Iron-gallium Alloys Research Articles

Magnetic property-texture relationships in galfenol rolled sheet stacks

Recent results in the area of galfenol (iron-gallium) alloy rolled sheet have yielded significant Goss ({110}<001>∥ rolling direction [RD]) texture development and large strain values, > 250 ppm. Goss-textured grain growth is promoted by the use of a grain boundary pinning second-phase particle. After multistage rolling and subsequent heat treatment, Goss grain areas as large as 125 cm2 develop in the RD–transverse direction (TD) plane. Goss grain <100> directions are typically within 15° of the RD inside these grains. Fully processed sheets were sectioned and bonded together to produce laminated stacks. Grain oriented and nongrain oriented stacks were characterized magnetically. Plotting strain data against H-field for both an Oriented Stack (OS) and a Nonoriented Stack (NonOS) yielded saturation stain values of 215 ppm and 70 ppm, at 48.3 MPa prestress, respectively. Magnetostrictive strain coefficient, d33, values of 20 nm/A and 4 nm/A were calculated for the OS and NonOS, respectively. Saturation magnetization values were found to be 1.3 T and 1.2 T for the OS and NonOS. Electron Backscatter Diffraction (EBSD) analysis was performed on cross sections of each laminated stack. EBSD mapping showed a large relative disparity in average grain size, taken from cross sections, of 470 μm and 84 μm for the OS and NonOS. Pole figures, contoured at a half-width of 10°, were analyzed and clearly show a high degree of Goss texture in the OS and a lack of any strong texture in the NonOS. The OS generated a maximum Multiple of Mean Uniform Density value > 16 while the NonOS produced a value < 2.

Evaluation of a miniature magnetostrictive actuator using Galfenol under tensile stress

We are, at present, developing miniature actuators using an iron–gallium alloy (Galfenol). Galfenol is an iron-based magnetostrictive material with magnetostriction exceeding 200 ppm, Young's modulus of 70 GPa and a high relative permeability (>100). The advantages of an actuator using this material are capability of miniaturization, stability against external force, low voltage driving and high power. In this study, a miniature vibrator using an E core of Galfenol under tensile stress up to 20 MPa was investigated. The vibrator did not fracture and maintained the magnetostriction even under a high tensile stress. In addition, the resonance frequency, unchanged under the tensile stress, was lower than the cutoff frequency, hence the vibrator can be driven with a low voltage even in resonance driving. The temperature rise in resonance driving was low and creep was not observed in resonance driving under tensile stress. The vibrator will be applicable in flat panel or bone conductive speakers.

Study on Micro-energy Harvesting Device Using Iron-Gallium Alloy

We propose a micro-energy harvesting device using an iron gallium alloy (Galfenol) that is capable of providing electrical energy through environmental vibrations. Galfenol is a ductile magnetostrictive material with high piezomagnetic constant, good machinability, and a large inverse magnetostrictive effect in which the magnetization can be varied by mechanical stress. The proposed device consists of two columns of Galfenol those ends are connected at the end with iron yokes, coils and a bias magnet. When bending force is applied on the mover with the other end fixed like a cantilever, the magnetization in one column increases because of tensile force due to the inverse magnetostrictive effect, and the other decreases due to compression. The time variation of the magnetization generates voltage on the wound coils. This energy harvesting device is advantageous over other types such as those using piezoelectric material, in size, high robustness, and low electrical impedance. In addition, the two columns structure requires low mechanical force to provide sufficient stress to change the magnetization. We fabricated a prototype using stress-annealed Galfenol with 314 coil turns and in experiments verified a maximum voltage of 0.48 V at forced vibration with a frequency of 333 Hz. The frequency response was also measured to understand the behavior at resonances of the 1st and 2nd bending modes as well as the effect of additional weight.

Understanding of large auxetic properties of iron-gallium and iron-aluminum alloys

Large auxetic properties of iron-gallium and iron-aluminum alloys have been investigated with both theoretical and experimental approaches. Tensile tests of single-crystal iron-gallium alloys with compositions of 12%–25% gallium were conducted to determine the composition dependent values of the Poisson’s ratio. Systematic density functional calculations revealed a simple correlation between the Poisson’s ratio and tetragonal shear modulus. We attribute the auxetic properties of these intermetallic alloys to the drastic reduction in C′ with the presence of metalloid atoms in the DO3-type structures.

Magnetostriction and Magnetic Heterogeneities in Iron-Gallium

Iron-gallium alloys Fe(1-x)Ga(x) exhibit an exceptional increase in magnetostriction with gallium content. We present small-angle neutron scattering investigations on a Fe(0.81)Ga(0.19) single crystal. We uncover heterogeneities with an average spacing of 15 nm and with magnetizations distinct from the matrix. The moments in and around the heterogeneities are observed to reorient with an applied magnetic field or mechanical strain. We discuss the possible roles played by nanoscale magnetic heterogeneities in the mechanism for magnetostriction in this material.

