Sintering maps have been developed for pure iron compacts. The maps have been drawn as a function of various sintering parameters such as particle size, green density, time and temperature. Two sets of diagrams have been drawn to define the sintering kinetics, namely, the field map and the neck growth/shrinkage map. A new and simple method has been developed to construct the field maps, which define the dominant mechanisms of mass transport that contribute to neck growth under a given set of conditions of sintering. Shrinkage maps, which show how far the neck is growing or give % linear shrinkage for a given neck size and temperature, are generated by numerically integrating, the sum of the contributions to neck growth from the different mechanisms of transport. The model developed is based on ideal geometry and does not take into account complex phenomena such as grain growth, pore coalescence or pore growth. The sintering equations and diagrams that have been developed for pure iron compacts have been used effectively in the present study to predict and analyze the results of experiments involving various attempts to enhance sintering in such compacts. Small additions of a selected group of elements were made to iron compacts in an attempt to provide activation of solid state sintering similar to that which is obtained when tungsten powder compacts are doped with nickel. A few of the dopants used with iron compacts produced a small increase in shrinkage and densification for a given set of sintering conditions. Based on the present results and on the several studies of tungsten - nickel compacts which are reported in the literature, a new theory of dopant activated sintering has been proposed. Consistent with this model, it is suggested that certain criteria must be met by the dopant-base metal combination if activated sintering is to be observed. Sintering enhancement based on ferrite stabilization in two systems, iron - phosphorus and iron - silicon has been studied. This approach to solid state sintering enhancement proved to be highly effective and it is believed to have important practical applications in the P/M parts industry. The results of these experiments were consistent with predictions based on the sintering theory and maps appropriate to the conditions of sintering employed. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

An attempt has been made to study the change in the electrical resistivity of a powder compact during the initial stages of hot-pressing. Theoretical models have been formulated on the basis of plastic deformation of spheres in a compact. The resistivity change during densification has been derived for various packing arrangements. For small deformation of spheres, the final equation is [formula omitted] and the more generalized equation for larger deformation is [formula omitted] where ơm and ơc are the conductivities of a compact of spheres having a relative density D, and at the theoretical density (D = 1), respectively. Do is the initial relative density of the compact before deformation. α is a constant depending on geometry and R is the radius of spheres at any stage of deformation in arbitrary units. The derived relationship was tested by: (a) measuring the electrical resistivity as a function of density during hot-pressing of compacts of glass spheres, (b) measuring the electrical resistivity of different compacts of nickel spheres at room temperature, and (c) comparing previous resistivity data with the theoretical equation. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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In this study, stress problems occurring in low tempera -ture cofired ceramic processes are analyzed by finite element package ANSYS. Sintering stresses of sintering processes and residue stresses in cooling processes are investigated. The thermal shrinkage coefficient are used to deal with the density variation due to the shrinkage mismatch between the green tape and silver paste in the sintering processes. Deleting the elements is used to treat the situation when the element stress exceeds its fracture stress. The residue stresses due to the mismatch of the thermal expansion coefficients in cooling processes are also discussed.

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Thesis--University of Florida. / Description based on print version record. Manuscript copy. Vita. Bibliography: leaves 122-125.

Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.