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Date of Award

5-1991

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science and Engineering

Supervisor

G.R. Purdy

Abstract

The crystallography and the interfacial structure of interphase boundaries in a Zr-2.5 wt% Nb alloy have been studied by transmission electron microscopy (TEM), and the results compared with the predictions of a model developed in this work. The α phase (HCP), when precipitated from β (BCC), usually forms as intragranular plates. The habit plane of an α plate is characterized by the regularly spaced dislocations, parallel to the long axis of the α plate. These dislocations, about 10nm apart, have a Burgers vector [0 1 0] with respect to β phase. The orientation relationship between α and β phases was found to deviate slightly from the ideal Burgers orientation relationship. Based on the O-lattice and invariant line analysis a geometrical model has been further developed. The cell structure of O-lattice, which is the key information in predicting the configuration of the interfacial dislocations, has been constructed by a simple calculation made in reciprocal space of the O-lattice. This is expected to improve the general application of the existing O-lattice model. The plane of the least lattice mismatch, determined by the O-lattice plane of the smallest spacing, is consistent with the observed habit plane. The optimum orientation relationship suggested based on the analysis of mismatch in the habit plane is shown to deviate slightly from the Burgers orientation, which is supported by experimental evidence. The analysis also indicated that the misfit in the habit plane could be accommodated completely by a set of to [0 1 0]ᵦ dislocations of ~10nm in spacing, lying along the invariant line, in agreement with the experimental observations.

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