Microstructure and properties of nanocrystalline Fe–Zr–Nb–B soft magnetic alloys with low magnetostriction

We have investigated the microstructure–property relationship of nanocrystalline Fe₈₅Zr_1.2Nb_5.8B₈ and Fe_85.5Zr₂Nb₄B_8.5 soft magnetic alloys in order to understand the origin of drastic change in the permeability regardless of the zero magnetostriction in these two alloy compositions. Plan-view and cross-section transmission electron microscopy (TEM) observations showed strongly textured α-Fe particles on the free surface of the Fe₈₅Zr_1.2Nb_5.8B₈ alloy ribbon, while uniform nanocrystalline microstructure was observed in the Fe_85.5Zr₂Nb₄B_8.5 alloy ribbon. The high Zr content of the latter improves the glass forming ability, thereby suppressing the surface crystallization, resulting in higher permeability. By adding Cu in the Fe–Zr–Nb–B alloy, uniform nanocrystalline microstructure was obtained, from which superior soft magnetic properties with zero magnetostriction was achieved.     

Structure and magnetic properties ofhigh-performanced Sm2（Co, Fe, Cu, Zr）17 alloys

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Structure and properties of cast and splat-quenched high-entropy Al–Cu–Fe–Ni–Si alloys

The effect of the composition and cooling rate of the melt on the microhardness, phase composition, and fine-structure parameters of as-cast and splat-quenched (SQ) high-entropy (HE) Al–Cu–Fe–Ni–Si alloys was studied. The quenching was performed by conventional splat-cooling technique. The cooling rate was estimated to be ~10⁶ K/s. Components of the studied HE alloys were selected taking into account both criteria for designing and estimating their phase composition, which are available in the literature and based on the calculations of the entropy and enthalpy of mixing, and the difference between atomic radii of components as well. According to X-ray diffraction data, the majority of studied Al–Cu–Fe–Ni–Si compositions are two-phase HE alloys, the structure of which consists of disordered solid solutions with bcc and fcc structures. At the same time, the Al_0.5CuFeNi alloy is single-phase in terms of X-ray diffraction and has an fcc structure. The studied alloys in the as-cast state have a dendritic structure, whereas, after splat quenching, the uniform small-grained structure is formed. It was found that, as the volume fraction of bcc solid solution in the studied HE alloys increases, the microhardness increases; the as-cast HE Al–Cu–Fe–Ni–Si alloys are characterized by higher microhardness compared to that of splat-quenched alloys. This is likely due to the more equilibrium multiphase state of as-cast alloys.     

Martensitic transformation and magnetic properties in Ni–Fe–Ga–Co magnetic shape memory alloys

Ni–Fe–Ga–Co is a promising system for magnetic shape memory alloy applications, due to its good ductility, mobile twin boundaries and high transformation temperatures. Unlike previous studies which focused on compositions with a Ga content of 27 at.%, here the martensitic transformation and magnetic properties over a large composition range of Ni_54−xFe₂₀Ga₂₆Co_x, Ni_54−xFe₁₉Ga₂₇Co_x, Ni_56−xFe₁₇Ga₂₇Co_x and Ni_54−xFe₁₈Ga₂₈Co_x (x = 0, 2, 4) are investigated. The martensitic transformation temperature T_m and the Curie temperature T_c can be tailored in a wide range by changing composition and heat treatment. A coupling of martensitic and magnetic transformations at ∼90 °C is found for Ni₅₂Fe₁₇Ga₂₇Co₄. Additionally, the effect of thermal cycling on the martensitic transformation of single- and two-phase Ni–Fe–Ga–Co alloys is discussed. Furthermore, an intermediate face-centered cubic phase induced by powderization and transformed into a body-centered cubic phase by aging is reported. The saturation magnetization is significantly decreased by powderization, while recovered by the subsequent aging.     

