Fe Ga Alloys Research Articles

Enhancement of magnetostriction in laser powder bed fusion Fe-Ga alloy by texture formation

Magnetostrictive Fe–Ga alloys have received much attention in sensing and harvesting applications owing to their outstanding mechanical and magnetostrictive properties. The largest magnetostriction in Fe–Ga is found along the <100> direction. Utilising additive manufacturing (AM) for preparation of Fe–Ga will expand the potential to manufacture complex shapes and geometries, if the strong <100> texture is formed. This study investigated the saturation magnetostriction of a polycrystalline Fe–Ga alloy prepared by laser powder bed fusion (L-PBF) under controlled processing parameters. The results revealed that the combination of a narrow hatch space and laser remelting treatment significantly enhances the apparent magnetostriction of the L-PBF Fe–Ga alloy. Notably, at a hatch space of 40 μm, the highest saturation magnetostriction is around 70 ppm. This value is almost three times higher than that of a polycrystalline Fe–Ga alloy with the same chemical composition where grains are randomly oriented.

Role of structural ordering on magnetostrictive property of Fe-Ga alloys

Role of structural ordering on magnetostrictive property of Fe-Ga alloys

Enhancing magnetostriction in FeAl alloys via crystal growth orientation tuning by a trace amount of Pt doping

Iron-based cubic alloy systems opened the door to the development of magnetostrictive materials with moderate magnetostriction, low cost, and good mechanical properties. At the as-cast state, the grain growth orientation of these alloy systems is close to random, which deteriorates magnetostriction. Doping with certain elements can tune the growth orientation to enhance magnetostriction. However, the driving force for the crystal growth along preferential orientation is still not clear. Here in this work, revealed by density functional theory (DFT) calculation, Pt doping can tune the crystal growth direction of FeAl along <100> crystal direction (same as easy magnetization direction), which can be utilized to realize 90° domain-switching and thus magnetostriction is enhanced greatly. These are confirmed by experimental results. The magnetostriction increases from 29 ppm to 80 ppm, representing a 176% enhancement through doping with 0.4 at.% Pt. The maze magnetic domain structures, observed by magnetic force microscope, are also preferentially <100> oriented and feature stripes. In consideration of the similarity between this study and our previous study on FeGa alloy (C. Zhou et al., 2020), it can be expected that our methods can be extended to other magnetostrictive materials and help develop polycrystals with desired orientations.

Order-disorder phase transitions in Fe81Ga19-RE ALLOYS (RE = Dy, Er, Tb, Yb) according to neutron diffraction data

New data on the phase compositions and structural transformations in a number of Fe81Ga19 alloys doped with trace amount (≤ 0.2 at.%) of rare earth elements are presented. The data are obtained in neutron diffraction experiments performed with high resolution and in continuous temperature scanning mode when heated to 900 °C and subsequent cooling. It has been established that structural rearrangements proceed in a generally identical manner both in the original Fe81Ga19 alloy and in its doped analogues. Slow heating and subsequent cooling of the alloys (rate ±2 °C/min) leads to the formation of clusters of the D03 phase with sizes in the range (200–300) Å in the matrix of the disordered A2 phase. The sizes and volume fraction of clusters (~0.3 of the sample volume) weakly depend on the specific composition. The degree of ordering of the clusters atomic structure changes with temperature according to a second-order phase transition and is close to unity at room temperature. The search for structural ordering corresponding to the modified D03 phase, discovered in a number of electron diffraction studies, did not lead to a positive result.

