Reorientation Of Martensite Variants Research Articles

Assessment of the mechanical and functional properties of nitinol alloys fabricated by laser powder bed fusion: Effect of strain rates

Laser Powder Bed Fusion-fabricated (LPBFed) nitinol shape memory alloys (SMAs), which undergo solid-solid phase transitions between austenite and martensite, are increasingly utilized in various technical fields and are subjected to a wide range of strain rates during service. This study pioneers the investigation of a comprehensive range of strain rates (3.16 × 10−6-10°/s), encompassing the strain rates used in quasi-static tensile tests reported in the existing literature, to understand their effects on the deformation mechanisms of LPBFed nitinol SMAs. Utilizing multi-scale characterization, including macroscopic mechanical evaluation, mesoscale analysis of deformation surfaces, and microscale examination of microstructure, we reveal distinct deformation behaviors at different strain rates. At lower strain rates, the mechanical behavior exhibits little sensitivity to changes in the strain rates, with stress-induced martensite transformation or martensite detwinning and variant reorientation being the primary deformation mechanisms. However, at higher strain rates, we observe significant variability in mechanical response, dominated by dislocation-induced slip and reduced occurrence of stress-induced martensitic transformation. This study provides the first comprehensive database for the engineering applications of LPBFed Nitinol SMAs and offers critical insights into optimizing mechanical and functional assessments for these advanced materials.

Stress-induced martensite reorientation and its related performances in trained β-Ti based shape memory alloy

In the present study, the influence of training on the microstructural evolution, martensitic transformation behavior and mechanical/functional properties of Ti–V–Al–Zr shape memory alloy was investigated systematically. With the increasing of training cycling number, the degree of martensite reorientation became larger and larger. Moreover, higher density of dislocations appeared in the interior of martensite variants, upon the excessive training cycling number was applied. The international stress can be brought into the matrix, which not only promoted to the ω→αˊˊ transition, but also made the martensite phase stabilizer and even suppressed the αˊˊ→β martensitic transformation during training process. The superior mechanical properties including maximum fracture stress of 906 MPa and the higher fracture strain of 33.6% can be obtained in Ti–V–Al–Zr shape memory alloy subjected with the training cycles number of 5th, which can be attributed to the matrix strengthening stemmed from work hardening and suppression of ω precipitation. Meanwhile, the lower critical stress for the martensite variant reorientation and enhanced matrix strength synergistically contributed to the superior strain recovery characteristics with total completely recoverable strain of 6% in Ti–V–Al–Zr shape memory alloy by controlling training cycles number of 5th. Meanwhile, the higher micro-hardness can be obtained by training.

Coupled magneto-mechanical response of laminate composites comprising a layer of Ni-Mn-Ga microparticles

Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs), exhibiting a giant magnetic field induced strain (MFIS), high work output and fast response, are highly promising materials for emerging technologies to be used in automotive, aerospace, and robotics industries, among others. Their magnetic-to-mechanical energy conversion ability is characterized by the coupled magneto-mechanical response they show when magnetic field and mechanical stress are simultaneously applied. In the present work we elaborated a series of laminated composites comprising a layered ensemble of single crystalline Ni-Mn-Ga microparticles built-in between Cu foils via small layers of silicone rubber. Such a simple and robust design enabled an in-depth study of the simultaneous influence of the magnetic field and compressive opposing stress on MFIS and the generated force of the particle layer driving out-of-plane magnetomechanical response of the laminate. Self-consistent parameters characterizing a magnetic field- and stress-induced martensitic variant reorientation in the particles were disclosed by the measurements and comprehensive analysis of both the magnetization curves under opposing constant stresses (complemented by tracking residual strains with X-ray µ-CT imaging) and compressive stress-strain dependences under transversal magnetic field. In particular, an accurate value of the magnetic-to-mechanical energy conversion coefficient, equal to Cme = (2.3 ± 0.13) MPa/T2, and the value of maximum magnetostress of about 2.3 MPa generated by microparticles were determined, in a good agreement with bulk Ni-Mn-Ga single crystals (SC). In contrast to bulk SC, particles are technologically and costly more efficient. They have much higher degree of freedom in terms of composites design allowing the development of advanced miniature actuators and sensors.

