Magnetic shape-memory alloy

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A magnetic shape-memory alloy (MSMA) is a type of smart material that can undergo significant and reversible changes in shape in response to a magnetic field. This behavior arises due to a combination of magnetic and shape-memory properties within the alloy, allowing it to produce mechanical motion or force under magnetic actuation. MSMAs are commonly made from ferromagnetic materials, particularly nickel-manganese-gallium (Ni-Mn-Ga), and are useful in applications requiring rapid, controllable, and repeatable movement.

Contents

Introduction

MSM alloys are ferromagnetic materials that can produce motion and forces under moderate magnetic fields. Typically, MSMAs are alloys of Nickel, Manganese and Gallium (Ni-Mn-Ga).

A magnetically induced deformation of about 0.2% was presented in 1996 by Dr. Kari Ullakko and co-workers at MIT. [1] Since then, improvements on the production process and on the subsequent treatment of the alloys have led to deformations of up to 6% for commercially available single crystalline Ni-Mn-Ga MSM elements, [2] as well as up to 10-12 % and 20% for new alloys in R&D stage. [3] [4]

The large magnetically induced strain, as well as the short response times make the MSM technology very attractive for the design of innovative actuators to be used in pneumatics, robotics, medical devices and mechatronics. [5] MSM alloys change their magnetic properties depending on the deformation. This companion effect, which co-exist with the actuation, can be useful for the design of displacement, speed or force sensors and mechanical energy harvesters. [6]

The magnetic shape memory effect occurs in the low temperature martensite phase of the alloy, where the elementary cells composing the alloy have tetragonal geometry. If the temperature is increased beyond the martensite–austenite transformation temperature, the alloy goes to the austenite phase where the elementary cells have cubic geometry. With such geometry the magnetic shape memory effect is lost.

The transition from martensite to austenite produces force and deformation. Therefore, MSM alloys can be also activated thermally, like thermal shape memory alloys (see, for instance, Nickel-Titanium (Ni-Ti) alloys).

The magnetic shape memory effect

The mechanism responsible for the large strain of MSM alloys is the so-called magnetically induced reorientation (MIR), and is sketched in the figure. [7] Like other ferromagnetic materials, MSM alloys exhibit a macroscopic magnetization when subjected to an external magnetic field, emerging from the alignment of elementary magnetizations along the field direction. However, differently from standard ferromagnetic materials, the alignment is obtained by the geometric rotation of the elementary cells composing the alloy, and not by rotation of the magnetization vectors within the cells (like in magnetostriction).

Magnetic shape memory working principle. Note that the deformation kink shown in the figure is only for illustration purposes, while in actual materials the kink is < 4 deg. MSM principle Schnetzler2016.png
Magnetic shape memory working principle. Note that the deformation kink shown in the figure is only for illustration purposes, while in actual materials the kink is < 4 °.

A similar phenomenon occurs when the alloy is subjected to an external force. Macroscopically, the force acts like the magnetic field, favoring the rotation of the elementary cells and achieving elongation or contraction depending on its application within the reference coordinate system. The elongation and contraction processes are shown in the figure where, for example, the elongation is achieved magnetically and the contraction mechanically.

The rotation of the cells is a consequence of the large magnetic anisotropy of MSM alloys, and the high mobility of the internal regions. Simply speaking, an MSM element is composed by internal regions, each having a different orientation of the elementary cells (the regions are shown by the figure in green and blue colors). These regions are called twin-variants. The application of a magnetic field or of an external stress shifts the boundaries of the variants, called twin boundaries , and thus favors one variant or the other. When the element is completely contracted or completely elongated, it is formed by only one variant and it is said to be in a single variant state. The magnetization of the MSM element along a fixed direction differs if the element is in the contraction or in the elongation single variant state. The magnetic anisotropy is the difference between the energy required to magnetize the element in contraction single variant state and in elongation single variant state. The value of the anisotropy is related to the maximum work-output of the MSM alloy, and thus to the available strain and force that can be used for applications. [8]

Properties

The main properties of the MSM effect for commercially available elements are summarized in [9] (where other aspects of the technology and of the related applications are described):

Fatigue Properties

The fatigue life of MSMAs is of particular interest for actuation applications due to the high frequency cycling, so improving the microstructure of these alloys has been of particular interest. Researchers have improved the fatigue life up to 2x109 cycles with a maximum stress of 2MPa, providing promising data to support real application of MSMAs in devices. [10] Although high fatigue life has been demonstrated, this property has been found to be controlled by the internal twinning stress in the material, which is dependent on the crystal structure and twin boundaries. Additionally, inducing a fully strained (elongated or contracted) MSMA has been found to reduce fatigue life, so this must be taken into consideration when designing functional MSMA systems. In general, reducing defects such as surface roughness that cause stress concentration can increase the fatigue life and fracture resistance of MSMAs. [11]

Development of the alloys

Standard alloys are Nickel-Manganese-Gallium (Ni-Mn-Ga) alloys, which are investigated since the first relevant MSM effect has been published in 1996. [1] Other alloys under investigation are Iron-Palladium (Fe-Pd) alloys, Nickel-Iron-Gallium (Ni-Fe-Ga) alloys, and several derivates of the basic Ni-Mn-Ga alloy which further contain Iron (Fe), Cobalt (Co) or Copper (Cu). The main motivation behind the continuous development and testing of new alloys is to achieve improved thermo-magneto-mechanical properties, such as a lower internal friction, a higher transformation temperature and a higher Curie temperature, which would allow the use of MSM alloys in several applications. In fact, the actual temperature range of standard alloys is up to 50 °C. Recently, an 80 °C alloy has been presented. [12]

Due to the twin boundary motion mechanism required for the magnetic shape memory effect to occur, the highest performing MSMAs in terms of maximum induced strain have been single crystals. Additive manufacturing has been demonstrated as a technique to produce porous polycrystalline MSMAs. [13] As opposed to fully dense polycrystalline MSMAs, porous structures allow more freedom of motion, which reduces the internal stress required to activate martensitic twin boundary motion. Additionally, post-process heat treatments such as sintering and annealing have been found to significantly increase the hardness and reduce the elastic moduli of Ni-Mn-Ga alloys.

Applications

MSM actuator elements can be used where fast and precise motion is required. They are of interest due to the faster actuation using magnetic field as compared to the heating/cooling cycles required for conventional shape memory alloys, which also promises higher fatigue lifetime. Possible application fields are robotics, manufacturing, medical surgery, valves, dampers, sorting. [9] MSMAs have been of particular interest in the application of actuators (i.e. microfluidic pumps for lab-on-a-chip devices) since they are capable of large force and stroke outputs in relatively small spatial regions. [10] Also, due to the high fatigue life and their ability to produce electromotive forces from a magnetic flux, MSMAs are of interest in energy harvesting applications. [14]

The twinning stress, or internal frictional stress, of an MSMA determines the efficiency of actuation, so the operation design of MSM actuators is based on the mechanical and magnetic properties of a given alloy; for example, the magnetic permeability of an MSMA is a function of strain. [10] The most common MSM actuator design consists of an MSM element controlled by permanent magnets producing a rotating magnetic field and a spring restoring a mechanical force during the shape memory cycling. Limitations on the magnetic shape memory effect due to crystal defects determine the efficiency of MSMAs in applications. Since the MSM effect is also temperature dependent, these alloys can be tailored to shift the transition temperature by controlling microstructure and composition.

Related Research Articles

Magnetostriction is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of materials' magnetization due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value, λ. The effect was first identified in 1842 by James Joule when observing a sample of iron.

<span class="mw-page-title-main">Magnetic refrigeration</span> Phenomenon in which a suitable material can be cooled by a changing magnetic field

Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures, as well as the ranges used in common refrigerators.

<span class="mw-page-title-main">Martensite</span> Type of steel crystalline structure

Martensite is a very hard form of steel crystalline structure. It is named after German metallurgist Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation.

<span class="mw-page-title-main">Austenite</span> Metallic, non-magnetic allotrope of iron or a solid solution of iron, with an alloying element

Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K (727 °C); other alloys of steel have different eutectoid temperatures. The austenite allotrope is named after Sir William Chandler Roberts-Austen (1843–1902). It exists at room temperature in some stainless steels due to the presence of nickel stabilizing the austenite at lower temperatures.

In materials science, superplasticity is a state in which solid crystalline material is deformed well beyond its usual breaking point, usually over about 400% during tensile deformation. Such a state is usually achieved at high homologous temperature. Examples of superplastic materials are some fine-grained metals and ceramics. Other non-crystalline materials (amorphous) such as silica glass and polymers also deform similarly, but are not called superplastic, because they are not crystalline; rather, their deformation is often described as Newtonian fluid. Superplastically deformed material gets thinner in a very uniform manner, rather than forming a "neck" that leads to fracture. Also, the formation of microvoids, which is another cause of early fracture, is inhibited. Superplasticity must not be confused with superelasticity.

In metallurgy, a shape-memory alloy (SMA) is an alloy that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. It is also known in other names such as memory metal, memory alloy, smart metal, smart alloy, and muscle wire. The "memorized geometry" can be modified by fixating the desired geometry and subjecting it to a thermal treatment, for example a wire can be taught to memorize the shape of a coil spring.

