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MM: Fachverband Metall- und Materialphysik

MM 35: Phase Transitions I

MM 35.1: Talk

Thursday, February 28, 2008, 10:15–10:30, H 0107

Magnetostrain in polycrystalline 5M Ni50Mn29Ga21 — •Uwe Gaitzsch, Martin Pötschke, Claudia Hürrich, Stefan Roth, Bernd Rellinghaus, and Ludwig Schultz — IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany

Magnetic shape memory alloys have been investigated due to the coupling of magnetic and mechanical properties. By moving twin boundaries in the martensitic state, magnetic-field-induced strain (MFIS) of at maximum 10 % can be achieved. So far, MFIS has only been shown in single crystals. To provide a suitable polycrystalline mircostructure, directional solidification was employed to get a coarse-grained, textured sample. These samples were heat treated for chemical homogenization and stress relaxation. In Ni50Mn29Ga21 samples with 5M crystal structure could be prepared. Structural characterization and texture investigations have been performed using X-ray diffraction techniques. Cubic samples were cut erosively from the ingots to allow for mechanical training via cyclic compression along different axes. One of the sample axes was along the direction of solidification. The training leads to a reduction of the twinning stress by over an order of magnitude as compared to an untrained sample. At the same time the mechanical strain could be increased to the crystallographic limit of 1- c/a. After training in a modified Instron testing machine their magnetic-field-induced strain was measured. By appropriate training up to 1 % of MFIS could be achieved in polycrystalline samples.

Financial support by the DFG within SPP 1239 is gratefully acknowledged.