Dresden 2009 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 13: Poster Ia: Electron Theory (1); Magnetic Imaging (2,3); Thin Films (4-25); MSMA (26-33); Magn. Semiconductors (34-42); Magn. Half Metals and Oxides (43-60)
MA 13.33: Poster
Dienstag, 24. März 2009, 10:15–13:00, P1A
Influence of Surface Condition and Training on the Twinning Stress of Ni-Mn-Ga Magnetic Shape-Memory Alloys — •Markus Chmielus1,2, Katharian Rolfs1, Cassie Witherspoon2, Walter Reimers3, Peter Müllner2, and Rainer Schneider1 — 1SF1, Helmholtz Centre Berlin for Materials and Energy, 14109 Berlin, Germany — 2Department of Materials Science and Engineering, Boise State University, Boise, Idaho 83725, USA — 3Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin, 10587 Berlin, Germany
While the effects of composition of Ni-Mn-Ga magnetic shape memory alloys (MSMAs) on structure, thermal, and magnetic properties have been well studied, effects related to the processing of MSMA single crystals have attracted less attention. Annealing, cutting, and surface preparation are known to impact the magneto-mechanical properties but no quantitative data is available. In this work, the influence of the surface roughness on the twinning stress is evaluated. During spark erosion cutting - commonly used to prepare single crystalline samples - a rough surface layer is produced. Directly after cutting, the single crystals exhibit a high twinning stress. After removal of a surface layer through electro polishing, the twinning stress reduces significantly. It is shown here, however, that a reduction of the twinning stress after each of several electro polishing steps is induced by mechanical training. This softening also occurs for unpolished Ni-Mn-Ga single crystals when subjected to the same training procedure. The results are discussed in terms of twin-surface and twin-twin interactions.