Orientador: Rezende Gomes dos Santos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-09T22:01:50Z (GMT). No. of bitstreams: 1 Eid_MarcoAntonio_M.pdf: 19245694 bytes, checksum: b272ecb88a2fa2a6affcf2a60d7e8d47 (MD5) Previous issue date: 2007 / Resumo: Apesar da importância tecnológica da solidificação de ligas metálicas sob fluxo de calor radial, relativamente poucos estudos estão sendo feitos nessa área. Neste trabalho, a solidificação da liga Al 4,5%Cu em molde de aço radial cilíndrico é analisada e comparada com a solidificação direcional em molde resfriado.Inicialmente a variação de temperatura em diferentes posições no metal e no molde foi medida durante a solidificação usando um sistema de aquisição de dados. Essas variações de temperatura foram introduzidas em um método numérico para determinar a variação do coeficiente de transferência de calor na interface metal/molde pelo método inverso. Os resultados para a solidificação unidirecional e radial foram comparados mostrando que o coeficiente de transferência de calor para o fluxo de calor radial é menor. A variação dos espaçamentos dendritos secundários foram medidos através de um microscópio óptico. Comparações entre os resultados mostraram maiores espaçamentos para fluxo de calor radial. Comparações entre variações e temperaturas calculadas numéricas e experimentalmente comprovaram que o método numérico descreve satisfatoriamente o processo de solidificação radial / Abstract: In spite of technological importance of solidification of metallic alloys under radial heat flow, relatively few studies have been carried out in this area. In this work the solidification of Al 4.5 wt% Cu cylinders against a steel massive mold is analyzed and compared with unidirectional solidification against a cooled mold. Initially temperature variations at different positions in the casting and in the mold were measured during solidification using a data acquisition system. These temperature variations were introduced in a numerical method in order to determine the variation of heat transfer coefficient at metal/mold interface by inverse method. The results for unidirectional and radial solidification were compared showing that the heat transfer coefficient is smaller for radial heat flux. The primary and secondary dendrite arm spacing variations were measured through optical microscopy. Experimental results for temperature variations were applied to estimate thermal parameters of the solidification process. Comparisons carried out between experimental and numerical data showed that the numerical method describes well the solidification processes under radial heat flux / Mestrado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

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Made available in DSpace on 2014-10-09T12:26:37Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:22Z (GMT). No. of bitstreams: 0 / A reconstrução tridimensional de superfícies de fratura de materiais compósitos do tipo CFRP é apresentada neste trabalho como um método possível para análise fractográfica desse material, cuja superfície de fratura pode apresentar uma rugosidade acentuada, com grande variação em altura. Dois métodos são apresentados para esse propósito: a reconstrução por foco variável, realizada com imagens de microscopia óptica e a reconstrução por paralaxe, realizada com par de imagens estéreo, obtidas por microscopia eletrônica de varredura. Uma avaliação é realizada para cada um dos dois métodos, discutindo seus limites e a eficiência de cada um deles, perante as dificuldades de análise de materiais compósitos unidirecionais e multidirecionais. O método de foco variável apresentou um excelente resultado de reconstrução, mas tem a necessidade de um número grande de imagens, tempo de dedicação do instrumento e limite de ampliação das imagens como fatores a serem considerados na escolha de melhor método. As inclinações da amostra, durante o método da paralaxe, revelam alterações nos histogramas das imagens adquiridas no sentido horário que limitam o uso do método para materiais com alta rugosidade. A obtenção de imagens em um único sentido e a construção de uma região de interesse, posicionada no centro da imagem são sugestões para tornar o método mais abrangente. A linearidade das projeções de características na imagem inclinada também sugere a possibilidade de realizar a reconstrução utilizando, em vez de apenas duas, múltiplas imagens obtidas no sentido anti-horário. As alterações propostas para modificar a rotina, são sugeridas para que o programa possa ser aplicado de forma mais abrangente, independente da qualidade da superfície de fratura observada. