Fe Ga Alloys Research Articles

Effects of Al addition on damping and mechanical properties of Fe–Ga alloy sheet

Extremely low room temperature (RT) ductility and severe discontinuous yielding behavior is a key issue preventing the practical application of Fe–Ga based alloys as structural-functional integration materials in critical fields. Here, we report a combination of Al addition and mechanical treatment that results in RT ductility enhancement of Fe–Ga alloys without discontinuous yielding behavior, while retaining high damping capacities. It was found that the RT ductility of Fe-Ga-Al alloy sheets has a significant increase with increasing Al content and the discontinuous yielding behavior almost disappears, and the enhanced ductility is suggested to originate from the interaction of dislocations and the secondary phase. For Fe82Ga16Al2 alloy sheet, the maximal damping value can reach up to ∼0.041, and then damping capacity gradually decreases with increasing Al content but still remains at a high level. The mechanism of damping reduction is suggested to be caused by the limitation of domain wall motion caused by the additional domains generated inside the main domains. This study provides a reference for optimizing the RT ductility of Fe–Ga based alloys while taking into account the functional properties, and is beneficial for promoting the engineering applications of Fe–Ga based alloys as structural-functional integration components.

Deformation twinning caused by warm rolling and secondary recrystallization in twin-roll strip casting Fe81Ga19 alloy

In the present work, the body-centered-cubic (BCC) Fe81Ga19 alloy was produced by twin-roll strip casting technology. The following warm rolling and slow heating heat treatment (from 800 ℃ to 1200 ℃, 20 ℃/h) was successfully applied to realize the secondary recrystallization of Goss grains. The magnetostrictive coefficient of the complete secondary recrystallization sheet was ~197 ppm. Deformation twins can be observed by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) in warm-rolled sheets. An in-situ compression experiment showed that deformation twinning was related to grain orientation. The twins first formed in the grains with a higher Schmid factor and then appeared in the lower Schmid factor grains with the increase of deformation. Besides, deformation twinning can adjust the grain orientation and further activate dislocation slip. The unique Slip-Twinning-Shearing plastic deformation mechanism of BCC Fe-Ga alloy provides the possibility to overcome the intrinsic brittleness and produce sheets by rolling technology.

Magnetostrictive bulk Fe-Ga alloys prepared by selective laser melting for biodegradable implant applications

Magnetostrictive Fe-Ga alloys have received extensive attention for their good mechanical properties and low saturation magnetization. However, the magnetostriction of bulk polycrystalline Fe-Ga alloys always suffers a major setback due to random grain orientation. In this study, selective laser melting (SLM) was used for the first time to manufacture bulk polycrystalline Fe81Ga19 alloys, and different scanning paths were determined for revealing the influences on grain orientation and magnetostrictive properties. The results showed that elongated columnar grains formed in the building direction due to the epitaxial growth during SLM. For zigzag scanning, grain orientation was parallel to the building direction while tilted by ∼17° for unidirectional scanning. And annular scanning resulted in mixed grain orientations in the alloys. Moreover, Fe81Ga19 alloy with zigzag scanning exhibited 〈100〉 preferred grain orientation. Consequently, the saturated magnetostriction of bulk Fe81Ga19 alloy with zigzag scanning reached ∼77.2 ppm, representing 23.9% and 25.1% increments compared with unidirectional and annular scanning, respectively. The Fe81Ga19 alloy with zigzag scanning also presented an ultimate compressive strength of 448.6 MPa and a degradation rate of 0.09 mm/y, as well as favorable biocompatibility. These results indicated that SLM might be a potential method for manufacturing magnetostrictive bulk Fe-Ga alloys for implant applications.

Seebeck-driven transverse thermoelectric generation in on-chip devices

An unconventional approach to enhance the transverse thermopower by combining magnetic and thermoelectric materials, namely the Seebeck-driven transverse thermoelectric generation (STTG), has been proposed and demonstrated recently. Here, we improve on the previously used sample structure and achieve large transverse thermopower over 40 μV K−1 due to STTG in on-chip devices. We deposited polycrystalline Fe–Ga alloy films directly on n-type Si substrates, where Fe–Ga and Si serve as the magnetic and thermoelectric materials, respectively. Using microfabrication, contact holes were created through the SiO x layer at the top of Si to electrically connect the Fe–Ga film with the Si substrate. These thin devices with simple structure clearly exhibited enhancement of transverse thermopower due to STTG, and the obtained values agreed well with the estimation over a wide range of the size ratio between the Fe–Ga film and the Si substrate.

