MSMnet: Magnetomechanics of Magnetic Shape Memory Alloys: Session 1
Program Organizers: Peter Müllner, Boise State University

Monday 4:00 PM
July 10, 2017
Room: Wrigley
Location: Hyatt Regency Chicago

Session Chair: Peter Müllner, Boise State University

4:00 PM  Invited
Elastic Constants of Fe-Pd and Non-modulated Ni-Mn-Ga Martensites: Hanus Seiner1; Petr Sedlák1; Martina Thomasova2; Michaela Janovská1; Oleg Heczko3; Takashi Fukuda4; Michal Landa1; 1Institute of Thermomechanics, Czech Academy of Sciences; 2Czech Technical University in Prague; 3Institute of Physics, Czech Academy of Sciences; 4Graduate School of Engineering, Osaka University,
    Single crystals of disordered Fe-Pd alloys are able to exhibit more than 4% reversible non-hysteretic strains under uniaxial compressive loads applied along the [001]-direction. The full anisotropic elastic tensor of the stress-induced tetragonal structure (at 4.3% axial strain) was studied by laser-ultrasonic methods; it was shown that this structure exhibits a strongly tetragonal elasticity with a pronounced difference between the shear moduli corresponding to shears along planes parallel and perpendicular to the loading direction. In this talk, these results will be compared with elastic constants of thermally-induced non-modulated Ni-Mn-Ga martensite determined by contact-less resonant ultrasound spectroscopy. As NM Ni-Mn-Ga exhibits similarly strong anisotropy and similar spatial arrangement of stiff and soft shearing planes, it can be concluded that the elasticity of the stress-induced tetragonal structure of Fe-Pd clearly resembles elasticity of thermally induced martensites, rather than of an elastically strained parent phase.

4:40 PM  
Twin Boundary Dynamics in Magnetic Shape Memory Alloy Ni-Mn-Ga: Andrey Saren1; Kari Ullakko1; 1Lappeenranta University of Technology
    Twin boundary (TB) dynamics in Ni-Mn-Ga 10M martensite was investigated. The motion of individual TBs of type 1 and 2 in saturation pulsed magnetic fields was experimentally studied, using laser Doppler vibrometry and high-speed camera techniques. A macroscopic model was developed, which successfully describes the experimental data. About an order of magnitude difference in saturation velocities, observed for type 2 and 1 TBs, we attribute to the difference in viscous-like damping forces. We found that dynamic twinning stresses can reach 1.5 and 2.9 MPa, for type 2 and 1 boundaries, respectively. These values are considerably higher compared to the static twinning stresses. Our results strongly indicate the inertia and velocity-dependent viscous-like damping as limiting factors for the TB motion, while the field-dependent resistance forces play only a minor role. We also demonstrate that in the case of the motion of multiple TBs, they cannot be considered as independently moving interfaces.

4:55 PM  
Power Law of Acoustic Emission Generated by Motion of Single Twin Boundary of Type I and II in Ni-Mn-Ga Magnetic Shape Memory Single Crystal: Oleg Heczko1; Oleksiy Perevertov; Vít Kopecký1; Ladislav Klimša1; Jaromír Kopeček1; Michal Landa1; 1Department of Functional Materials, the Institute of Physics, the Czech Academy of Sciences
    Acoustic emission (AE) and twinning stress was measured during the forced slow motion (with constant rate of strain) of single twin boundary resulting in structure reorientation in 10M ferromagnetic martensite of Ni-Mn-Ga single crystal. The twinning stress needed for the reorientation was about 1 MPa for Type I and about 0.1-0.2 MPa for Type II twin boundary, which rendered magnetically induced reorientation or magnetic shape memory effects in low magnetic field. The stress fluctuation during the motion of the single twin boundary was correlated to AE amplitude. The distribution of AE amplitudes followed the power law with different exponents for different boundaries indicating universal avalanche-like processes but also the dissimilarity of these boundaries. Stress and AE measurements were related to optical and SEM observations of twin microstructures particularly to the first direct observation of a-b twin laminate in the vicinity of the mobile twin boundary of both types.

5:15 PM  
Reversible Martensitic Transformation under Low Magnetic Fields in Magnetic Shape Memory Alloys: Ibrahim Karaman1; Nickolaus Bruno1; Daniel Salas1; Shujuan Wang1; Yuriy Chumlyakov2; 1Texas A&M University; 2Siberian Physical Technical Institute
    Magnetic field-induced martensitic transformations in NiCoMnIn meta-magnetic shape memory alloys were studied under constant and varying mechanical loads to understand the role of coupled magneto-mechanical loading on the transformation characteristics and the magnetic field levels required for reversible martensitic transformations. The samples with two distinct microstructures were tested along the [001] austenite crystallographic direction using a custom designed magneto-thermo-mechanical characterization device. Measurements revealed that these alloys were capable of generating entropy changes of 14 J kg-1 K-1 or 22 J kg -1 K-1, and corresponding magnetocaloric cooling, and reversible shape changes as high as 5.6 % with only 1.3 T, or 3 T applied magnetic fields, respectively. Thus, this alloy is suitable for near room temperature devices, such as magnetocaloric regenerators, and the field levels generated by permanent magnets can be sufficient to completely transform the alloy reversibly if the loading sequence developed, herein, is employed.