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Magnetic-field-induced recovery strain in polycrystalline Ni–Mn–Ga foam
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View: Figures


Image of FIG. 1.
FIG. 1.

Schematic of the neutron diffraction texture experiment at the E3 beamline of the Helmholtz Centre Berlin for Materials and Energy. (a) Shows a scan without tilting, and (b) with the tilting step, . During the texture measurement operated in mode, is kept constant for each step while the entire Euler cradle (with the sample) is rotated around . The detector is spanning a and area of .

Image of FIG. 2.
FIG. 2.

Schematic of the modified magnetomechanical experiment. The foam (1) is glued to the sliding head (2) and holder (3). The sample holder is bolted to a tube (4), which is placed in the rotating field (field axis shown). An light emitting diode (5) is used to illuminate the foam surface, so that it can be observed with the optical camera (6). Different areas of the surface can be magnified with lenses (7). A tube (8) is used to direct heated and cooled air onto the sample. A thermocouple (9) measures the temperature on the foam surface. The dashed-dotted line marks the rotation axis of the magnetic field. The magnetic field vector is oriented perpendicular to the rotation axis.

Image of FIG. 3.
FIG. 3.

X-ray tomography slices of the foam sample in the plane along the axis (parallel to the shortest dimension of the sample). is the thickness of the sample in the direction. Arrows indicate cracks.

Image of FIG. 4.
FIG. 4.

neutron diffractogram of the foam sample. The sample was continuously rotated around its longest axis . The indexes “10M” and “14M” indicate diffraction peaks that belong to 10M and 14M fundamental structure reflections.

Image of FIG. 5.
FIG. 5.

neutron diffractograms of the foam sample for each step. Each point of the diffractogram represents the sum over a range of ±5° of the value indicated. Only the 10M and 14M (specified by the subscript) fundamental reflections of grains that were identified by two {440} type reflections are indicated in the figure.

Image of FIG. 6.
FIG. 6.

orientation map showing the six identified 10M (△) and 14M (◻) grains, labeled 1–6. Repeated labels are due to symmetry or twinning.

Image of FIG. 7.
FIG. 7.

Two superimposed video frames for the foam sample in a rotating magnetic field. The magnetic field direction of the two frames was perpendicular. The frames are arranged such that the top left corner regions exactly coincide. The larger the distance from this region the more the superimposed images shift apart. Two dashed lines on the right indicate the deformation from one frame to the other.

Image of FIG. 8.
FIG. 8.

Compressive loading/unloading stress-strain curves of the foam sample during static magnetomechanical test with a cross-head displacement rate of 0.125 mm/min parallel to the sample’s -axis. The first load/unload cycle was performed without magnetic field. During the second loading cycle, the sample was mechanically loaded without magnetic field, but unloaded in the 1 T magnetic field in direction. The third load/unload cycle was performed within this 1 T magnetic field.

Image of FIG. 9.
FIG. 9.

Magnetization measurements of the foam sample. (a) shows the magnetization at an external magnetic field of 100 mT and rotated around the sample’s shortest axis ( axis). (b) Magnetization curves in the easy (7°) and hard (97°) magnetization directions [as identified in (a)]. In (b) the demagnetization of the sample in different directions is taken into account.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Magnetic-field-induced recovery strain in polycrystalline Ni–Mn–Ga foam