scholarly journals Recent Developments in Ni-Mn-Ga Foam Research

2009 ◽  
Vol 635 ◽  
pp. 119-124 ◽  
Author(s):  
Peter Müllner ◽  
Xue Xi Zhang ◽  
Yuttanant Boonyongmaneerat ◽  
Cassie Witherspoon ◽  
Markus Chmielus ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Grain Boundaries ◽  
Single Crystals ◽  
Cyclic Strain ◽  
Martensite Phase ◽  
Magnetic Shape Memory ◽  
Magnetic Shape Memory Alloys ◽  
Major Barrier

Grain boundaries hinder twin boundary motion in magnetic shape-memory alloys and suppress magnetic-field-induced deformation in randomly textured polycrystalline material. The quest for high-quality single crystals and the associated costs are a major barrier for the commercialization of magnetic shape-memory alloys. Adding porosity to polycrystalline magnetic-shape memory alloys presents solutions for (i) the elimination of grain boundaries via the separation of neighboring grains by pores, and (ii) the reduction of production cost via replacing the directional solidification crystal growth process by conventional casting. Ni-Mn-Ga foams were produced with varying pore architecture and pore fractions. Thermo-magnetic training procedures were applied to improve magnetic-field-induced strain. The cyclic strain was measured in-situ while the sample was heated and cooled through the martensitic transformation. The magnetic field-induced strain amounts to several percent in the martensite phase, decreases continuously during the transformation upon heating, and vanishes in the austenite phase. Upon cooling, cyclic strain appears below the martensite start temperature and reaches a value larger than the initial strain in the martensite phase, thereby confirming a training effect. For Ni-Mn-Ga single crystals, external constraints imposed by gripping the crystal limit lifetime and/or magnetic-field-induced deformation. These constraints are relaxed for foams.

Effects of Surface Pinning, Locking and Adaption of Twins on the Performance of Magnetic Shape-Memory Alloys

2011 ◽  
Vol 684 ◽  
pp. 177-201 ◽  
Author(s):  
Markus Chmielus ◽  
Peter Müllner
Keyword(s):  
Magnetic Field ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Surface Damage ◽  
Magnetic Shape Memory ◽  
Magnetic Shape Memory Alloys ◽  
Fatigue Lifetime ◽  
Twin Density ◽  
External Constraints ◽  
The Magnetic Field

We study the effect of surface modifications and constraints on the mechanical properties of Ni-Mn- Ga single crystals, which are imposed by (i) structural modifications near the surface, (ii) mounting to a solid surface, and (iii) guiding the stroke. Spark eroded samples were electropolished and characterized before and after each polishing treatment. Surface damage was then produced with spark erosion and abrasive wearing. Surface damage stabilizes and pins a dense twin-microstructure and prevents twins from coarsening. The density of twins increases with increasing degree of surface deformation. Twinning stress and hardening rate during mechanical loading increase with increasing surface damage and twin density. In contrast, when a damaged surface layer is removed, twinning stresses, hardening rate, and twin density decrease. Constraining the sample by mounting and guiding reduces the magnetic-field-induced strain by locking twins at the constrained surfaces. . For single-domain crystals and for hard magnetic shape-memory alloys, external constraints strongly reduce the magnetic-field-induced strain and the fatigue lifetime is short. In contrast, for selfaccommodated martensite and for soft magnetic shape-memory alloys, the twin-microstructure adapts well to external constraints and the fatigue lifetime is long. The performance of devices with MSMA transducers requires managing stress distributions through design and control of surface properties, microstructure, and constraints.

Magnetic-field-induced changes in magnetic shape memory alloys

2008 ◽  
Vol 481-482 ◽  
pp. 258-261 ◽  
Author(s):  
P. Entel ◽  
M.E. Gruner ◽  
W.A. Adeagbo ◽  
A.T. Zayak
Keyword(s):  
Magnetic Field ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Magnetic Shape Memory ◽  
Magnetic Shape Memory Alloys ◽  
Induced Changes

A Memory Variable Approach to Modeling the Magneto-Mechanical Behavior of Magnetic Shape Memory Alloys

