Ph.D. defence: Nucleation of Recrystallization studied by EBSP and 3DXRD – Niels Bohr Institute - University of Copenhagen

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Ph.D. defence: Nucleation of Recrystallization studied by EBSP and 3DXRD

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.