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Copper based alloys play important role in high heat flux applications, particularly in rocket technology, the liner of the combustion chamber, and also in other heat transfer vessels. In these applications, one needs excellent high-temperature strength without sacrificing the thermal conductivity significantly. However, it is a challenging and difficult task to significantly improve the balance between strength and conductivities (electrical and thermal) of Cu-based alloys. In general, microstructural attributes, responsible for increasing mechanical strength of the alloy, also affect the transport properties by creating scattering centers. Hence, delicate optimization is needed for developing balanced alloy system for better performance. A substantial amount of research efforts has therefore been focused on devising methodologies to synthesize copper based alloys with a good combination of strength and conductivity. The present thesis deals with the development of a newer class of high strength high conductivity copper base alloy through tuning of phase transformation and careful additions of ternary and quaternary alloying elements and ultimately by microstructural engineering. In this thesis, we report the development of novel high strength high conductivity Cu-based alloy series in the Cu-Fe-Si system through rapid solidification process using suction casting apparatus. We have also optimized the alloys by altering and fine tuning the alloy compositions in order to achieve balanced and optimum properties. The strength of copper can be increased by various strengthening mechanisms. In general, precipitation hardening, dispersion strengthening and solid solution strengthening are the three most effective mechanisms for improving the strength of copper. Among these, solid solution strengthening has the most detrimental effect on the transport properties due to the presence of solute atoms which act as prominent scattering centres. Precipitation hardened copper alloys are often unable to retain strength at high temperatures, due to the coarsening of the precipitates. Currently, efforts are being made to develop newer dispersion strengthened copper alloys. These alloys contain a fine dispersion of nanometer sized oxides or other intermetallic compounds in the copper matrix. Dispersion strengthened copper alloys show impressive mechanical strength as well as thermal stability. In this thesis, we have explored the possibility of obtaining structurally ordered intermetallic dispersions through exploiting immiscibility of solutes in copper based alloys. The immiscibility promotes precipitation and decrease the solid solubility of solute elements in the matrix which in turn minimizes the scattering process and thus offers the possibility of improved transport properties. These ordered and coherent dispersion of intermetallic particles in the continuous copper matrix, dispersed during solidification, are believed to be the main contributor to the improvement of mechanical strength of the alloy. Crystallographically ordered structure and the coherency strain associated with the intermetallic particles in the copper matrix, together contribute to the mechanical strength through the mechanism of order hardening and coherency strengthening. These also, promote a low interfacial energy between precipitates and matrix in the alloy. This low interfacial energy reduces the driving force for coarsening process and thus helps in retaining the mechanical strength at elevated temperatures. Releasing of coherency strain at the precipitate-matrix interface with increasing temperature also yields a dramatic effect on the enhancement of thermal conductivity at high service temperatures. In the current study, we have selected three alloy compositions in the Cu-Fe-Si system at the higher end of copper. These are Cu-20Fe-5Si (at%), Cu-2.5Fe-2.5Si (at%) and Cu-1.0Fe-1.0Si (at%) respectively. We have systematically increased the concentration of copper, and altered the ratio of Fe and Si in order to achieve the better combination of properties (mechanical and transport) through fine tuning the microstructure. The present sets of alloys have been chill cast by the suction casting technique. This rapid solidification process, associated with moderate undercooling, is capable of accessing the submerged metastable miscibility gap of the Cu-Fe binary system. The higher quenching rate moves the system far away from equilibrium and hence, the solidification process occurs at the non-equilibrium regime. Rapid solidification of a copper rich Fe-Cu melt promotes the precipitation of the γFe from copper solid solution due to the immiscibility of Fe and Cu. In this scenario, the addition of a small quantity of silicon as a ternary element leads to its partition to both copper and iron rich phases. However, the larger chemical affinity between Fe and Si, leads to the formation of an ordered structure. However, the FCC crystal field of the copper matrix tends to promote an FCC based novel L12 ordered structure