Fe Ga Alloys Research Articles

The role of deformation twins in recrystallization texture formation of the FeGa alloy

It has been found that at cold axial deformation of the (Fe83.4Ga16.6)99.9(NbC)0.1 alloy by hydrostatic extrusion, along with the slip processes, deformation twins are formed. The orientations of these formations in the plane perpendicular to the deformation direction coincide with the crystallographic planes {100} or {110}. It is believed that in bcc alloys, the axial deformation texture <110> is stable and undergoes only a small scattering upon recrystallization. Using the EBSD technique in this work, we have shown that the desired <100> / / DD grains can grow into a deformed <110> / / DD matrix upon primary recrystallization. At the same time, recrystallization of as-deformed samples leads to almost complete destruction of the original texture. The <100> orientation probably develops in connection with the presence of nuclei in the form of the least deformed twins, which are not observed in ordinary iron alloys. This feature of Fe-Ga alloys gives principal possibility of creating necessary cube texture and achieve a high magnetostriction value.

Formation of crystallographic texture in Fe-Ga alloys during various types of plastic deformation and primary recrystallization

The regularities of texture formation in FeGa-based alloys during deformation at medium degrees (about 60 %) and primary recrystallization were studied. Deformation was realized by two methods: rolling and hydrostatic extrusion to study the deformation behavior and the texture formation processes. After deformation, the samples were subjected to annealing to initiate primary recrystallization. The structure and texture after deformation and recrystallization were studied using EBSD technique. It was shown that FeGa-based alloys have a greater tendency to form {hkl}<100> texture during primary recrystallization, compared to other wide-used soft magnetic materials with body-centered cubic (bcc) lattice. Alloying by boron enhances this tendency and results in a uniform texture after recrystallization. As a result, a high level of functional properties was achieved through the implementation of cost-effective deformation and annealing operations.

Magnetic field effects on the corrosion and electrochemical corrosion of Fe83Ga17 alloy

FeGa alloys are competitive as new magnetostrictive materials due to their excellent comprehensive properties. These alloys are used under seawater coupled with a magnetic field; therefore, it is essential to study the effect of a magnetic field on the corrosion and electrochemical corrosion behaviors. Uniform magnetic fields of 0.15 T were applied in the tests. The corrosion tests indicated that the presence of a parallel magnetic field inhibited corrosion. Conversely, the presence of a perpendicular magnetic field promoted corrosion. These effects were attributed to the action of the magnetic field gradient force. The electrochemical corrosion tests showed that an applied parallel magnetic field enhanced the electrochemical corrosion, and the Lorentz force was responsible for these magnetic field effects.

Enhanced damping capacity of ferromagnetic Fe-Ga alloys by introducing structural defects

The irreversible motion of magnetic domain walls in ferromagnets can dissipate a large portion of the elastic energy, and the associated damping capacity is proportional to the magnetostriction constant. In contrast, here we found that the damping capacity of the large magnetostriction Fe-Ga alloys can be enhanced by 2–3 times through introducing structural defects including interfacial dislocations and stacking faults, despite that these defects deteriorate the magnetostriction. These structural defects were introduced by aging the BCC (body-centered-cubic) solution-treated precursor, for which the formation of mechanically harder FCT (face-centered-tetragonal) and /or FCC (face-centered-cubic) phases can result in high-density partial dislocations at the semi-coherent phase interfaces and quasi-periodically stacked nano-layer substructure inside the FCC variants. The structural defects act as extra damping sources besides the magnetic domain walls because the structural accommodation of the semi-coherent phase interfaces between BCC and FCT/FCC nanoprecipitates with different elastic moduli and the nano-layer substructure towards long-range ordered periodical stacking can dissipate a large portion of mechanical energy. These findings suggest that introducing structural defects provides fresh freedom to design high damping ferromagnetic materials.