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<span class="mw-page-title-main">Maraging steel</span> Steel known for strength and toughness

Maraging steels are steels that are known for possessing superior strength and toughness without losing ductility. Aging refers to the extended heat-treatment process. These steels are a special class of very-low-carbon ultra-high-strength steels that derive their strength not from carbon, but from precipitation of intermetallic compounds. The principal alloying element is 15 to 25 wt% nickel. Secondary alloying elements, which include cobalt, molybdenum and titanium, are added to produce intermetallic precipitates.

Exchange bias or exchange anisotropy occurs in bilayers of magnetic materials where the hard magnetization behavior of an antiferromagnetic thin film causes a shift in the soft magnetization curve of a ferromagnetic film. The exchange bias phenomenon is of tremendous utility in magnetic recording, where it is used to pin the state of the readback heads of hard disk drives at exactly their point of maximum sensitivity; hence the term "bias."

<span class="mw-page-title-main">Heusler compound</span> Type of metallic alloy

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<span class="mw-page-title-main">Alloy steel</span> Steel alloyed with a variety of elements

Alloy steel is steel that is alloyed with a variety of elements in amounts between 1.0% and 50% by weight, typically to improve its mechanical properties.

In materials science, pseudoelasticity, sometimes called superelasticity, is an elastic (reversible) response to an applied stress, caused by a phase transformation between the austenitic and martensitic phases of a crystal. It is exhibited in shape-memory alloys.

<span class="mw-page-title-main">Magnetic domain</span> Region of a magnetic material in which the magnetization has uniform direction

A magnetic domain is a region within a magnetic material in which the magnetization is in a uniform direction. This means that the individual magnetic moments of the atoms are aligned with one another and they point in the same direction. When cooled below a temperature called the Curie temperature, the magnetization of a piece of ferromagnetic material spontaneously divides into many small regions called magnetic domains. The magnetization within each domain points in a uniform direction, but the magnetization of different domains may point in different directions. Magnetic domain structure is responsible for the magnetic behavior of ferromagnetic materials like iron, nickel, cobalt and their alloys, and ferrimagnetic materials like ferrite. This includes the formation of permanent magnets and the attraction of ferromagnetic materials to a magnetic field. The regions separating magnetic domains are called domain walls, where the magnetization rotates coherently from the direction in one domain to that in the next domain. The study of magnetic domains is called micromagnetics.

<span class="mw-page-title-main">Nickel titanium</span> Alloy known for shape-memory effect

Nickel titanium, also known as nitinol, is a metal alloy of nickel and titanium, where the two elements are present in roughly equal atomic percentages. Different alloys are named according to the weight percentage of nickel; e.g., nitinol 55 and nitinol 60.

Gallium manganese arsenide, chemical formula (Ga,Mn)As is a magnetic semiconductor. It is based on the world's second most commonly used semiconductor, gallium arsenide,, and readily compatible with existing semiconductor technologies. Differently from other dilute magnetic semiconductors, such as the majority of those based on II-VI semiconductors, it is not paramagnetic but ferromagnetic, and hence exhibits hysteretic magnetization behavior. This memory effect is of importance for the creation of persistent devices. In (Ga,Mn)As, the manganese atoms provide a magnetic moment, and each also acts as an acceptor, making it a p-type material. The presence of carriers allows the material to be used for spin-polarized currents. In contrast, many other ferromagnetic magnetic semiconductors are strongly insulating and so do not possess free carriers. (Ga,Mn)As is therefore a candidate material for spintronic devices but it is likely to remain only a testbed for basic research as its Curie temperature could only be raised up to approximately 200 K.

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Twinning-Induced Plasticity steel which is also known as TWIP steel is a class of austenitic steels which can deform by both glide of individual dislocations and mechanical twinning on the {1 1 1}γ<1 1 >γ system. They have outstanding mechanical properties at room temperature combining high strength and ductility based on a high work-hardening capacity. TWIP steels have mostly high content in Mn and small additions of elements such C, Si, or Al. The steels have low stacking fault energy at room temperature. Although the details of the mechanisms controlling strain-hardening in TWIP steels are still unclear, the high strain-hardening is commonly attributed to the reduction of the dislocation mean free path with the increasing fraction of deformation twins as these are considered to be strong obstacles to dislocation glide. Therefore, a quantitative study of deformation twinning in TWIP steels is critical to understand their strain-hardening mechanisms and mechanical properties. Deformation twinning can be considered as a nucleation and growth process. Twin growth is assumed to proceed by co-operative movement of Shockley partials on subsequent {111} planes.