Reversible reorientation of martensite variants in stress-induced martensite aged Co35Ni35Al30 single crystals

The paper reports the temperature dependence of the reversible reorientation of martensite variants during loading/unloading along the [001]B2||[001]L10-direction in compression in stress-induced martensite (SIM) aged at 423 K for 0.5 h under a compressive stress of 500 MPa applied along the [110]B2||[100]L10-direction Co35Ni35Al30 single crystals. A wide temperature range of reversible strain from 203 K to 413 K (210 K) is observed due to the stabilisation of the tetragonal L10-martensite variant V1 ([001]B2||[001]L10) during SIM-aging in these single crystals. The reversible strain in the range of 157 K (203 K<Tt<As=Af=360 K) is because of the reorientation of the L10-martensite variants V1-V2/V3. The superelasticity at Tt>Af=360 K occurred due to the stress-induced B2-L10(V2/V3) martensitic transformation (MT). Rubber-like behaviour develops in the range of 52 K (203 K<Tt<Mf*=255 K) and is characterised by a narrow stress hysteresis of 13 MPa and a reversible strain of −12.0 % due to the movement of the twinning boundaries (reversible twinning) in L10-martensite. The reversible strain reaches −10.2 % in the temperature range from Mf*=255 K to As=Af=360 K. This strain is associated with a new mechanism of L10-martensite variant reorientation, which occurs through a sequence of reverse and forward stress-induced L10(V1)-B2-L10(V2/V3) MTs and leads to the stages on the stress–strain curves. The reverse L10(V1)-B2 MT at loading and forward B2-L10(V1) MT at unloading on the first stage of the stress–strain curves are characterised by low critical stresses of 8–23 MPa, a narrow stress hysteresis of 3–19 MPa and a completely reversible strain of −6.0 %, which is stable for 100 loading/unloading cycles.

Hyflex CM and EDM from Shape Memory to Control Memory.

The new era in endodontics has been established with the introduction of nickel titanium (NiTi) alloys, and later on the automation of mechanical preparation. By changing the phase transformation temperatures of NiTi alloy, the manufacturers alter the phase composition to have a NiTi with new mechanical properties. These mechanical properties can be achieved either by thermal, mechanical treatments or both. Moreover, many machining procedures (e.g. twisting, electrical discharge machining), were developed. The higher flexibility of thermomechanically treated NiTi alloys was found as the main advantages of these alloys with the improvement of cyclic fatigue resistance when compared to conventional NiTi. Austenitic alloys have superelastic properties due to stress-induced martensite transformation and consequently try to springback to their original shape after distortion. In contrast, the martensitic instruments have ability to reorientation of martensite variants when heated. So these instruments easily deformed and show a shape memory effect. Moreover, the use of martensitic alloy results in more flexible files, with an increased cyclic fatigue resistance compared with austenitic alloy. So, continued development in the manufacturing treatment of NiTi alloys has resulted in the producing of controlled memory (CM) wire. These materials do not possess superelastic properties at neither room nor body temperature. This article reviews the development process, features and properties of Hyflex file and Hyflex EDM file made from CM wire. Keywords: NiTi alloy, CM wire, Hyflex EDM, Heat treated NiTi

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

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.

Fundamental Investigations of the Deformation Behavior of Single-Crystal Ni-Mn-Ga Alloys and Their Polymer Composites via the Introduction of Various Fields

To meet the great requirements of future technologies, such as robots, single-crystal (SC) Ni-Mn-Ga alloys and their composites were designed and investigated in this study. Ferromagnetic shape memory alloys (FSMAs) are promising materials for applications in high-speed actuators, which are core components of robots; however, there are some issues of embrittlement and small deformation strain. Therefore, in this work, we first prepared SC Ni-Mn-Ga alloys for fundamental investigations of the shape deformations under the application of different fields (e.g., compressive and magnetic fields). Second, the SC Ni-Mn-Ga alloys were integrated with polymers of epoxy resin or silicone rubber to solve the embrittlement problem. The obvious two-stage yielding and sudden intensifying of the magnetization both suggest martensite variant reorientation (MVR) under the compressive and magnetic fields, respectively. Micro-computed tomography (μCT) and an X-ray diffractometer were utilized for the observations of shape deformation brought about by the MVR of the SC Ni-Mn-Ga particles in the polymer matrix. Clear MVR and shape deformation could be found in the compressed composites.

