Stress-Induced Twin Boundary Motion in Particulate Ni-Mn-Ga /Polymer Composites

Abstract

Composites of Ni-Mn-Ga particles in a polyurethane matrix can be made by mixing the particles with the polymer, and allowing them to cure under a magnetic field to texture the composites. These composites show large hysteresis and mechanical losses, when subjected to a cyclic stress, that were far larger than the matrix polymer ones. The additional losses are attributed to the motion of twin boundaries in the filler particles and provide a way for obtaining mechanical energy absorption in a wide frequency range. By means of X-ray and neutron diffraction we present evidence that confirms that twins are present in the particles and that they do move when mechanically loading the composite

Neutron Diffraction Studies of Magnetic Shape Memory Alloys

“…This was done recently in NiMnGa-polymer composites that show very large energy absorption and were developed as efficient dampers. Such an study was already published in the former volume of this series [34] and in other journals [35,36] so that it will only be mentioned briefly here. X-ray diffraction in NiMnGa alloys is less sensitive that way neutron diffraction to low angle peaks that are the most representative of the variant's orientation.…”

Magnetic Shape Memory - Polymer Hybrids

“…Several polymers and elastomers have been studied as matrix materials with Ni-Mn-Ga MSM as filler. To name some, polyurethane [9], silicone [10] and epoxy [6,11] have been used as matrix. Significant differences e.g., in the curing time exist among the polymers, which may set limitations to manufacturing and use of hybrids.…”

On the Relationship of Ni Volume Fraction in Polymer Matrix Composite to its Impact Property

“…Ferromagnetic shape memory alloys, most notably Ni-Mn-Ga, show large stress induced strains with significant hysteresis [8][9][10][11][12][13][14]. Because, it shows twin boundary motion which leads to reorientation of the crystal [15,18]. But, Ni-Mn-Ga composition is not cost effective and brittle in nature [1,3].…”