Elastocaloric materials are a class of advanced materials. These materials show a big change in temperature when mechanical stress is applied and then removed.

References

  1. 1 2 Ullakko, K. (1996). "Magnetically controlled shape memory alloys: A new class of actuator materials". Journal of Materials Engineering and Performance. 5 (3): 405–409. doi:10.1007/BF02649344. ISSN   1059-9495. S2CID   137352650.
  2. ↑ Wilson, Stephen A.; Jourdain, Renaud P. J.; Zhang, Qi; Dorey, Robert A.; Bowen, Chris R.; Willander, Magnus; Wahab, Qamar Ul; Willander, Magnus; Al-hilli, Safaa M. (2007-06-21). "New materials for micro-scale sensors and actuators: An engineering review". Materials Science and Engineering: R: Reports. 56 (1–6): 1–129. doi:10.1016/j.mser.2007.03.001.
  3. ↑ Sozinov, A.; Lanska, N.; Soroka, A.; Zou, W. (2013-01-14). "12% magnetic field-induced strain in Ni-Mn-Ga-based non-modulated martensite". Applied Physics Letters. 102 (2): 021902. doi:10.1063/1.4775677. ISSN   0003-6951.
  4. ↑ Pagounis, E.; Szczerba, M. J.; Chulist, R.; Laufenberg, M. (2015-10-12). "Large magnetic field-induced work output in a NiMnGa seven-layered modulated martensite". Applied Physics Letters. 107 (15): 152407. doi:10.1063/1.4933303. ISSN   0003-6951.
  5. ↑ T. Schiepp, A Simulation Method for Design and Development of Magnetic Shape Memory Actuators, PhD Thesis, University of Gloucestershire, 2015.
  6. ↑ Karaman, I.; Basaran, B.; Karaca, H. E.; Karsilayan, A. I.; Chumlyakov, Y. I. (2007-04-23). "Energy harvesting using martensite variant reorientation mechanism in a NiMnGa magnetic shape memory alloy". Applied Physics Letters. 90 (17): 172505. doi:10.1063/1.2721143. ISSN   0003-6951.
  7. ↑ Faehler, Sebastian (2007-08-23). "An Introduction to Actuation Mechanisms of Magnetic Shape Memory Alloys". ECS Transactions. 3 (25): 155–163. doi:10.1149/1.2753250. ISSN   1938-6737. S2CID   62395907.
  8. ↑ L. Straka, Magnetic and Magneto-Mechanical Properties of Ni-Mn-Ga Magnetic Shape Memory Alloys, PhD Thesis, Aalto University, 2007.
  9. 1 2 "The MSM net". The MSM net. Retrieved 2016-11-16.
  10. 1 2 3 Gabdullin, N; Khan, S H (2015-02-16). "Review of properties of magnetic shape memory (MSM) alloys and MSM actuator designs". Journal of Physics: Conference Series. 588: 012052. doi: 10.1088/1742-6596/588/1/012052 . ISSN   1742-6596. S2CID   56145183.
  11. ↑ Lawrence, T.; Lindquist, P.; Ullakko, K.; Müllner, P. (2016-01-27). "Fatigue life and fracture mechanics of unconstrained Ni–Mn–Ga single crystals in a rotating magnetic field". Materials Science and Engineering: A. 654: 221–227. doi: 10.1016/j.msea.2015.12.045 . ISSN   0921-5093.
  12. ↑ Pagounis, E.; Chulist, R.; Szczerba, M. J.; Laufenberg, M. (2014-07-15). "High-temperature magnetic shape memory actuation in a Ni–Mn–Ga single crystal". Scripta Materialia. 83: 29–32. doi:10.1016/j.scriptamat.2014.04.001.
  13. ↑ Acierno, Aaron; Toman, Jakub; Kimes, Katerina; Mostafaei, Amir; Boin, Mirko; Wimpory, Robert; Chmielus, Markus (August 2020). "Grain Growth, Porosity, and Hardness Changes in Sintered and Annealed Binder-jet 3D Printed Ni-Mn-Ga Magnetic Shape Memory Alloys". Microscopy and Microanalysis. 26 (S2): 3082–3085. doi: 10.1017/S1431927620023764 . ISSN   1431-9276. S2CID   225351376.
  14. ↑ Rashidi, Saman; Ehsani, Mohammad Hossein; Shakouri, Meisam; Karimi, Nader (2021-11-01). "Potentials of magnetic shape memory alloys for energy harvesting". Journal of Magnetism and Magnetic Materials. 537: 168112. doi:10.1016/j.jmmm.2021.168112. ISSN   0304-8853.
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