Development of NiMnGa/Polymer Composite Materials

In this paper the recent development of NiMnGa-particles-embedded polymer-matrix magnetodriven composites achieved by our group is described. The NiMnGa single-crystal particles can be easily fabricated by mechanically crushing the polycrystalline ingots due to intrinsic intergranular brittleness. The elastic back stress from the matrix polymer induces the reverse reorientation of martensite variants after removing the magnetic field. However, the actuation strain observed was very small around 10ppm which was 1/1000 times lower than the calculated value. Some possible reasons for the disagreement are that the crystallographic orientation of NiMnGa particles is random distribution, lattice defects introduced during crushing suppress reorientation of martensite variants, and that the elastic restriction from the matrix polymer is higher than expected. Therefore, the martensite variant reorientation behavior of the NiMnGa/silicone composites has been investigated from the viewpoint of (1) volume fraction of matrix polymer, (2) elastic modulus of polymer and (3) direction of magnetic field applied. And also, the internal structures of the composites were directly evaluated by microfocused X-ray computed tomography (µ-CT).