Regensburg 2010 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 8: Magnetic Shape Memory Alloys
MA 8.12: Vortrag
Montag, 22. März 2010, 18:15–18:30, H22
Training of polycrystalline NiMnGa alloys — •Robert Chulist1, Martin Pötschke2, Andrea Böhm3, Carl - Georg Oertel1, Werner Skrotzki1, and Erik Rybacki4 — 1Institut für Strukturphysik, Technische Universität Dresden, D-01062 Dresden, Germany — 2Institut für Metallische Werkstoffe, Leibniz-Institut für Festkörper- und Werkstoffforschung, D-01069 Dresden, Germany — 3Fraunhofer-Institut für Werkzeugmaschinen und Umformtechnik, D-01187 Dresden, Germany — 4Geoforschungszentrum Potsdam, D-14473 Potsdam, Germany
In order to achieve magnetic field induced strain in NiMnGa alloys a training process is applied. This process consists of successively compressing the sample along two or three axes. As a result the twinning stress is reduced and the strain is maximized. To study the effect of training, two samples with 5M modulated structure were used: bi-crystal and polycrystal deformed by high pressure torsion. Within the individual parent austenitic grains the initial orientation is characterized by three different martensitic variants separated by twin boundaries. Compression of the samples results in the motion of the twin boundaries changing the volume fraction of particular variants. Local orientation measurements by electron backscatter diffraction directly confirm twin boundary motion. The training process finally leading to a single variant state will be discussed with respect to initial microstructure and number of martensitic variants.