Specific of mechanical alloying of solid-liquid binary system Fe-Ga and effect of different process control agents

Mechanical alloying allows obtaining nonequilibrium structures in various systems, often possessing unique properties, including magnetic ones. Considering the unusual structural features of the magnetostrictive Fe-Ga alloy, this approach may be promising for this system. In this work, extensive experimental studies were carried out aimed at studying the features of mechanical alloying of Fe-Ga. The object of the study was the system Fe-20 wt% Ga in which disordered solid solution α-Fe(Ga) is formed. It was shown that high-intensity milling is an effective tool for mechanical alloying of solid-liquid binary system Fe-Ga, but a serious problem is a low powder recovery, less than 50 %. To solve this problem, various process control agents were tested. Their influence on powder recovery, process kinetics, particle size, carbon contamination, and magnetic properties was studied using a large set of techniques such as XRD, SEM, EDS, VSM, LIBS, and others. It has been shown that, based on a combination of factors, the optimal process control agent for this system is ethanol in an amount of 1 wt%

Magnetization and phase transformation in Fe-Ga and Fe-Ge alloys

The magnetic properties and structural states of Fe-Ga and Fe-Ge alloys, known for their large magnetostriction, have been investigated. Experimental characterizations are supported by ab initio calculations and Monte Carlo simulations to reveal the complex interplay between magnetic properties and structural changes. Our findings are in agreement with previous investigations and show that the Curie temperature (TC) of these alloys changes gradually with increasing alloying element concentration while the A2 solid solution is being realized. Further alloying of Fe-Ga leads to the transition from a single-phase to a two-phase A2 + D03 state and results in two distinct TC values. At the same time Fe-Ge shows a more complex behavior with several phase transitions influencing the magnetic ordering temperatures. Theoretical calculations suggest a significant correlation between the magnetic moments, exchange interactions, and observed TC trends. It is shown that the D03 phase is characterized by the lowest TC among other phases. Using Monte Carlo simulations, we found that in ferromagnetic state of Fe-Ge alloy the D03 ordering develops homogeneously, while in Fe-Ga it follows a nucleation and growth scenario.

Tetragonal phases in Fe-Ga alloys: A quantitative study

Tetragonal phases in Fe-Ga alloys: A quantitative study

Magnetostrictive strain-sensitivity synergy for laser-beam powder bed fusion processed Fe81Ga19 alloys by magnetic field annealing

Magnetostrictive Fe–Ga alloys have been demonstrated potentialities for numerous applications, whereas, suffering a tradeoff between large magnetostrictive strain and high sensitivity. Herein, bulk polycrystalline Fe81Ga19 alloys were prepared by laser-beam powder bed fusion (LPBF) and then annealed in magnetic field for manipulating the comprehensive magnetostrictive properties. Results indicate that <001> oriented grains are developed in the LPBF-prepared Fe81Ga19 alloys due to high temperature gradient. After magnetic field annealing (MFA), the magnetic domains within the alloys gradually transformed into well-arranged stripe domains, especially, flat and smooth 90° domains were established in the alloys annealed at 2600 ​Oe. As a result, the induced <001> orientation grains and 90° domains contributed to an improved effective magnetic anisotropy constant (57.053 ​kJ/m3), leading to an enhanced magnetostrictive strain of 92 ​ppm. Moreover, the MFA-treated alloys also displayed enhanced magnetostrictive sensitivity (0.097 ​ppm/Oe) owing to the smooth domain structures and low dislocation densities, demonstrating a fruitful strain-sensitivity synergy. In addition, good magnetostrictive dynamic response and enhanced compressive yield strength were also observed for the prepared alloys. This work demonstrates that LPBF and MFA might be an attractive strategy to resolve the tradeoff between strain and sensitivity, providing a basis for the preparation of high-performance magnetostrictive materials.

Short-Range Order in Gallium Solid Solutions in α-Iron

Short-range order in soft magnetic FeGa alloys containing from 3 to 25 at % Ga was studied using nuclear gamma resonance (Mössbauer) spectroscopy. The Mössbauer spectra were analyzed via fitting with subspectra corresponding to different configurations of the neighborhoods of the Fe atoms with Ga in the first and second coordination shells. It has been shown that in samples of alloys containing from 3 to 17 at % gallium, the short-range order is almost independent of the heat treatment conditions (quenching from a paramagnetic state or exposure in a ferromagnetic state) and is characterized by the presence of pairs of Ga atoms in the position of the second neighbors (B2-type clusters). At a Ga content of 17 to 21 at %, the portion of B2 clusters turns out to be significantly higher after quenching than after annealing, which correlates with the observed effect of heat treatment on the magnitude of magnetostriction. As the Ga concentration (21–25 at %) further increases, the observed features in the distribution of Ga atoms indicate the appearance and growth of D03 phase regions.

