Orientador: Noé Cheung / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-27T15:01:42Z (GMT). No. of bitstreams: 1 Faria_JonasDias_M.pdf: 8725613 bytes, checksum: 4224f8e05e9dbca09ceebfbb4e419859 (MD5) Previous issue date: 2015 / Resumo: Diversas aplicações industriais, tais como aquelas típicas dos setores automotivo e aeronáutico, que necessitam de resistência mecânica, utilizam ligas do sistema Al-Cu. As ligas do sistema ternário Al-Cu-Ag são empregadas como modelo para o estudo de ligas eutéticas ternárias, além do uso em certo número de aplicações técnicas, como a soldagem em alta temperatura de Al com liga Ag-Cu. Entretanto, não consta na literatura o estudo dos efeitos, em ligas do sistema Al-Cu solidificadas em regime transitório, nos parâmetros microestruturais e nas propriedades mecânicas em decorrência da adição de Ag. Nesse sentido, o objetivo principal deste trabalho consiste na investigação dos efeitos da adição de 4%Ag nos parâmetros de solidificação: velocidade de crescimento (VL) e taxa de resfriamento (?), na microestrutura e nas propriedades mecânicas da liga Al-4%Cu solidificada unidirecionalmente no sentido vertical ascendente em regime transitório. São apresentadas leis experimentais para as ligas Al-4%Cu e Al-4%Cu-4%Ag que correlacionam os espaçamentos dendríticos primário (?1), secundário (?2) e terciário (?3) com VL e ?. Foram realizadas análises de difração de raios-X para a caracterização das fases cristalinas presentes na microestrutura das ligas. O difratograma da liga binária detectou a presença dos intermetálicos ?-Al2Cu, Al-Cu, Al4Cu9 e Al6Fe e, para o caso da liga ternária, adicionalmente foi detectado o intermetálico ?-Ag3Al. Composições químicas de regiões do contorno da dendrita, assim como de seu interior, foram obtidas com o auxílio de um microscópio eletrônico de varredura acoplado a um sistema de análise por energia dispersiva. Diversas posições ao longo do lingote foram analisadas através da técnica de fluorescência de raios-X com objetivo de determinar o perfil de macrosegregação. Constatou-se que a microdureza não é influenciada pela variação tanto em ?1 quanto em ?2 da liga Al-4%Cu. Os intermetálicos ?-Ag2Al e ?-Ag3Al são responsáveis pelo aumento de dureza devido a sua interação com ?3 e outros intermetálicos. Observou-se que a liga Al-4%Cu-4%Ag apresentou limite de resistência à tração (?u), limite de escoamento (?e) e alongamento específico (?) superiores aos da liga Al-4%Cu / Abstract: Al-Cu alloys are used in several industrial applications, such as automotive and aerospace manufacturing, which demand mechanical strength performance. The Al-Cu-Ag ternary alloy system has been investigated to obtain a better understanding on ternary eutectic alloys besides its inherent applications, such as the high temperature soldering of Al with Ag-Cu alloy. However, studies concerning the effects on microstructure and hardness due to Ag addition on Al-Cu alloys solidified under transient conditions, are not found in literature. In this sense, the main objective of this work consists of investigating the solidification parameters such as growth (VL) and cooling (?) rate, microstructure and mechanical properties regarding the effects of adding 4wt% Ag on a Al-4wt%Cu alloy directionally solidified vertically upwards under unsteady-state solidification conditions. Experimental growth laws correlating the primary (?1), secondary (?2) and tertiary (?3) dendritic spacings with VL and ? are proposed for Al-4wt%Cu and Al-4wt%Cu-4wt%Ag alloys. X-ray diffraction analyses were performed in order to determine the crystalline phases present in the alloys microstructure. The diffractogram of the binary alloy detected the presence of ?-Al2Cu, Al-Cu, Al4Cu9 and Al6Fe intermetallics and, for the case of the ternary alloy, the ?-Ag3Al intermetallic was detected too. Chemical compositions at the boundary regions of the dendrite, as also inside the dendrite, were obtained using a scanning electron microscope connected to an energy-dispersive spectrometer system. Several positions along the ingot were analyzed through the X-ray fluorescence technique permitting the determination of macrosegregation profile. It is shown that the microhardness is not influenced by the variation in ?1 as well as in ?2 of the Al-Cu alloy. The ?-Ag2Al and ?-Ag3Al intermetallics are responsible for the hardness increase due to the interaction with ?3 and other intermetallics. It was observed that the Al-4wt%Cu-4wt%Ag alloy exhibited yield (?e), ultimate tensile strength (?u) and elongation (?) superior to the Al-4wt%Cu ones / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22067号 / 工博第4648号 / 新制||工||1725(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 安田 秀幸, 教授 辻 伸泰, 教授 宇田 哲也 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