2013 ◽  
Author(s):  
Doug LaMaster ◽  
Heidi Feigenbaum ◽  
Isaac Nelson ◽  
Constantin Ciocanel
Keyword(s):  
Magnetic Field ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Mechanical Strain ◽  
Magnetization Vector ◽  
Unit Cell ◽  
Magnetic Shape Memory ◽  
Magnetic Shape Memory Alloys ◽  
Short Side ◽  
Recoverable Strain

Magnetic shape memory alloys (MSMAs) have attracted interest because of their considerable recoverable strain (up to 10%) and fast response time (1 kilohertz or higher). MSMAs are comprised of martensitic variants that have tetragonal unit cells and a magnetization vector that is innately aligned with the short side of the unit cell. These variants rotate either to align the magnetization vector with an applied magnetic field or to align the short side of the unit cell with an applied compressive stress. This reorientation leads to a mechanical strain and an overall change in the material’s magnetization, allowing MSMAs to be used as actuators, sensors, and power harvesters. This paper builds upon the work of Kiefer and Lagoudas [4,5] as well as improvements proposed by LaMaster et al. [1] to present a thermodynamic based model to predict the response of an MSMA to axial mechanical loading and transverse magnetic loading. This work is unique, however, in its use of a memory variable, which references the last stable configuration. This is similar to the approach used by Saint-Sulpice [2] in modeling SMA wires. The resulting model has zero driving force for reorientation of variants at the beginning of any load and again when the load is removed. Thus the model predicts what is seen physically, that the material is stable when no magneto-mechanical load is present. Furthermore, this model is more physical and less empirical than others in the literature, having only 2 material parameters associated with the stress-strain or stress-field response. In addition, this model includes evolution rules for the magnetic domain volume fractions and the angle of rotation of the magnetization vectors based on thermodynamic requirements. The resulting model is calibrated and predictions are compared with both the more established Keifer and Lagoudas model as well as experimental data. Results show decent correlation with experiments. The model can be further improved by calibrating the demagnetization factor to experimentally measured changes in magnetic field.

Further Insight on the Power Harvesting Capabilities of Magnetic Shape Memory Alloys

2015 ◽  
Author(s):  
Roger Guiel ◽  
Jason L. Dikes ◽  
Constantin Ciocanel ◽  
Heidi P. Feigenbaum
Keyword(s):  
Magnetic Field ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Compressive Stress ◽  
Power Output ◽  
Axial Magnetic Field ◽  
Magnetic Shape Memory ◽  
Bias Magnetic Field ◽  
Magnetic Shape Memory Alloys ◽  
Power Harvesting

Magnetic shape memory alloys are a relatively new class of materials that are suitable for actuation, sensing, and power harvesting. The power harvesting capability comes from the change in magnetization that the material exhibits when internal martensitic variants change orientation. In typical power harvesting tests, the material is loaded with axial compression in the presence of a bias magnetic field applied normal to the compressive loading direction. However, previous results suggest that having a component of the bias magnetic field applied axially, parallel to the compressive stress, can increase the power output of MSMAs. Furthermore, most of the MSMAs power harvesting results reported to date focused on the open circuit voltage that the material can generate during cyclic loading. However, this information is not indicative of the true power harvesting capability of the material and one has to focus on the power output of the material instead. This paper presents voltage trends and power output data for a MSMA sample exposed simultaneously to a cyclic compressive stress and bi-axial magnetic field.

Hysteresis effects in the magnetic-field-induced reverse martensitic transition in magnetic shape-memory alloys

2010 ◽  
Vol 108 (4) ◽  
pp. 043914 ◽  
Author(s):  
Thorsten Krenke ◽  
Seda Aksoy ◽  
Eyüp Duman ◽  
Mehmet Acet ◽  
Xavier Moya ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Martensitic Transition ◽  
Magnetic Shape Memory ◽  
Magnetic Shape Memory Alloys ◽  
The Magnetic Field

Magnetic properties of single crystals of Ni-Mn-Ga magnetic shape memory alloys

2004 ◽  
Author(s):  
Shannon P. Farrell ◽  
Richard A. Dunlap ◽  
Leon M. Cheng ◽  
Rosaura Ham-Su ◽  
Michael A. Gharghouri ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Single Crystals ◽  
Magnetic Shape Memory ◽  
Magnetic Shape Memory Alloys
Sign in / Sign up

Export Citation Format

Share Document