The characterization of structure,thermal stability and magnetic properties of Fe–Co–B–Si–Nb bulk amorphous and nanocrystalline alloys

Recently bulk amorphous alloys have attracted great attention due to their excellent magnetic properties. The glass-forming ability of bulk amorphous alloys depends on the temperature difference (ΔT_x) between glass transition temperature (T_g) and crystallization temperature (T_x). The increase of ΔT_x causes a decrease of the critical cooling rate (V_c) and growth of the maximum casting thickness of bulk amorphous alloys. The aim of the present paper is to characterize the structure, the thermal stability and magnetic properties of Fe₃₆Co₃₆B₁₉Si₅Nb₄ bulk amorphous alloys using XRD, Mössbauer spectroscopy, DSC and VSM methods. Additionally the magnetic permeability μ_i (at force H ≈ 0.5 A/m and frequency f ≈ 1 kHz) and the intensity of disaccommodation of magnetic permeability Δμ/μ(t₁) (Δμ = μ(t₁ = 30 s) ? μ(t₂ = 1800 s)), have been measured, where μ is the initial magnetic permeability measured at time t after demagnetisation, the Curie temperature T_C and coercive force H_c of rods are also determined with the use of a magnetic balance and coercivemeter, respectively.Fe–Co–B–Si–Nb bulk amorphous alloys were produced by pressure die casting with the maximum diameters of 1 mm, 2 mm and 3 mm.The glass transition temperature (T_g) of studied amorphous alloys increases from 807 K for a rod with a diameter of 1 mm to 811 K concerning a sample with a diameter of 3 mm. The crystallization temperature (T_x) has the value of 838 K and 839 K for rods with the diameters of 1 mm and 3 mm, respectively. The supercooled liquid region (ΔT_x = T_x ? T_g) has the value of about 30 K. These values are presumed to be the origin for the achievement of a good glass-forming ability of the Fe–Co–B–Si–Nb bulk amorphous alloy. The investigated amorphous alloys in the form of rods have good soft magnetic properties (e.g. M_s = 1.18–1.24 T). The changes of crystallization temperatures and magnetic properties as a function of the diameter of the rods (time of solidification) have been stated.     

Structure and mechanical properties of as-cast Ti–Si alloys

In the present work, the microstructure and mechanical properties of as-cast Ti–Si alloys with a Si content ranging from 1 to 12.5 wt% prepared using a dental cast machine were investigated and compared with commercially pure titanium (c.p. Ti). X-ray diffraction (XRD) for phase analysis was conducted using a diffractometer. Three-point bending tests were performed to evaluate the mechanical properties of all specimens and their microstructure and fractured surfaces were observed using scanning electron microscopy (SEM). Experimental results indicated that the diffraction peaks of the Ti–Si alloys matched those of α-Ti and Ti₅Si₃. All the Ti–Si alloys had higher bending strengths and bending moduli than those of c.p. Ti. For example, the bending strength of Ti–5Si was about 2.6 times that of c.p. Ti, and both Ti–10Si and Ti–12.5Si had the highest bending moduli, which were about 1.8 times higher than that of c.p. Ti. Additionally, Ti–1Si exhibited ductile properties and Ti–3Si and Ti–5Si had a combination of brittleness and ductility. When the Si content was 7.5 wt% or greater, the alloys showed brittle properties. Judging from the results of the mechanical properties and deformation behavior, Ti–1Si, Ti–3Si, and Ti–5Si can be considered highly feasible alloys for prosthetic dental applications if other properties necessary for dental casting are obtained.     