of the Fe3Si intermetallic particles instead of the ordered DO3 structure of Fe3Si composition normally observed in the bulk alloy. This nano meter sized L12 ordered particles maintain a cube-on-cube orientation relationship with the surrounding copper matrix and are associated with large coherency strain. A good lattice matching between these L12 ordered particles and copper matrix will promote a low interfacial energy and thus, a low driving force for particle coarsening. The present thesis is divided into eight chapters. The first chapter introduces the present work and the organization of the thesis. In the second chapter, current status in the development of the copper alloys and the general principle of alloy developments has been described. This includes both experimental and theoretical developments that can be used for developing high strength Cu based alloys. Chapter three, titled as „experimental procedure‟, describes the detailed description of materials and experimental techniques, adopted for the current studies. There are three chapters that deal with the main results of the thesis. Chapter eight, describes the suggestion for future work. The fourth chapter, titled as „Chill cast Cu75Fe20Si5 alloy: Microstructural Evolution and Properties‟, explores the detailed microstructural evolution of the Cu75Fe20Si5 alloy. This chapter also discusses the microstructure-property correlations. The microstructure of the alloy exhibits a multi-scale hierarchical structure during rapid solidification. The solidified microstructure contains Fe-rich globules with DO3 ordered structure, embedded in the continuous Cu-rich matrix. The continuous copper matrix also contains nanometer sized (average diameter 12 nm) coherent particles that exhibit Ashby-Brown strain contrast. Characterization of these phases has been carried out by a combination of X-ray diffraction, electron probe microanalysis and transmission electron microscopy coupled with energy dispersive spectroscopy. This multi-scale complex copper alloy (Cu75Fe20Si5 ) has achieved a remarkable yield and ultimate tensile strength at both room temperature and elevated temperatures in comparison to other copper based alloys. The yield strength and ultimate tensile strength at room temperature are 516±17 MPa and 635±14 MPa respectively whereas yield strength and ultimate tensile strength at 6000C turn out to be 95±11 MPa and 105±12 MPa respectively. In spite of achieving good mechanical strength, this alloy suffers from deterioration of electrical and thermal conductivity due to the presence of high volume fraction of the second phase and alloying elements. The room temperature electrical resistivity of this alloy shows that it is 10 times higher than that of pure copper (alloy resistivity = 1.70E-05 Ohm-cm at 250C and pure Copper- 1.68 × 10-6 Ohm-cm at 200C ). The thermal conductivity of this alloy turns out to be 88 W/m.K at 500C and 161 W/m.K at 6000C respectively which is much smaller in comparison to pure copper ( pure copper ≈ 401 W/m.K at 50 to 6000C). Attempts have been made to overcome the lowering of the transport properties by careful alteration of alloy compositions and fine tuning the microstructure. A new alloy with composition Cu-2.5Fe-2.5Si (at %) has been synthesized in order to achieve better transport properties without significantly sacrificing the mechanical strength. In this new alloy, we have reduced the volume fraction of the second phase (Fe-rich DO3 ordered globules) by lowering the addition of the alloying elements. We have also tried to alter the Fe to Si ratio in such a way that we can retain nanometer sized coherent particles in the matrix that provides strengthening. We arrived at a Fe and Si atom ratio of 1:1. The study of this alloy is presented in chapter five titled as „Chill cast Cu95Fe2.5Si2.5 alloy: Microstructural Evolution and Properties‟. Microstructural characterization indicates that the alloy contains only the nano meter sized coherent L12 ordered particles in the copper matrix. These particles show the Ashby-Brown strain contrast and are rich in iron and silicon. The absence of the high volume fraction of DO3 ordered Fe-rich globular phase and the smaller addition of the alloying elements ensure an improvement in the transport properties. The average resistivity value of this alloy at 250C is 3.5053 × 10-6 (Ohm-cm). This value represents a dramatic improvement in electrical properties in comparison to the Cu75Fe20Si5 alloy (Cu75Fe20Si5 alloy: 1.70E-05 Ohm-cm at 250C). The result is even better when we consider the temperature dependent thermal conductivity of the Cu95Fe2.5Si2.5 alloy. The thermal conductivity of this alloy turns out to be 236 W/m.K at 500C and 313 W/m.K at 6000C respectively. Though the thermal conductivity at room temperature is lower than pure copper, the gap reduces with increasing temperature (pure copper ≈ 401 W/m.K at 50 to 6000C and Cu75Fe20Si5 alloy: 88 W/m.K at 500C and 161 W/m.K at 6000C). This trend of temperature dependent thermal conductivity has made this alloy as one of the potential candidates for high-temperature applications. In situ heating experiment using transmission electron microscope (up to 4500C) and the heat treatment analysis at 6000C confirm that these L12 ordered particles are structurally stable at high temperatures and believed to be the main contributor to high mechanical strength in the alloy through the mechanism of order hardening and coherency strengthening. Coherent nature of the interface between the ordered particles and copper matrix also promotes low interfacial energy in the alloy and thus offers resistance to coarsening at elevated temperatures. Along with the attractive transport properties, this alloy also exhibits its success of retaining mechanical strength at both ambient and high temperatures as compared to the earlier alloy. The room temperature yield strength and ultimate tensile strength of this alloy are recorded as 580±18 MPa and 690±16 MPa respectively whereas the yield strength and ultimate tensile strength at 6000C of this alloy obtained as 128±8 MPa and 150±10 MPa respectively. Thus newly modified alloy exhibits an excellent balance between mechanical strength and conductivity (electrical and thermal) and can be regarded as a promising alloy for high strength high heat flux applications. The possibilities of the Cu95Fe2.5Si2.5 alloy as a potential candidate for high strength high conductivity application has provided the motivation for further optimization of the composition of this class of alloy. Mechanical strength and transport properties of a precipitation strengthened alloy always depends on the structure, shape, volume fractions and the number densities of the precipitate particles. Electrical and thermal conductivity are also sensitive to the presence of third elements and the number densities of the precipitates in the alloy. Thus, optimization of the volume fraction and the number density of the precipitates can yield a better alloy. With this objective, we have further increased the concentration of copper while keeping the Fe and Si atom ratio fixed at 1:1. Chapter six, titled as „Chill cast Cu98Fe1.0Si1.0 alloy: Microstructural Evolution and Properties‟ describes the microstructural evolution and microstructure-property correlation of this new alloy. Characterization analysis (X-ray diffraction, electron probe microanalysis and transmission electron microscopy) confirms that the microstructure of this alloy contains similar kind of nanometer sized L12 ordered particles with lower number density as compared to Cu95Fe2.5Si2.5 alloy (Relative planar number density of the particles: Cu98Fe1.0Si1.0 = 0.13 and Cu95Fe2.5Si2.5 = 0.20). This nano sized coherently ordered particles show the similar Ashby-Brown strain contrast and are rich in iron and silicon similar to the Cu95Fe2.5Si2.5 alloy. This dilute alloy exhibits slight improvement in transport properties in comparison to the earlier Cu95Fe2.5Si2.5 alloy. The electrical resistivity of this alloy at 250C is 3.438E-6 Ohm-cm (Cu95Fe2.5Si2.5 = 3.5053 × 10-6 Ohm-cm at 250C). The thermal conductivity values of this alloy are 243 W/m.K and 338 W/m.K at 500C and 6000C respectively (Cu95Fe2.5Si2.5 = 236 W/m.K at 500C and 313 W/m.K at 6000C). This increase in transport properties is associated with further compositional dilution and the presence of lower number density of the ordered particles in the copper matrix. The mechanism of strengthening is similar to the earlier alloys. The only difference lies in the fact that this present alloy contains lower number density of the L12 ordered particles in the copper matrix. This lower number density is responsible for the loss in mechanical strength of this alloy. The room temperature yield strength and the ultimate tensile strength of this present alloy are 467±16 MPa and 558±12 MPa whereas yield strength and ultimate tensile strength at 6000C are recorded as 102±13 MPa and 110±12 MPa respectively. Though the alloy exhibits some loss in mechanical strength, the values are still attractive in comparison to other commercially available copper based alloys. Both the alloy Cu98Fe1.0Si1.0 and Cu95Fe2.5Si2.5 demonstrate an excellent balance of mechanical strength and transport properties and have the potential to become a high strength and high conductivity materials for high temperature applications. Chapter seven is entitled as „Comparison between the alloy systems‟. In this chapter, we have presented a comparison of our new alloys with other commercially available Cu-base alloys. The thesis ends with a chapter titled as “Suggestions for future work”. We have included a descriptive note for possible future extension of our current work in this chapter.

