Magnetocrystalline anisotropy and twinning stress in Ni-Mn-Ga ferromagnetic shape memory alloys

Okamoto, Nariaki; Fukuda, Takashi; Kakeshita, Tomoyuki

doi:10.1088/1742-6596/51/1/073

Cited by 15 publications

(6 citation statements)

References 9 publications

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“…To facilitate comparison, the magnetic stress limit calculated according to the model introduced above is also shown. Relatively flat temperature dependence over a broad temperature range was also observed by Okamoto et al , 149,150 which would suggest type II boundaries, but the nature of the boundaries was not discerned.…”

Section: Highly Mobile Twin Boundaries In Ni–mn–gamentioning

confidence: 55%

Magnetic shape memory effect and highly mobile twin boundaries

Heczko

2014

Materials Science and Technology

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The magnetic shape memory effect can be classified as an example of the multiferroic effect combining ferro-elasticity and (ferro)magnetism. After short overview of all known effects the focus is on magnetic field induced structure reorientation (MIR) in the martensite of Ni–Mn–Ga. In this material giant deformations of up to 12 have been observed in moderate magnetic fields. The phenomenology of the effect is first discussed and a model presented. The properties of Ni–Mn–Ga relevant to MIR are then considered. One necessary condition for MIR is a highly mobile twin boundary or interface between two differently oriented martensite variants (ferroelastic domains). In 10M modulated martensite, two types of mobile twin boundary (type I and type II) are observed with complex layered microstructures consisting of a hierarchy of twinning systems. The boundaries strongly differ according to the magnitude and temperature dependence of the twinning stress. Finally, the nature of these boundaries and their different behaviour is reviewed.

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Section: Highly Mobile Twin Boundaries In Ni–mn–gamentioning

confidence: 55%

Magnetic shape memory effect and highly mobile twin boundaries

Heczko

2014

Materials Science and Technology

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“…Ferromagnetic Ni-Mn-Ga alloys are known for their large, fast and reversible magnetic-field-induced strains (MFIS) [1][2][3], which are made possible by twin boundary reorientation induced either by a magnetic field and/or external stress [4]. However, the MFIS is highly dependent upon the chemical composition [5], which defines the crystal structure and phase transformation temperatures [6], and also, as a defect-controlled property, depends on how many obstacles such as grain boundaries and other crystal defects the twin boundary movement needs to overcome during straining [7].…”

Section: Introductionmentioning

confidence: 99%

Effect of process parameters on non-modulated Ni-Mn-Ga alloy manufactured using powder bed fusion

Nilsén

Ituarte

Salmi

et al. 2019

Additive Manufacturing

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Increasingly, metal parts made by additive manufacturing are produced using powder bed fusion (PBF). In this paper we report upon the combined effects of PBF parameters, including power and scan speed, in layer-by-layer manufacturing of gas atomized non-modulated (NM) Ni-Mn-Ga alloy. The effects of process parameters upon PBF is studied by applying nine different parameter sets in the as-printed state and after homogenization and ordering. The chemical composition of the samples is analyzed using EDX attached to an SEM, and the crystal structures are determined by X-ray diffraction. The phase transformation temperatures are measured using a low-field ac susceptibility measurement system and the magnetic properties are measured with a vibrating sample magnetometer (VSM). Before the heat-treatment, all as-printed samples showed paramagnetic behavior with low magnetization and no phase transformations could be observed in the susceptibility measurements. After annealing, the samples recovered the ferromagnetic behavior with comparable magnetization to annealed gas atomized powder. The as-printed samples were composed of a mixture of different crystal structures. However, after annealing the original NM structure with a = b = 5.47 Å and c = 6.66 Å with a c/a-ratio of 1.22 was recovered and crystallographic twins could be observed in an SEM.

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“…To quantitively analyze the necessary shear stress ( τ ) required for the MVR of the single-crystal Ni–Mn–Ga cube, some calculations were conducted, and their results are discussed in this section. It is known that for the shape deformation of the composite materials, the necessary shear stress ( τ ) could be expressed as Equation (2) [ 38 , 39 , 43 ]:

where s indicates the shear strain [ 43 ], while Δ E shows the energy difference of different two specific variants (i.e., Variant 1 and Variant 2). In the case of the 5M-martensite phase, the typical c / a is around 0.94 [ 44 , 45 ] and the shear strain ( s ) is reported to be approximately 0.12 [ 46 ].…”

Section: Resultsmentioning

confidence: 99%

Investigations of Shape Deformation Behaviors of the Ferromagnetic Ni–Mn–Ga Alloy/Porous Silicone Rubber Composite towards Actuator Applications

et al. 2023

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Ferromagnetic shape memory alloys (FSMAs), which are potential candidates for future technologies (i.e., actuators in robots), have been paid much attention for their high work per volume and rapid response as external stimulation, such as a magnetic field, is imposed. Among all the FSMAs, the Ni–Mn–Ga-based alloys were considered promising materials due to their appropriate phase transformation temperatures and ferromagnetism. Nevertheless, their intrinsic embrittlement issue and sluggish twin motion due to the inhibition of grain boundaries restrict their practicability. This study took advantage of the single-crystal Ni–Mn–Ga cube/silicone rubber composite materials to solve the two aforementioned difficulties. The single-crystal Ni–Mn–Ga cube was prepared by using a high-temperature alloying procedure and a floating-zone (FZ) method, and the cubes were verified to be the near-{100}p Ni–Mn–Ga alloy. Various room temperature (RT) curing silicone rubbers were utilized as matrix materials. Furthermore, polystyrene foam particles (PFP) were used to provide pores, allowing a porous silicone rubber matrix. It was found that the elastic modulus of the silicone rubber was successfully reduced by introducing the PFP. Additionally, the magnetic field-induced martensite variant reorientation (MVR) was greatly enhanced by introducing a porous structure into the silicone rubber. The single-crystal Ni–Mn–Ga cube/porous silicone rubber composite materials are considered to be promising materials for applications in actuators.

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Magnetocrystalline anisotropy and twinning stress in Ni-Mn-Ga ferromagnetic shape memory alloys

Cited by 15 publications

References 9 publications

Magnetic shape memory effect and highly mobile twin boundaries

Magnetic shape memory effect and highly mobile twin boundaries

Effect of process parameters on non-modulated Ni-Mn-Ga alloy manufactured using powder bed fusion

Investigations of Shape Deformation Behaviors of the Ferromagnetic Ni–Mn–Ga Alloy/Porous Silicone Rubber Composite towards Actuator Applications

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