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UBC Theses and Dissertations

Sintering and its enhancement in ferrous powder compacts Subrahmanyam, Gowri


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.

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