Magnetic FeCo Alloy Research Articles

Diffusion kinetics of borided of low entropy soft magnetic FeCo alloy

Abstract The growth kinetics of boride layers were investigated by boronizing the FeCo low entropy alloy produced by arc melting reverse vacuum system with the pack boriding method at temperatures of 1173 K, 1223 K, 1273 K and for 2, 4, 6 h. FeCo alloy has a single-phase FCC crystal structure and there are linear cracks and homogeneously distributed point voids in its microstructure. The hardness of FeCo alloy is between 170 HV0.05 and 265 HV0.05. The boride layer appearance has a sawtooth appearance, and the layer thickness varies between 62 µm and 172 µm depending on temperature and time. According to the XRD pattern, (CoFe)B and (CoFe)B2 triple phases are present on the boride layer surface. With pack boriding, the hardness of the boride layer increased up to 2262 HV0.05, and the surface hardness of the alloy improved by 8–10 times. The boride layer activation energy of the FeCo alloy boronized with pack boriding was calculated as 89.065 kJ mol−1.

Self-Assembly MXene-rGO/CoNi Film with Massive Continuous Heterointerfaces and Enhanced Magnetic Coupling for Superior Microwave Absorber

HighlightsThe rGO/CoNi nanosheets embedded between the MXene layers can continue to serve as a conductive channel, ensuring carrier migration and proper conductive loss capability.Owing to the strong magnetic coupling between the magnetic FeCo alloy nanoparticles on the rGO substrate, the entire MXene-rGO/CoNi film exhibits a strong magnetic loss capability.Self-assembly MXene-rGO/CoNi films hold excellent microwave absorption performance − 54.1 dB at 13.28 GHz.

FeCo alloy nanoparticle decorated cellulose based carbon aerogel as a low-cost and efficient electromagnetic microwave absorber

Magnetic FeCo alloy nanoparticle decorated cellulose-based carbon aerogel (FeCo@CCA) exhibits efficient electromagnetic microwave absorption performance with a RLmin of −49.5 dB and an EAB of 10.88 GHz.

FeCo/ZnO Composite Nanofibers for Broadband and High Efficiency Microwave Absorption

AbstractIn this work, a novel nanofibrous absorber composed of FeCo alloy and ZnO nanoparticles (denoted as FeCo/ZnO NFs) is fabricated through electrospinning and subsequent calcination and hydrogen reduction. Benefiting from the advantages of their unique 1D and derived 3D network hierarchical structure, as well as the good synergistic effect between magnetic FeCo alloy and dielectric ZnO within the 1D nanospace, the present FeCo/ZnO NFs exhibit outstanding microwave absorption properties with an optimal reflection loss value of −83.4 dB and an effective absorption bandwidth of 8 GHz (10.0–18 GHz) at a small coating thickness of only 1.3 mm. Such performance is remarkably superior to those of many previously reported magnetic ZnO‐based absorbers, highlighting the great application potential of FeCo/ZnO NFs in the field of microwave absorption.

Domain observation in electrochemically deposited FeCo nano-rods by MOKE microscopy and micromagnetics

Highly magnetic FeCo alloy films were deposited on Indium Tin Oxide (ITO) substrates by electrochemical deposition technique using different electrolytes. Synchrotron X-Ray Diffraction studies confirms the formation of pure FeCo films. The films deposited using different electrolytes results in varied morphology viz. flower-like and tilted nano-rod like structures. The magnetic studies of the films reveals that the rod-like structures shows single phase hysteresis loops with low coercivity ~155 Oe in the in-plane and ~337 Oe in the out of plane configuration. The higher coercivity in the out of plane configuration arising due to pinning effects is modelled by Monte-Carlo simulations to estimate the effective anisotropy constant. The domain configurations observed at various fields using Magneto Optic Kerr Effect Microscopy shows that the magnetization reversal process follows 180° domain motion. Such domain motion is a manifestation of higher stiffness constant as explained by the micromagnetic simulations.