Primary Analysis of Frequency Characteristics in a Miniature Self-Propelling Device Using Fe-Ga Alloys (Galfenol)

The present paper describes the theoretical analyses, design and experimental verification of a magnetostrictive actuating device, the locomotion of which is inspired by the motion of the smooth impact drive mechanism reported previously by a number of researches of our group. The proposed device is different from the reported device driven by a piezoelectric actuator. The proposed device is actuated by a micro magnetostrictive actuator constructed using an iron-gallium alloy. The proposed magnetostrictive actuating device is an interesting linear-moving mechanism and takes advantage of impact forces coupled with friction forces to achieve a long stroke with fine position resolution. The results of experiments indicate that the maximum speed of the prototype is approximately 1.0 mm/s at a current of 300 mA with a frequency of 4 kHz.

Rigid band model for prediction of magnetostriction of iron-gallium alloys

Using the highly precise full potential linearized augmented plane wave method, we determined atomic structure and the magnetostriction of Fe100−xGax with x<19%. It is demonstrated that the extraordinary enhancement of magnetostrictive coefficient of Fe100−xGax at low concentration stems from intrinsic electronic origins. Moreover, we recognized the potential of using a rigid band model for the prediction of magnetostriction of intermetallic alloys, through studies of ternary alloys with Zn substitution into Fe87.5Ga12.5.

Stress and magnetic field-dependent Young's modulus in single crystal iron–gallium alloys

The variability in Young's modulus of single crystal iron–gallium (Galfenol) alloys having 16, 17.5, 19, 24.7 and 29 at% gallium is investigated using experiments and simulations. Some of these alloys showed more than 60% change in Young's modulus along the 〈1 0 0〉 directions on varying their magnetization and stress states compared to their modulus at magnetic saturation. A function, Δ E( σ, H), is defined such that the variability of modulus is bound between 0% and 100%. The observations are related to the inherent magnetomechanical coupling in the material. An energy-based non-linear constitutive model is used to predict the variable modulus in Galfenol as a continuous function of stress and magnetic field. Model predictions showed good correlation with experimental results.

Translatory and Bending Micro Magnetostrictive Actuator using Iron–Gallium Alloys (Galfenol): A New Actuation Approach for Microrobots

There is strong demand for microactuators in medical and industrial fields. For example, minimally invasive surgery has been progressing, and a series of microactuators useful for positioning, grasping and cutting in a narrow space are required. For this purpose, we are investigating micro magnetostrictive actuators using iron–gallium alloy (Galfenol). Galfenol is an iron-based magnetostrictive material with magnetostriction greater than 200 p.p.m., a high relative permeability μ r greater than 100 and a Young's modulus of around 70 GPa. This material is machinable by conventional cutting techniques, and can operate under tensile, bending and impact loads without any degradation in performance. Therefore, a microactuator using Galfenol has advantages over conventional actuators such as electrical motors and piezoelectric actuators in terms of design simplicity, low drive voltage requirements and high robustness. In this paper, we describe two types of actuators consisting of a U-shape core of Galfenol — one providing 1 longitudinal d.o.f. and 2-d.o.f. bending deformation, and the other propelling by a friction drive. These actuators are simple and small, and easily integrated into actuation parts of microrobots.

The Effect of Field Annealing on Highly Textured Polycrystalline Galfenol Strips

Iron-Gallium alloys (Galfenol) possess a body centered cubic (BCC) alpha-Fe structure with the gallium atoms substituted throughout the lattice structure. Polycrystalline metals are often isotropic due to their overall random crystallographic orientation, however single crystal and strongly textured polycrystalline BCC metals exhibit a high degree of anisotropy in their physical characteristics. Galfenol has an anisotropic magnetostriction with the maximum performance achieved in the lang100rang direction. Previous field annealing experiments on polycrystalline Galfenol strips have shown a great disparity in the results. This paper uses EBSD to examine the influence of crystal orientation of grains on magnetostriction under various stresses to determine if the disparity is due to the number and/or orientation of the crystals comprising the strip. The saturation magnetostrictions and elastic moduli for each grain are predicted based on the crystal angle measured using EBSD, and the averaged maximum magnetostriction for each sample is calculated with the force balanced between each grain in a sample. The experimental saturation magnetostrictions at 700 Oe agree well with the calculated results. The highest built-in uniaxial anisotropy after magnetic annealing is about 1 kJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and all the samples in this study showed performance improvement after field annealing.