Achievement of large magnetostriction in [001]-textured Mn1-Ni CoSi/epoxy composites at room temperature

• Ni substitution is the most effective way to tune the metamagnetic transition. • [001]-textured composites are successfully prepared under a magnetic field of 1 T. • The best scheme to obtain good magnetostrictive behavior is given. • Large and reversible megnetostriction are obtained in the textured composites. • The compress strength is enhanced to be 60 times larger than before. As a new kind of high-magnetostriction alloy, MnCoSi shows large magnetostriction during a metamagnetic transition. However, this alloy suffers from low strength, which is caused by the cracks generated from a martensitic transformation during cooling. In this paper, we will report that curing the mixture of MnCoSi-based powders and epoxy under a magnetic field is a promising method to enhance the strength and, meanwhile, maintain good magnetostrictive property. The MnCoSi-based powders used here have a low content of Ni, which can sharply reduce the critical field needed to drive the metamagnetic transition and tune the metamagnetic transition to be second-order. Profited from this improvement, [001]-textured Mn 1- x Ni x CoSi/epoxy composites with enhanced strength and reversible magnetostriction are produced under a magnetic field of 1 T. The obtained magnetostriction is comparable to that of famous Terfenol-D and Fe-Ga alloys. Besides, the factors that can influence the texture and magnetostriction are discussed here.

A new active anti-vibration system using a magnetostrictive bimetal actuator

This paper introduces a new vibration reduction system using a magnetostrictive (Fe-Ga alloy) bimetal actuator. The proposed method (i) uses a magnetostrictive bimetal actuator instead of prevalent single material ones that need an auxiliary temperature control system and (ii) utilises a novel disturbance rejection control scheme that eliminates an unknown disturbance, without needing knowledge of its dynamics. In experiments, the vibration source is demonstrated as an unbalanced motor attached to the tip of a cantilever beam, resembling a beam-like element subject to ambiance vibrations. In the first step, the fundamental of this anti-vibration system is introduced and described. Then, analytical and data-driven modelling for the combination of the beam, the motor, and the bimetal is reported. These follow by model validation and impulse response analysis. Then, the proposed control system is introduced in detail. Experimental results indicate that the control system results in 33.6% decrease in beam vibration amplitude. Furthermore, the presented method in this paper can be employed as a design guideline for future applications.

Characteristic Twin Formation in Body-centered Cubic Fe–Ga Alloy Single Crystals with Different Orientations

Characteristic Twin Formation in Body-centered Cubic Fe–Ga Alloy Single Crystals with Different Orientations

Modeling and Design of Resonant Magnetic Field Sensors in the Scheme of Differential Magnetostrictive Actuation With Compact Bias Magnetic Circuit

A type of differential resonant magnetic field sensor is developed by employing the composite elements of FeGa plates, piezoelectric quartz crystal double-ended tuning forks (DETFs) and bias permanent magnets. The model and analysis show that the differential design brings the benefits of doubled sensitivity, increased linearity and low temperature drift. Importantly, a small and compact magnetic circuit containing a pair of permanent magnets and dual FeGa plates ensures the generation of differential actuation, which not only reduces the leakage flux but also improve the field-sensitivity and resolution. The magnetic circuit model based on the “lumped parameters” method is established. As an important aid, the distribution of magnetic flux density along the longitudinal direction of the FeGa alloy is simulated by finite element analysis software. In order to avoid the prediction error caused by parameter errors, simulations in different conditions are carried out for comparative analysis. This method ensures the magnetic circuit provides qualified magnetic field. The experimental results show that the differential resonant magnetic field sensor with frequency readout has the characteristics of high sensitivity of 4.4 Hz/Oe, high resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${&lt; }3.04\times 10^{-4}$ </tex-math></inline-formula> Oe, low temperature drift and excellent linear (non-linearity error of 1.3%FS) and low hysteresis (1.5%FS) over its measurement full scale (FS) of ±100Oe.

