No description available.

Yeung Man Hau. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 52-53). / Text in English; abstract also in Chinese. / Yeung Man Hau. / Chapter Chapter 1 --- Introduction / Chapter 1. --- Background of solidification --- p.1 / Chapter 1.1 --- The driving force for solidification / Chapter 1.2 --- Capillarity effect (or Gibbs-Thomson effect) / Chapter 2. --- Nucleation --- p.3 / Chapter 3. --- Growth --- p.4 / Chapter 3.1 --- Constrained growth and unconstrained growth / Chapter 3.2 --- Directional solidification / Chapter 4. --- Growth of pure substances --- p.6 / Chapter 4.1 --- Metals / Chapter 4.2 --- Stability of planar S/L interface / Chapter 4.3 --- Non-metals / Chapter 5. --- Solidification of single-phase binary alloys --- p.7 / Chapter 5.1 --- Equilibrium solidification / Chapter 5.2 --- Constitutional undercooling / Chapter 5.3 --- Stability of planar S/L morphology / Chapter 5.4 --- Minimum scale of perturbation in directional growth / Chapter 5.5 --- Development of growth morphology / Chapter 5.6 --- Growth rate of cell/dendrite tip / Chapter 5.7 --- Arm spacing and coarsening / Chapter 6. --- Solidification of binary eutectic alloys --- p.11 / Chapter 6.1 --- Classification / Chapter 6.2 --- Growth of lamellar eutectics / Chapter 6.3 --- Stability of planar morphology / Chapter 6.4 --- Coupled zone (Competitive growth of eutectic and dendrites) / Chapter 6.5 --- Off-eutectic solidification / Chapter 7. --- Solidification of ternary eutectic alloys --- p.14 / References --- p.16 / Figures --- p.17 / Chapter Chapter 2 --- Experimental Methods / Chapter 1. --- Fused silica tube cleaning --- p.37 / Chapter 2. --- Alloy preparation --- p.37 / Chapter 3. --- Undercooled specimen preparation --- p.38 / Chapter 4. --- Specimen examination --- p.38 / Chapter 5. --- TEM sample preparation --- p.39 / References --- p.40 / Figures --- p.41 / Chapter Chapter 3 --- Solidification of Undercooled Molten Pd60 .5Cu25Si14.5 Alloy / Chapter 1. --- Introduction --- p.44 / Chapter 2. --- Experimental --- p.46 / Chapter 3. --- Results --- p.46 / Chapter 3.1 --- Thermal profiles / Chapter 3.1.1 --- Temperature-time chart plotter (plotter) / Chapter 3.1.2 --- Differential thermal analysis (D TA) / Chapter 3.2 --- Microstructures / Chapter 3.2.1 --- Effect of undercooling on the microstructure / Chapter 3.2.2 --- Effect of quenching after 1st exothermic peak on the microstructure / Chapter 3.2.3 --- Effect of annealing at the onset temperature of 1st exothermic peak on the microstructure / Chapter 3.2.4 --- Effect of using slower cooling rate on the microstructure / Chapter 4. --- Discussions --- p.50 / Chapter 5. --- Conclusion --- p.51 / References --- p.52 / Figures --- p.54

Solidification from the melt is an essential step in nearly all conventional processes to produce bulk materials for industrial applications. Rapid quenching from the liquid state at cooling rates of 102 to 106K/s or higher has developed into a new technology for processing novel materials. InxGa1 - xSb a ternary III-V compound semiconductor was synthesized by using the rapid spinning cup (RSC) technique. Several compositions of these alloys were batched and cast into ingots in evacuated sealed quartz tubes. These ingots were then melted and ejected onto a rapidly rotating copper disk. This resulted in the generation of flakes or powders depending on the rpm of the disk. Microstructural characterization of the flakes and powders was performed using XRD, SEM and TEM. Efforts were also made to measure the bulk resistivity of the annealed flakes to see the effect of annealing on ordering of the phases.