Electronic structure and transport properties of Fe–Al alloys

Electronic structure of iron-aluminides (Fe_1−xAl_x) has been calculated for a range of aluminum concentration (0⩽x⩽0.5) by using first principles density functional theory to explain the variation of electrical resistivity with increasing Al content. The Fe–Al intermetallics are modeled by a cluster of 15 atoms confined to their bulk geometry. The location of Al atoms as a function of concentration, x was determined by minimizing the total energy of the clusters. The electronic structure was determined by calculating the total as well as partial density of states around each of the Fe and Al atoms. With increasing Al concentration, the transfer of Al 3p electrons into the minority 3d orbital of Fe not only has a profound effect on the magnetic properties of these intermetallics, but affects their transport properties as well. For example, the observed anomaly in the electrical resistivity of Fe_1−xAl_x that peaks at x=0.33 is found to be a direct consequence of the filling of the Fe 3d orbital with Al valence electrons. The density of states is characterized by three distinct features: a narrow 3d band just below the Fermi energy originating from the Fe atoms, an Al s-band lying deeper in energy, and an Al p-band above the Fermi energy. The energy gap between Al 3p and Fe 3d density of states decreases with increasing Al concentration and for x=0.40, the density of states at the Fermi energy is a strongly hybridized p–d state giving Fe_1−xAl_x metallic-like properties. These features are consistent with the recent photoemission studies carried out at the synchrotron facility at Lawrence Livermore National Laboratory. An anomaly in the temperature dependence of electrical resistivity is also explained in terms of the unique electronic and magnetic structure of these intermetallics.     

Microstructure and magnetic properties of rapidly solidified Sm（CobalFe0.11Cu0.10Zrx）7 alloys

Effects of Zr content on the structural, morphological, and magnetic properties of rapidly quenched Sm（CoF0.11CU0.10Zrx）7 （x=0 0.04） alloys were investigated. The Zr-free ribbon crystallizes with the 2：17H structure as a major phase while the ribbons with Zr addition adopts the 2：17R structure type. The ribbons with x-0.03 exhibits a highest coercivity, Hci=933.7 kA/m, because a smaller uniform cellular structure along with a lamellar phase is formed. The decrease of Hci above x〉0.03 is mainly related to the formation of 2：7 phase.     

Structure and magnetic properties of a multi-principal element Ni–Fe–Cr–Co–Zn–Mn alloy

A nanocrystalline alloy with a nominal composition of Ni₂₀Fe₂₀Cr₂₀Co₂₀Zn₁₅Mn₅ was produced by mechanical alloying and processed using annealing treatments between 450 and 600 °C for lengths from 0.5 to 4 h. Analysis was conducted using x-ray diffraction, transmission electron microscopy, magnetometry, and first-principles calculations. Despite designing the alloy using empirical high-entropy alloy guidelines, it was found to precipitate numerous phases after annealing. These precipitates included a magnetic phase, α-FeCo, which, after the optimal heat treatment conditions of 1 h at 500 °C, resulted in an alloy with reasonably good hard magnetic properties. The effect of annealing temperature and time on the microstructure and magnetic properties are discussed, as well as the likely mechanisms that cause the microstructure development.     

Fe–B–Si–Zr soft magnetic bulk glassy alloys

The present work is devoted to fabrication of Fe–B–Si–Zr multi-component bulk glassy alloys with good mechanical and soft magnetic properties. Glass formation in Fe–B system is first considered with an empirical cluster-plus-glue-atom model. A basic composition formula [B–B₂Fe₈]Fe is proposed as the framework for multi-component alloy design. Considering the structural stability of the model glass, Si and Zr are introduced to the [B–B₂Fe₈] cluster to replace the center B and shell Fe atoms, from which a series of Fe–B–Si–Zr alloys with composition formulas [Si–B₂Fe_8−xZr_x]Fe (x = 0–0.6) are derived. Copper mold casting experiment shows that bulk glassy alloys are formed within the Zr content range of x = 0.2–0.6, and the largest glass-forming ability appears at [Si–B₂Fe_7.6Zr_0.4]Fe with a critical size of 2.5 mm. The bulk glassy alloys exhibit high fracture strength as large as 3850 MPa. Magnetic property measurement indicates that these alloys exhibit good magnetic softness with high saturation magnetization (1.26–1.48 T) and low coercive force (1.6–6.7 A/m). The alloying effects of Si and Zr on bulk glass formation, thermal glass stability and magnetic softness are discussed with the empirical model.     