Investigations of the Crystallographic Orientation on the Martensite Variant Reorientation of the Single-Crystal Ni-Mn-Ga Cube and Its Composites for Actuator Applications

High-speed actuators are greatly required in this decade due to the fast development of future technologies, such as Internet-of-Things (IoT) and robots. The ferromagnetic shape memory alloys (FSMAs), whose shape change could be driven by applying an external magnetic field, possess a rapid response. Hence, these materials are considered promising candidates for the applications of future technologies. Among the FSMAs, the Ni-Mn-Ga-based materials were chosen for their large shape deformation strain and appropriate phase transformation temperatures for near-room temperature applications. Nevertheless, it is widely known that both the intrinsic brittleness of the Ni-Mn-Ga alloy and the constraint of shape deformation strain due to the existence of grain boundaries in the polycrystal inhibit the applications. Therefore, various Ni-Mn-Ga-based composite materials were designed in this study, and their shape deformation behaviors induced by compressive or magnetic fields were examined by the in situ micro CT observations. In addition, the dependence of the martensite variant reorientation (MVR) on the crystallographic directions was also investigated. It was found that most of the MVRs are active within the magnetic field range applied in the regime of the &lt;100&gt;p, &lt;110&gt;p, and &lt;111&gt;p of the single-crystal {100}p Ni-Mn-Ga cubes.

Microstructural Model of Magnetic and Deformation Behavior of Single Crystals and Polycrystals of Ferromagnetic Shape Memory Alloy

In this article, a microstructural model of the Heusler alloy with the shape memory effect caused by the application of an external magnetic field is constructed. The dynamics of the magnetization process are described using the Landau–Lifshitz–Gilbert equation. For the numerical implementation of the model using the finite element method, the variational equations corresponding to the differential formulation of the magnetic problem are used. Such an approach makes it possible to reduce (weaken) the requirements for the smoothness of the sought solution. The problem of magnetization of single crystals of the Ni2MnGa alloy, which has a “herringbone”-type martensitic structure (a twinned variant of martensite), is considered. In each element of the twin, the magnetic domains with walls of a certain thickness are formed. The motion and interaction of these walls and the rotation of magnetization vector in the walls and domains under the action of the external differently directed magnetic fields are studied. These processes in the Heusler alloy are also accompanied by the detwinning process. A condition for the detwinning of a ferromagnetic shape memory alloy in a magnetic field is proposed, and the effect of the reorientation (detwinning) of martensitic variants forming a twin on the magnetization of the material and the occurrence of structural (detwinning) deformation in it are taken into account. First, the processes of magnetization and structural deformation in a single grain are considered at different angles between the anisotropy axes of twinned variants and the external magnetic field. For these cases, the magnetization curves are constructed, and the deformed states are identified. The model described such experimental facts as the detwinning process and the jump in magnetization on these curves as a result of this process. It was shown that the jump occurred at a certain magnitude of the strength of the applied external magnetic field and a certain direction of its action relative to the twinning system. Then, based on the obtained results, deformed states arising due to the detwinning process were determined for various (isotropic and texture-oriented) polycrystalline samples, and magnetization curves taking into account this process were constructed for these materials.

Investigation of the martensite variant reorientation of the single crystal Ni-Mn-Ga alloy via training processes and a modification with a silicone rubber

The shape changes of the Ni-Mn-Ga alloys, which could be driven via a manipulation of temperature, stress, and/or magnetic-field, are considered as promising materials for the application of future technologies, such as robots and smart medical devices. The single crystal (SC) Ni49Mn30Ga21 (at.%) alloy, which possessed a 7-modulated (7M) martensite phase, was prepared by a floating-zone (FZ) technique. The fundamental thermal analysis, phase identification, crystallographic orientation determination, magnetic properties, mechanical properties, and microstructure observations were carried out for the evaluations of the SC Ni-Mn-Ga alloy. Prior to the training processes via an introduction of certain compressive stress cycles, no martensite variant reorientation (MVR) could be observed in the magnetization-magnetic field (M–H) curves. During the training processes, it was obviously found that the stress for the commencement of the MVR was reduced gradually. An apparent MVR was thereafter realized after some specific training procedures. This could be attributed to the less pinning effect at the twin boundaries of the SC Ni-Mn-Ga alloy. In addition, obvious shape changes were revealed after the introduction of an external magnetic field to the SC Ni-Mn-Ga alloy. It was further found that the imposed MVR could be constrained by integrating the SC Ni-Mn-Ga alloy with a silicone rubber.

Phenomenological modeling for magneto-mechanical couplings of martensitic variant reorientation in ferromagnetic shape memory alloys

Phenomenological modeling for magneto-mechanical couplings of martensitic variant reorientation in ferromagnetic shape memory alloys

Effects of volume fraction between single crystal Ni-Mn-Ga ferromagnetic shape memory alloy and silicone rubber on the martensite variant reorientation

Owing to the rapid development of future technologies, IoT, actuators, and sensors inside robots have attracted much attention. Among the actuator materials, ferromagnetic shape memory alloys (FSMA), whose shape change could be manipulated by controlling its temperature, stress, and/or magnetic-field, are considered to be appropriate actuator materials. Besides, FSMA further possesses high work/volume ratio and fast response further allowing it a promising actuator material. Polycrystalline and single crystalline Ni-Mn-Ga alloys were successfully fabricated by arc-melting and floating-zone methods, respectively. Phase constituents of the Ni-Mn-Ga alloys were verified to be the single 5-modulated (5M) martensite phase, whose martensite variant reorientation (MVR) could be triggered by either applying an external magnetic field or a stress field. An in-situ observation of the martensitic transformation from 373 K to 273 K was clearly revealed. The MVR of the Ni-Mn-Ga alloy driven by an external magnetic field was also confirmed. Besides, typical stress plateau was discerned while a compressive stress was applied to the Ni-Mn-Ga alloy. Effects of ratios of the Ni-Mn-Ga alloy to the silicone rubber showed a good correlation and has been well-explained. Furthermore, it was found that a threshold range of approximately 7 vol.%−13 vol.% of the Ni-Mn-Ga alloy is the lowest requirement for the commencement of MVR.

On the power and efficiency of Ni2MnGa magnetic shape memory alloy power harvesters

The martensite variant reorientation in Ni2MnGa magnetic shape memory alloys (MSMAs) causes a change in their bulk magnetization, that can be harvested into useful voltage/power by means of a pick-up coil. The coil may be placed directly surrounding an MSMA element or to the side of the MSMA element wrapped around a magnetic core. This paper reports new power harvesting data generated with a bi-axial magnetic field and a surrounding coil and full strain field data for an MSMA subject to load similar to what is seen during power harvesting, then compares the performance of MSMA-based power harvesters with different designs to determine which give the best output. For this comparison, we provide a framework for evaluating the performance of MSMA-based power harvesters reported in the literature. This framework involves normalizing the results to the design characteristics of the respective harvesters, i.e. number of turns of the pickup coil, cross-sectional area of the pickup coil, frequency of excitation, and sample size, to allow for a direct comparison of power harvesters’ output. Results show that power harvesting with the bi-axial field and a surrounding coil does not generate as much power as previously thought. The strain maps reveal the potential for perpendicular twin boundaries that block each other’s motion limiting variant reorientation and correspondingly the harvester’s power output. The paper concludes that the largest change in magnetic flux density, which is the driver for power harvesting, occurs in the side coil setup with an optimized magnetic circuit and it recommends using this configuration for future MSMA-based power harvester designs for maximum power output.

Strain Amplitude Dependence of Internal Friction in a Cu–Al–Mn Shape Memory Alloy

Strain amplitude (SA) dependence of internal friction (IF) in a Cu–Al–Mn shape memory alloy (SMA) is investigated. Microstructure observation is conducted with the aim to clarify related mechanisms. It is found that the IF measured during the continuous heating process shows a nonmonotonous dependence on SA, that is, the IF increases first and then decreases. The increase of IF can be attributed to the mergence of martensite laths promoted by the reorientation of martensite variants, whereas the decrease of IF is related to the decrease in the density of moveable interfaces. The isothermal IF measured at low temperatures increases monotonously with the increase in SA, because the density of movable interfaces and the sliding distance of these interfaces in the tangential direction increase. Thermal cycles can significantly improve the isothermal IF because of the annihilation of quenched‐in vacancies and the reorientation of martensite variants. At around 240 °C, the isothermal IF in all specimens shows a nonmonotonous dependence on SA, which can be ascribed to the dragging effect of quenched‐in vacancies on dislocations and the breakaway of dislocations from these vacancies when the SA is high enough.

Interactions between martensitic NiTi shape memory alloy and Nb nanowires in composite wire during tensile deformation

This study investigated the interactions between martensitic NiTi shape memory alloy and Nb nanowires in composite wire during tensile loading by means of in-situ high-energy X-ray diffraction. Nb nanowires have significant influence on the transformation behavior, annealed texture, and martensite variant reorientation behavior including texture evolution and load transfer among martensite variants of NiTi matrix. Meanwhile, the existence of densely distributed Nb nanowires increases the internal stress in NiTi matrix generated during martensite reorientation process, and causes the negative axial lattice stresses of all unfavored NiTi martensite variants after reorientation when the composite wire is under axial tensile stress. In addition, an exceptionally large elastic strain of 4.7% was produced over Nb nanowires after tensile deformation . Meanwhile, heterogeneous strain distribution exists in Nb nanowires, and it is associated with heterogeneous martensite reorientation strain of NiTi matrix. • Interactions between martensitic NiTi alloy and Nb nanowires is investigated. • Nanowires inhibit NiTi martensitic transformation and deformation twinning. • Nanowires induce the negative lattice stresses of all unfavored NiTi variants. • Inhomogeneous strain distribution exists in nanowires.

Facilitation of detwinning through controlling crystal structure in Ti–Zr–Ni–Pd high temperature shape memory alloys

Ti–(Zr, Hf)–Ni alloys, in which Zr or Hf is added to Ti–Ni shape memory alloys, are expected to be excellent high temperature shape memory alloys because they have martensitic transformation temperatures above 100°C and high strength at elevated temperatures by utilizing H-phase precipitation. However, during reorientation of martensite variants, deformation stress increases with applied strain without showing a plateau region, making it difficult to obtain a large shape recovery strain. In the martensite phase of Ti–(Zr, Hf)–Ni alloys, thin and dense (001)B19′ compound twins are introduced during the martensitic transformation, and the detwinning of martensite variants becomes difficult to occur, resulting in the increase in deformation stress during the variant reorientation. Therefore, we propose a new alloy-design concept to control the crystal structure by adding a fourth element in order to facilitate detwinning. In this paper, we first considered the cause of (001)B19′ compound twinning in Ti–(Zr, Hf)–Ni alloys, and then selected Pd as the fourth element to change the crystal structure for preventing the formation of (001)B19′ compound twins. Experimental investigations of the effects of alloy composition on the crystal structure, transformation temperatures, and precipitate formation realized this alloy-design concept through presenting a candidate composition range of Ti–(15–20)Zr–49.7Pd and surrounding Ni-containing alloys for new high temperature shape memory alloys which readily undergo detwinning.

Observation of magnetic domain evolution in constrained epitaxial Ni–Mn–Ga thin films on MgO(0 0 1) substrate

• The evolutions of the magnetic domain of a typical epitaxial Ni–Mn–Ga thin film were investigated through wide-field magneto-optical Kerr-microscopy. • The abrupt magnetization changes in the hysteresis loops can be observed in the Type-Y area with the applied magentic field parallel to the twin interfaces. • The abrupt magnetization changes in the hysteresis loops should be attributed to the magnetic domain evolution instead of the magnetically induced variant reorientation. Epitaxial Ni–Mn–Ga thin films have promising application potential in micro-electro-mechanical sensing and actuation systems. To date, large abrupt magnetization changes have been observed in some epitaxial Ni–Mn–Ga thin films, but their origin - either from magnetically induced martensite variant reorientation (MIR) or magnetic domain evolution - has been discussed controversially. In the present work, we investigated the evolutions of the magnetic domain and microstructure of a typical epitaxial Ni–Mn–Ga thin film through wide-field magneto-optical Kerr-microscopy. It is demonstrated that the abrupt magnetization changes in the hysteresis loops should be attributed to the magnetic domain evolution instead of the MIR.

