<p>The field of superplasticity is reviewed, with particular reference to the mode of deformation and viability for industrial application. Superplastic and conventional Zn-Al eutectoid alloys are compared with regard to the pressures and time required and the problems associated with the production of shaped hollow components from billet material, using extrusion followed by pressure forming. A possible industrial process is suggested and economically assessed in a Supplement to the Dissertation. </p> / Thesis / Master of Engineering (ME)

No description available.

No description available.

The theory of the lamellar eutectoid reaction by volume diffusion has been extended to account for solute segregation within the product phases and the effect of dilute third element additions. It has been demonstrated for symmetric binary systems that the segregation can account for 10% or more of the free energy stored in the product phases and can lead correspondingly to a predicted lamellar spacings appreciably greater than those obtained when segregation is neglected. This segregation is relatively high in the systems Cu-In, Cu-Be and Ag-Cd and may account for the fact that a secondary coarse-grained pearlitic reaction follows the initial fine grained one in these systems. The binary theory has been-used to analyse the available data for the eutectoid reaction in the Cu-Al and Fe-C systems and satisfactory agreement is obtained. The theory for ternary systems, while complete in principle, proves to be. intractable in all but the simplest version of the solution thermodynamics. It is concluded that the effect of the third element on the binary eutectoid reaction is mainly through its effect on the phase diagram, the ternary cross effects in the diffusion matrix tending to cancel out. Any additional element which lowers the eutectoid temperature will retard the reaction. / Thesis / Doctor of Philosophy (PhD)

No description available.

A otimização de sistemas do tipo Ti-Si-X requer que os sistemas binários estejam constantemente atualizados. O sistema Ti-Si foi investigado experimentalmente desde a década de 50 e poucos estudos usaram os dados experimentais para calcular o diagrama de fases Ti-Si usando modelamento termodinâmico. A otimização mais recente do sistema Ti-Si foi realizada em 1998, descrevendo a fase Ti5Si3 como um intermetálico não estequiométrico contendo três sub-redes e mostrando a presença da fase intermetálica estequiométrica Ti3Si. Dada a recente disputa sobre a cinética de precipitação e a estabilidade das fases Ti3Si e Ti5Si3 nos sistemas Ti-Si e Ti-Si-X, o canto rico em titânio do sistema Ti-Si (estável e metaestável) foi otimizado no presente trabalho. Os limites de estabilidade de fases, os valores dos erros pelo método dos mínimos quadrados do procedimento de otimização e os desvios padrões relativos das variáveis calculadas foram discutidos para inspirar a realização de mais trabalhos experimentais para investigar as reações eutetóides estáveis e/ou metaestáveis, ?->? + Ti3Si e ?->? + + Ti5Si3; e para melhorar cada vez mais as otimizações termodinâmicas do diagrama de fases do sistema Ti-Si. / The thermodynamic optimization of Ti-Si-X systems requires that the binary systems are constantly updated. The Ti-Si system has been experimentally investigated since the 1950\'s and few investigations have used this experimental data to calculate the Ti-Si phase diagram using thermodynamic modeling. The most recent assessment of the Ti-Si system was performed in 1998, describing the Ti5Si3 phase as a non-stoichiometric intermetallic containing three sublattices and showing the presence of the stoichiometric Ti3Si phase. In the light of the dispute over the precipitation kinetics and stability of Ti3Si and Ti5Si3 phases in Ti-Si and Ti-X-Si systems, the present work assessed the Ti-rich corner of the stable (featuring Ti3Si phase) and metastable Ti-Si phase diagrams. The phase boundaries, the values of the error of the least-square method of the optimization procedure and the relative standard deviation of the calculated variables were discussed in order to inspire further experimental work to investigate the stable and/or metastable eutectoid reactions, ?->? + Ti3Si e ?->? +Ti5Si3, and to improve the thermodynamic assessments of the Ti-Si phase diagram.

