Nucleation of Recrystallization studied by EBSP and 3DXRD
PhD defence by Stine Stenfatt West
Abstract: When a deformed crystalline material is annealed,
recrystallization will typically take place. In this process new
perfect crystals nucleate and grow, consuming the deformation structure.
Traditionally, nucleation theories state that the crystal orientations
of these new grains were already present in the deformed state, but
several experiments have shown the emergence of what appears to be new
orientations.
The purpose of the present project was to observe nucleation of
recrystallization both on surfaces and in the bulk of high-purity
aluminum. Special focus was on the possible formation of nuclei with
orientations not present in the deformed matrix before annealing.
A series of experiments was carried out using electron backscattered
diffraction (EBSP). These were considered to provide a valuable
background to support the results to be obtained by 3DXRD. Nuclei were
observed both with parent orientations and new orientations not present
before annealing.
Experiments using the three-dimensional X-ray diffraction (3DXRD)
microscope also successfully observed nucleation of recrystallization.
The nuclei most easily found with the 3DXRD method are those with
orientations different from the deformed structure and the method was
thus ideal for this study. 6 nuclei of new orientations were found in
the bulk of a sample after annealing.
An orientation imaging map was reconstructed from the bulk of the
sample before and after annealing. Such reconstructions have only been
done before with completely recrystallized samples, so this was a
unique opportunity to compare orientations observed locally in the bulk
of a deformed sample before annealing with the orientations of the
nuclei.