Preparation of Carbon Encapsulated Magnetic FeCo Alloy Nanoparticles Supported on Carbon Nanotubes for Enhanced Microwave Absorption

A mixture of multi-walled carbon nanotubes in an ethanol solution of Fe(NO3)3.9H2O and Co(NO3)2.6H2O, were used to prepare an Fe2O3-CoO catalyst supported on carbon nanotubes by a supercritical fluid drying method. The carbon encapsulated FeCo nanoparticles were prepared by the catalytic decomposition of methane over the catalyst at 850°C for 30 mins. The morphology and microstructure of the catalyst and carbon encapsulated nanoparticles (CEP) were characterized by XRD, FESEM, EDS and TEM analyses. The electromagnetic characteristics and microwave absorption properties of the CEP product were also studied. Results show that the CEP product possesses high complex permittivity and good permeability in the microwave frequency range from 2 to 18 GHz. The maximum absorption peak was observed at 9.44 GHz for a large reflection loss (R) of 13.3 dB, with a band width of 7.4 GHz and 2.56 GHz, at R <- 5 dB and R <- 10 dB, respectively.

Preparation of magnetic Fe-Co alloy using texture controlled technique

Microstructure and texture controlled 48Fe-52Co at% alloy was prepared by repeated cold-rolling and recrystallization through heat treatment at temperatures below order-disorder phase transformation using Fe and Co foils. Furthermore, distortion of controlled texture orientated cubic crystal structured 48Fe-52Co at% alloy along the 〈0 0 1〉 direction was attempted by introducing nitrogen interstitially through plasma nitriding. The textural analysis suggested that the microstructure is composed of micron-sized grains randomly aligned along rolling direction (RD). Furthermore, from the results of orientation distribution function (ODF), the dominance γ-fiber was confirmed in as-rolled samples. However, in recrystallized sample, the intensity of rotated-cube orientation increased while the presence of γ-fiber decreased. Furthermore, a complete rotated-cube orientation was realized in nitrided texture. The appearance of the prominent X-ray diffraction peak (2 0 0) in all samples indicated the presence of rotated-cube orientation. However, the FWHM of (2 0 0) peak of the nitrided sample was broader than the rest. This was attributed to the diffusion of nitrogen into the matrix during plasma nitriding and internal nitriding was confirmed from the EDX analysis. However, further investigation is necessary to understand the behavior of nitrogen.Magnetic properties of as-rolled 48Fe-52Co at% alloy inferred from in-plane magnetic hysteresis loops was similar Fe foil. Furthermore, magnetic properties of recrystallized and nitrided 48Fe-52Co at% alloy were different from Fe-Co particles or crushed bulk Fe-Co alloy prepared by arc melting. However, the internal diffusion of nitrogen was not adequate enough to bring about a considerable change in the magnetic properties. We believe that considerable crystal distortion to induce change in the magnetic properties can be exerted by introducing interstitial carbon and the addition of third or fourth elements.

Synthesis and Magnetic Properties Evaluation of Monosized FeCo Alloy Nanoparticles Through Microemulsion Method

In this study, the microemulsion method as a facile and promising synthesis method was employed in order to prepare magnetic FeCo alloy nanoparticles with several Fe/Co weight ratio. For this purpose, a micellar system was applied and the reaction of Fe and Co salts reduction was proceeded in the confined spaces in liquid phase. The electromagnetic waves absorption test was conducted to determine the optimum absorbent sample. The results showed that the sample of prepared in the weight ratio of 70:30 possesses a uniform spherical morphology with an average particle size of less than 10 nm. Furthermore, AFM micrograph confirmed the formation of non-agglomerated uniform spherical nanoparticles. The evaluation of magnetic property of the synthesized samples showed that Fe70Co30 nanoparticles dedicated the highest magnetic saturation of 115 emu g−1. In addition, The magnitude of electromagnetic absorption (return loss) of this sample was measured to be −8.1 dB at 16 GHz which was at the lowest level compared with other samples highlighting the significant effect of Fe/Co weight ratio on final magnetic properties of the alloy system.

Large-scale controlled synthesis of magnetic FeCo alloy with different morphologies and their high performance of electromagnetic wave absorption

Magnetic materials of FeCo alloy with different morphologies (nanocube, nanoplate and flower-like structure) have been synthesized by controlling the molar ratio of Fe2+ to Co2+, concentrations of cyclohexane and PEG-400. The structure and morphology were characterized by several analytical techniques, including XRD, SEM, TEM, XPS and VSM. The microwave-absorbing properties were measured by a vector network analyzer. The SEM and TEM photographs reveal that the edge length of FeCo nanocube is about 215 nm, the diameter and thickness of the nanoplate is 100 and 15 nm, respectively. The average diameter of flower-like FeCo is about 1.5 μm. The investigation of the electromagnetic wave absorbability revealed that flower-like FeCo exhibited excellent electromagnetic wave absorption properties compared with FeCo nanocube and FeCo nanoplate due to the special structure. The maximum reflection loss of flower-like FeCo was up to −43 dB at 13.1 GHz and the absorption bandwidth with the reflection loss below −10 dB was 5.8 GHz (from 2.7 to 5.4 GHz and from 12 to 15.1 GHz) with a thickness of 3.4 mm. Furthermore, this work offers a simple solvothermal route to fabricate shape and size-controlled FeCo alloy, which can be used as an attractive candidate for new type of electromagnetic wave absorbers.

Mechanical and magnetic properties of spark plasma sintered soft magnetic FeCo alloy reinforced by carbon nanotubes

Abstract

Synthesis and properties of graphene and graphene/carbon nanotube-reinforced soft magnetic FeCo alloy composites by spark plasma sintering

The effect of the addition of graphene nanoplatelets (GNP) and graphene nanoplatelet/carbon nanotube (GNT) mixtures on the mechanical and magnetic properties of spark plasma sintered soft magnetic FeCo alloys was studied. Three different volume fractions (0.5, 1 and 2 vol%) of GNPs and GNTs were investigated. Ball milling was used to disperse the GNPs in monolithic FeCo powder, while magnetic stirring and ultrasonic agitation were used to prepare hybrid GNT prior to ball milling. The highest saturation induction (B sat) of 2.39 T was observed in the 1 vol% GNP composite. An increase in the volume fraction of the ordered nanocrystalline structure was found to reduce the coercivity (H c) of the composites. The addition of CNTs to the GNP composite prevented grain growth, leading to grain refinement. An 18 % increase in hardness was observed in the 1 vol% GNP composite as compared to the as-received FeCo alloy. A reduction in tensile strength was observed in all of the composite materials, except for the 0.5 vol% GNT composite, for which a value of 643 MPa was observed. Raman spectroscopy indicated a reduction in the defect density of the GNPs after adding CNTs.

Facile and controlled synthesis of FeCo nanoparticles via a hydrothermal method

Magnetic FeCo alloy nanoparticles have been synthesized by reduction of FeSO4 and CoCl2 with hydrazine in concentrated alkaline media via a hydrothermal route. The size could be controlled by synthetic conditions such as reaction time and temperature, respectively. The obtained samples were characterized by XRD, SEM, TEM, and VSM techniques. Magnetic investigations show the ferromagnetic behavior with saturation magnetization higher than 148.2 emu/g and maximum coercivity up to 411.0 Oe at room temperature. The present method is simple, inexpensive, surfactant-free, and may stimulate technological interests. Such FeCo alloy nanoparticles may have potential applications in biomedical field and magnetic storage devices.

Structure and physical-mechanical properties of equiatomic ordering FeCo alloy obtained by quenching from the liquid state

The fine structure of ordering soft magnetic FeCo alloy obtained by quenching from the liquid state has been studied by transmission and scanning electron microscopy. The effect of ultrafast quenching and subsequent annealing on the structural aspects of the processes of crystallization, atomic ordering, and polymorphic transformation has been investigated. The reasons for the increase in the alloy plasticity as a result of quenching from the liquid state are established.

Metastable phase formation in undercooled Fe-Co melts under terrestrial and parabolic flight conditions

Soft magnetic Fe-Co alloys display primary fcc phase solidification for>19,5 at% Co in conventional near-equilibrium solidification processes. Undercooled Fe-Co melt drops within the composition range of 30 to 50 at% Co have been investigated with the electromagnetic levitation technique. The solidification kinetics was measured in situ using a high-resolution Siphotodiode. Melt drops were undercooled up to 263 K below the liquidus temperature and subsequently quenched onto a chill substrate in order to characterize the solidification sequence and microstructure. The transition from stable fcc phase to metastable bcc primary phase solidification has been observed after reaching a critical undercooling level. The critical undercooling increases with rising Co content. The growth velocity drops obviously after transition to metastable bcc phase formation. Parabolic flight experiments were performed in order to study the phase selection under reduced gravity conditions. Under microgravity conditions, a much smaller critical undercooling and an increased life time of the metastable bcc phase were obtained. This result was validated with TEM investigations. The appearance of Fe-O particles gives an indirect hint for an intermediate fcc phase formation from the metastable bcc phase at elevated temperature.