by Chan Kim Wai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references. / by Chan Kim Wai. / Chapter Chapter I --- Introduction / Chapter 1.1 --- Rapid solidification / Chapter 1.1.1 --- Rapid quenching --- p.1-1 / Chapter 1.1.2 --- Undercooling --- p.1-2 / Chapter 1.2 --- Grain refinement / Chapter 1.2.1 --- What is grain refinement? --- p.1-5 / Chapter 1.2.2 --- Previous results in grain refinement / Chapter 1.2.2.1 --- Pure metals (or dilute alloys) --- p.1-5 / Chapter 1.2.2.2 --- Alloys --- p.1-9 / Chapter 1.2.2.3 --- Semiconductor --- p.1-10 / Chapter 1.2.3 --- Critical crystal growth velocity V* --- p.1-11 / Chapter 1.2.4 --- Proposed models to grain refinement / Chapter 1.2.4.1 --- Dynamic nucleation and cavitation --- p.1-12 / Chapter 1.2.4.2 --- Remelting (melt-back) --- p.1-14 / Chapter 1.2.4.3 --- Interdendritic fluid flow --- p.1-15 / Chapter 1.2.5 --- Volumetric manifestation of grain refinement --- p.1-15 / Chapter 1.3 --- Aim of this project --- p.1-16 / References / Figures / Chapter Chapter II --- Experimental / Chapter 2.1 --- Pure palladium / Chapter 2.1.1 --- Sample preparation and procedure --- p.2-1 / Chapter 2.1.2 --- Limitation and choice of flux --- p.2-2 / Chapter 2.1.3 --- High temperature furnace --- p.2-3 / Chapter 2.1.4 --- Measurement of specific volume / Chapter 2.1.4.1 --- Theory --- p.2-4 / Chapter 2.1.4.2 --- Setup --- p.2-5 / Chapter 2.1.5 --- Observing internal morphology --- p.2-5 / Chapter 2.2 --- Palladium with insoluble impurity / Chapter 2.2.1 --- Choice of insoluble impurities --- p.2-6 / Chapter 2.2.2 --- Sample preparation --- p.2-7 / References / Figures / Chapter Chapter III --- Results and Discussion / Results / Chapter 3.1 --- Pure palladium / Chapter 3.1.1 --- Specific volume --- p.3-1 / Chapter 3.1.2 --- Grain structure and internal voids --- p.3-2 / Chapter 3.2 --- Palladium with insoluble impurity / Chapter 3.2.1 --- Pinning effect of insoluble impurities --- p.3-3 / Chapter 3.2.2 --- Pd-Ni-S system / Chapter 3.2.2.1 --- Grain refinement in Pd99.9Ni-S)0.1 --- p.3-4 / Chapter 3.2.2.2 --- Change of ΔT* with addition of sulfur --- p.3-5 / Chapter 3.2.2.3 --- Internal voids --- p.3-5 / Discussion / Chapter 3.3 --- Dynamic nucleation of Pd-Ni-S system --- p.3-6 / Chapter 3.4 --- Void formation of pure palladium and Pd-Ni-S --- p.3-6 / Chapter 3.5 --- Grain refinement and specific volume --- p.3-7 / Reference / Figures

No description available.

The main aim of this work is to investigate heterogeneous nucleation of solidification of metals and alloys by a combination of differential scanning calorimetry and transmission electron microscopy using a newly modified entrained particle technique. Attention is focused on investigating (a) heterogeneous nucleation of Cd, In and Pb particle solidification by Al in rapidly solidified Al-Cd, Al-In and Al-Pb binary alloys; (b) effects of various ternary additions such as Mg, Ge and Si on heterogenous nucleation of solidification of Cd and Pb solidification by Al; (c) heterogenous nucleation of solidification of Si by solid Al in hypoeutectic Al-Si alloys. In addition, the melting behaviour of Cd, In and Pb particles embedded in an Al matrix is investigated. The rapidly solidified microstructures of melt spun Al-Cd, Al-In and Al-Pb alloys consist of faceted 5-200nm diameter Cd, In and Pb particles homogeneously distributed throughout an Al matrix. Cd particles exhibit an orientation relationship with the Al matrix which can be described as {111}_Al//{0001}_Cd and andlt;110andgt;_Al//andlt;112and#773;0andgt;_Cd, and In and Pb particles exhibit a near cube-cube and cube-cube orientation relationship with the Al matrix respectively. Cd, In and Pb particles embedded in the Al matrix exhibit distorted truncated octahedral or truncated octahedral shapes surrounded by {111}_Al and {100}_Al facets. The solid Al-solid Cd, solid Al-solid In surface energy anisotropies are constant over the temperature range between room temperature and Cd and In melting points respectively. The solid Al-liquid Cd and solid Al-liquid In surface energy anisotropies decrease with increasing temperature above Cd and In melting points. Solidification of Cd, In, Pb particles embedded in an Al matrix is nucleated catalytically by the surrounding Al matrix on the {111}_Al faceted surfaces with an undercooling of 56, 13 and 22K and a contact angle of 42°, 27° and 21° for Cd, In and Pb particles respectively. Addition of Mg to Cd particles embedded in Al increases the lattice disregistry across the nucleating plane, but decreases the undercooling before the onset of Cd(Mg) particle solidification. Addition of Ge to Al decreases the lattice disregistry across the nucleating plane, but increases the undercooling before the onset of Pb particle solidification embedded in the Al(Ge) matrix. These results indicate that chemical interactions dominate over structural factors in determining the catalytic efficiency of nucleation solification in Al-Cd-Mg and Al-Pb-Ge alloys. Contact between Si precipitates and Pb particles embedded in an Al matrix decreases the undercooling before the onset of Pb particle solidification. The equilibrium melting point of Cd particle in the melt spun Al-Cd alloy is depressed because of capillarity, and the depression of equilibrium melting point increases with decreasing particle size. In the melt spun Al-In and Al-Pb alloys, however, most of the In and Pb particles embedded within the Al matrix grains are superheated, and the superheating increases with decreasing particle size. The heterogeneous nucleation temperature for Si solidification by Al depends sensitively on the purity of the Al. Na and Sr additions have different effects on the Si nucleation temperatures. With an Al purity of 99.995%, Na addition increases the Si nucleation temperature, while Sr addition does not affect or decreases the Si nucleation undercooling, depending on the amount of Sr addition. The solidified microstructure of liquid Al-Si eutectic droplets embedded in an Al matrix is affected by the Si nucleation undercooling. With low Si nucleation undercooling, each Al-Si eutectic liquid droplet solidifies to form one faceted Si particle, however, with high Si nucleation undercooling, each Al-Si eutectic liquid droplet solidifies to form a large number of non-faceted Si particles embedded in Al.

edited by N. J. Grant and B. C. Giessen. Section I. / Includes bibliographical references and index.

No description available.

"Tautologically, castability is a critical requirement in any casting process. The two most important factors impacting castability are the susceptibility of a metal to hot tearing and the degree of casting fluidity a material possesses. This work concerns itself with fluidity of molten metal. Since experimental investigations into casting fluidity began, researchers have sought to maximize fluidity through superheat, mold temperature, alloy chemistry, melt cleanliness, and mold design. Researchers who have examined the published results in the field have remarked on the difficulty of making quantitative comparisons and drawing conclusions from the data. Ragone developed a horizontal vacuum fluidity apparatus and an analytical expression for fluid length to help resolve these issues. This was expanded on by Flemings et al. Still, the comparison of results is complicated by experimental uncertainties and a plurality of experimental procedures. This work seeks to resolve these issues through an analysis of experimental uncertainties present in existing fluidity tests and the development of an improved test and procedure which is very precise, accurate, and reliable. Certain existing tests and software packages have been shown to be unsuitable for quantitative fluidity measurement. Expressions for experimental uncertainty in fluidity testing have been derived. The capability to predict variations in fluidity as a function of alloy chemistry and other variables whose range of values are intrinsic to the economics of the process will help to more accurately determine the superheat needed for successful castings and will in turn lead to a decrease in scrap rates. This will enable metal casters to more reliably cast thin sections, and to reduce cycle time or scrap rate to achieve productivity goals. Superheat was shown to remain the dominant factor in fluidity, but the test allowed investigation of alloy modifications within an alloy specification in this alloy system. Factors known to have negative effects on structural properties were found often to have neutral or positive impacts on fluidity. A deep understanding of variations in fluidity measurements is the next necessary step in a century-long quest to understand how best to make metal castings through the use of fluidity experiments."

