Thermal and Magnetic Properties of Stress-Induced Martensites in Ni-Mn-Ga Alloys

Chernenko, V.A.; Amengual, A.; Cesari, E.; Кокорин, В. В.; Zasimchuk, I. K.

doi:10.1051/jp4:1995214

Cited by 26 publications

(25 citation statements)

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“…This value of parameter κ results in a ∆S mag = 14.3 J/kg K, which corresponds to a Q mag = 4.1 J/g, with T M ≈ 285 K for this alloy. The estimated Q mag is similar to the experimental value of the transformation heat Q ≈ 4.2 J/g reported for this alloy [22,23]. It can be concluded, therefore, that the magnetic subsystem of this alloy is the main contributor to transformation heat and entropy change.…”

Section: Evaluation Of Magnetic and Non-magnetic Contributions To ∆S supporting

confidence: 72%

Entropy Change Caused by Martensitic Transformations of Ferromagnetic Shape Memory Alloys

L’vov

Cesari

Kosogor

et al. 2017

Metals

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Abstract:In this paper, our most recent findings on the influence of magnetic order on the main transformational caloric and elastic properties of shape memory alloys (SMAs) are reviewed. It is argued that ferromagnetic order has a strong influence on the temperature interval of martensitic transformation (MT), the characteristics of stress-induced MT, and the shear elastic modulus of SMA. The problem of separation of the magnetic contributions to the entropy change ∆S and heat Q exchanged in the course of martensitic transformation (MT) of SMA is considered in general terms, and theoretical formulas enabling the solution of the problem are presented. As an example, the ∆S and Q values, which were experimentally determined for Ni-Mn-Ga and Ni-Fe-Ga alloys with different Curie temperatures T C and MT temperatures T M , are theoretically analyzed. It is shown that for Ni-Mn-Ga martensites with T M < T C , the ratio of elastic and magnetic contributions to the entropy change may be greater or smaller than unity, depending on the temperature difference T C -T M .

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Section: Evaluation Of Magnetic and Non-magnetic Contributions To ∆S supporting

confidence: 72%

Entropy Change Caused by Martensitic Transformations of Ferromagnetic Shape Memory Alloys

L’vov

Cesari

Kosogor

et al. 2017

Metals

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“…The lattice constant a 0 in the austenite phase at room temperature is 0.582 nm. On cooling, the cubic phase distorts by a diffusionless martensitic transformation to a lower symmetry martensite phase which can be tetragonal, orthorhombic, or monoclinic [19,20]. The stoichiometric martensitic phase has point group I4/mmm ( Figure 1-2 b), but the more common off-stoichiometry martensites have more complex structures.…”

Section: Physical Propertiesmentioning

confidence: 99%

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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“…1,[13][14][15] Moreover, it has been experimentally confirmed that the martensitic structures encountered in Ni-Mn-Ga alloys affect their magnetic properties. 16) In this paper emphasis will be given to certain details of the relationship between the crystallographic peculiarities of martensite and its magnetic characteristics. In particular, a possible influence of c/a value on the magnitude of magnetostrain effect for a given magnetic field amplitude will be highlighted.…”

Section: Introductionmentioning

confidence: 99%

New Aspects of Structural and Magnetic Behaviour of Martensites in Ni-Mn-Ga Alloys

et al. 2002

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The structural changes and magnetic anomalies accompanying martensitic transformations in Ni-Mn-Ga alloys are briefly discussed. The role of lattice tetragonality of martensite in the reduction of magnetic field needed for the observation of large magnetostrain effect is theoretically analyzed, considering the compensation of the magnetic anisotropy. The possibility of the field reduction is based on the previously observed lattice parameter dependence on the temperature and proper fit of the alloy specimen shape. The model shows that a significant reduction of the magnetic field needed for the giant MSE can take place in martensites with 0.98 < c/a < 1.04.

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Thermal and Magnetic Properties of Stress-Induced Martensites in Ni-Mn-Ga Alloys

Cited by 26 publications

References 0 publications

Entropy Change Caused by Martensitic Transformations of Ferromagnetic Shape Memory Alloys

Entropy Change Caused by Martensitic Transformations of Ferromagnetic Shape Memory Alloys

Energy absorption in Ni-Mn-Ga-polymer composites

New Aspects of Structural and Magnetic Behaviour of Martensites in Ni-Mn-Ga Alloys

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