidus e tempos locais de solidificação. O trabalho analisa também a dependência dos espaçamentos interdendríticos em relação às variáveis térmicas de solidificação e ao teor de soluto da liga. Esses parâmetros dendríticos experimentais, referentes à solidificação das ligas AI 5 e 9 % Si, são comparados com os principais modelos teóricos de crescimento dendrítico da literatura. Os resultados experimentais obtidos através de ensaios mecânicos são correlacionados com. a microestrutura dendrítica, estabelecendo-se leis experimentais / Abstract: Experiments were conducted to analyze the horizontal unsteady state directional solidification of hypoeutectic AI-Si alloys. A combined theoretical and experimental approach was developed to quantitatively determine solidification thermal variables such as: transient metal/mold heat transfer coefficients, tip growth rates, thermal gradients, tip cooling rates and local solidification time. The work also focused on the dependence of dendrite arm spacings on the solidification thermal variables and on alloy solute content. The experimental data concerning the solidification of AI 5 and 9 wt % Si alloys were compared to the main predictive dendritic models in the literature. Experimental laws were set correlating experimental data obtained from mechanical tests and the dendritic microstructure / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Orientadores: Amauri Garcia, Wislei Riuper Osorio / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-13T18:01:29Z (GMT). No. of bitstreams: 1 Peixoto_LeandroCesardeLorena_M.pdf: 5871010 bytes, checksum: f7403606c814ec8a30965352f0a93e87 (MD5) Previous issue date: 2009 / Resumo: Produtores de baterias chumbo-ácido têm modificado os processos de produção e composição química das ligas utilizadas nas grades das baterias com intuito de diminuir o seu peso final, bem como reduzir os custos de produção e também aumentar o ciclo de vida útil e a resistência à corrosão. As morfologias das estruturas de solidificação, caracterizadas principalmente por arranjos celulares e dendríticos, e suas grandezas representadas por espaçamentos celulares e dendríticos controlam a distribuição de soluto, segundas fases dentro das regiões intercelulares ou interdendríticas, que determinam as propriedades finais. O comportamento mecânico e as características estruturais dos componentes de bateria têm papel importante no desempenho das baterias. O presente trabalho pretende contribuir para o entendimento do desenvolvimento microestrutural de ligas diluídas do sistema Pb-Sn (Pb-1,0%Sn e Pb-2,5%Sn) que possuem elevada importância para a indústria na fabricação de componentes de baterias automotivas e estacionárias. Os experimentos de solidificação realizados em dispositivo no qual o calor é extraído somente pelo sistema de resfriamento a água, localizado na base do conjunto lingote/lingoteira (solidificação ascendente). As variáveis térmicas de solidificação foram determinadas a partir do registro de temperaturas de termopares posicionados dentro da lingoteira em diferentes posições em relação à superfície refrigerada do lingote. Amostras das mencionadas ligas Pb-Sn foram utilizadas para analisar as influências das variáveis térmicas de solidificação e da concentração de soluto nas macro e microestruturas resultantes e na resistência mecânica. Foram determinados os limites de resistência à tração e alongamentos específicos em função do espaçamento celular e a influência da microestrutura no comportamento eletroquímico foi avaliada por intermédios dos ensaios de espectroscopia de impedância eletroquímica, extrapolação de Tafel, curvas de polarização e análise por circuito equivalente em solução eletrolítica de ácido sulfúrico. Observou-se que a resistência a corrosão diminui e o limite de resistência a tração aumenta com a diminuição do espaçamento celular. / Abstract: Lead-acid batteries manufacturers have modified the manufacturing processes and the chemical composition of alloys used in battery grids in order to decrease their weight as well as to reduce the production costs, and to increase the battery life-time cycle and the corrosion-resistance. The morphological microstructures characterized by cellular and dendritic arrays and its correspondents cellular and dendrite arm spacings control the solute distribution, second phases in the intercellular and interdendritic regions affecting the resulting properties. The mechanical behavior and microstructural characteristics of lead-acid battery components have an important role in the battery performance. The present work aims to contribute to the understanding of the microstructural development of dilute Pb-1,0 wt.