Synergistic effects of laser powder bed fusion and annealing on the texture-selective recrystallization of magnetostrictive Fe-Ga-NbC alloys for biomedical applications

IntroductionMagnetostrictive Fe-Ga alloys have garnered extensive attention owing to their excellent magnetic properties and acceptable biocompatibility. Nevertheless, the polycrystalline Fe-Ga alloys currently available tend to display random texture orientations, which constrain their magnetostrictive performance. ObjectivesTo regulate the texture orientation of Fe-Ga-NbC alloys and thereby enhancing magnetostriction. MethodsIn this study, a processing route comprising laser powder bed fusion (LPBF) followed by secondary recrystallization annealing (800, 1000, and 1200 °C, respectively) was developed to prepare Fe-Ga-NbC alloys. ResultsThe results showed that the LPBF-ed (Fe81Ga19)99(NbC)1 alloys exhibited a high content of high energy grain boundaries (HEGBs) due to the repeated melting and solidification. In subsequent annealing process, the migration of HEGBs induced the rearrangement and recrystallization of grains, during which NbC was found to locate at the grain boundaries and influence the migration path of HEGBs via selective pinning, thereby resulting in a strong Goss texture. With the rise in annealing temperature, the content of Goss texture gradually increased from the initial 3.9 % to 71.3 % at 1200 °C, leading to enhanced magnetostriction, lower saturation magnetization and coercivity. Furthermore, in alternating magnetic fields, the alloys annealed at 1200 °C also exhibited higher magnetostriction than the LPBF-ed alloys. And a noteworthy grain coarsening was also observed after annealing, accompanied by a discernible inclination of magnetic domains towards strip domains. Additional, cell tests demonstrated that the prepared alloys had satisfactory biocompatibility and the ability to promote osteogenic differentiation. ConclusionThese findings indicated that the LPBF-ed and annealed Fe-Ga-NbC alloys might be a promising alternative as magnetostrictive-driven materials for biomedical applications.

Nanoprecipitation induced giant magnetostriction: A time-resolved small-angle neutron scattering study of the vacancy-assisted kinetics

Solid-state precipitation is an effective strategy for tuning the mechanical and functional properties of advanced alloys. Structure design and modification necessitate good knowledge of the kinetic evolution of precipitates during fabrication, which is strongly correlated with defect concentration. For Fe-Ga alloys, giant magnetostriction can be induced by the precipitation of the nanoscale tetragonal L60 phase. By introducing quenched-in vacancies, we significantly enhance the magnetostriction of the aged Fe81Ga19 polycrystalline alloys to ∼305 ppm, which is close to the level of single crystals. Although vacancies were found to facilitate the generation of the L60 phase, their impact on the precipitation mechanism and kinetics has yet to be revealed. This study combined transmission electron microscopy (TEM) and time-resolved small-angle neutron scattering (SANS) to investigate the precipitation of the L60 phase during the isothermal aging at 350 and 400 °C, respectively. The evolution of L60 nanophase in morphology and number density in as-cast (AC) and liquid nitrogen quenched (LN) Fe81Ga19 alloys with aging time were quantitatively compared. Interestingly, the nucleation of the L60 phase proceeds progressively in AC while suddenly in LN specimens, indicating the homogenous to heterogeneous mechanism switching induced by concentrated vacancies. Moreover, excess vacancies can change the shape of nanoprecipitates and significantly accelerate the growth and coarsening kinetics. The magnetostrictive coefficient is optimized when the size (long-axis) of L60 precipitates lies between 100 and 110 Å with a number density between 3.2–4.3 × 10–7 Å–3. Insight from this study validates the feasibility of achieving high magnetoelastic properties through precise manipulation of the nanostructure.