Structure and magnetic properties of Mn-doped CuO solids

The CuO doped with 5%-20% Mn(molar fraction) solids were sintered from CuO and MnO2 powder at high temperature (1 273 K) for 8 h. X-ray diffraction was used to determine the solid crystallinity and to address the formation of secondary phases. It is found that it is difficult to achieve pure Cu1-xMnxO phase using standard solid phase reaction. However, sintering under a pressure of 27.7 MPa significantly reduces the undesirable second phase CuMn2O4, providing a route to achieve pure Cu3-x MnxO phase. SQUID magnetometry was employed to characterize the magnetic properties. Mn-doped CuO presents ferromagnetic characteristics below 70 K. Electrical transport properties were measured in a current-perpendicular-to-plane(CPP) geometry using the PPMS, which suggests variable-range hopping mechanism.     

Structure and magnetic properties of amorphous and polycrystalline Fe3O4 thin films

Half-metallic Fe3O4 films prepared by-DC magnetron reactive sputtering with a tantalum（Ta） buffer layer was investigated. Primary emphasis is placed on the structural impact on its magnetic properties. The experimental results show that the amorphous Fe3O4 films exhibit a superparamagnetic response at a large-scale from 20 nm to 150 nm, and the magnetoresistance （MR） isn＇t detected. By contrast, the polycrystalline Fe3O4 films possess large saturation magnetization Ms of 420 A/（kg.cm） and a clear magnetoresistance with a field of 40 kA/m. The unusual properties for the amorphous Fe3O4 film are attributed to the existing large density of the similar structure as anti-phase boundaries in the film.     

Effect of Mn addition on the structural and magnetic properties of Fe–Pd ferromagnetic shape memory alloys

The effect of Mn addition on the structural and magnetic properties of Fe–Pd ferromagnetic shape memory alloys is investigated. In particular, a complete characterization of the influence of the partial substitution of Fe by Mn has been performed on Fe_69.4?xPd_30.6Mn_x (x = 0, 1, 2.5 and 5) alloys. The substitution of 1% Fe by Mn fully inhibits the undesirable irreversible face-centered tetragonal to body-centered tetragonal transformation without decreasing the face-centered cubic to face-centered tetragonal temperature. In addition, the substitution of 2.5% Fe by Mn gives rise to the highest thermoelastic transformation temperature observed to date in the Fe–Pd system, probably due to an increase in the valence electron concentration. The magnetocaloric effect has been evaluated in this alloy system for the first time. Nevertheless, the low values obtained suggest that the Fe–Pd alloys are not good candidates for magnetic refrigeration applications.     

Structure and magnetic properties of Pr0. 1CexTb0.9-xFe1.9 alloys

1　INTRODUCTIONTerfenol D ( Tb0.27 Dy0.73 Fe2 ) exhibits largemagentostriction and minimized magnetic anisotro py at room temperature[1], so it is widely used inactuators and transducers. But the main raw mate rials of Terfenol D are expensive Tb and Dy. Ac cording to the single ion model[2], CeFe2 and PrFe2compounds have larger magnetostriction thanTbFe2 and DyFe2 at 0 K. In addition, Ce and Prare much cheaper than Tb and Dy. So Ce basedand Pr based compo…     

The effect of melt-spinning processing parameters on crystal structure and magnetic properties in Fe–Mn–Ga alloys

We have succeeded to fabricate body-centered cubic (bcc) single phase of Fe–Mn–Ga alloys using melt-spinning technique. Heusler type L2₁ structure of Fe₂MnGa alloy are predicted to have half-metallic properties, however bulk Fe₂MnGa alloys crystallize into face-centered cubic (fcc) lattice with small admixture of bcc phase. By changing either ejection temperature or rotation speed of melt-spinning processing parameters, fcc or bcc lattice can be obtained from same precursor ingot. For stoichiometric Fe₂MnGa as-spun alloy, super-lattice diffraction peaks indicative of L2₁ structure are observed from XRD measurements. The as-spun bcc alloys transform into ferromagnetic hexagonal lattice by thermal annealing.     

Preparation and characterisation of melt-spun Al–Cu–Fe quasicrystals

Three Al–Cu–Fe alloys with compositions of Al_60–65Cu_20–27.5Fe_12.5–15 were prepared by conventional casting and further processed by melt-spinning. The structures formed were examined to get an insight into the interrelated effects of synthesis, processing and microstructure of Al–Cu–Fe alloys. The study aimed at answering the questions such as whether the production of single-phase quasicrystalline ribbons is possible by the melt-spinning process and what is the role of the degree of undercooling in the development of microstructure in melt-spun ribbons.The icosahedral ψ-Al₆₅Cu₂₀Fe₁₅ phase forms by a peritectic reaction between the primary β-AlFe phase and the liquid, as the temperature decreases. At the later stages of cooling, the monoclinic λ-Al₁₃Fe₄ phase and the tetragonal θ-Al₂Cu phase are formed in the cast alloys, as a result of peritectic reactions. In the rapidly solidified alloys, the formation of the tetragonal θ-Al₂Cu phase and, in the case of alloy Al₆₀Cu₂₅Fe₁₅, the monoclinic λ-Al₁₃Fe₄ phase is avoided, apparently due to high degree of undercooling. Thus, the production of single-phase quasicrystalline ribbons is not possible by the melt-spinning process, at least by using the cooling rate of 5–7×10⁴ °C/s. In addition to phase selection, the degree on undercooling influences, for example, the composition of the ψ-Al₆₅Cu₂₀Fe₁₅ phase and the grain morphology in melt-spun ribbons.     

Effect of swaging on microstructure and tensile properties of W–Ni–Fe alloys

The objective of this study was to investigate the effect of swaging on the microstructure and tensile properties of high density two phase alloys 90W–7Ni–3Fe and 93W–4.9Ni–2.1Fe. Samples were liquid phase sintered under hydrogen and argon at 1480 °C for 30 min and then 15% cold rotary swaged. Measurement of microstructural parameters in the sintered and swaged samples showed that swaging slightly increased tungsten grain size in the longitudinal direction and slightly decreased tungsten grain size in the transverse direction. Swaging increased the contiguity values in both longitudinal and transverse directions. Swaging led to more severe deformations at the edges than at the center of the specimens. Solidus and liquidus temperatures of the nickel-based binder phase in the sintered and swaged samples were determined by differential scanning calorimetry measurements. An increase in tensile strength with a reduction in ductility was observed due to strain hardening by swaging.     

Fe–B–P–Cu nanocrystalline soft magnetic alloys with high Bs

The effects of the addition of Cu on the crystallization processes, nanostructures and soft magnetic properties for the Fe_80.8–84.8B_8–10P_6–8Cu_1.2 alloys were investigated. The Fe–B–P–Cu alloys show two separated distinct exothermic peaks upon heating due to the addition of Cu. Furthermore, the interval temperature between each one for the Fe_82.8B₉P₇Cu_1.2 alloy is 103 K, and the first and second exothermic peaks result from the phase transition from amorphous to α-Fe and then to Fe₃(B,P), respectively. A uniform nanocrystalline structure composed of α-Fe grains with a 17 nm diameter was realized by annealing just above the first exothermic peak, and this nanocrystalline alloy exhibits high B_s of 1.70 T and low H_c of 4.9 A/m. Therefore, the nanocrystalline Fe–B–P–Cu soft magnetic alloy with high B_s and low H_c has a large industrial advantage due to miniaturization, high efficiency and low material cost of electric devices.     

Quantitative relationships between magnetic properties,microstructure and composition of WC–Co alloys

A quantitative relationship between WC grain size, Co content and coercivity has been derived using data from a wide range of WC–Co alloys. The relationship has been found to agree with data from independent investigations.     

Effect of Al on microstructure and magnetic properties of mould-cast Nd60Fe40−xAlx alloys

Mould-cast Nd₆₀Fe_40−xAl_x (x=0, 5, 10) alloys were studied to clarify the effect of Al on the structural and magnetic properties. For binary Nd₆₀Fe₄₀, the metastable hard magnetic A₁ phase forms along with the Nd₂Fe₁₇ equilibrium phase. Partial substitution of Fe by Al favours the formation of the hard magnetic metastable A₁ phase manifested by a large magnetization.