No description available.

Ce travail se concentre sur l’étude des chandeliers en bronze, en cuivre et en laiton en Europe entre le XIIIe et le XVIIe siècle, entreprise dans une perspective interdisciplinaire. Abandonnés depuis la fin du XIXe siècle au champ méprisé des arts mineurs et populaires, les chandeliers n’ont depuis cette époque jamais véritablement été considérés comme une thématique de recherche à part entière. Le caractère anépigraphe de ces objets ordinaires et l’impossibilité de lier facilement les modèles produits à des espaces de productions spécifiques ont jusqu’ici cantonné les problématiques à des questions stylistiques et typologiques.L’objectif de cette étude se fonde sur un principe de déconstruction historiographique afin de dépasser l’approche traditionnellement adoptée qui enlise les recherches dans des considérations aporétiques. La recherche fait appel à plusieurs types de sources – écrites, archéologiques, iconographiques et analytiques - dont l’alliance vise la recontextualisation des chandeliers. Il s’agit de décrire et d’analyser l’itinéraire d’un type d’ustensile dans les sociétés médiévale et moderne dans les deux contextes, profane et religieux, dans lesquels ils ont été utilisés. C'est pourquoi l’historicisation des chandeliers se construit, dans le cadre de cette étude, sur leurs matérialités.La recherche s’intéresse ainsi à la reconstitution des chaînes opératoires de la production métallurgique, à la caractérisation des hommes qui travaillent le cuivre et ses alliages ainsi qu’à celle des matériaux, à la diffusion de l’objet à travers la société et aux usages, pratiques, culturels, symboliques ou dévotionnels, qui lui sont attachés. Les réflexions contribuent également à souligner que l’interrogation croisée des champs disciplinaires permet de comprendre en quoi la typologie des sources, en ce qu’elles concernent différents groupes sociaux, différents contextes, différents protagonistes et différentes réalités lexicales, influence la façon de percevoir ces objets / This work focuses, from an interdisciplinary perspective, on bronze, copper and brass candlesticks produced in Europe between the 13th and the 17th century. These objects have been neglected since the end of the 19th century and abandoned to the despised field of minor and popular arts. Since that time, they have never been considered as a real research topic. Since these ordinary objects are anepigraphic and because of the impossibility to attribute them to specific workshops, the research have been reduced to stylistic and typological issues.This study aims at overcoming the traditional approach that confines research into aporetic considerations. It mobilized several types of sources – written ones, archaeological ones, iconographic ones and analytical ones – to study candlesticks in context. They contributed to describe and analyze the life course of an ordinary utensil in medieval and modern societies in both secular and religious contexts. This is why the historicization of candlesticks is here built on materiality.This work focuses on metallurgical production, on copper alloys craftsmen, on the composition of alloys, on the diffusion of candlesticks in society and on practical, cultural, symbolic and devotional uses. The discussion also points out that this methodology helps to understand how the different types of sources, because they concern different social groups, different contexts, different protagonists and different lexical realities, influence how these objects were perceived

Abstract not available

For thesis abstract select View Thesis Title, Contents and Abstract

The area of research dealing with joining of dissimilar metals has been active in recent time. Although fusion and non-fusion techniques of joining have been effectively used for manufacturing components, a comprehensive scientific understanding of the process is lacking. This void exists both in fusion and non-fusion welding methods. The present investigation addresses some of these aspects. The investigation consists of two sections - Part A and Part B. Part A is on Friction welding and Part B deals with Fusion welding using laser. Each section has two chapters each. Following an introductory chapter, basic aspects of friction welding is presented in chapter 2. Chapter 3 deals with the work on friction welding of Fe-Cu