Tetragonal Fe3B Research Articles

Magnetic and structural properties of nanocomposite permanent magnet produced from crystallization of Pr4Fe67Nb4Cu2Zr1B22 alloy

Present research work narrates synthesis, structural, thermal and magnetic characteristics of Pr4Fe67Nb4Cu2Zr1B22 nanocomposite magnets. Amorphous Pr4Fe67Nb4Cu2Zr1B22 rods were produced through injection casting technique and permanent magnetic characteristics were obtained by one-step annealing the amorphous rods. XRD analysis elucidated that as-cast rods have amorphous phase structure and annealed magnets have tetragonal Pr2Fe14B hard phase, cubic structural α-Fe phase and tetragonal Fe3B soft phase. Optimal annealed magnet composed of 63% Pr2Fe14B hard phase, 26% α-Fe and 11% Fe3B soft phases with mean grain sizes around 51.6 ± 1 nm for Pr2Fe14B, 25.4 ± 2 nm for α-Fe and 21.5 ± 2 nm for Fe3B phases. Microscopic and atomic probe studies showed that the annealed magnet consists of Pr2Fe14B, α-Fe, Fe3B nanosized grains interlinked with thin grain boundaries. Henkel curve evidenced the existence of inter-grain exchange coupling between magnetic nanophase grains. Magnetic hysteresis measurements revealed that Pr4Fe67Nb4Cu2Zr1B22 nanocomposite magnet yielded maximum magnetic characteristics such as coercivity Hc of 382 kA/m, remanence Br of 0.70 T and maximum energy product (BH)max of 64.2 kJ/m3 with rare earth to iron ratio 4:67.

Structure, Microstructure, Hyperfine, Mechanical and Magnetic Behavior of Selective Laser Melted Fe92.4Si3.1B4.5 Alloy

A disordered ε-FeSi crystalline structure was produced by selective laser melting in Fe92.4Si3.1B4.5 powder alloys fabricated with different laser powers at a laser scanning speed of 0.4 m/s. The phase formation, microstructure, roughness, microhardness, and hyperfine and magnetic properties were studied using X-ray diffraction, scanning electron microscopy, atomic force microscopy, a profilometer, a microdurometer, transmission 57Fe Mössbauer spectrometry and vibrating sample magnetometry. The aim of this work was therefore to study the effect of laser power on the phase formation, microstructure, morphology, and mechanical, hyperfine and magnetic properties. The XRD patterns revealed the coexistence of a bcc α-Fe0.95Si0.05, a tetragonal Fe2B boride phase and a disordered ε-FeSi type structure. The existence of the disorder was confirmed by the presence of different FeSi environments observed in the Mössbauer spectra. The Fe2B boride contained about 51–54% of Fe atoms. The porosity and roughness decreased whereas laser power increased. The sample produced with a laser power of 90 W had a smooth and dense surface, high microhardness (~1843 Hv) and soft magnetic properties (saturation magnetization Ms = 200 emu/g and coercivity Hc = 79 Oe).

Effect of Cu and Co addition on non-isothermal crystallization kinetics of rapidly quenched Fe-Sn-B based alloys

Crystallization kinetics of rapidly quenched Fe-Sn-B alloys under non-isothermal conditions were studied using differential scanning calorimetry. Formation of crystalline phases was analyzed by X-ray diffraction. Nominal chemical compositions were Fe81Sn7B12, (Fe3Co1)81Sn7B12 and (Fe81Sn7B12)99Cu1. Alloys were prepared by planar flow casting in the form of ribbons approximately 20 µm thick and 6 mm wide. Mechanism of crystallization was studied under framework of the Johnson-Mehl-Avrami-Kolmogorov model. Alloys exhibit two stages of crystallization. Results show decrease in activation energy of the first stage of crystallization with addition of Cu and increase with addition of Co. Crystallization mechanism of the first stage of crystallization for Fe81Sn7B12 and (Fe81Sn7B12)99Cu1 alloy starts as growth with increasing nucleation rate and continues as growth with decreasing nucleation rate. Addition of Co changes mechanism of crystallization. Which in case of (Fe3Co1)81Sn7B12 alloy starts as a growth with increasing nucleation rate. Then changes to growth with decreasing nucleation rate. After which nucleation rate decreases to zero. Rest of crystallization stage is governed by growth of pre-existing nuclei. In the first stage of crystallization α-Fe phase with bcc structure crystallizes from amorphous matrix. In the second stage of crystallization the remaining amorphous matrix crystalizes into tetragonal Fe2B phase and hexagonal FeSn phase. After the first stage of crystallization, 50 % to 55 % volume of studied alloys were crystalized. Addition of Cu decreases crystalline size of α-Fe crystallites by 60 % and decreases concentration of Sn in α-Fe phase by 0.8 at. %. Addition of Co doesn't affect the size of α-Fe crystallites and decreases the concentration of Sn in α-Fe phase by 1.7 at. %.

Damage induced by helium ion irradiation in Fe-based metallic glass

The changes in structure and surface morphology of metallic glasses Fe80Si7.43B12.57 and Fe68Zr7B25 before and after the irradiation of He ions with the energy of 300 keV were investigated, and were compared with that of the tungsten. The results show that after the He2+ irradiation, metallic glass Fe68Zr7B25 still maintained amorphous. While a small amount of metastable β-Mn type phase nanocrystals formed in metallic glass Fe80Si7.43B12.57 at the fluence of 4.0 × 1017ions/cm2 (19dpa). The nanocrystals transformed into α-Fe phase and tetragonal Fe2B phase as the fluence increased to 1.0 × 1018ions/cm2 (47dpa). Then the new orthogonal Fe3B phase and β-Mn type phase nanocrystals appeared when the fluence increased further, and the quantities of nanocrystals increased. Blisters and cracks appeared on the surface of tungsten under the irradiation fluence of 1.0 × 1018ions/cm2, however only when the fluence was up to 1.6 × 1018ions/cm2, could cracks and spalling appear on the surfaces of metallic glasses.

Magnetic properties of Mo-stabilized bulk Fe3B magnet

Fe3B is a metastable high temperature phase and exists in orthorhombic and tetragonal structures. Here, we report on synthesis, structural and magnetic properties of tetragonal (P42/n) Fe3B stabilized by a very small substitution of Mo (1–3at.%) for Fe. The (Fe0.98Mo0.02)3B compound possesses a high Curie temperature of 780K and high saturation magnetization of 175A·m2/kg (1.60T). Magnetocrystalline anisotropy field of around 0.8T and anisotropy energy of 340kJ/m3 have been determined for magnetically-oriented fine particles of (Fe0.98Mo0.02)3B.

Mössbauer study of amorphous alloys Fe85–x Cr x B15 (x = 0–20)

Mossbauer spectra of amorphous alloys Fe85–x Cr x B15 (x = 0–20) are measured at 91 K. Distributions of 57Fe hyperfine fields are recovered from the experimental spectra. The data are analyzed using a nanocrystal model. It is found that atoms of chrome replace iron atoms in nanocrystals of type α-Fe with orthorhombic o-Fe3B and tetragonal Fe3B phases. The local magnetic moments of iron atoms in the nanocrystal phases are estimated. Replacing iron atoms with atoms of chrome sharply reduces the local magnetic moments of iron atoms in nanocrystals of amorphous alloys.

Crystallization of Fe83B17 amorphous alloy by electric pulses produced by a capacitor discharge

Heating of conductive materials by electric current is used in many technological processes. Application of electric pulses to metallic glasses induces their fast crystallization, which is an interesting and complex phenomenon. In this work, crystallization of the Fe83B17 amorphous alloy induced by pulses of electric current produced has been studied using X-ray diffraction and transmission electron microscopy. Ribbons of the alloy were directly subjected to single pulses of electric current 250 µs long formed by a capacitor discharge. As the value of $$\smallint I^{2} {\text{d}}t$$ was increased from 0.33 to 2.00 A2 s, different crystallization stages could be observed. The crystallization began through the formation of the nuclei of α-Fe. At high values of $$\smallint I^{2} {\text{d}}t$$ , α-Fe and tetragonal and orthorhombic Fe3B and Fe23B6 were detected in the crystallized ribbons with crystallites of about 50 nm. Thermal annealing of the ribbons at 600 °C for 2 min resulted in the formation of α-Fe and tetragonal Fe3B. It was concluded that pulses of electric current produced by a capacitor discharge induced transformation of the Fe83B17 amorphous phase into metastable crystalline products.

Study of residual stresses, microstructure, and hardness in FeB and Fe2B ultra-hard layers

Boriding is a thermochemical diffusion-based process of achieving ultra-hard surface on metals. Two distinct crystalline phases, i.e. tetragonal Fe2B and orthorhombic FeB can exist in the surface layer penetrated by boron ions. In our contribution, we have studied the microstructure, the hardness, and the spatial distributions of both phase composition and residual stresses (RS) in samples exhibiting either single-phase Fe2B or duplex Fe2B-cum-FeB character. The indispensable knowledge of the elastic constants used in the stresses calculations from the measured strains by X-ray diffraction were gained from the refined lattice parameters of both iron borides employing density functional theory implemented in CASTEP software by Materials Studio. In the studied case, there is only minor occurrence of preferred orientation in the Fe2B phase and the evaluated RS have compressive character gradually decreasing from its maximum value on the very surface.

Synthesis and characterization of Fe–B nanoparticles for potential magnetic applications

The crystallization and structure of Fe-B nanoparticles (NPs) of different sizes formed in a single process by gas aggregation from Fe80B20 targets were analyzed by transmission electron microscopy. It is con- cluded that all NPs are covered by an amorphous Fe-B shell while the crystal structure of the NPs core depends on their size. Large NPs with diameters C30 nm are mono- crystalline tetragonal Fe3B, small diameter NPs (B20 nm) are completely amorphous whereas in middle size NPs, with diameters between 20 and 30 nm, difference Fe-B phases (tetragonal Fe3B and orthorhombic FeB) together with defaulted areas are observed. This work opens new possibilities to produce Fe-B NPs tailoring their magnetic properties by controlling their size and composition.

Magnetostriction of the polycrystalline Fe80Al20 alloy doped with boron

The doping of Fe80Al20 polycrystalline alloy with 2% of boron increased the total magnetostriction twofold compared to a sample without boron. A value close to 80ppm was achieved at 300K. The microstructures of the boron-doped alloys show a dendritically solidified matrix with interdendritic α-FeAl and/or Fe3Al and Fe2B eutectic between the grains. The XRD analysis reveals an increase in the volume fraction of α-FeAl and a correspondent decrease of the Fe3Al phase volume fraction as the boron content increases. The increase of the volume fraction of this tetragonal Fe2B phase in the samples doped with boron causes the decrease of the strong volume magnetostriction that was observed in the alloy without boron. There is some evidence that the improvement of the magnetostriction magnitude due to the addition of boron to the Fe80Al20 alloy could reach the maximal magnetostriction if the 1:1 optimal ratio of the volume fractions of the α-FeAl and Fe3Al phases could be reached.

Effect of the Nb content on the amorphization process of the mechanically alloyed Fe–Co–Nb–B powders

Mechanical alloying was used to prepare Fe57Co21Nb7B15 (7Nb) and Fe61Co21Nb3B15 (3Nb) powder mixtures in a high-energy planetary ball mill under argon atmosphere. Thermal stability, structural and magnetic properties were followed by differential scanning calorimetry, X-ray diffraction, vibrating sample magnetometry and Mössbauer spectrometry. For the Fe57Co21Nb7B15 powders, an amorphous matrix (∼69%) where nanocrystalline bcc FeCo, bcc Nb(B), tetragonal Fe2B and orthorhombic Fe3B type phases were embedded is reached after 96h of milling. However, for the Fe61Co21Nb3B15 mixture, the partially amorphous structure (∼75%) is achieved within 48h of milling. Further milling time (up to 96h) gives rise to the primary crystallization of α-Fe in addition to bcc FeCo, orthorhombic FeB, tetragonal Fe2B and tetragonal Fe3B type borides. Lower Nb content powders (3Nb) exhibit higher saturation magnetization, Ms, higher coercive field, Hc, and lower glass transition temperature values than those of the 7Nb powders.

Investigation of high temperature phase stability, thermal properties and evaluation of metallurgical compatibility with 304L stainless steel, of indigenously developed ferroboron alternate shielding material for fast reactor applications

Towards the cause of serving economic power production through fast reactors, it is necessary to bring in functionally more efficient and innovative design options, which also includes exploration of cheaper material alternatives, wherever possible. In this regard, the feasibility of using a commercial grade ferroboron alloy as potential alternate shielding material in the outer subassemblies of future Indian fast reactors has been recently investigated from shielding physics point of view. The present study explores in detail the high temperature thermal stability and the metallurgical compatibility of Fe–15.4B–0.3C–0.89Si–0.17Al–0.006S–0.004P–0.003O (wt.%) alloy with SS 304L material. In addition, the high temperature specific heat and lattice thermal expansion characteristics of this alloy have also been investigated as a part of the present comprehensive characterisation program. The Fe–15 wt.%B alloy is constituted of principally of two boride phases, namely tetragonal Fe 2B and orthorhombic FeB phases, which in addition to boron also contains some amount of C and Si dissolved in solid solution form. This Fe–B alloy undergoes a series of phase transformation as a function of increasing temperature; the major ones among them are the dissolution of Fe 2B-lower boride in the matrix through a eutectic type reaction, which results in the formation of the first traces of liquid at 1500 K/1227 °C. This is then followed by the dissolution of the major FeB boride phase in liquid and the melting process is completed at 1723 K/1450 °C. In a similar manner, the thermal stability studies performed on combined Fe–B + 304L steel reaction couples revealed that a pronounced pre-melting or liquid phase formation occurs at a temperature of 1471 K/1198 °C, which is lower than the melting onset of both Fe–B and SS 304L. It is found that within the limits of experimental uncertainty, this pre-melting phenomenon occurred at the same fixed temperature of 1471 K/1198 °C, irrespective of the mass ratios of Fe–B and 304L steel. Further, it is also found that SS 304L is completely soluble in Fe–B alloy and the fused product upon solidification formed a mixture of complex intermetallic borides, such as (Fe,Cr)(B,C), (Fe,Cr) 2(B,C) and (Fe,Ni) 3B. In the temperature range 823–1073 K (550–800 °C), the SS 304L clad is found to interact strongly with the Fe–B alloy. The diffusion layer thickness or the attack layer depth ( x) is found to vary with time ( t) up to about 5000 h, according to the empirical rate law, x 2 = k( T) t. The temperature sensitivity of the rate constant, k( T) is found to obey the Arrhenius law, k( T) = k o exp(− Q/ RT), with Q = 57 kJ mol −1, being the effective activation energy for the overall diffusional interaction of Fe–B and SS 304L. The room temperature specific heat capacity of Fe–B alloy is found to be 538 kJ kg −1 K −1. The C P values measured over 300–1350 K, is found vary smoothly with temperature according to the expression, C P/kJ kg −1 K −1 = 0.62094 + 0.00012 T + 10685.81 T −2. The lattice thermal expansion of both FeB and Fe 2B phases are found to be anisotropic in that the c-axis expansion is found to be more than that along a and b axes. The room temperature volume thermal expansivity of FeB and Fe 2B phases are found to be of the order of 48 × 10 −6 K −1 and 28 × 10 −6 K −1, respectively. The thermal expansion of FeB is found to be more temperature sensitive than that of Fe 2B.

Atomic and magnetic structures of Fe70Al5B25 amorphous alloys

The short-range order around boron, aluminum, and iron atoms in Fe75B25 and Fe70Al5B25 amorphous alloys has been studied by 11B and 27Al nuclear magnetic resonance at 4.2 K and 57Fe Mossbauer spectroscopy at 87 and 295 K. The average magnetic moment of iron atoms μ(Fe) in these alloys has been measured by a vibrating sample magnetometer. It has been revealed that the substitution of aluminum atoms for iron atoms does not disturb μ(Fe) in the Fe70Al5B25 alloy, gives rise to an additional contribution to the 11B NMR spectrum in the low-frequency range, and shifts maxima of the distribution of hyperfine fields at the 57Fe nuclei. In the Fe70Al5B25 amorphous alloy, the aluminum atoms substitute for iron atoms in the nearest coordination shells of boron and iron atoms. This alloy consists of nanoclusters in which boron and iron atoms have a short-range order of the tetragonal Fe3B phase type.

Kinetic study of non-isothermal crystallization in Fe 78Si 9B 13 metallic glass

This paper reports the differential scanning calorimetric (DSC) studies of metallic glass ribbon Fe 78Si 9B 13 at different heating rates. It is found that Fe 78Si 9B 13 metallic glass exhibits two-stage crystallization on heating. In order to calculate the activation energies for crystallization various thermal models are employed. The average values of the activation energies ( E c) were calculated and found to be 342 ± 10 and 351 ± 8 kJ/mol for the first and second phase, respectively. Kinetic parameters such as Avarmi exponent or reaction order ( n), dimensionality of growth ( m), and frequency factor ( K o) are also discussed. The reaction orders obtained for the two stages of crystallization were n 1 = 4 and n 2 = 5, confirming the bulk crystallizations of the samples. The deduced K o values for the two crystallization peaks are calculated to be 9.8 × 10 18 and 4.6 × 10 18 s −1. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques are used to identify the crystallized phases and morphology of the annealed samples, respectively. Rietveld X-ray profile fittings are also performed that revealed the obtained phases for the Fe 78Si 9B 13 metallic glass were cubic α-Fe(Si) and tetragonal Fe 2B with volume fraction of 44% and 56%, respectively.

57Fe NMR study of amorphous and rapidly quenched crystalline Fe-B alloys

Amorphous and crystalline Fe-B alloys (5–25 at % B) were studied using pulsed 57Fe nuclear magneticr esonance at 4.2 K. The alloy samples were prepared from a mixture of the 57Fe and 10B isotopes by rapid quenching from the melt. In the microcrystalline Fe-(5–12 at %) B alloys, the resonance frequencies were measured for local states of 57Fe nuclei in the tetragonal and orthorhombic Fe3B phases and also in α-Fe. The resonance frequencies characteristic of 57Fe nuclei in α-Fe crystallites with substitutional impurity boron atoms in the nearest neighborhood were also revealed. In the resonance frequency distribution P(f) in the amorphous Fe-(18–25) at % B alloys, there are frequencies corresponding to local Fe atom states with short-range order of the tetragonal and orthorhombic Fe3B phases. As the boron content decreases below 18 at %, the P(f) distributions are shifted to higher frequencies corresponding to 57Fe NMR for atoms exhibiting a short-range order of the α-Fe type. The local magnetic structure of the amorphous Fe-B alloys is also considered.

Microstructure and mechanical behaviour of nano-eutectic Fe83B17 alloy prepared by a self-propagating high temperature synthesis combining rapid solidification

The limited room temperature ductility of nanostructured materials with uniform grain size distribution restricts practical applications. To circumvent this problem, we employ a self-propagating high temperature synthesis combining a rapid solidification process to prepare the bulk nano-eutectic Fe83B17 alloy, which can lead to simultaneous high strength and large ductility. The microstructure of the Fe83B17 alloy has been examined in detail using x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The Fe83B17 alloy is composed of the eutectic of tetragonal Fe2B and α-Fe phases. The t-Fe2B and α-Fe phases display a fine lamellar eutectic structure with lamellar spacing of about 50 nm. The size of the eutectic colonies is in the range 3–25 µm. High yield strength (1089 MPa) and large ductility (∼24.9%) are observed simultaneously in mechanical behaviour tests. The rotation of the eutectic colonies, accompanying viscosity plastic flows to release the localization of the shear stress, can contribute to the simultaneous high strength and large ductility.

Influence of heat treatment on magnetostrictions and electrical properties of (Fe 1Co 1) 76Mo 8Cu 1B 15

The investigation of magnetostriction of (Fe 1Co 1) 76Mo 8Cu 1B 15 metallic glass upon structural changes has been performed on samples with different thermal history. The samples have been annealed for 0.5 h at different temperatures ranging from 573 to 973 K. Measurements of saturation magnetostriction λ S, volume magnetostriction ω and forced magnetostriction ∂ ω/∂H have been performed using direct capacitance method. For the set of annealed samples, the temperature dependence of lambda(s) exhibits local maximum at 828 K. Above 828 K, there is a decrease of lambda(s) by about 1/3 of its maximal value. The dependence of the value of ∂ ω/∂H on the annealing temperature exhibits local minima at 573 and 923 K and local maximum at 678 K. These extremes in λ S and ∂ ω/∂H are related to the changes in CSRO and TSRO, to relaxation processes and to internal stresses. The transformation process has been monitored by temperature dependencies of electrical resistivity. Amorphous samples crystallized after annealing at temperatures above 678 K into nanocrystalline supersaturated solid solution bcc-Fe(Co, Mo) and above 873 K into B 24Fe 84Mo 8, CoMoB and traces of B 2Mo 2Fe and tetragonal Fe 3B. As-quenched samples exhibit the Curie temperature at around 600 K, in the vicinity of the glass transition temperature. At room temperatures, the ribbon exhibits isotropic characteristics. Thermal treatment induces magnetic anisotropy formed in the direction parallel to the ribbon axis during relaxation annealing while during crystallization its direction becomes perpendicular to the ribbon axis. Remanence appears after heat treatment above 920 K.

Structural and Mössbauer Effect Investigations of Amorphous FeCuNbSiB Alloys Nanocrystallized (VITROPERM) in Magnetic Field

Melt-spun amorphous ribbons of nominal composition Fe73Cu1Nb3Si16B7, annealed at 560-580 degrees C for 1 hour in a magnetic field (H) applied along the width in the ribbon plane, develop uniaxial magnetic anisotropy with easy axis along H and exhibit several novel attributes. The samples labelled as S20 and S150 are nanocomposites consisting of ferromagnetic nanocrystalline grains (volume fraction approximately equal to 84% and 81%) of mean size d = 13(2) nm embedded in a ferromagnetic amorphous matrix and possess a magnetic permeability as large as 20,000 and 150,000, respectively. While nearly 55% of the nanocrystalline grains have a cubic DO3 Fe3Si-like structure with actual Si concentration of about 22 at.%, the remaining 45% nanocrystalline grains have tetragonal Fe3B and hexagonal Fe2Si structure. Since the crystalline volume fraction of Fe3B and Fe2Si nanocrystals is more in the sample S20, this sample exhibits stronger local magnetic anisotropy and hence lower permeability.

NMR study of rapidly quenched crystalline and amorphous Fe-B alloys

Amorphous and microcrystalline Fe-B alloys (4–25 at % B) obtained by rapid quenching of the melt were studied using the pulsed nuclear magnetic resonance (NMR) of 11B nuclei at 4.2 K. Alloy samples were prepared from both a natural isotope mixture and a mixture of the 56Fe and 11B isotopes. The NMR spectra were measured as a function of the boron content. The maximum hyperfine fields at the 11B nuclei sites are 25–29 kOe and overlap the values of the hyperfine fields at the 11B nuclei sites in the tetragonal and orthorhombic Fe3B phases and also in the α-Fe phase containing boron as a substitutional impurity. The short-range order and local atomic structure of the amorphous Fe-B alloys were determined. The amorphous alloys are found to consist of microregions (clusters) with a short-range order similar to that in the tetragonal or orthorhombic Fe3B phase or the α-Fe phase.

Growth of boride layers on the 13% Cr steel surface in a mixture of amorphous boron and KBF4

Two borides FeB and Fe2B were found to form as separate layers at the interface between a 13% Cr steel and boron at 850–950 °C and reaction times up to 12 h. The average chromium content is 8 at.% in the FeB layer and 9 at.% in the Fe2B layer. Both layers are characterized by a pronounced texture. The strongest reflections are {002} and {020} for the orthorhombic FeB phase and {002} for the tetragonal Fe2B phase. Diffusional growth kinetics of boride layers are close to parabolic and can alternatively be described by a system of two non-linear differential equations, producing a good fit to the experimental data. Annealing of a borided steel sample in the absence of boriding media results in disappearance of the FeB layer. Microhardness values are 17.9 ± 1.5 GPa for the FeB layer, 16.1 ± 0.9 for the Fe2B layer and 5.9 ± 0.3 GPa for the steel base. The abrasive wear resistance of the FeB layer is 25 times greater than that of the steel base. The Fe2B layer yields about a 15-fold increase in wear resistance of steel samples.