Soft Magnetic FeCo Alloys. Alloy Development, Processing, and Properties

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Soft magnetic FeCo alloys: alloy development, processing, and properties

FeCo intermetallic alloys are well known to possess a unique combination of high saturation magnetisation, high Curie temperature, low magnetocrystalline anisotropy and good strength. They are ideally suited for applications requiring high flux densities. Intense research and development efforts over the years resulted in significant improvements in mechanical properties and better understanding of phase transformations in FeCo alloys. However, the high cost of the alloys has prevented their widespread applications. Emerging needs for soft magnetic materials to operate at high temperatures have caused renewed interest in FeCo alloys. The earlier studies are summarised in this review with special emphasis on phase transformations, processing, mechanical, magnetic and electrical properties of binary, ternary and more complex FeCo alloys. Current interest in developing nanocrystalline and thin films based on FeCo compositions is also summarised. The research areas that need to be addressed are also emphasised to clearly elucidate the effects of alloying additions and processing on the electrical and magnetic properties and on the high temperature mechanical properties of these alloys.

Magnetic annealing of plated high saturation magnetization soft magnetic FeCo alloy films

Plated high saturation magnetization soft magnetic FeCo films were annealed in magnetic field; their stress, microstructure, and magnetic properties were investigated. The FeCo films consistently showed a reduced tensile stress after magnetic annealing at temperatures above 255°C. The annealing temperature was found to be the primary factor in reducing the tensile stress, while annealing time was secondary. The FeCo films showed improved soft magnetic properties when subjected to an easy axis annealing with reduced coercivities along both the easy axis and hard axis. Hard axis annealing on these FeCo films caused a switched easy and hard axis in these films when the annealing temperature is above 255°C.

Mechanical properties of soft magnetic FeCo alloys

The brittle fracture of stoichiometric FeCo has long been a puzzle given its high-symmetry B2 crystal structure, 1/2〈111〉{110} slip, low ordering temperature and relatively low strength. Macroalloying with vanadium (≈2%) improves ductility significantly in the disordered state, but only moderately in the ordered state. Brittle fracture is intergranular in the binary stoichiometric alloy, but is usually transgranular cleavage in the vanadium-containing alloy. Boron and carbon additions are shown not to suppress grain-boundary fracture nor improve the ductility of stoichiometric FeCo, but they produce significant ductility improvements in the ternary FeCo–2V alloy. The mechanism appears to be slip refinement by fine precipitates. It is also shown that for boron-doped (30 wppm) stoichiometric FeCo, the optimum vanadium content for good ductility is 2.1–2.5 wt.%.

Effect of annealing in hydrogen on composition and properties of rapidly quenched Fe-Co-B and Fe-B-Si alloy ribbons

It is shown that soft magnetic Fe-Si and Fe-Co alloy ribbons can be produced by extraction of boron from rapidly quenched Fe-Si-B and Fe-Co-B ribbons. Fe-Si-B and Fe-Co-B alloys of different compositions were rapidly quenched to ribbons about 10 mm wide and 20–25 μm thick. The ribbons were annealed in wet hydrogen between 700 and 900 °C, followed by an annealing at 1100 °C in dry hydrogen. After proper annealing, the ribbons are composed of single-phased Fe-Si or Fe-Co solid solution with the boron having been extracted completely. Soft magnetic properties will be discussed as a function of composition and annealing parameters. It is also possible to produce a Co foil in this way.

Post debinding treatment of injection moulded parts by isostatic pressing: I.H. Moon et al (Hanyang University, Seoul, Korea)

It is shown that soft magnetic Fe-Si and Fe-Co alloy ribbons can be produced by extraction of boron from rapidly quenched Fe-Si-B and Fe-Co-B ribbons. Fe-Si-B and Fe-Co-B alloys of different compositions were rapidly quenched to ribbons about 10 mm wide and 20–25 μm thick. The ribbons were annealed in wet hydrogen between 700 and 900 °C, followed by an annealing at 1100 °C in dry hydrogen. After proper annealing, the ribbons are composed of single-phased Fe-Si or Fe-Co solid solution with the boron having been extracted completely. Soft magnetic properties will be discussed as a function of composition and annealing parameters. It is also possible to produce a Co foil in this way.