Figures of merit of magnetostrictive single crystal iron–gallium alloys for actuator and sensor applications

Energy density, magnetomechanical coupling factor and a dimensionless sensing gage factor of 〈1 0 0〉 oriented single crystal iron–gallium alloys with 16, 17.5, 19, 24.7 and 29 at% gallium were studied as functions of stress and magnetic field. To estimate these quantities, the samples were characterized under different quasi-static stress and magnetic field conditions. The experimental behavior was modeled using an energy-based non-linear approach. Both the experimental data and the model simulations were used to calculate material parameters such as magnetic permeability, piezo-magnetic strain coefficient ( d 33), inverse piezo-magnetic coefficient (stress sensitivity, d* 33) and Young's modulus in the material. These quantities were used to obtain energy density, magnetomechanical coupling factor and sensing gage factor as functions of magnetomechanical conditions. Maximum energy density of around 3 kJ/m 3, magnetomechanical coupling factor higher than 0.75 and sensing gage factor on the order of 10 3 were calculated.

Miniature spherical motor using iron–gallium alloy (Galfenol)

We propose a miniature spherical motor using iron–gallium alloy (Galfenol). This motor consists of four rods of Galfenol with square cross-section, a wound coil, a permanent magnet, an iron yoke and a spherical rotor placed on the edge of the rods. The magnetomotive force of the magnet provides bias magnetostriction for the rods and an attractive force that maintains the rotor on the rods. When currents of 180° phase difference flow in pairs of opposing coils, a torque is exerted on the rotor by pushing (expansion) and pulling (contraction) of the rods. Rotation about a single axis is realized by a sawtooth current, such that the rotor rotates with slow expansion and slips at the rapid contraction. The motor can be fabricated at small sizes and driven with a low voltage, suitable for application as a microactuator for rotating the camera and mirror in endoscopes.

Effect of B and Cr on Mechanical Properties and Magnetostriction of Iron-Gallium Alloy

Effects of B and Cr additions on magnetostriction and the mechanical properties ofpolycrystalline Fe 83 Ga 17 alloy were investigated. Small addition of B increased magnetostriction of Fe 83 Ga 17 alloy slightly, and improved the room temperature ductility and tensile strength significantly. The elongation and tensile strength of the (Fe 83 Ga 17 ) 99 B 1 alloy increased to 3.56% and 548 MPa compared with that of Fe 83 Ga 17 alloy respectively. The Cr addition was shown to improve the room temperature mechanical properties of Fe 83 Ga 17 alloy beneficially. The maximum magnetostriction of (Fe 83 Ga 17 ) 98 Cr 2 alloy was 70 x 10 -6 . The influences of B and Cr additions on the fracture mode of Fe 83 Ga 17 alloy were also studied in this paper.

Magnetic domains in magnetostrictive Fe–Ga alloys

Lorentz microscopy was applied to the observation of magnetic domains in iron-gallium (Fe–Ga) alloys. Results did not show any link between the magnetic domains and the magnetostriction enhancement by Ga addition, but did reveal that the drastic decrease in magnetostriction for Fe–31.2 at. % Ga was due to the presence of large scale precipitates. Magnetic domain features did not change in the alloys of A2, D03, A2+D03, A2+B2+D03, and A2+fine scale precipitates. Large scale precipitates within the slow-cooled Fe–31.2 at. % Ga affected both the distribution and wall motion of magnetic domains.

Two-DOF Micro Magnetostrictive Bending Actuator for Wobbling Motion

We propose a two-DOF micro bending actuator using Iron-Gallium alloy (Galfenol). The actuator consists of two parallel beam structures using Galfenol core, square rod of 1-mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area and 11-mm length with ditches of 0.3-mm width. The beams in the core are wound coils and bonded to an iron end cap to construct close magnetic circuit. The orthogonal parallel beams which the push-pull elongation prebiased by permanent magnets provide bending deformation in two directions, X and Y. The advantages of the actuator are simple and rigid configuration generating high force and the identical first bending resonance frequencies of X, Y inherited form the symmetric structure. The displacement, linear round zero current, was observed varied from -15 to 15 mum at both directions. The wobbling motion with amplified displacement around resonance frequencies was also demonstrated. The actuator driven by small power supply will be applicable for cutting or drilling device for, e.g., minimally invasive surgery.