As a result of the intense air-water interaction in the spray nozzle, air-mist spray is one of the most promising technologies for attaining high heat transfer. CFD simulations and multivariable linear regression were used in the first part of this study to analyze the air-mist spray produced by a flat-fan atomizer and to predict the heat transfer coefficient using the casting operating conditions such as air pressure, water flow rate, cast speed and standoff distance. For the air-mist spray cooling simulation, a four-step simulation method was utilized to capture the turbulent flow and mixing of the two fluids in the nozzle, as well as the generation, transport, and heat transfer of droplets. Analysis of the casting parameters showed that an increase in air pressure results in efficient atomization, increases the kinetic energy of the droplets and produces smaller droplet size thus, the cooling of the slab increases significantly. Also, a decrease in water flow rate, standoff distance and casting speed would result in more efficient cooling of the steel slab. The second part of the study investigated the solidification of steel in the secondary cooling region. Caster geometry and casting parameters were studied to evaluate their impact on the solidification of steel. The parameters studied include roll gap, roll diameter, casting speed and superheat. It was found that a smaller ratio of roll gap to roll diameter is more efficient for adequate solidification of steel without any defect. Casting speed was found to have a significant effect on the solidification of steel while superheat was found to be insignificant in the secondary zone solidification. The result from the air-mist spray cooling was integrated into the solidification model to investigate the solidification of steel in the entire caster and predict the surface temperature, shell growth and metallurgical length. To replicate real casting process, temperature dependent material properties of the steel were evaluated using a thermodynamic software, JMatPro. The air-mist spray model was majorly investigated using ANSYS Fluent 2020R1 CFD tool while the solidification of steel was studied using STARCCM+ CFD software. Using the findings from this study, continuous casting processes and optimization can be improved.

The master thesis deals with processes of segregation in austenitic-ferritic stainless steels. The introductory part consists of characteristics features of austenitic-ferritic steels and theoretical analysis of segregation processes. The second part shows practical measurements of segregation in experimental casting. Macrosegregation was measured on a spectrometric analyzer and simultaneously solved in the simulation program MAGMA. The aim of this thesis is to verify the effect of solidification time and dwell time between liquidus and solidus temperature on the chemical heterogeneity of duplex stainless steel casting of about 500 [mm]. Chemical heterogeneity was solved for selected alloying and accompanying elements such as C, Mo, Ni, Mn, Cr. The microsegregation was not addressed. Comparison of the mechanical properties of cast and heat treated duplex steel was done by tensile testing of samples cut from the center of the casting.

Diploma thesis deals with the possibility of using solidification technology to transform the hazardous waste with the aim to achieve the material utilization of solidification products. The aim of the thesis is to determine a suitable solidification formula for solidification product made of hazardous waste that will ensure properties of the solidification product, those will allow its placing on the market.

This thesis is dedicated to the field of manufacture of heavy steel castings with resulting properties which are influenced by long solidification time. During the long solidification time a segregation process of additives in the steel occurs which results in numerous metallurgical defects. The work was intended to observe the macrosegregation effects in the wall of a heavy experimental steel casting respectively a part of a real superheavy casting intended for cement furnaces (weight 210 t). The steel casting for the research was manufactured in the joint-stock company of VHM where such heavy castings are commonly produced for the market. The supplied piece of the steel casting was cut into the smaller pieces for the better examination. The examination resulted in information about the casting macrostructure and chemical heterogeneity of chosen elements in the casting wall. The heterogeneity of the chosen elements (C, Mn, Si, Cr, S, P) is clearly shown in the worked out visual concentration maps. Based on the experimental data the measured results of segregations were confronted with the results of segregation modelling with the use of the commercial simulation software ProCAST. It resulted in the conclusion that the prediction of segregations is not in accordance with the reality. Furthermore, the results from the experimental casting are shortly compared with previously manufactured castings of the same type and the results summarizing the found range of macrosegregations of the tested sample are interpreted in the work conclusion.