Laser-beam powder bed fusion of magnetostrictive Fe81Ga19 alloys: parameter optimization, microstructural evolution and magnetostrictive properties

Magnetostrictive Fe-Ga alloys, featuring with good machinability, high Curie temperature, and high permeability, have received increasing attention in fields such as actuators, implants, and energy harvesting. Unfortunately, bulk polycrystalline Fe-Ga alloys usually suffer poor magnetostrictive strains compromised by the randomness of grain structure and the intricate phase constitution. The current study was centered on the fabrication of bulk polycrystalline Fe81Ga19 alloys with tailored grain morphology and phase arrangement utilizing laser-beam powder bed fusion (LPBF) technology. Particular emphasis was laid on investigating the repercussions of LPBF process parameters on the microstructure and magnetostrictive performance. The findings illustrated a non-linear interplay between laser power and the relative density of laser powder bed fusion-fabricated (LPBFed) Fe81Ga19 alloys, marked by an initial augmentation followed by a subsequent decrement. Similarly, a consistent trend was observed for the LPBFed alloys at varying scan speeds. In particular, the LPBFed Fe81Ga19 alloys exhibited a highest density at optimized process parameters (laser power set at 120 W paired with a scan speed of 100 mm s−1) due to suitable laser energy input during LPBF process. It was experimentally shown that elongated columnar grains and disorder A2 phase structures were obtained within the alloys attibutes to the high temperature gradient and rapid cooling kinetics intrinsic to LPBF, contributing to a desirable magnetostrictive strain of ∼87 ppm for bulk polycrystalline Fe81Ga19 alloys. Moreover, a good dynamic magnetostrictive response of the LPBFed alloys was confirmed by the near-synchronous variations between magnetostrictive behavior and alternating magnetic fields. It can be derived from these findings that LPBF process may be a promising method to prepare bulk magnetostrictive Fe-Ga alloys for versatile applications.

Tailoring nano-heterogeneity to enhance magnetostriction in Goss grain-oriented Fe81Ga19 alloy thin sheets by aging treatment

The magnetostriction of Fe–Ga thin sheets can be significantly improved by secondary recrystallization, but the effect of the nano-heterogeneity on the magnetostriction of Fe–Ga thin sheets with preferred texture is still an open question. This paper studies the feasibility of tailoring nano-heterogeneity to enhance the magnetostriction of <001>-oriented Fe–Ga thin sheets by aging treatment. The secondary recrystallization of Goss ({110}<001>) texture with magnetostriction of 220 ± 12 ppm is achieved in Fe81Ga19 thin sheets after annealing at 950 °C. The magnetostriction and magnetic properties exhibit nonlinear changes with the increase of aging temperature. A peak magnetostriction of 244 ± 5 ppm is obtained in Fe81Ga19 thin sheets after aging at 450 °C, about 11% more than that of Fe–Ga thin sheets after secondary recrystallization. The effect of aging treatment on the magnetostriction of Fe–Ga thin sheets depends on the characteristics of the nano-scale L60 phase and causes lattice distortion. The increase of the volume fraction of the nano-scale L60 phase at the aging temperature of 450 °C leads to a much larger distortion and enhancement of the magnetostriction. As the aging temperature is lower than 400 °C or higher than 550 °C, the decrease of volume fraction or the coarsening of L60 phases, respectively, results in the decrease in the distortion of the A2 matrix.

Morphology and kinetics of nanoheterogeneities in Fe81Ga19–Tb alloy: A small-angle neutron scattering study

The formation of nanoprecipitates in the Fe81Ga19 alloy doped with Tb (∼0.1 at. %) was studied by small-angle neutron scattering (SANS). Measurements at room temperature for several samples pre-aged at a fixed temperature in the range of (300–700)°C revealed a dilute system of precipitates with a characteristic size at nanoscale (<1000 Å) growing with an increase in ageing temperature. In situ measurements during isothermal ageing at 300 °C for 3 h revealed fast (order of 10 min) formation of precipitates. SANS analysis is consistent with the results of neutron diffraction experiments, which suggest the microstructure of this alloy as a matrix of disordered atomic structure (A2 phase) with embedded precipitates of the structurally and magnetically ordered D03 phase.

Multifactorial impacts of B-doping on Fe81Ga19 alloys prepared by laser-beam powder bed fusion: Microstructure, magnetostriction, and osteogenesis

Magnetostrictive Fe-Ga alloys have captivated substantial focus in biomedical applications because of their exceptional transition efficiency and favorable cytocompatibility. Nevertheless, Fe-Ga alloys always exhibit frustrating magnetostriction coefficients when presented in bulk dimensions. It is well-established that the magnetostrictive performance of Fe-Ga alloys is intimately linked to their phase and crystal structures. In this study, various concentrations of boron (B) were doped into Fe81Ga19 alloys via the laser-beam powder bed fusion (LPBF) technique to tailor the crystal and phase structures, thereby improving the magnetostrictive performance. The results revealed the capacity for quick solidification of the LPBF process in expediting the solid solution of B element, which increased both lattice distortion and dislocations within the Fe-Ga matrix. These factors contributed to an elevation in the density of the modified-D03 phase structure. Moreover, the prepared Fe-Ga-B alloys also exhibited a 〈001〉 preferred grain orientation caused by the high thermal gradients during the LPBF process. As a result, a maximum magnetostriction coefficient of 105 ppm was achieved in the (Fe81Ga19)98.5B1.5 alloy. In alternating magnetic fields, all the LPBF-prepared alloys showed good dynamic magnetostriction response without visible hysteresis, while the (Fe81Ga19)98.5B1.5 alloy presented a notable enhancement of ∼30 % in magnetostriction coefficient when compared with the Fe81Ga19 alloy. Moreover, the (Fe81Ga19)98.5B1.5 alloy exhibited favorable biocompatibility and osteogenesis, as confirmed by increased alkaline phosphatase (ALP) activity and the formation of mineralized nodules. These findings suggest that the B-doped Fe-Ga alloys combined with the LPBF technique hold promise for the development of bulk magnetostrictive alloys that are applicable for bone repair applications.

Phase diagram of ternary Co–Fe–Ge system (I): Experimental

Co–Fe–Ge is an important material system for magnetic and catalyst applications. However, phase equilibria information of the Co–Fe–Ge ternary system is limited. Ternary Co–Fe–Ge alloys equilibrated at 950 °C were prepared. The microstructures, chemical compositions and crystal structure of each phase were determined. The phase equilibria isothermal section at 950 °C of the Co–Fe–Ge ternary system was then proposed. A continuous solid solution phase was formed between the Co5Ge3 and Fe5Ge3 phases and was labeled the β(Co,Fe)5Ge3 phase. There are five three-phase regions in the system at 950 °C. A wide α2 single-phase, and liquid phase regions with large composition ranges being confirmed at the Ge-poor and Ge-rich sides, respectively.

Direct-Contact Seebeck-Driven Transverse Magneto-Thermoelectric Generation in Magnetic/Thermoelectric Bilayers.

Transverse thermoelectric generation converts temperature gradient in one direction into an electric field perpendicular to that direction and is expected to be a promising alternative in creating simple-structured thermoelectric modules that can avoid the challenging problems facing traditional Seebeck-effect-based modules. Recently, large transverse thermopower has been observed in closed circuits consisting of magnetic and thermoelectric materials, called the Seebeck-driven transverse magneto-thermoelectric generation (STTG). However, the closed-circuit structure complicates its broad applications. Here, STTG is realized in the simplest way to combine magnetic and thermoelectric materials, namely, by stacking a magnetic layer and a thermoelectric layer together to form a bilayer. The transverse thermopower is predicted to vary with changing layer thicknesses and peaks at a much larger value under an optimal thickness ratio. This behavior is verified in the experiment, through a series of samples prepared by depositing Fe-Ga alloy thin films of various thicknesses onto n-type Si substrates. The measured transverse thermopower reaches 15.2 ± 0.4µVK-1, which is a fivefold increase from that of Fe-Ga alloy and much larger than the current room temperature record observed in Weyl semimetal Co2MnGa. The findings highlight the potential of combining magnetic and thermoelectric materials for transverse thermoelectric applications.

