Magnetically controlled shape memory effect in Ni2MnGa intermetallics

Ullakko, K.; Huang, Junjie; Кокорин, В. В.; O’Handley, R. C.

doi:10.1016/s1359-6462(96)00483-6

Cited by 259 publications

(152 citation statements)

References 4 publications

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“…Since then, there have been a number of studies regarding various aspects of phase transformations in this alloy. Furthermore, Ullakko et al [2] have demonstrated that martensite phase in Ni-Mn-Ga alloy exhibits anomalous magnetostriction of 0.15 %; this value is comparable to so-called giant magnetostriction in Tbo.3Dyo.7Fe2 (commercially available as Terfenol-D). The observed large magnetostriction is due to the magnetically induced twinning/detwinning in the martensite and thus appropriated to call it as "twinning magnetostriction".…”

Section: Introductionmentioning

confidence: 93%

Phase transformation and microstructures in Ni-Mn-Ga ferromagnetic shape memory alloys

et al. 2001

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Abstract. Composition dependence of martensitic transformation and magnetic transformation has been studied on Ni-Mn-Ga ferromagnetic shape memory alloys. A good correlation was found between the transformation temperatures and valence electron density (e/a). Martensitic transformation temperature increases rapidly with e/a, while the Curie temperature exhibits only a mild dependence. Crystal structure of martensite also changes with e/a. At a lower e/a (near the stoichiometric Heusler composition) the martensite was bet with the modulation of five layers period of {110}L2I planes; at a higher e/a, it was fct without the modulation. Transformations from the parent phase to an intermediate phase and then to martensite phase were observed in situ using a cold stage for Ni-23.0Mn-25.6Ga. The sample exhibits so-called "tweed" structures in the parent phase. The tweed contrast becomes more pronounced as the temperature approaches M s . This is accompanied by increasing intensity of diffuse streaks along <110> directions. At 230 K the satellite spots appeared at l/6<220> positions, corresponding to the intermediate phase. On further cooling martensite plate formed and the structure changed continuously to the modulated bet.

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Section: Introductionmentioning

confidence: 93%

Phase transformation and microstructures in Ni-Mn-Ga ferromagnetic shape memory alloys

et al. 2001

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“…Unfortunately it was found that fields of several Teslas were needed to shift the transformation temperature a single degree Kelvin, making this mode of actuation impractical. However, in 1996 a strain comparable to the best magneto-elastic materials was observed in a single crystal of off-stoichiometric Ni 2 MnGa, for a field of less than one Tesla [6]. The strain output reported in these alloys continued to increase, and by 2001 strains of up to 6% were reported in tetragonal single crystals of Ni-Mn-Ga [7,8,9,10,11,12].…”

Section: Contentsmentioning

confidence: 98%

Energy absorption in Ni-Mn-Ga-polymer composites

Feuchtwanger

Michael

Juang

et al. 2003

Journal of Applied Physics

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In recent years Ni-Mn-Ga has attracted considerable attention as a new kind of actuator material. Off-stoichiometric single crystals of Ni 2 MnGa can regularly exhibit 6% strain in tetragonal martensites and orthorhombic martensites have shown up to 10% strain when subjected to a magnetic field. These crystals are brittle and the production of single crystals can be quite costly. Terfenol-D, a commercially available giant-magnetostrictive material, suffers from some of the same drawbacks. It was found that composite materials made from Terfenol-D particles in a polymeric matrix could solve the issue of the brittleness while retaining a large fraction of the strain output of the alloy. At first glance a similar approach could be used to solve the brittleness issue of Ni-Mn-Ga, but the low blocking force of these alloys reduces the chances of achieving a Ni-Mn-Ga/polymer composite actuator. However, the stress-strain loops for Ni-Mn-Ga show a large mechanical hysteresis. This ability to dissipate energy makes this alloys very desirable for damping applications, and by putting particles of Ni-Mn-Ga in a composite, their brittleness becomes less of an issue.It is shown that by curing Ni-Mn-Ga/polymer composites under a magnetic field it is possible to align the particles in chains and to orient them so they will respond to a uniaxial load. The magnetic measurements show that there are twin boundaries in the particles that can be moved by an external stress. Stress-induced twin boundary motion in the particles is confirmed more directly by x-ray diffraction measurements, transmission electron microscope micrographs, and scanning electron microscope micrographs. Finally we demonstrate the ability of the Ni-Mn-Ga/polymer composites to dissipate mechanical energy when subjected to cyclic loads. The Ni-Mn-Ga/polymer composites can dissipate more than 70% of the energy they are given in every cycle, while pure polymer, Fe-filled and Terfenol-filled control samples dissipate less than 50% of the input energy in every cycle. The additional loss in these composites is shown to be due to the motion of twin boundaries. Simple numerical models reproduce the cyclic stress-strain behavior of the composites and explain non-conventional features observed in the Ni-Mn-Ga composites.

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“…In these alloys, an external magnetic field can induce large strains when applied in the martensitic state. 3,4 In Ni 2 MnGa, these strains can be as large as 10% in a field of about 1 T. The field-induced strain is due to the reorientation of the tetragonal martensite variants by twin boundary motion. The driving force for the reorientation is provided by the difference in the Zeeman energy ⌬M · H of neighboring variants.…”

Section: Introductionmentioning

confidence: 99%

Martensitic transitions and the nature of ferromagnetism in the austenitic and martensitic states ofNi−Mn−Snalloys

et al. 2005

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Structural and magnetic transformations in the Heusler-based system Ni 0.50 Mn 0.50−x Sn x are studied by x-ray diffraction, optical microscopy, differential scanning calorimetry, and magnetization. The structural transformations are of austenitic-martensitic character. The austenite state has an L2 1 structure, whereas the structures of the martensite can be 10M, 14M, or L1 0 depending on the Sn composition. For samples that undergo martensitic transformations below and around room temperature, it is observed that the magnetic exchange in both parent and product phases is ferromagnetic, but the ferromagnetic exchange, characteristic of each phase, is found to be of different strength. This gives rise to different Curie temperatures for the austenitic and martensitic states.

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Magnetically controlled shape memory effect in Ni2MnGa intermetallics

Cited by 259 publications

References 4 publications

Phase transformation and microstructures in Ni-Mn-Ga ferromagnetic shape memory alloys

Phase transformation and microstructures in Ni-Mn-Ga ferromagnetic shape memory alloys

Energy absorption in Ni-Mn-Ga-polymer composites

Martensitic transitions and the nature of ferromagnetism in the austenitic and martensitic states ofNi−Mn−Snalloys

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