Performance of Fe–Ga alloy rotational vibration energy harvester with centrifugal softening

With the development of vibration energy harvesting, sensor nodes for wireless monitoring are being increasingly powered by harvesting vibrations in rotating environments such as car tires and fan blades. Considering the diverse installation positions of vibration energy harvesters on rotating carriers, the centrifugal forces of the cantilever beams exhibit remarkable differences during rotation. Crucial factors for the performance of vibration energy harvesting include the deformation of the harvester cantilever beam, which is affected by the centrifugal force, and the influence of the pre-magnetization field on the Villari effect of specific alloys. We propose a rotational vibration energy harvester based on an Fe–Ga alloy and establish a mathematical model for magnetostrictive vibration energy harvesting by leveraging centrifugal softening. In addition, we perform a systematic theoretical analysis of the factors influencing the harvester performance considering centrifugal softening, rotation radius, and arrangement of the pre-magnetization field. The theoretical findings are verified on a prototype, and the system characteristics are investigated experimentally. The maximum output voltage reaches 3.36 V, and the energy harvesting efficiency reaches 22.86% when the harvester undergoes rotation at 330 r min−1. Moreover, the harvester is applied in a low-power temperature sensor for real-time temperature monitoring, indicating the validity and applicability of the proposed rotational vibration energy harvester. The results demonstrate that an appropriate use of the centrifugal softening and the pre-magnetization field can enhance the energy harvesting efficiency of a harvester operating at a low rotational frequency.

Structure and texture in rolled Fe82Ga18 and (Fe82Ga18)99B1 alloys after annealing under high magnetic field

The structure and crystallographic texture formation processes in two Fe–Ga magnetostrictive alloys during annealing of deformed samples under high magnetic field (HMF) 20 T have been studied. It was shown that the effect of the magnetic field on the structure transformation during annealing depends on the features of the recrystallization in alloys. In the case of recrystallization in a single-phase binary Fe-Ga alloy, the application of HMF along the rolling direction promotes the formation of <100> grains along this direction. This leads to a twofold increase in the magnetostriction of the polycrystalline sample. In the same alloy, but with the presence of particles of the second phase, HMF does not affect the texture. The reasons for this phenomenon were discussed. In addition, it was found that in both alloys, the application of HMF during annealing retards the processes of structure evolution.

Temperature-Induced Phase Transitions of Fe-Ga Alloys for Sensors

Slow cooled arc melted Fe-Ga alloys with different compositions were characterized. GI-XRD confirms the BCC structure and existence of single phase A2 in 17 at.% of Ga and multiphase A2 and L12 in 30 at. % of Ga. The Ga defects migrates during annealing and reduces the lattice. The Galfenol alloy with the 30 at.% of Ga has an A2 phase around 400 oC and an L12 phase around 560 oC. The formation of the L12 structure is due to an exposure in high temperature region. The magnetostriction of Fe83 - Ga17 and Fe70 - Ga30 alloys seems to be 64 and 27 ppm. Decrement of magnetostriction is due to change in anisotropy coefficient.

A High-Sensitivity Resonant Magnetic Sensor Based on Graphene Nanomechanical Resonator.

This paper presents a novel resonant magnetic sensor consisting of a graphene nanomechanical oscillator and magnetostrictive stress coupling structure, using Si/SiO2 substrate and Fe–Ga alloy, respectively. In this device, the deformation of the Fe–Ga alloy resulting from the external magnetic field changed the surface tension of the graphene, resulting in a significant change in the resonance frequency of graphene. Using the finite element analysis, it could be found that the response of the resonance frequency revealed a good linear relationship with the external magnetic field (along the x-axis) in the range of the 1 to 1.6 mT. By optimizing the sizes of each component of the magnetic sensor, such as the thickness of the Si/SiO2 substrate and the Fe–Ga alloy, and the length of the graphene, the sensitivity could even reach 834 kHz/mT, which is three orders of magnitude higher than conventional resonant magnetic devices. This provides a new method for highly sensitive and miniaturized magnetic sensors.

