Studies of Grain Boundaries in Materials Subjected to Diffusional Creep

Thomas Nørbygaard

    Research output: Book/ReportPh.D. thesis

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    Grain boundaries in crystalline Cu(2%Ni) creep specimens have been studied by use of scanning and transmission electron microscopy in order to establish the mechanism of deformation. Creep rate measurements and dependencies were found to fit reasonably well with the model for diffusional creep (Nabarro-Herring) and this impression was strengthened considerably by the microstruc-tural finds.

    Manual and automated EBSD surface scans have been performed on a speci-men supplied with an inert reference grid in order to correlate individual grain boundary structure (in terms of deviation from CSL) with the activity displayed during diffusional creep testing. It was found that boundaries with low deviation from perfect Σ did not contribute macroscopically to the creep strain.

    A resist deposition procedure was examined to improve the reference surface grid so as to allow determination of the grain boundary plane by use of simple stereomicroscopy directly on the surface. The etched pattern deteriorated heav-ily during creep testing, supposedly because of dislocation creep, due to exces-sive creep stress.

    Grain boundaries have been studied and characterised by TEM providing an insight into the diversity of twin boundary structures. Ledges on low deviation Σ3 and Σ9 were observed repeatedly and the presence of these is proposed to relate to the inactivity of such boundaries. A handful of examples showed ledged boundaries emitting dislocations into the lattice, presumably because of stress accumulation due to restrictions on GBD movement from the ledge struc-ture.
    Original languageEnglish
    Place of PublicationRoskilde
    PublisherRisø National Laboratory
    Number of pages108
    ISBN (Print)87-550-3147-1
    ISBN (Electronic)87-550-3149-8
    Publication statusPublished - 2002
    SeriesDenmark. Forskningscenter Risoe. Risoe-R

    Note re. dissertation

    The present thesis has been submitted for fulfilment of the requirements set for obtaining the Ph.D. degree at Copenhagen University.


    • Risø-R-1379(EN)
    • Risø-R-1379

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