A otimização de sistemas do tipo Ti-Si-X requer que os sistemas binários estejam constantemente atualizados. O sistema Ti-Si foi investigado experimentalmente desde a década de 50 e poucos estudos usaram os dados experimentais para calcular o diagrama de fases Ti-Si usando modelamento termodinâmico. A otimização mais recente do sistema Ti-Si foi realizada em 1998, descrevendo a fase Ti5Si3 como um intermetálico não estequiométrico contendo três sub-redes e mostrando a presença da fase intermetálica estequiométrica Ti3Si. Dada a recente disputa sobre a cinética de precipitação e a estabilidade das fases Ti3Si e Ti5Si3 nos sistemas Ti-Si e Ti-Si-X, o canto rico em titânio do sistema Ti-Si (estável e metaestável) foi otimizado no presente trabalho. Os limites de estabilidade de fases, os valores dos erros pelo método dos mínimos quadrados do procedimento de otimização e os desvios padrões relativos das variáveis calculadas foram discutidos para inspirar a realização de mais trabalhos experimentais para investigar as reações eutetóides estáveis e/ou metaestáveis, ?->? + Ti3Si e ?->? + + Ti5Si3; e para melhorar cada vez mais as otimizações termodinâmicas do diagrama de fases do sistema Ti-Si. / The thermodynamic optimization of Ti-Si-X systems requires that the binary systems are constantly updated. The Ti-Si system has been experimentally investigated since the 1950\'s and few investigations have used this experimental data to calculate the Ti-Si phase diagram using thermodynamic modeling. The most recent assessment of the Ti-Si system was performed in 1998, describing the Ti5Si3 phase as a non-stoichiometric intermetallic containing three sublattices and showing the presence of the stoichiometric Ti3Si phase. In the light of the dispute over the precipitation kinetics and stability of Ti3Si and Ti5Si3 phases in Ti-Si and Ti-X-Si systems, the present work assessed the Ti-rich corner of the stable (featuring Ti3Si phase) and metastable Ti-Si phase diagrams. The phase boundaries, the values of the error of the least-square method of the optimization procedure and the relative standard deviation of the calculated variables were discussed in order to inspire further experimental work to investigate the stable and/or metastable eutectoid reactions, ?->? + Ti3Si e ?->? +Ti5Si3, and to improve the thermodynamic assessments of the Ti-Si phase diagram.

Cost-effective machining of hardened steel (>60 HRC) components such as a large wind turbine bearing poses a significant challenge. This thesis investigates a new laser tempering based hybrid turning approach to machine hardened AISI 52100 steel parts more efficiently and cost effectively. The approach consists of a two step process involving laser tempering of the hardened workpiece surface followed by conventional machining at higher material removal rates using lower cost ceramic tooling to efficiently cut the laser tempered material. The specific objectives of this work are to: (a) study the characteristics of laser tempering of hyper-eutectoid 52100 hardened steel, (b) model the laser tempering process to determine the resulting hardness, and (c) conduct machining experiments to evaluate the performance of the laser tempering based hybrid turning process in terms of forces, tools wear and surface finish. First, the microstructure alterations and phase content in the surface and subsurface layers are analyzed using metallography and x-ray diffraction (XRD) respectively. Laser tempering produces distinct regions consisting of - a tempered white layer and a dark layer- in the heat affected subsurface region of the workpiece. The depth of the tempered region is dependent on the laser scanning conditions. Larger overlap of laser scans and smaller scan speeds produce a thicker tempered region. Furthermore, the tempered region is composed of ferrite and martensite and weak traces of retained austenite (~ 1 %). Second, a laser tempering model consisting of a three dimensional analytical model to predict the temperature field generated by laser scanning of 52100 hardened steel and a phase change based hardness model to predict the hardness of the tempered region are developed. The thermal model is used to evaluate the temperature field induced in the subsurface region due to the thermal cycles produced by the laser scanning step. The computed temperature histories are then fed to the phase change model to predict the surface and subsurface hardness. The laser tempering model is used to select the laser scanning conditions that yield the desired hardness reduction at the maximum depth. This model is verified through laser scanning experiments wherein the hardness changes are compared with model predictions. The model is shown to yield predictions that are within 20 % of the measured hardness of the tempered region. Using the laser scanning parameters determined from the laser tempering model, cutting experiments using Cubic Boron Nitride (CBN) tools and low cost alumina ceramic tools are conducted to compare the performance of laser tempering based hybrid turning with the conventional hard turning process. The machining experiments demonstrate the possibility of higher material removal rates, lower cutting forces, improved tool wear behavior, and consequently improved tool life in the laser tempering based process. In addition, the laser tempered based hybrid turning process produce is shown to yield lower peak-to-valley surface roughness height than the conventional hard turning process. Furthermore, it is found that lower cost ceramic tools can be used in place of CBN tools without compromising the material removal rate.