Mechanical spectroscopy of atomic ordering in Fe-(16−21)Ga-RE alloys

Anelasticity of Fe-(16−21)at% Ga-RE (rare earth RE = La, Tb, Dy, Er, Yb elements) alloys at room and elevated temperatures is studied in a sub-resonance mechanical spectroscopy. Two thermally-activated and two transient effects are recorded in most of the studied alloys. To explain these phenomena, structure and phase transitions in several binary and ternary Fe-Ga alloys are investigated. The D03 ordering of rapidly cooled alloys with the A2 structure at heating at around 300 °C and the disordering at heating and the D03 ordering at cooling around 500 °C for annealed samples are proved using three in situ techniques: neutron diffraction, vibrating sample magnetometry, and internal friction and supported by positron annihilation experiments. Thermally activated transitory effects are tentatively explained by stress-induced reorientation of Ga-Ga, vacancy-vacancy pairs, and carbon atoms jumps.

Fe13Ga9 intermetallic in bcc-base Fe–Ga alloy

Fe−Ga alloys (Galfenols) are of interest due to their pronounced magnetostriction, whereby the mechanistic understanding is limited. By means of powder X-ray and neutron diffraction it is shown that as-cast Fe-38.4 at%Ga alloy consists of Fe13Ga9 intermetallic with a monoclinic Ni2In/NiAs-related structure, which coexists with bcc solid solution. By means of electron backscatter diffraction it is shown that the Fe13Ga9 intermetallic develops with two different but closely related orientation relationships with respect to the matrix, which can be derived by the relation between the atomic structures of Fe13Ga9 and the matrix. First principles calculations reveal that Fe13Ga9 should be stable at 0 K and that this phase may also expected to develop in alloys for lower Ga contents and may have to be considered upon interpreting macroscopically observed magnetostriction.

Large and sensitive magnetostriction in ferromagnetic composites with nanodispersive precipitates

Large and sensitive magnetostriction (large strain induced by small magnetic fields) is highly desired for applications of magnetostrictive materials. However, it is difficult to simultaneously improve magnetostriction and reduce the switching field because magnetostriction and the switching field are both proportional to the magnetocrystalline anisotropy. To solve this fundamental challenge, we report that introducing tetragonal nanoprecipitates into a cubic matrix can facilitate large and sensitive magnetostriction even in random polycrystals. As exhibited in a proof-of-principle reference, Fe–Ga alloys, the figure of merit—defined by the saturation magnetostriction over the magnetocrystalline anisotropy constant—can be enhanced by over 5-fold through optimum aging of the solution-treated precursor. On the one hand, the aging-induced nanodispersive face-centered tetragonal (FCT) precipitates create local tetragonal distortion of the body-centered cubic (BCC) matrix, substantially enhancing the saturation magnetostriction to be comparable to that of single crystal materials. On the other hand, these precipitates randomly couple with the matrix at the nanoscale, resulting in the collapse of net magnetocrystalline anisotropy. Our findings not only provide a simple and feasible approach to enhance the magnetostriction performance of random polycrystalline ferromagnets but also provide important insights toward understanding the mechanism of heterogeneous magnetostriction.

Dynamic precipitation and the resultant magnetostriction enhancement in [001]-oriented Fe-Ga alloys

Precipitation of dispersive nanoparticles has recently been found to yield superfunctional properties, such as the large and sensitive magnetostriction in body-centered-cubic (bcc) Fe-Ga alloys with face-centered-tetragonal (fct) nanoprecipitates, and applying this strategy to grain-aligned alloys may allow one to obtain better performance. However, the internal stress generated during directional solidification may alter the precipitation behaviors by accelerating atomic clustering, therefore, a careful analysis of the morphology of precipitates and solute partitioning is needed. Herein, we investigated the dynamic precipitation behavior in a directionally solidified Fe73Ga27 alloy with [001] orientation. Through comparisons with random polycrystalline sample subjected to the same aging treatment, we find that the [001]-oriented sample produces sparser fct nanoprecipitates and extra interfacial omega nanoprecipitates. The internal stress accelerates Ga partitioning between the fct nanoprecipitates and the matrix, hence reducing their nucleation sites. The internal stress also alters the mutual elastic interactions between matrix and precipitates, where the Bain strains of fct nanoprecipitates are mostly accommodated by forming Ga-enriched omega nanoprecipitates and {112}<111> stacking faults at the phase front, unlike that for random polycrystalline sample, where the Bain strains are accommodated by local tetragonal distortion of the matrix. As a result, the magnetostriction enhancement ratio is 40% for the grain-aligned sample, weaker than ~165 % for the random polycrystalline sample. Our results not only shed lights on the precipitation difference between stress-containing and stress-free aging conditions but also help to guide the microstructure design of superfunctional alloys in which the type, number density and size of nanoprecipitates should be carefully controlled.

Performance of Vibration Power Generators Using Single Crystal and Polycrystal Magnetic Cores of Fe–Ga Alloys

The performance of a vibration power generator using a single crystal core of Fe–Ga alloy was compared with that of a generator using a Fe–Ga alloy polycrystal core with a similar Ga concentration. When the generator using the polycrystal core was forcibly vibrated by 1-G acceleration, the vibration frequency dependence of the open-circuit voltage showed a peak with a maximum value of about 0.14 V at the first resonance frequency due to the inverse magnetostrictive effect. On the other hand, the generator using a single crystal core with a &lt;100&gt; direction parallel to the external stress direction exhibited a maximum value of about 0.26 V, about two-times larger than that of the device using the polycrystal core. Consequently, a vibration energy generator using a single crystal core of Fe–Ga alloy has advantages in performance over a generator using a polycrystal core.

Highway Implementation Test of Battery-Free Health Monitoring System Using Magnetostrictive Vibration Power Generation

In recent years, it has become a world problem that periodic inspection of aging transport infrastructures need huge costs and manpower. As a solution for it, we propose a magnetostrictive vibration power generator from vehicle-induce highway vibrations for battery-free LPWA(Low Power Wide Area) module. We investigate the magnetostrictive vibration power generator, which is suitable for power supply because it has features of simple, robust, and high output. In this paper, we applied this generator to vehicle-induced highway vibration. First, we scale up our generators for increasing output power to generate practical electric power under highway vibrations. The size of the large type generator is 150mm×60mm×50mm and 0.6kg in weight utilizing 16mm×2mm×50mm plate of iron-gallium (Fe-Ga) alloy. Then, we reproduced the highway vibrations in laboratory with simulative vibration experiment system to measure character of generator. We confirmed that it generates a peak voltage of 7V, instantaneous maximum power of 36mW, and total power 52mJ from reproduced highway vibrations for 5minutes. Finally, we tested this system in field, and succeeded in activating battery-free LPWA modules from vehicle-induced highway vibration.

超小型磁歪式振動発電デバイスと高効率電力変換回路の提案

In this study, a magnetostrictive vibrational power generator was proposed for high-frequency vibration occurring in a machine tool and high-efficiency power conversion circuit for a battery-free wireless sensor. A conventional device was miniaturized according to the scale effect, and a device composed of a Fe-Ga alloy plate, of 2×0.25×8 mm3 with a frame of 0.5 mm thickness, was fabricated and evaluated. As a result, a generated voltage of 2 V and effective power of 234 μW were confirmed at a vibration of 522 Hz and 10 m/s2. In addition, the operating principle was verified in the power conversion circuit composed of an LC circuit (resonant circuit), a diode and a storage capacitor. As a result, it was confirmed that by using a large inductance, the Q value could be increased, and a considerable amount of energy could be stored in a 330 μF capacitor.

MODELING OF MAGNETOSTRICTION IN DOPED ALLOY FeGa

In this work, we have carried out computer simulation using the density functional theory of the magnetostrictive properties of Ni and Nd modified FeGa alloy. It is shown that the experimentally observed decrease (increase) in the coefficient λ001 upon the addition of Ni (Nd) dopants is associated with an increase (decrease) in the antibonding character of the chemical bond between iron atoms in the first and second coordination spheres of the dopant atom as compared to the situation when, to enhance the magnetostrictive effect gallium was used. The electronic structure of the FeGa alloy is theoretically investigated by the methods of density functional theory. The work is aimed at explaining the difference in the change in the magnetostrictive properties of the material when using different types of alloying elements. The effect of interest is explained by the change in the nature of the chemical bond between the iron atoms of the first and second coordination spheres around the impurity atom due to the dopant. An increase in the bonding nature of the electron orbitals between these atoms leads to a decrease in the magnetostrictive effect, and its weakening leads to the opposite effect.