Low-temperature metastable-to-equilibrium phase transitions in Fe–Ga alloys

Significant differences between the properties of Fe–Ga alloys (Galfenols) in their metastable and equilibrium states, as well as discrepancies between existing Fe–Ga phase diagrams and for the transition rates for the metastable to equilibrium state have been detected and discussed. In view of both the fundamental understanding and the technological importance of these alloys, the exact knowledge of the equilibrium phase diagram, metastable phases, and the transition rates between different phase states towards equilibrium are necessary and require further clarification. We have studied the influence of alloy composition, annealing temperature and annealing time (up to 1800 h) on the metastable-to-equilibrium phase transitions in binary Fe–Ga using a coherent set of complementing methods, including diffraction methods (X-ray and neutron diffraction), scanning electron microscopy, and electron backscatter diffraction. We propose several important changes to the low-temperature part of the binary Fe–Ga diagram close to the Fe-rich corner and a new method based on interdiffusion couples for varying the structure and phase states of Fe–Ga alloys.

EMF study of liquid Al–Fe–Ge alloys

Abstract The thermodynamic properties of ternary liquid Al–Fe–Ge alloys have been studied in the temperature range of 1050 – 1250 K by the electromotive force (EMF) technique with a liquid electrolyte. The ternary alloys are characterized by negative deviations from Raoult’s law.

Enthalpies of mixing of liquid Al–Fe–Ge alloys

Abstract The partial and integral enthalpies of mixing of Al–Fe–Ge melts have been measured by high-temperature calorimetry at 1740 ± 5 K. The integral enthalpies of mixing at 1173 K, are about 4 to 6 kJ mol–1 less negative than determined by electromotive force measurement [9]. The integral enthalpies of mixing have been also estimated on the basis of the Bonnier geometric model. The calculated values show a reasonable agreement with experimental data for x Ge &gt; 0.3. A difference between experimental and estimated integral enthalpies of mixing (up to 2.5 kJ mol–1) is observed for ternary alloys with low germanium content.

Atomic scale understanding of Kurdyumov-Sachs path during BCC to FCC phase transformation in iron-gallium alloy

The Kurdyumov and Sachs (K-S) orientation relationship between body-centered-cubic (bcc) and face-centered-cubic (fcc) phases has been observed in numerous systems undergone displacive component-involved phase transformations. However, the atomic level evidence for its theoretical path containing two steps of lattice shear is still rare. In this work, we provided an atomic-scale understanding of the K-S path by capturing the early-stage phase transformation from bcc to fcc via a coupled diffusional-displacive mechanism in an aged Fe72Ga28 alloy. Nano-embryonic product phases are directly observed, formed firstly by one lattice shear of (211¯)-bcc planes along [1¯11¯]-bcc direction and further lattice shear of the (011)-bcc planes along [1¯1¯2]-fcc direction. The thermally-activated atomic diffusions are involved in the formation of equilibrium fcc phase. These results may not only help to understand the diverse phase transformations in Fe-Ga alloys, but also add atomistic insights towards the solid-state transformation mechanism between bcc and fcc phases.

Mechanism of High Magnetic Field Effect on the D03-L12 Phase Transition in Fe-Ga Alloys

Mechanism of High Magnetic Field Effect on the D03-L12 Phase Transition in Fe-Ga Alloys

Electronic structure modification and negative magnetostriction in Fe-Ga alloy of D03 structure with Ga content variation

The influence of a change in the Ga content on the magnetostrictive properties of the Fe3Ga alloy with the D03 structure has been studied by density functional theory methods. The change in the stoichiometry of the alloy under study was carried out by replacing the Fe atoms with Ga. The replacement leads to a significant change in the electronic structure of the systems under study, which leads to a significant increase in the density of electronic states near the Fermi level. This effect leads to an increase in the magnetoelastic energy, which leads to an increase in the value of the magnetostrictive coefficient λ001. A further increase in λ001 occurs due to a decrease in the shear modulus, which occurs due to an increase in the number of loosening bonds in the system with an increase in the Ga content. The resulting dependence of λ001 on the Ga content, although they show an increase in the absolute value of the coefficient λ001, but give its negative values, in contrast to the positive value of magnetostriction observed in the experiment. Solving the problem of matching the sign of the theoretical and experimental values of the magnetostrictive coefficients requires further research.

Electronic Properties and Magnetostriction in Fe-Ga Alloy of D03 Structure

Electronic Properties and Magnetostriction in Fe-Ga Alloy of D03 Structure

Structure and Texture Formation in Rolled Fe-Ga Alloys During Annealing Under a High Magnetic Field

Structure and Texture Formation in Rolled Fe-Ga Alloys During Annealing Under a High Magnetic Field