Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 39.

Thesis (M.S.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xviii, 70 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 68-69).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1967. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available online.

No description available.

The possible deformation behaviour of spheres in a compact has been theoretically analyzed and experimentally verified. The change in contact area radius 'a' relative to the particle radius R has been related to the bulk density and bulk strain for four possible modes of packing: simple cubic (Z = 6), orthorhombic (Z = 8), rhombohedral (Z = 12), and body-centered cubic (Z = 8). An equation relating the above parameters can be represented by D — D。= [formula omitted] D。(a/R)² for different types of packings, D and D。 being the densities at any a/R and at a/R = 0, respectively. It has been shown experimentally by deforming monosized lead spheres at room temperature, 50 and 100°C in a cylindrical die, that the overall deformation is similar to that of the orthorhombically packed spheres. A change in the coordination number Z during the deformation process was also observed and may partially account for the deviation from the theoretically predicted values. Similar experiments using sapphire and K-Monel spheres were also carried out in the temperature range 1570 - 1700°C and 800 - 1000°C respectively. The results showed that the deformation behaviour was very similar to that of the lead spheres. A study of the geometry of deformation revealed that most of the spheres deformed in a random manner, although individual colonies of orthorhombic, tetragonal and rhombohedral packings were observed. It was also observed that the deformed faces that were approximately perpendicular to the direction of pressing were about 2.2 times larger than those parallel to the direction of pressing. This observation has been subsequently used to modify the theoretical models. The particle rearrangement and plastic flow have been found to be the predominant mechanisms for the densification of lead, K-Monel, and sapphire spheres under the experimental conditions used in this investigation. The criterion for yielding of two hemispheres of the same material in contact was used to incorporate the yield strength in the basic density equation. This equation has been found to fit the data obtained during the hot-pressing of the spheres. It has been observed that the deformation of sapphire single crystal spheres takes place by a complex deformation process. The presence of the basal and prismatic slip has been identified in the spheres deformed at 1570 and 1700°C. Presence of cross slip is also confirmed by the optical and electron micrographs at these temperatures. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

