Nucleation of Recrystallization studied by EBSP and 3DXRD

Stine West

    Research output: Book/ReportPh.D. thesisResearch

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    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. Special focus was on the possible formation of nuclei with orientations not present in the deformed matrix before annealing. To facilitate the nucleation studies, a well-annealed starting material was prepared from high-purity aluminum with a large average grain size and almost straight grain boundaries mostly forming triple junctions with angles close to 120°. The large grain size was necessary in order to ease determination of the nucleation sites and the analysis of orientation relationships between nuclei and parent grains. A series of experiments was carried out using Electron Backscattered diffraction Patterns (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. The rotation axes between the orientations of the nuclei and the orientations seen before annealing was correlated to the predicted deformation structure. A correlation was seen between this rotation axis and the normals to {111} slip planes of high activity, which were expected to form slip plane aligned dislocation boundaries. This axis is also the axis of misorientation associated with GNBs of twist character forming on {111} planes. 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. The comparison was again based on the predicted deformation structure of the parent grains. The majority of the nuclei were seen to be rotated around the [100] axis, which was a possible misorientation axis associated with the predicted GNBs aligned with {010}.
    Original languageEnglish
    Place of PublicationRoskilde
    PublisherRisø National Laboratory
    Number of pages201
    ISBN (Print)978-87-550-3760-1
    Publication statusPublished - Aug 2009


    • Materials characterization and modelling
    • Materials research
    • Risø-PhD-50(EN)
    • Risø-PhD-50


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