Hierarchical twinning and light impurity doping enable high-performance GeTe thermoelectrics

Microstructure engineering fulfilled by phase transformation elicits the reduced thermal conductivity κ in thermoelectric materials. We demonstrate that the multiscale hierarchical twinning structure could exist in the GeTe alloys as the phase transformation from cubic β-GeTe to rhombohedral α-GeTe is manipulated by two-step cooling. The coexistence of nanoscale and microscale herringbone structures yields the low-lying κ, attributing to the reorientation of martensitic variants and pile-up of martensitic twinning. Dilute dopants of Cu and Bi/Sb further suppresses hole carrier concentration nH to the order of 1020 cm−3, leading to the enhanced power factor PF = S2ρ−1 of α-GeTe. Meanwhile, the phase diagram engineering probes the solubility limit of Cu in the single-phase GeTe, diminishing the formation of undesired impurity phases. These strategies boost the peak zT value to 1.5 at 698 K in the light-doped Bi0.01Cu0.01Ge0.98Te alloy. The multiscale twin hierarchy and carrier optimization synergistically enhance the thermoelectric performance of GeTe-based alloys that provide a new chapter in search of green energy resources out from phase change materials.

Facilitation of Detwinning Through Controlling Crystal Structure in Ti-Zr-Ni-Pd High Temperature Shape Memory Alloys

Ti-(Zr, Hf)-Ni alloys, in which Zr or Hf is added to Ti-Ni shape memory alloys, are expected to be excellent high temperature shape memory alloys because they have martensitic transformation temperatures above 100°C and high strength at elevated temperatures by utilizing H-phase precipitation. However, during reorientation of martensite variants, deformation stress increases with applied strain without showing a plateau region, making it difficult to obtain a large shape recovery strain. In the martensite phase of Ti-(Zr, Hf)-Ni alloys, thin and dense (001)B19′ compound twins are introduced during the martensitic transformation, and the detwinning of martensite variants becomes difficult to occur, resulting in the increase in deformation stress during the variant reorientation. Therefore, we propose a new alloy design concept to control the crystal structure by adding a fourth element in order to facilitate detwinning. In this paper, we first consider the cause of (001)B19′ compound twinning in Ti-(Zr, Hf)-Ni alloys, and then select Pd as the fourth element to change the crystal structure for preventing the formation of (001)B19′ compound twins. Experimental investigations of the effects of alloy composition on the crystal structure, transformation temperatures, and precipitate formation realized the concept with presenting a candidate composition range of Ti-(Zr, Hf)-Pd-based alloy systems for new high temperature shape memory alloys which readily undergo detwinning.

Evolution of microstructure and crystallographic texture of Ni-Mn-Ga melt-spun ribbons exhibiting 1.15% magnetic field-induced strain

The microstructure and texture evolution of 10M Ni-Mn-Ga melt-spun ribbons were thoroughly evaluated by high-energy synchrotron radiation and electron backscatter diffraction. The as-spun ribbons were subjected to annealing treatment in order to tailor microstructure, atomic order degree, and crystallographic texture. The optimum annealing treatment at 1173 K for 72 h produced a homogenous <100> fiber texture and induced grain growth to the size that spans the entire ribbon thickness. This in turn reduced microstructural constraints for twin variant reorientation in the direction perpendicular to the ribbon surface. On the other hand, a homogenous radial microstructure ensured in-plane stress/strain compatibility giving rise to strain accommodation during variant reorientation. Particular attention was also given to the evaluation of atomic order, which to the largest extent controls the characteristic transformation temperatures. It also lowered the twinning stress to a level sufficiently low for martensitic variant reorientation under magnetic field. As a result, 1.15% magnetic field-induced strain without the aid of mechanical training in the self-accommodated state was achieved.