The Mechanisms of Pressure Sintering

[PhD thesis]. Cambridge, UK: University of Cambridge

Ashby, M. F. (supervisor)

1978

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- Abstract
Evidence from pressure data in the literature suggests that no single mechanism is entirely responsible for pressure sintering. When sîntering without an applied pressure, there are at least five different mechanisms which can control the sintering kinetics. The addition of an applied pressure enhances some of these mechanisms and introduces several new ones. Not all of these mechanisms have been adequately moddelled. In particular, very little attention has been paid to power-law creep as a mechanism for pressure sintering.

The dissertation begins with the construction of a comprehensive theory for isostatic pressure sintering. The theory is based on a homogeneous compact in which a single particle or pore can be isolated and assumed to represent the macroscopic behaviour of the compact. The implications of this assumption are considered, withi particular reference to particle rearrangement and grain growth. A set of mechanism rate equations. is developed, incorporating some existing models, and developing new ones where required. These are then used to construct pressure sintering mechanism maps, which illustrate as a function of applied pressure, temperature, and density the range of dominance of each mechanism, the total densification rate, and the time required to reach a given density.

The mechanism maps are used to help analyze the results of experimental studies available in the literature. It is found that there is a consistent offset between experimental data and theory, which is thought to be due to the die pressing geometry used in the experiments. This analysis points out the need for model experiments using an isostatic pressing geometry, and a machine for carrying out such experiments is described. Despite the difference between theory and experiment, the correlation is good enough for maps to allow a more reliable analysis of the data than has been possible previously. In particular they are helpful where two competing mechanisms contribute about equally to sintering, and can be of great use in extrapolating data outside the range of experimentation. Other uses for the maps are also discussed.