Orientadores: Amauri Garcia, Noe Cheung / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-14T16:40:44Z (GMT). No. of bitstreams: 1 Dias_AntonioCarlosPires_M.pdf: 13091267 bytes, checksum: c4c7c0e72c88328cba1119cc9cd6d650 (MD5) Previous issue date: 2009 / Resumo: As ligas de solda à base de estanho apresentam excelente fluidez e temperaturas de trabalho ideais para a união de componentes eletrônicos. A solda com ligas do sistema estanho chumbo é a mais comum para soldas em eletrônica. Entretanto, há muitas preocupações com o uso do chumbo, devido aos diversos efeitos adversos na saúde humana e contaminação do meio ambiente. Por essas razões, na maioria dos países o chumbo já é condenado e proibido de ser incorporado em diversos produtos. Neste sentido, a indústria eletrônica está de olho em soldas livres de chumbo que possam substituir a clássica solda estanho-chumbo. É objetivo deste trabalho analisar a solidificação de ligas eutéticas dos sistemas Sn-Ag e Sn-Cu, que são duas ligas com potencial de substituição. Foram desenvolvidos experimentos para determinar a influência do acabamento superficial da chapa molde nos parâmetros térmicos de solidificação durante a solidificação direcional ascendente em regime transitório de extração de calor de ligas eutéticas Sn-Pb, Sn-Cu e Sn-Ag. Foram utilizados dois tipos de acabamentos superficiais na chapa molde: lixado e ranhurado, para investigar as condições de afinidade metal/substrato. Foi desenvolvida uma abordagem teórico-experimental para determinar quantitativamente as variáveis térmicas, tais como: coeficiente de transferência de calor global (hg) e velocidade de deslocamento da frente de solidificação. As micro estruturas de solidificação foram caracterizadas e os espaçamentos dendríticos secundários (?2) foram medidos na direção longitudinal dos lingotes, e correlacionados com as variáveis térmicas que atuaram durante a solidificação. / Abstract: Tin based alloys for welding applications have excellent fluidity and adequate temperature working range to join electronic components. The most used tin alloys for welding is the eutectic Sn-Pb alloy. However, there are some concerns about lead, due to hazardous effects to health and to environment. Due to theses reasons, many countries condemn and prohibit the use of lead in several products. In this sense, the electronic industries are looking for lead-free solder alloys with a view to replace the traditional Sn-Pb eutectic alloy. The aim of this work is to analyze the solidification of Sn-Ag and Sn-Cu eutectic alloys which are potential alloys candidates to replace the eutectic Sn-Pb alloy. Experiments were conducted to determine the influence of the mold wall roughness on the thermal solidification parameters during the upward unsteady-state directional solidification of eutectic Sn-Pb, Sn-Cu and Sn-Ag alloys. Two different kinds of surface mold finishing, sanded and grooved, were used in order to analyze metal/substrate affinity. A combined theoretical and experimental approach has been used to quantitatively determine such thermal variables, i.e., transient global heat transfer coefficient (hg) and solidification growth rates. The microstructures have been characterized and the secondary (?2) dendrite arm spacings were measured along the castings length and correlated to transient solidification thermal variables. / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica