Dresden 2009 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 21: Magnetic Shape Memory Alloys I
MA 21.8: Vortrag
Mittwoch, 25. März 2009, 12:00–12:15, HSZ 103
Ni-Mn-Ga: annealing for microstructure development — •Franziska Thoss1, Martin Pötschke1, Gaitzsch Uwe1, Jens Freudenberger1, Wolfgang Anwand2, Stefan Roth1, Bernd Rellinghaus1, and Ludwig Schultz1 — 1IFW Dresden — 2FZ Dresden-Rossendorf
Recently the Magnetic Shape Memory Effect was observed in polycrystalline alloys near the stoichiometric composition Ni2MnGa. The microstructure plays a crucial role for the achievable magnetic field induced strain, because grain boundaries inhibit twin boundary motion.
The microstructure development with regard to grain growth behavior was investigated for polycrystalline Ni-Mn-Ga samples of various compositions. Therefore, the influence of the annealing temperature and annealing time was studied. Grain growth was only observed for compositions with a Ni-content of less than 50 at.-%. The suspected existence of constitutional vacancies as a possible reason for the different grain growth behavior of such compositions was excluded by Positron Annihilation Spectroscopy. In order to activate grain boundary motion and henceforth grain growth in the MSM-active alloy Ni50Mn29Ga21 the samples were compressed during the first minute at the annealing temperature at various degrees of deformation. At a deformation between 8 % and 10 % compression we observed a sharp threshold towards grain growth.