C. Hürrich, M. Pötschke, S. Roth, B. Rellinghaus, L. Schultz, IFW Dresden, Dresden, Germany
The alloy Ni-Mn-Ga arose great interest for its application as a magnetic shape memory material. This effect is caused by reorientation of twin variants by an external magnetic field. So far most of the experiments were concentrated on single crystals. But, this effect can also be realised in polycrystals which can be prepared much more efficiently. Here, polycrystalline samples were prepared by directional solidification with a <100> fibre texture of the high temperature cubic phase parallel to the heat flow. Afterwards a heat treatment was applied for chemical homogenization and stress relaxation in the austenitic state. Then the samples were heated up to the austenitic state and cooled down under load. The microstructure was analysed by Electron Back Scatter Diffraction (EBSD) before and after that treatment. Mechanical training in three directions was tracked by recording stress-strain curves. With increasing the number of training cycles the strain also increases.This work is supported by DFG within SPP 1239.
Summary: Ni-Mn-Ga polycrystalline samples, microstructure, mechanical training, stress-strain curves