couple. Fe-Cu couple is a system with positive heat of mixing. After a brief introduction on various non-equilibrium processes that can occur in this system, experimental details and results are presented. Using the results an attempt is made to understand the flash formation, formation of pores at the interface and the formation of chemically altered zone. It is observed that a chemically altered layer forms predominantly on the Cu side of the interface. It consists of Fe entrapped as fragments/fine crystals and as solid solution in Cu matrix. This zone has higher thickness at the edges than at the center. The mechanism of formation of this interfacial layer which is central to the joining process is related to the fracture and transport of fragments during plastic deformation. Fe forms solid solution in copper under non-equilibrium conditions promoted by shear energy. Using the concept of ballistic mixing, the formation of solid solution is explored. Using nano-indentation experiments mechanical properties of the weldment is estimated and an attempt is made to correlate mechanical properties with the amount of second element present in that location. The chapter 4 in part A deals with the friction welding of Ni-Ti couple. Ni-Ti system has negative heat of mixing and it forms a number of intermetallics. After a brief introduction to the chapter, various experimental techniques and strategies followed to carry out the experiments are explained. Following these, the results are presented. It is observed that TiNi3 formed at initial stage. Theories based on effective heat of formation and surface energy also predict the nucleation of TiNi3. With the continuation of frictional processes, the formation of TiNi and Ti2Ni phases were also observed. Formation of Ti2Ni was shown to greatly accelerate due to shear process. In this system two complementary processes like ballistic mixing and thermal assisted diffusion accelerate Ti2Ni formation. From mechanical tests it is found that Ti2Ni layer in the weldment is weak and hence formation of Ti2Ni in the weldment is detrimental. In chapter 5 an introduction to fusion welding of dissimilar metals is presented as background materials for the subsequent chapters. Chapter 6 deals with nature of segregation of Ag during laser welding of Fe-Ni couple. Ag is used as a tracer to probe fluid flow in the Fe-Ni couple during laser welding. Ag is immiscible both in Fe and Ni whereas Fe and Ni form a complete solution at an elevated temperature and in liquid state. Besides the experimental work, numerical simulation of the weld pool were carried out using homogeneous mixture model using SIMPLER algorithm. Experiments and simulations indicate that fluid flow is asymmetrical and in the deep penetration welding strong convection in the pool drives the tracer to the top of the pool. Overall distribution of the tracer is due to the combined effect of convection and diffusion. In shallow welding there exists a boundary region where tracer does not penetrate. In chapter 7 the results of instrumented indentation experiments on laser welded Fe-Cu weldment has been presented. It was earlier reported that during laser welding of Fe-Cu couple, a variety of microstructures evolves at various locations in the weldment and hardness of the weldment were found to be very high. Here an attempt has been made to explore in details the origin of such a high hardness. The chapter starts with a description of various microstructures that are observed in this weldment followed by the various procedures used for extracting data from instrumented indentation tests. It is followed by the presentation of the experimental results. It is found that rule of mixture along with Hall-Petch strengthening explains the observed increase in hardness of the weldment. The fine scale microstructure consisting of alternate Fe rich and Cu rich layers increases the hardness of the weldment. On copper side of the weldment, composition and scale of microstructure fluctuates and so also the hardness. Finally in chapter 8 overall conclusions of the various chapters in the thesis have been summarised.

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-06-22T13:42:56Z No. of bitstreams: 0 / Made available in DSpace on 2016-06-22T13:42:56Z (GMT). No. of bitstreams: 0 / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP