Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 21: Magnetic Shape Memory Alloys I

MA 21.10: Vortrag

Mittwoch, 25. März 2009, 12:30–12:45, HSZ 103

Preparation of textured Ni-Mn-Ga alloys — •Martin Pötschke, Uwe Gaitzsch, Claudia Hürrich, Franziska Thoss, Stefan Roth, Bernd Rellinghaus, and Ludwig Schultz — IFW Dresden, Helmholzstr. 20, 01069 Dresden

NiMnGa alloys have gained large research interest because of their possible application as magnetic shape memory materials. This effect is caused by the motion of twin boundaries in a magnetic field. Up to now most of the research was concentrated on single crystals. However, the preparation of single crystals is a time consuming and cost intensive process and compositional changes along the growth axis as well as segregations may occur. This is why for technical applications there is a great interest in polycrystals. To extend this effect to polycrystals, directional solidification was applied in order to prepare coarse grained, textured samples. Stationary casting in a pre-heated ceramic mold mounted on a copper plate was employed to generate a heat flow towards the bottom of the sample and thereby a directional solidification in the opposite direction. The martensitic transformation temperature which strongly depends on the composition was monitored by DSC, and it is shown that the chemical homogeneity along the sample axis is improved in likewise treated samples. The preferred solidification-induced growth direction was determined by EBSD. Investigations on the influence of MnS - precipitates in the samples, originating from the used rare Manganese, are discussed. The results are compared to samples, which were prepared by a Bridgeman method with draw rates in the range of several 100 mm/h to obtain a texture.