A combined EBSD and machine learning study of predicting deformation twinning in BCC Fe81Ga19 alloy

Compared to face-centered cubic (FCC) metals, body-centered cubic (BCC) metals demonstrate more intricate deformation behavior and microstructural characteristics because of the influence of intrinsic unstable stacking faults and defect structure. To investigate the unique phenomenon of deformation twinning in Fe81Ga19 alloy with BCC structure at moderate temperature and low strain rate, four twin nucleation models were constructed using a combination of electron backscatter diffraction (EBSD) technique and machine learning. These models are aimed to predict twin nucleation of grains and explore the relationship between twin nucleation and microstructural attributes. The study revealed that amongst the 235 grains analyzed during in-situ compressive deformation, 32 grains experienced twinning. Nine attributes influencing twin nucleation were selected and ranked according to their importance. Grain area, average image quality, neighboring grain count, and the Schmid factor of twinning systems exhibited significant influence on twin nucleation. Decision tree and tree ensemble (XGBoost) achieved 94% and 96% accuracy, respectively, on the test set, showcasing robust generalization capability. Due to the optimization of hyperparameters, support vector machine (SVM) and artificial neural network (ANN) exhibited outstanding performance. The ANN model achieved an accuracy of 97% and an F1 score of 0.91 on the test set, while the SVM model achieved an accuracy of 98% and an F1 score of 0.94, indicating superior performance. Furthermore, the study revealed that the twinning stress in Fe81Ga19 alloy exhibited weak responsiveness to temperature during deformation, and the intrinsic factors of grains were identified as crucial factors influencing twin nucleation.

Cross-shaped Fe-Ga alloy three-dimensional force tactile sensor and friction recognition

A three-dimensional force tactile sensor was designed based on magnetostrictive and tunnel magnetoresistance effects. The voltage output model of the 3D force sensor was derived, establishing the relationship between the output voltage and the three-dimensional force applied to the sensor. The structure of the sensor unit was optimized using COMSOL Multiphysics simulation software. An experimental platform was set up to test the static and dynamic performance of the sensor. The experimental results showed that the sensitivity of the sensor unit was 164.63 mV/N within the range of − 1.5 N to 1.5 N, and the average error between the experimental and theoretical values of the output voltage was 3.41%. The sensitivity of the sensor to normal forces in the range of 0 N to 6 N was 41.365 mV/N, and the sensitivity to tangential forces in the range of 0 N to 3 N was 49.636 mV/N. The dynamic voltage output of the sensor varied by no more than 4.65%, and the response time was shorter than that of human skin. The sensor was installed on the joints of a robotic hand and used to slide along the surface of an object. By comparing the output voltages of each unit, the friction coefficient of the object's surface could be accurately identified. The results showed that the sensor exhibited good static and dynamic characteristics, enabling perception of object information and precise manipulation of the robotic hand, thus improving the human-machine interaction process.

Diffusive and displacive phase transitions in Fe-Ga alloys

Phase transitions between structurally ordered phases in Fe–Ga alloys have been studied upon their heating to 850 °C and subsequent cooling to room temperature by neutron diffraction in real-time mode. The transitions between four types of phases have been analyzed: D03 → L12 (both cubic phases), L12 ↔ D019 (cubic – hexagonal), D019 ↔ A2 (hexagonal – cubic). It has been established that all phase transitions include stage of the formation of a disordered state and have a combined, diffusive-displacive nature. The diffusion stages are necessary for the disordering and ordering of the structure, the displacive stage provides a change in the type of the crystal lattice. It can be concluded that the formation of an intermediate disordered state followed by a transition to the final equilibrium state is less energy-consuming than the direct transition to the final state. During the observed transformations, no traces of predicted intermediate structurally ordered tetragonal phases were found. These results may provide new insight into the microscopic basis for the formation of enhanced magnetostriction in Fe–Ga alloys.