Morphology evolution and enhanced magnetostriction of (Fe0.81Ga0.19)99.9Tb0.1 crystals prepared by liquid metal cooling Bridgman directional solidification

Previously the magnetostriction of FeGa alloys was enhanced in melt spun ribbons due to the solid solution of trace rare earth elements. Unfortunately, applications of the ribbons are limited. Here, (Fe0.81Ga0.19)99.9Tb0.1 crystals were prepared by liquid metal cooling Bridgman directional solidification over the wide withdraw rate range of 7.2–18000 mm/h. With the increasing withdraw rate, an evolution from<001>-oriented single crystals possessing cellular morphology, to<001>-oriented polycrystals possessing dendritic morphology, and then to randomly-oriented polycrystals was observed. Simultaneously, the solid solution of trace Tb element was promoted, which was evidenced by the decrease of the Tb-rich precipitates and the strengthened magnetocrytalline anisotropy energy. As a result, the magnetostriction effect was significantly enhanced. Large magnetostriction of 390 ppm, which was 30% higher than that of binary Fe0.81Ga0.19 crystal, was realized in the<001>-oriented (Fe0.81Ga0.19)99.9Tb0.1 crystal grown at a withdraw rate of 3600 mm/h.

Influence of Ga content and high temperature annealing on the short range order and magnetostriction of Fe–Ga single crystals

Large magnetostriction observed in Fe–Ga alloys makes them a very important class of alloys for use in a wide range of actuation and sensing applications. This study of quantitative measurements of short-range order (SRO) in a series of Fe–Ga alloys provides valuable insights into the correlations of magnetostrictive responses with an increase in the Ga concentration and annealing. A quantitative assessment of SRO in the first seven shells around an atom in as-grown and high-temperature annealed [001]-oriented Fe–Ga alloy single crystals with Ga contents in the range of 5–20 at. % was carried out using the diffuse peaks in the forbidden (100) peak region of the θ–2θ high-resolution x-ray diffraction pattern. The SRO parameter values obtained indicate that very little short-range ordering occurs in Fe–Ga alloys with low Ga concentrations and ordering is limited to the first few shells. With an increase in Ga content, SRO increases with ordering occurring out to further shells. High temperature annealing decreases SRO parameters to levels approaching random solid solution. The decrease in short-range ordering with high-temperature annealing correlates with the increase in magnetostriction and confirms the hypothesis that the difference in the extent of ordering is the source of the observed high sensitivity of magnetostriction to changes in thermal history.

In-grain phase separation and structural ordering in Fe–Ga alloys seen from reciprocal space

Single crystal synchrotron diffraction was used for detailed analysis of ordering effects in alloys with a nominal composition of Fe80.5Ga19.5 and Fe73.1Ga26.9. The first composition manifests a disordered average A2 structure with local fluctuations resembling a D03 ordering motif in the lengthscales of ~50 Å. In Fe73.1Ga26.9 alloy ordered over a long range, a D03 matrix coexists with ~100 Å inclusions of a new ordered phase, presumably hexagonal with lattice parameters a ≈ 8a0 and c ≈ 12a0, where a0 = 2.87 Å is the unit cell dimension of body-centered cubic Fe.

Composition dependence of tracer diffusion coefficients in Fe–Ga alloys: A case study by a tracer-diffusion couple method

The problem of estimation of the tracer diffusion coefficients is solved by utlizing a novel radiotracer-diffusion couple technique in the absence of a suitable radioisotope of one of the components and reliable thermodynamic parameters. This is demonstrated by generating reliable and reproducible mobility data in the alloys of the Fe–Ga system with a strong composition dependence of the diffusion coefficients. Tracer- (59Fe) and inter-diffusion are simultaneously measured in three couples Fe/Fe-16 Ga, Fe/Fe-24 Ga and Fe-16 Ga/Fe-24 Ga at 1143 K in at.%). The results obtained for the couples with different end-members are in an excellent agreement with each other for the overlapping composition intervals. The influence of the molar volume on the measured tracer- (59Fe) and inter-diffusion coefficients is evaluated. Using thermodynamic calculations, the Ga tracer diffusion coefficient and the vacancy wind factor are determined via the Darken-Manning relation for the composition range of 0–24 at.% Ga. The results in this study confirm the reliability of the radiotracer-diffusion couple technique for producing highly accurate diffusion data. As a result, this helped for optimizing the mobility description of the bcc phase of the Fe–Ga system. The Ga tracer diffusion coefficients are further estimated via experimental determination of the ratio of the Fe and Ga tracer diffusivities at the Kirkendall marker planes and utilizing the Fe tracer diffusion coefficients measured directly by the radiotracer method.