%Sn and Pb-2.5 wt.%Sn alloys which are widely applied in the manufacturing of automobile and stationary lead-acid batteries. A water-cooled vertical upward unidirectional solidification system was used to obtain the samples. The experimental set-up was designed in such a way that the heat was extracted only through the water-cooled bottom, promoting upward directional solidification. Thermal readings were obtained by thermocouples positioned at different distances from the heat-extracting surface at the casting bottom. Pb-Sn alloy samples were used to analyze the effects of the thermal solidification variables and solute content on the resulting macro and microstructures and on the mechanical properties. The ultimate tensile strength and the elongation were determined as a function of the cellular arm spacing. The effect of the resulting microstructure on the electrochemical corrosion behavior was also analyzed based on electrochemical parameters, determined by Tafel plots, polarization curves and an equivalent circuit analysis after corrosion tests carried out in a sulphuric acid solution. It was observed that the corrosion resistance decreases and the ultimate tensile strength increases with decreasing cellular spacing. / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Orientadores: Amauri Garcia, Wislei Riuper Ramos Osório / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-21T02:28:07Z (GMT). No. of bitstreams: 1 Garcia_LeonardoRicheli_D.pdf: 14084477 bytes, checksum: f9b96fac198700cfcafeecf1edca6f9b (MD5) Previous issue date: 2012 / Resumo: A preocupação ambiental sobre a toxicidade do Pb combinada com normas rígidas, estão gradualmente proibindo a aplicação de Pb em ligas de soldas. As ligas alternativas Sn-Ag e Sn-Bi podem estar entre as mais promissoras candidatas à substituição das ligas de solda sem chumbo em função de apresentarem propriedades compatíveis com as da liga Sn-Pb. A fim de adequar os produtos aos novos requisitos, produtores de componentes microeletrônicos necessitam desenvolver novas ligas de solda. Estudos sobre a influência da taxa de resfriamento sobre a microestrutura e as propriedades mecânicas resultantes e as características de recobrimento dessas ligas necessitam ser realizados. Esse trabalho tem exatamente esse objetivo, e no qual é realizado um estudo experimental comparativo das principais características da tradicional liga Sn-Pb e das ligas Sn-Ag e Sn-Bi visando a aplicação dessas ligas como ligas alternativas de solda. As seguintes atividades foram desenvolvidas para atingir tais propósitos: i) solidificação unidirecional das ligas Sn-Ag (hipoeutética Sn-2%Ag e eutética Sn-3,5%Ag) e Sn-Bi (Sn-10, 20 e 40%Bi); ii) ensaios de mergulho de lâminas de cobre nas ligas Sn-Ag e Sn-Bi fundidas e; iii) ensaios de tração de acordo com as especificações da norma ASTM E 8M/04. Foi utilizado um dispositivo de solidificação vertical ascendente para obter os lingotes das ligas e os correspondentes perfis térmicos. Variáveis térmicas de solidificação como: taxa de resfriamento, velocidade de solidificação e tempo local de solidificação foram determinadas para as ligas Sn-Ag e Sn-Bi. Essas variáveis experimentais foram correlacionadas com os espaçamentos dendríticos secundários (l2) e foram propostas equações experimentais de crescimento dendrítico. A espessura da camada solidificada, a área recoberta e as microestruturas resultantes das ligas no substrato de cobre foram avaliadas após o ensaio de mergulho em diferentes temperaturas. Verificou-se que, considerando-se as ligas Sn-Ag e Sn-Bi examinadas, a liga Sn- 40%Bi apresenta maior resistência mecânica e a liga Sn-3,5%Ag apresenta molhabilidade similar quando comparada com a tradicional liga de solda Sn-40%Pb / Abstract: The increasingly environmental concern over the toxicity of Pb combined with strict regulations, are gradually banning the application of Pb-based solders. Sn-Ag and Sn-Bi solder alloys are among the most