Shape Memory Alloys: A Summary of Recent Achievements

2008 ◽  
Vol 583 ◽  
pp. 21-41 ◽  
Author(s):  
Peter Entel ◽  
Vasiliy D. Buchelnikov ◽  
Markus E. Gruner ◽  
Alfred Hucht ◽  
Vladimir V. Khovailo ◽  
...  
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Shape Memory ◽  
Shape Change ◽  
Heusler Alloys ◽  
Systematic Change ◽  
Magnetic Shape Memory ◽  
Electronic Density ◽  
Modulated Phases ◽  
Modulated Structures

The Ni-Mn-Ga shape memory alloy displays the largest shape change of all known magnetic Heusler alloys with a strain of the order of 10% in an external magnetic field of less than one Tesla. In addition, the alloys exhibit a sequence of intermediate martensites with the modulated structures usually appearing at c/a < 1 while the low-temperature non- modulated tetragonal structures have c/a > 1. Typically, in the Ni-based alloys, the martensitic transformation is accompanied by a systematic change of the electronic structure in the vicinity of the Fermi energy, where a peak in the electronic density of states from the non-bonding Ni states is shifted from the occupied region to the unoccupied energy range, which is associated with a reconstruction of the Fermi surface, and, in most cases, by pronounced phonon anomalies. The latter appear in high-temperature cubic austenite, premartensite but also in the modulated phases. In addition, the modulated phases have highly mobile twin boundaries which can be rearranged by an external magnetic field due to the high magnetic anisotropy, which builds up in the martensitic phases and which is the origin of the magnetic shape memory effect. This overall scenario is confirmed by first-principles calculations.

scholarly journals A first-principles study of the martensitic instabilities in magnetic shape memory alloys

2007 ◽  
Vol 1050 ◽  
Author(s):  
Peter Entel ◽  
Markus Ernst Gruner ◽  
Alfred Hucht
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Shape Memory ◽  
First Principles ◽  
Shape Change ◽  
Heusler Alloys ◽  
Phase Changes ◽  
Magnetic Shape Memory ◽  
Electronic Density ◽  
Modulated Phases

AbstractAmong the magnetic shape memory Heusler alloys, Ni-Mn-Ga near stoichiometry displays the largest shape change in the martensitic 5M or 7M structure with a strain of the order of 10% in an external magnetic field of less than one Tesla. In addition, the alloys exhibit a sequence of intermediate martensites with the modulated structures usually appearing at c/a < 1 while the low-temperature nonmodulated tetragonal structures have c/a > 1. Typically, the martensitic phase changes are accompanied by a shift of a peak in the electronic density arising from the non-bonding Ni states, a reconstruction of the associated Fermi surface, and, in some cases, by pronounced phonon anomalies. These appear in the cubic high-temperature austenitic and premartensitic phases but also in the modulated phases. In addition, the modulated phases have highly mobile twins which can be rearranged under the action of an external magnetic field due to the high magnetic anisotropy, which builds up in martensite and which is at the origin of the magnetic shape memory effect. First-principles calculations confirm the overall scenario.

Magnetic Shape Memory - Polymer Hybrids

2016 ◽  
Vol 879 ◽  
pp. 133-138 ◽  
Author(s):  
Ilkka Aaltio ◽  
Frans Nilsén ◽  
Joonas Lehtonen ◽  
Yan Ling Ge ◽  
Steven Spoljaric ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Shape Memory ◽  
Single Crystals ◽  
Magnetic Particles ◽  
Shape Change ◽  
Shape Memory Polymer ◽  
Raw Material ◽  
Magnetic Shape Memory ◽  
Polymer Hybrids ◽  
The Magnetic Field

Martensitic Ni-Mn-Ga based alloys are known for the Magnetic Shape Memory (MSM) effect, which upon application of an external magnetic field can generate a strain up to 12 % depending on the microstructure of the martensite. The MSM effect occurs by rearrangement of the martensite variants, which is most advantageous in single crystals. Single crystals are, however, rather tedious to produce and there has been attempts to achieve MSM effect in polycrystals. However, in polycrystals the magnetic field induced shape change remains low as compared to single crystals. As an alternative to the former, hybrid MSM materials offer several advantages. When compared to single crystals, hybrids have extended freedom of shaping, lower raw material price, relatively large MSM strain and easier manufacturability. Embedding MSM particles into a suitable polymer matrix results in actuation function or good vibration damping performance. In the present study we report on the mechanical, structural and magnetic properties of MSM polymer hybrids, which are prepared by mixing gas-atomized Ni-Mn-Ga MSM powder into epoxy matrix and aligning the magnetic particles in a magnetic field.

Martensitic and Magnetic Transformation Behaviors in Ni50Mn34.5In15.5-xGdx Metamagnetic Shape Memory Alloys

2011 ◽  
Vol 480-481 ◽  
pp. 75-79
Author(s):  
Li Na Bai ◽  
Jian Jun Zhang ◽  
Gui Xing Zheng
Keyword(s):  
Magnetic Field ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Melt Spinning ◽  
Lattice Structure ◽  
Heusler Alloys ◽  
Machining Performance ◽  
Magnetic Shape Memory ◽  
Magnetic Shape Memory Alloys ◽  
Ongoing Research

Magnetic Shape Memory Alloys（MSMA）have attracted considerable attention due to their potential application in actuators driven by temperature and magnetic field . Research on shape memory alloys found that the Heusler alloys of MSMA body-centered cubic lattice structure were occured giant strains by magnetic fields[1-4]. Japanese scholars found the new magnetic Shape Memory Alloys Ni-Mn-In and Ni-Co-Mn-In Heusler alloys completely under the control of the magnetic shape fields in 2005[5-7]. In applied MSMA fields, the Ni-Mn-In Heusler alloys start the possibility of using shape memory effect only driven by magnetic field. However, the high brittleness of polycrystalline intermetallic compounds hinders the practical use. Until now, the investigated alloys are ongoing research to resolve, the investigation was carried out to employ rapid quenching by melt spinning to produce Mn–Ni–In Heusler alloys by JLSánchez Llamazares et al [8], and the ribbons of Ni-Mn-In Heusler alloys grain preferential texture. We use the rare earth Gd to improve machining performance of the new alloys, and study the change of microstructure and magnetic properties of alloys which may be a subject of significant scientific and technological interests.

