MSMnet: Magnetomechanics of Magnetic Shape Memory Alloys: Session 2
Program Organizers: Peter Müllner, Boise State University

Tuesday 2:00 PM
July 11, 2017
Room: Wrigley
Location: Hyatt Regency Chicago

Session Chair: Heidi Feigenbaum, Northern Arizona University

2:00 PM  
Crystal Structure and Twin Boundaries Type II in 14M Ni-Mn-Ga-Fe Martensite: Oleksii Sozinov1; Aleksandr Soroka1; Petr Veřtát2; Martin Zeleny3; Kari Ullakko1; 1Material Physics Laboratory, Lappeenranta University of Technology; 2Institute of Physics, Academy of Sciences of the Czech Republic; 3NETME Centre, Faculty of Mechanical Engineering, Brno University of Technology
    It was discovered recently that the twin boundaries (TBs) type I and type II have essentially different mobility properties in Ni-Mn-Ga 10M martensite. TBs type II exhibit extremely low twinning stress (TS), order of 0.1 MPa, as well as extremely weak temperature dependence of the TS. To clarify the nature of TBs type II high mobility, the role of the crystal structure and the lattice distortion, we are focusing on the comparison of the TB type II properties in 10M and 14M martensites with slightly distorted tetragonal and orthorhombic unit cell, correspondingly. We studied in 14M Ni-Mn-Ga-Fe martensite single crystal samples the twinning elements and the satellite peak intensities connected with the 7-layer lattice modulation, experimentally and by calculations based on currently widely accepted nano-twinning model. We found discrepancy between experimental and calculated values and suggest a modification of the nano-twinning model.

2:20 PM  
Porosity and Phase Evolution in 3D Printed Ni-Mn-Ga Magnetic Shape Memory Alloy Micro-trusses: Shannon Taylor1; Peter Mullner2; Ramille Shah1; David Dunand1; 1Northwestern University; 2Boise State University
    Monocrystalline Ni-Mn-Ga magnetic shape memory alloys with compositions near the Ni2MnGa Heusler phase exhibit large reversible magnetic field induced strains (MFIS) at room temperature mediated by twin boundary motion. However, in polycrystalline Ni-Mn-Ga, the incompatibilities between neighboring twinning grains results in a negligible MFIS. The introduction of porosity between the grains alleviates the twinning mismatch and greatly enhances the MFIS of polycrystalline Ni-Mn-Ga. Micro-trusses with hierarchical porosity are created via direct extrusion 3D printing of liquid particle-based inks synthesized from graded volatility solvents, an elastomeric polymer binder, and elemental Ni and Mn powders and Ga liquid followed by heat treatments for binder removal, sintering, homogenization, and chemical ordering. Ex situ metallography and in situ X-ray tomography studies of the porosity and phase evolution during sintering and interdiffusion will be presented. The effect of grain size and porosity on the magnetomechanical properties will also be presented.

3:00 PM  
Magnetically Controlled Ni-Mn-Ga Polymer Composites at Dynamic Loading: Frans Nilsén1; Ilkka Aaltio1; Simo-Pekka Hannula1; 1Aalto University
    Magnetically controlled Ni-Mn-Ga shape memory composites are potential candidates for damping and actuator solutions. The combination of ductile polymer and magnetically active Ni-Mn-Ga powder, despite of the smaller magnetic field induced response, has many advantages compared to conventional single crystals used in Ni-Mn-Ga actuators. Most important of these are higher flexibility and ease of manufacturing. In this paper, polymer composite structures with magnetically aligned particle chains with c-axis along the long direction of the samples were manufactured from 35 vol-% of heat-treated gas atomized Ni-Mn-Ga particles and of 65 vol-% Hysol 9455 epoxy. The properties of the composites were tested using a laboratory made high-frequency dynamic mechanical testing instrument, with a 10M Ni-Mn-Ga single crystal used as reference, and with 3 MPa compression tests with and without magnetic field. When the magnetic field is applied perpendicular to the aligned particle chains during straining the displacement amplitude of the composite changes.

3:30 PM Break