Variations in the cellular magnetic domain structure in Fe–Ga alloys

The so-called cellular magnetic domain structure has been widely observed in Fe–Ga alloys of different compositions and heat treatment. It has attracted attention for producing desirable magnetic properties and also for arousing controversy over its cause and identity. Two existing models, one based on novel charge density waves and the other based on traditional V-lines from the classical magnetic domain theory, give contradictory interpretations of the cellular domains in Fe–Ga alloys, which remain to be clarified. The cellular domains observed in Fe–Ga alloys so far are highly periodic, consisting of parallel chains of rectangular cells. This paper reports on the presence of various deviations in the cellular domains from the previously known ideal periodic cellular structure in Fe–Ga alloys and explores the implications of those variations. The variations include changes in the cell shape, spacing, branching, and nesting. It is shown that the observed variations in the cellular domains can be explained well by the V-line model where the competition between elastic and wall energy drives the pattern formation process. In comparison, the disagreements of the charge density wave model with the experimental observations are addressed. Similar cellular domain variations observed previously in Fe–Si alloys are also discussed, confirming the generic aspects of the cellular domains and their variations in cubic magnetostrictive materials. The findings provide insights into the magnetic domain phenomena in Fe–Ga alloys.

Structural, magnetic and electronic properties of Fe-Ga-Tbx (0 ≤ x ≤ 1.85) alloys: Density-functional theory study

The structural, magnetic and electronic properties of Fe-Ga-Tbx (0 ≤x≤ 1.85) alloys have been studied by means of density functional theory. It was shown that the addition of Tb atoms into Fe–Ga alloy increases the lattice parameter and the magnetostriction. The largest value of tetragonal magnetostriction is observed for the composition Fe79.69Ga19.53Tb0.78 with a value of 596 ppm from the simulation. From the Density of States calcualtions, the increase in magnetostriction is attributed to the presence of nonbonding states around the Fermi level. The simulated Curie temperature of the studied compositions was in good agreement with the available experimental data.

Quantitative determination of short-range order in magnetostrictive Fe-12.5 at. % Ga alloy single crystals

FeGa alloys are an important class of magnetostrictive materials for use in actuators and sensors. Quantitative determination of short-range order is critical for a fundamental understanding of the correlation of thermal history with magnetostriction in these and other α-Fe based alloys. This paper presents quantitative assessments of short-range order (SRO) from the diffuse peaks in the high-resolution x-ray diffraction scan data of as-grown and high-temperature annealed Fe-12.5 at. % Ga alloy single crystals. The peak analyzed was the diffuse peak in the forbidden (100) peak region of the diffraction pattern of bcc Fe-12.5 at. % Ga alloy single crystals. The [001]-oriented Fe-12.5 at. % Ga alloy single crystals were obtained using the vertical Bridgman technique. To quantitatively assess SRO in these alloy single crystals, the x-ray scattering intensities obtained were converted to absolute intensity in electron scattering units. To do this, reference scans were performed on a fully dense polystyrene sample. A Python language based code was used for the analysis of short-range order, and the values for the SRO coefficients up to the seventh shell were determined. These values agree with the type of ordering indicated by (111) scans of these crystals.

Structure and Properties of Fe–Ga Alloys as Promising Materials for Electronics

This review article is devoted to studies of the structure and properties of Fe–Ga alloys that serve as functional materials with high magnetostriction. Particular attention is paid to diffraction methods that allow one both to monitor phase transformations in real time and identify phase structures and microheterogeneities in their structure. Based on the studies published in recent decades, the existing equilibrium diagrams and mechanisms of formation of elastic and anelastic properties, including magnetostriction and internal friction, are critically analyzed.