Micro-magnetostrictive vibrator using iron–gallium alloy

A micro-magnetostrictive vibrator using an iron–gallium alloy (Galfenol) drive element was investigated. Galfenol is an iron-based magnetostrictive material with magnetostrictions greater than 200 ppm, a high relative permeability μ r > 70 and a Young’s modulus of ∼70 GPa. This material is machinable by conventional cutting techniques, and can operate under tensile, bending, and impact loads without degradation in performance. A micro-actuator using Galfenol, therefore, has advantages over a PZT type actuator in design simplicity, low drive voltage requirements, high robustness, and a wide temperature operating range. This paper describes the design, fabrication process, and performance of a micro-vibrator which utilizes either an un-annealed or stress-annealed Galfenol pin as the drive element. A displacement of 1.2 μm was observed with a high bandwidth of 30 kHz and a high tensile robustness withstanding a suspended weight of 500 g (6 MPa). The vibrator was also verified to be useful as a speaker which can generate clear sound from the power of a portable music player.

Analysis of the effect of gallium content on the magnetomechanical behavior ofsingle-crystal FeGa alloys using an energy-based model

The magnetomechanical behavior of single-crystal iron–gallium alloys with varying galliumcontent was found to be strongly dependent on the Ga content (Atulasimha 2006 PhD Thesis).An energy-based model (Atulasimha 2006 PhD Thesis, Armstrong and William 1997 J.Appl. Phys. 81 2321) is employed to simulate the strikingly different actuation behavior(λ–H and B–H curves under different compressive stresses) and validated against experimental data for19, 24.7 and 29 at.% Ga, [100] oriented, slow-cooled single-crystal FeGa alloys.The effect of gallium content on the model parameters, specifically the cubicmagnetocrystalline anisotropy constants and the Armstrong-smoothing factorΩ, their physical significance and ultimately their effect on the magnetomechanical behaviorare analyzed and explained.

The effect of magnetic field annealing on single crystal iron gallium alloy

In this study, we investigate magnetic field annealing of Fe82.5Ga17.5 single crystal disks with two easy axes ([100] and [010]) in the plane of the disk. Magnetic annealing was conducted with a high magnetic field (H&amp;gt;12kOe) applied along the [100] or [010] easy axes of the demagnetized, as-grown, slow-cooled sample. Strain measurements were recorded both before and after the magnetic annealing of the samples from a demagnetized state. After each annealing protocol, the resultant built-in uniaxial anisotropy constants were measured using torque magnetometry and also using an approach that calculates anisotropy based on magnetization curves. The built-in anisotropy constant after magnetic annealing strongly depends on annealing protocol. The calculated anisotropy constants determined for each sample show consistent trends for each annealing condition using the two different anisotropy measurement methods. The maximum uniaxial anisotropy constant was 4.24kJ∕m3 and the built-in effective prestress was −19.9MPa after field annealing.

Micromagnetostrictive vibrator using a U-shaped core of iron-gallium alloy (Galfenol)

A micromagnetostrictive vibrator using a U-shaped core made of iron-gallium alloy (Galfenol) was investigated. The vibrator consists of a Galfenol core, with a 1mm2 cross section, a length of 5.8mm, and a 0.3mm separation between the prongs of the “U,” driving coils, and an iron yoke to close the magnetic loop. The Galfenol vibrator is superior to the PZT type in its high mechanical strength, low drive voltage requirements, and wide temperature operating range, and compared to our previous cylindrical type vibrator has a simpler construction and higher bandwidth. A displacement of 1.2μm (220ppm) was verified for the prototype with a 5.8mm long Galfenol core; the high magnetostriction &amp;gt;200ppm is inherited from the stress-annealed Galfenol. The displacement was also maintained under a 21MPa tensile stress (1.5kg hanging weight). Incorporation of a Nd–B–Fe magnet into the magnetic circuit successfully shifted the operating point to the linear portion of the magnetostrictive curves. This biasing effect is useful in reducing the drive voltage.

Energy-based quasi-static modeling of the actuation and sensing behavior of single-crystal iron-gallium alloys

An energy based model [W. D. Armstrong, J. Appl. Phys. 81, 2321 (1997); J. Atulasimha, Ph.D. thesis, Aerospace Engineering, University of Maryland, College Park, MD, 2006] is employed to predict the actuation (λ−H and B−H at various compressive stresses) and sensing behavior (B−σ and ε−σ at various bias fields) of single-crystal FeGa alloys. The significant feature of this formulation is that, in addition to modeling actuation behavior, the sensing behavior can be predicted based on parameters estimated from the actuator characteristics. These predictions are then validated against experimental data for furnace cooled 19 at. % [100] oriented single-crystal FeGa alloys. Furthermore, an attempt is made to couple the energy-based sensing model with a lumped-parameter model that simulates the magnetic interaction between the magnetostrictive specimen and the magnetic circuit comprising the transducer. This enables a prediction of the variation in field through the sample due to changes in reluctance of the magnetostrictive sample with stress, as well as the impact of this variation in field on the B−σ and ε−σ curves. These predictions are benchmarked against experimental data, wherein the bias field varies due to change in sample reluctance with application of compressive stress while the drive current to the transducer is maintained constant.