Cette thèse a été centrée sur l’étude de la formation d’une phase martensitique dans les aciersFe-Ni-C et sur la diffusion des atomes de carbone dans cette phase à basse température. Lamodélisation à l’échelle atomique a été utilisée. Pour décrire ces phénomènes, deux approchesont été développées: un modèle discret basé sur la théorie de la fonction de densité atomique(ADF) et une approche quasiparticulaire basée sur la théorie atomique de Fratons (AFT). Dansun premier temps, pour montrer l’universalité de notre approche, nous avons appliqué l'AFTpour modéliser la cinétique d'auto-assemblage des atomes initialement désordonnés à desstructures ordonnées complexes. Cette approche a ensuite été appliquée à l'étude detransformation austénite/martensite. Il a été montré que le germe de martensite se développecomme agrégat multivariant dans la matrice austénitique. En utilisant des figures de pôles etdes diagrammes de diffraction simulés, ces variants ont été identifiés et comparés aux donnéesexpérimentales. La diffusion du carbone dans la phase de martensite a été étudiée en utilisantla théorie ADF. Deux systèmes avec différentes propriétés élastiques, Fe-C et Fe-Ni-C, ont étéconsidérés. Il a été montré qu’au cours du premier stade de vieillissement, les atomes decarbone subissent une décomposition spinodale sur les interstices octaédriques du réseautétragonal centré de martensite et forment les zones riches en carbone. Ensuite, la morphologie«tweed-like» des zones riches en carbone est développée. Les résultats des simulations sontun bon accord avec les images expérimentales obtenues par sonde atomique tomographique.La relation entre une mise en ordre de Zener et la concentration des zones riches en carbone aété discutée. / This thesis examines the formation of martensite in Fe-Ni-C steels and the diffusion of carbonatoms in this phase at low temperatures. To achieve this goal the atomistic modeling have beenused. To describe these phenomena two different approaches were developed: a discretemodel based on the Atomic Density Function (ADF) theory and the quasiparticle approachesbased on the Atomic Fraton Theory (AFT). First, the AFT was tested to model a self-assemblykinetics of initially disordered systems to three different classes of ordered one: singlecomponent crystals with fcc and diamond structures, two component crystals with zinc-blendstructure, and polymers with single-strand and double-stranded helixes structures. Then thisapproach was applied to model austenite/martensite transformation. It was shown thatmartensite nucleus grows as multivariant aggregate in austenite matrix. Using pole figures andsimulated diffraction patterns these variants were identified and compared with the experimentaldata. The carbon diffusion in martensite phase was studied using ADF theory. Two systemswith the different elastic properties corresponding to the Fe-C and Fe-Ni-C systems wereconsidered. It was shown that during a first stage of aging the carbon atoms undergo a spinodaldecomposition on the octahedral interstices of bcc lattice and form the carbon-rich zones. Then"tweed-like" morphology of carbon-rich zones is developed. The simulations results are a goodagreement with experimental images obtained by atom probe tomography. The relationbetween Zener ordering and the concentration of carbon reach zones is discussed.

In Rahmen dieser Arbeit wurde ein Simulationsprogramm für Gießprozesse weiterentwickelt. Zunächst wurden die Richtigkeit der mathematischen Lösung und die Sensibilität der Software bestätigt. Dazu wurde ein Vergleich der berechneten mit den experimentellen Werten durchgeführt. Zur Messung der Wanddicke des erstarrenden Gussteils wurde eine neue Methode zur Visualisierung der Berechnungsergebnisse erarbeitet. Anhand zweier Beispiele zur Berechnung eines dünnwandigen, komplizierten Al-Gussteils und eines exothermischen Speisers wurde eine korrekte Nutzung neuer Gießtechnologien aufgezeigt. Das Simulationssystem wurde speziell für das Stranggießen modifiziert. Die neu entwickelten Berechnungsalgorithmen sowie die Visualisierungsmöglichkeiten erlauben eine exakte Modellierung des Strangabzuges in der Gießmaschine. Auch in diesem Falle liefert der Vergleich zwischen den durchgeführten Berechnungen und den erzielten Versuchswerten die Richtigkeit und Exaktheit der neu eingesetzten Methode.

The presented work reports on the solidification studies in two alloy systems: the niobium bearing γ-TiAl, relevant for the automotive and aero-engine applications, and aluminium rich Raney-Ni, precursor alloys for catalyses used in the chemical industry. The time-resolved observations of equilibrium liquid-solid phase transformations, as well as non-equilibrium solidification from the undercooled melt, are performed by combination of in situ structural studies using high-energy X-rays at a synchrotron source and the electromagnetic levitation technique. Containerless processing assured the contamination-free environment leading to high undercooling levels even at moderate cooling rates. For the critical part of the Ti-Al-Nb phase diagram an equilibrium involving the liquid phase is deduced from the phase transformations gathered on heating periods of levitation experiment. New experimental data on the partial liquidus and solidus surfaces are delivered as well as the information on the nature of the reactions along the univariant lines. These data provide a valuable contribution to the reassessment of the thermodynamic description. The primary phase selection as function of undercooling is studied in ternary Ti-Al-Nb alloys. The metastable formation of the cubic β phase within the primary solidification region of the hexagonal α phase is observed with increasing melt undercooling. Furthermore, the microstructure evolution of the β solidifying Ti-46Al-8Nb alloy discloses the transition to the thermal growth mode for ∆T>200−250 K, accompanied by complete solute trapping. Supplemented with the data on the solidification velocity determined as function of melt undercooling, this results are discussed within the local non-equilibrium model of the free dendrite growth. The in situ observations of the non-equilibrium solidification of the binary Al-Ni system give insight into multiple phase transformation sequence. The achieved undercooling levels up to 320 K for the aluminium alloys containing 18–31.5 at.% Ni did not alter the primary phase selection. However, during further cooling of L+Al3Ni2 semisolid samples the peritectic formation of a metastable decagonal quasicrystalline phase is observed providing a critical undercooling below the peritectic temperature of Al3Ni phase is reached. On further cooling the metastable phase subsequently transforms into the equilibrium Al3Ni. A similar solidification pathways are expected for the Raney-Ni alloys produced by gas atomisation, where the associated high cooling rates allowed to retain the metastable phase at room temperature.

No description available.