promising candidates for Pb-free alternatives due to their compatible properties with the Sn-Pb solder alloy. In order to adequate products to such restriction requirements, electronic components manufacturers have to meet such requirements by developing new lead-free solder alloys. Studies focusing on the influence of the cooling rate on the resulting microstructures and on both the mechanical properties and recovery of these alloys need to be carried out. This work has precisely such objective, in which a comparative experimental study of the main features of the traditional Sn-Pb alloy and Sn-Ag and Sn-Bi alloys is carried out with a view to application of the latter alloys as alternative solder materials. The following activities were developed to attain such purpose: i) unidirectional solidification of Sn-Ag alloys (hypoeutectic Sn-2 wt.% Ag, eutectic Sn-3.5 wt.% Ag), and Sn-Bi alloys (Sn-10, 20 and 40 wt.% Bi); ii) copper blades dipped in both molten Sn-Ag and Sn-Bi alloys (hot dipping) and iii) tensile testing according to specifications of ASTM standard E 8M/04. An upward vertical solidification system has been used to obtain the alloys ingots and their correspondent thermal profiles. Solidification thermal variables such as: the cooling rate, tip growth rate and local solidification time have been determined for Sn-Ag and Sn-Bi alloys. Such experimental variables have been correlated with secondary dendrite arm spacings (l2) and experimental equations of dendritic growth have been proposed. The thickness of the coating layers, the spreading areas and the resulting microstructures of these alloys on the copper substrates were evaluated after the hot dipping procedures at different temperatures. It was found that, of the examined Sn-Ag and Sn-Bi alloys, the Sn-40 wt.% Bi alloy has offered the highest mechanical strength and the Sn- 3.5 wt.% Ag alloy has shown similar wettability when compared with the traditional Sn-40 wt.% Pb solder alloy / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Este trabalho trata da avaliação da técnica de conformação por expansão fluidostática (bulge forming) através de uma matriz com múltiplas cavidades. Duas ligas de especificação AA5083 e Pb-60Sn foram submetidas ao processo de superplasticidade (Superplastic Forming) para a verificação de diferentes parâmetros de trabalho e comparação com os resultados por simulação numérica. Uma das principais conclusões obtidas é que o método multidomo foi válido para o estudo do fenômeno superplástico. Os testes foram realizados através do método de pressão constante, onde foi possível obter variáveis como tensão, taxa de deformação e índice de sensibilidade a taxa de deformação. Uma importante implicação deste processo é o controle correto do tempo de trabalho com cavidades conformadas em ensaios distintos. / This study aims to evaluate the forming technique fluidostatic expansion (bulge forming) through a die with multiple cavities. Two AA5083 alloy and Pb-60Sn specification were submitted to superplasticity process (superplastic forming) for checking different working parameters and comparison with the results in numerical simulation. One of the main conclusions is that the multidomo method was valid to study the superplastic phenomenon. The tests were performed using the constant pressure method, where it was possible to obtain variables such as stress, strain rate and the strain rate sensitivity index. An important implication of this process is the correct control of working time with shaped cavities in separate trials.

No presente estudo foi analisada a distribuição de tensões, na região anterior de modelo fotoelástico, gerada por arcos de intrusão de incisivos inferiores. Compararam-se as tensões entre diferentes arcos. E ainda, em cada tipo de arco, compararam-se as tensões entre terços radiculares e entre incisivos. O modelo fotoelástico foi construído simulando a extrusão dos incisivos. Foram confeccionados sessenta arcos de intrusão, sendo quinze de cada tipo de mecânica: arco contínuo de Burstone, arco utilitário de Ricketts, arco com dobra de ancoragem usado na mecânica de Begg e arco com curva de Spee reversa usado na mecânica de Tweed. A força de ativação foi mensurada em 50gf na região da linha média. O modelo fotoelástico foi observado em polariscópio circular, na configuração de campo escuro, e fotografado. As fotografias frontais foram analisadas, e as ordens de franjas em cada região registradas. A repetibilidade do método foi identificada pela análise de kappa. A comparação entre as tensões foi realizada pelo teste de Kruskall-Wallis complementado com teste de Dunn. Os resultados obtidos permitiram concluir que na região apical, as maiores magnitudes de tensões foram geradas pelo arco utilitário de Ricketts, seguido pelo arco contínuo de Burstone. Na região média, as maiores magnitudes de tensões foram geradas pelo arco utilitário de Ricketts, seguida por arco contínuo de Burstone, arco com dobra de ancoragem e arco com curva de Spee reversa. Na região cervical, as maiores magnitudes de tensões foram decorrentes do arco utilitário de Ricketts, seguido por arco com curva de Spee reversa e arco com dobra de ancoragem. Os arcos contínuos de Burstone apresentaram as menores tensões na região cervical. Ao se comparar as ordens de franjas entre os terços radiculares, de cada dente, em todos os arcos analisados, as maiores magnitudes de tensões foram observadas nas regiões cervicais. Ao se comparar as ordens de franjas entre os dentes, em cada terço radicular, no arco contínuo de Burstone, as maiores magnitudes de tensões foram observadas nos incisivos laterais. Entretanto, no arco utilitário de Ricketts e no arco com dobra de ancoragem, as maiores magnitudes de tensões foram observadas nos incisivos centrais. No arco com curva de Spee reversa, as maiores magnitudes de tensões foram identificadas nos incisivos esquerdos. Portanto, os resultados do presente estudo permitiram a visualização e compreensão dos efeitos dos diversos arcos de intrusão. Entretanto, estes resultados devem ser observados com cautela, requerendo mais pesquisas que confirmem a reprodutibilidade do método e dos resultados. / In the present study, the distribution of stresses caused by intrusion arches on lower incisors, in the anterior region of photoelastic model, was analyzed. The stresses were compared among the different arches. Additionally, stresses were also compared among the root thirds, as well as among the incisors for each arch type. The photoelastic model was constructed simulating the extrusion of incisors. Sixty intrusion arches were made up, corresponding to fifteen of each type: Burstone continuous arches, Ricketts utility arches, anchorage bend arches used in Begg mechanics and reverse Spee curved arches used in Tweed mechanics. Activation force was measured at 50gf in the midline. The photoelastic model was observed under circular polariscope, in dark-field configuration, and photographed. Frontal photographs were analyzed, and fringe order in each region was recorded. Method repeatability was identified by kappa analysis. A comparison among stresses was carried out using Kruskall-Wallis test and complemented by the Dunn test. Results obtained led to the conclusion that in the apical region, the major stress magnitudes were generated by the Ricketts utility arch, followed by the Burstone continuous arch. In mid-region, the major stress magnitudes were generated by Ricketts utility arch, followed by the Burstone continuous arch, anchorage bend arch, and arch wire with a reverse curve of Spee. In the cervical region, the major stress magnitudes stemmed from Ricketts utility arch, followed by arch with reverse curve of Spee and the anchorage bend arch. The Burstone continuous arches presented the least stresses in the cervical region. On comparing fringe orders among root thirds, of each tooth, in all arches analyzed, major magnitudes of stresses were observed in the cervical regions. On comparing fringe orders among teeth, in each root third, the major magnitudes of stresses were observed in lateral incisors in Burstone continuous arches. However, in both Ricketts utility arches and anchorage bend arches the major stresses magnitudes were observed in central incisors. In arch with a reverse curve of Spee the major magnitudes of stresses were identified in left incisors. Consequently the results in the present study allowed a visualization and understanding of the effects of the diverse intrusion arches. However, such results should be observed with caution, requiring further study to confirm method reproducibility as well as results.