A study is made of the temperature dependence of the lattice scattering mobility of electrons in germanium. Previous work on this subject has been restricted to a range of temperatures from 100°K to 300°K. In this range it is possible to use specimens in which the only scattering the electron suffers is that due to the lattice vibrations; the lattice mobility can then be deduced in a straightforward manner from measurements of the Hall constant and conductivity of the material. It was found that over this restricted temperature range the temperature dependence of the lattice mobility could be represented approximately by the form μαΤ⁻¹‧⁶⁶. It has, however, been predicted, on theoretical grounds, that such a simple power law dependence is insufficient, especially when the temperature range is greater. The present work carries out an extension of the measurements to higher temperatures and studies more carefully the approximation of a simple power law dependence. It is found that if the lattice mobility is expressed in the form μαΤ⁻a, then a has to be considered as increasing from about 1.7 to 1.9 between 200 and 400°K. These results are in qualitative agreement with the theoretical predictions. In order to extend the temperature range, strongly n-type specimens of germanium were required. Several basic and permanent crystal preparation facilities, including a crystal grower and wire-saw cutter, were designed and constructed. The conductivities and Hall coefficients of several specimens, prepared with different concentrations, were measured over the appropriate temperature range. The lattice mobility in these specimens cannot be deduced directly from such measurements as the electrons also suffer scattering from the ionized impurities present. An analysis is given which enables the lattice effects to be separated from the impurity effects. This analysis is based on an assumed power law dependence of the lattice relaxation time on temperature and of the impurity scattering relaxation time on temperature and impurity concentration. The separation of these two scattering effects is performed in a way almost independent of the other factors on which they depend. Some information was also obtained on the impurity scattering mobility. This slightly favours a screened rather than a cut-off Coulomb scattering potential. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Natural convection in liquid metals has been studied by direct observation of the fluid flow, using radioactive tracer techniques. The study is of importance in understanding the solidification of metals since fluid flow strongly influences the heat and mass transfer in the system which in turn strongly influences the structure, homogeneity, and mechanical properties of the solid metal produced. The system examined in this investigation was a rectangular liquid cell of variable thickness, positioned on edge. A small driving force for natural convection was imposed across the liquid cell and when steady state conditions were reached, a small amount of the same material containing a radioactive isotope was added to the top of the cell. The tracer material was picked up by the flow and after a given time interval the liquid was quenched to fix the tracer position. The resultant solid block was autoradiographed to determine the distribution of the added radioactive material. Thermal convection was observed in liquid tin and liquid lead using radioactive Sn¹¹³ and radioactive TI²º⁴ respectively. The results show that the flow rates increase with increasing temperature difference across the liquid cell, increasing average temperature, and increasing liquid cell thickness. Flow rates with Grashof numbers from 10⁶ to 10⁸ were experimentally observed. A finite difference numerical solution for the problem of thermal convection is presented for Prandtl numbers of 10.0, 1.0, 0.1, and 0.0127 with Grashof numbers from 2 x 10³ to 2 x 10⁷. The experimental results for liquid tin (Pr = 0.0127) are found to approach the theoretical analysis for large cell thicknesses and large temperature differences. The flow behavior of various types of fluids is compared with liquid metals to show that non-metallic analogies to .metallic flow problems have very limited value. Solute convection is experimentally considered from three different viewpoints; a) independent solute convection, b) the influence of solute convection on thermal convection, and c) the thermal and solute conditions for complete liquid mixing. It was found that there must be a horizontal density inversion across the whole liquid cell for complete mixing to occur throughout the liquid zone. Interdendritic liquid flow resulting from the natural convection in the residual liquid pool was observed in lead-tin alloys. The flow penetrated into the solid-liquid zone to a point of approximately 12 - 22 % solid for primary dendrite spacings of from 700 to 1000 microns. Several experimental models are presented for interdendritic flow. A three-dimensional wire mesh model predicts that the finer the dendrite structure, the greater the flow penetration into the solid-liquid zone. The experimental results for the lead-tin alloys compared favorably with the model. As an extension of the fluid flow considerations, an investigation was carried out to determine macrosegregation in castings which have imposed fluid flow patterns. The macrosegregation present in stationary, rotated, and oscillated castings of Al - 3 wt. % Ag was determined by measuring the distribution of radioactive silver added to the melt. It was found that, no significant macrosegregation was present in the stationary and rotated castings. Extensive macro-segregation was detected in the oscillated casting. For the oscillated case the macrosegregation can be accounted for on the basis of the long range movement of dendrite fragments which break and/or melt off in the solid-liquid interface region. This movement is a direct result of turbulent waves associated with the oscillation. The maximum silver concentration is shown to be related to the columnar-to-equiaxed transition. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Electron beam hearth remelting is extensively used in refining of superalloys, titanium alloys and the recycling of these materials. The removal of impurities and exhogenous particles during the hearth melting operation depends primarily on the time at temperature relationship developed within a pool of molten metal. In the past hearth melters have acted largely on empirical evidence to specify such parameters as melt rates, power levels and skull sizes. This work describes a mathematical model which could be used to predict certain parameters (such as pool volume or alloy element evaporation rates) when given skull geometry, power input and melt rate. A three dimensional steady state heat transfer model of both the skull and water cooled copper mould during electron beam hearth remelting has been developed. The model has been used to investigate the effects of surface temperature, liquid motion, power input, skull geometry, presence of the hearth mould and melt rate on parameters such as pool volume during skull melting. In general the choice of any combination of operating parameters depends on a balance between the refining capacity of the process (i.e. liquid volume) and the loss of alloy elements by evaporation. In the case of melting pure materials (e.g. CP titanium) the balance is between refining capacity and efficient energy use. It was found that forced convection is significantly more effective in increasing the volume of the liquid pool than any other single parameter. Increasing the power input to the skull, increasing the skull width and removing the water cooled copper mould from around the skull also increase the pool volume. The evaporation rates of alloy elements within the skull were most effected by changes in the power distribution and the degree of liquid motion. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate