Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 21: Magnetic Shape Memory Alloys I

MA 21.7: Vortrag

Mittwoch, 25. März 2009, 11:45–12:00, HSZ 103

Twin variant distribution and twin boundary motion in single and polycrystalline Ni2MnGa imaged by electron back-scatter diffraction — •Nils Scheerbaum, Jian Liu, Ludwig Schultz, and Oliver Gutfleisch — IFW Dresden, Institut für Metallische Werkstoffe, P.O. Box 270116, D-01171 Dresden, Germany

Magnetic shape memory (MSM) alloys show large magnetic field induced strain of several percent caused by a magnetic field-induced twin boundary motion within the martensite phase. Ni2MnGa single crystals show a maximum strain of 6% or 11% depending on the present martensite phase (5M or 7M, respectively). The existence of mobile twin boundaries is crucial in MSM alloys. Therefore, the twin distribution was analysed by electron back-scatter diffraction (EBSD) in a Ni49Mn27Ga24 single crystal (at.%) as well as in polycrystalline Ni50.9Mn27.1Ga22.0 fibres (produced by crucible melt extraction, 60-100um diameter, several mm length). EBSD was done at room temperature, at which in both samples the ferromagnetic 5M martensite phase is present (determined by XRD and magnetometry). In the single crystal, the twin variants are separated from each other by straight twin boundaries. Due to constraints from grain boundaries in the polycrystal, the twin boundaries are not always straight and their density increases near grain boundaries, especially in corners, where several grains touch. Both samples show magnetic field induced twin boundary motion giving rise to 1% and 6% strain for polycrystalline fibres and single crystal, respectively. This was investigated by magnetic measurements and imaged by EBSD for polycrystalline fibres.