Application of EBSD to the Crystallographic Investigation on Ni-Mn-Ga Alloys

2012 ◽  
Vol 706-709 ◽  
pp. 1879-1884 ◽  
Author(s):  
Zong Bin Li ◽  
Yu Dong Zhang ◽  
Claude Esling ◽  
Hao Yang ◽  
Ji Jie Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Shape Memory ◽  
Shape Change ◽  
Memory Performance ◽  
Crystallographic Investigation ◽  
Orientation Relationships ◽  
Magnetic Shape Memory ◽  
Ferromagnetic Shape Memory Alloys ◽  
Electron Backscattered Diffraction ◽  
Martensitic Variants

For off-stoichiometric Ni2MnGa ferromagnetic shape memory alloys, a large shape change could be induced through the rearrangement of martensitic variants under an external magnetic field. Insight into the orientation relationships of martensitic variants and the characteristics of variant boundaries is thus essential for understanding the magnetic shape memory performance. In this paper, a thorough crystallographic investigation was made on the incommensurate 7M modulated martensite in one polycrystalline Ni50Mn30Ga20alloy by means of X-ray diffraction and SEM electron backscattered diffraction (EBSD). Locally, there are four differently-oriented martensitic variants, being twin related to one another. The twin interface planes are coherent and they are in coincidence with the respective twinning planes (K1). A primary exploration was performed to improve the microstructure by repeated magnetic field training during phase transition. The present investigation could offer useful guidance to develop specific technique for microstructure optimization.

Concepts and Physical Phenomena in Magnetic Shape Memory Science

2008 ◽  
Vol 52 ◽  
pp. 3-14 ◽  
Author(s):  
Volodymyr A. Chernenko
Keyword(s):  
Magnetic Field ◽  
Shape Memory ◽  
Heusler Alloys ◽  
Strain Effect ◽  
Lattice Instability ◽  
Magnetic Shape Memory ◽  
Crystal Lattices ◽  
Mode Behavior ◽  
Soft Crystal ◽  
Physical Phenomena

The magnetically weakly anisotropic cubic Ni-Mn-Ga Heusler alloys exhibit martensitic transformation resulting in martensitic phases with elastically soft crystal lattices and strong magnetocrystalline anisotropies. The magnetic state of these martensites is coupled with a highly mobile twin structure through the ordinary magnetoelastic interactions giving rise to a giant magnetic-field-induced-strain effect. This effect is the key ingredient of a new scientific field. In the present article, the basic phenomena and concepts of this field, such as lattice instability, soft-mode behavior, electron concentration, ferromagnetic shape memory effect, magnetic-field-induced superelasticity, twinning strain-induced change of magnetization, and magnetoelastic mechanism of magnetostress are briefly reviewed.

scholarly journals Material Design, Processing, and Engineering Requirements for Magnetic Shape Memory Devices

2020 ◽  
Author(s):  
Andrew Armstrong
Keyword(s):  
Magnetic Field ◽  
Shape Memory ◽  
Operating Temperature ◽  
Shape Change ◽  
Material Design ◽  
Material Surface ◽  
Magnetic Shape Memory ◽  
Valence Electron Density ◽  
Novel Technology ◽  
Vertical Field

For magnetic shape memory (MSM) alloys, a magnetic field stimulates a shape change. We use the shape change to build devices such as micro-actuators, sensors, and microfluidic pumps. Currently, (as a novel technology,) devices suffer from some material and magnetic driver shortcomings. Here we address the issues related to operating temperature, repeatability, failure, and magnetic driver development. To increase the operating temperature of the MSM material, we alloyed Fe and Cu to Ni-Mn-Ga. We showed that the element-specific contribution to the valence electron density as parameter systematically determines the effect of each element on the variation of the martensite transformation temperature of the 10M phase. To stabilize the material, we developed a micro-shotpeening process that adds stresses to the material surface, thereby inducing a fine twin microstructure. The treatment allowed nearly full magnetic-field-induced strain, and extended fatigue life of the material from only one thousand cycles in the electropolished state to more than one million cycles in the peened state. We measured the effect of the peening process on material actuation when in MSM pump configuration. In the polished state, the deformation was stochastic, with a sharp-featured, faceted shrinkage. In the treated state, the deformation was smooth and repeatably swept along the surface akin to a wave. To actuate the MSM micropump without electromotor, we developed a linear electromagnetic actuation device and evaluated its effectiveness in the switching mechanism of the material. By compressing the magnetic field between opposing coils, we generated a strong magnetic field, which caused a localized region to switch at selected poles. In the next iteration of the drive, we inserted the MSM sample between two linear pole arrangements of high pitch density to approximate a moving vertical field. The incremental stepping of the vertical field between poles caused translation of the switched region. The results of this dissertation demonstrate the suitability of MSM alloys for high-precision, persistent, and reliable actuators such as micropumps.

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