Berlin 2008 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 35: Phase Transitions I

MM 35.2: Vortrag

Donnerstag, 28. Februar 2008, 10:30–10:45, H 0107

Controlling the microstructure in NiMnGa alloys — •Martin Pötschke, Franziska Thoss, Uwe Gaitzsch, 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. So far, this effect has only been demonstrated in single crystals. However, the preparation of single crystals is a time consuming and cost intensive process and compositional changes along the crystal 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. 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. Additional annealing steps which are necessary to further improve the chemical homogeneity, coarsening of grains, and stress relaxation effect the texture. Investigations on the texture development during annealing are discussed.

Financial support by the DFG within SPP 1239.