Microstructure and magnetic properties of plasma-sprayed Fe73.5Cu1Nb3Si13.5B9 coatings

Amorphous and nanocrystalline Fe_73.5Cu₁Nb₃Si_13.5B₉ coatings were formed by plasma-spraying micron-sized powders onto H62 brass substrates and aluminum pipes. The coatings are about 0.2-0.3 mm in thickness with fully dense and low porosity. The microstructure of the coatings is classified into two regions, namely, a full amorphous phase region and homogeneous dispersion of α-Fe nanoscale particles with a scale of 30-70 nm. The hardness of the amorphous and nanocrystalline coatings is about 960 HV_100g. Coercivity (Hc), saturation induction (B₈₀₀), and initial relative permeability (μ_i) of the coatings are 144 A/m, 0.27 T, 249, respectively, under 800 A/m direct current (DC) magnetic field. The magnetic shielding performance is good under DC magnetic field and its magnetic shielding effectiveness (SE) is 10-12 dB at coating thickness of 0.45 mm under static magnetic field of 2-40 Oe. The SE increases by increasing the coating thickness when the magnetic field frequencies are 50, 100 and 200 Hz with an intensity of 0.85 Oe. The results indicate that the amorphous and nanocrystalline alloy coatings can be good for some magnetic shielding applications.     

Effect of P on crystallization behavior and soft-magnetic properties of Fe83.3Si4Cu0.7B12 − xPx nanocrystalline soft-magnetic alloys

The P content dependences of the crystallization behavior, thermal stability and soft-magnetic properties of high Fe content Fe_83.3Si₄Cu_0.7B_12 − xP_x (x = 0 to 8) nanocrystalline soft-magnetic alloys were investigated. P addition is very effective in widening the optimum annealing temperature range and refining of bcc-Fe grain size in addition to the increasing of nanocrystalline grain density. Uniform nanocrystalline bcc-Fe grains with average size of about 20 nm and number density of 10²³-10²⁴ /m³ were prepared at around x = 6-8 for the annealed Fe_83.3Si₄Cu_0.7B_12 − xP_x alloys. The coercivity H_c markedly decreases with increasing x and exhibits a minimum at around x = 6-8, while the saturation magnetic flux density B_s shows a slight decrease. Fe_83.3Si₄Cu_0.7B₆P₆ nanocrystalline alloy exhibits excellent soft-magnetic properties with a high saturation magnetic flux density B_s of 1.77 T, low coercivity H_c of 4.2 A/m and high effective permeability μ_e of 11,600 at 1 kHz.     

Nanocrystallization kinetics of amorphous Fe81B13.5Si3.5C2 magnetic ribbons

The kinetics of the nanocrystallization of amorphous Fe₈₁B_13.5Si_3.5C₂ ribbon is studied. The changes in the microstructures and magnetic properties of ribbons annealed at 425 and 495 °C for 0.5-10 h were investigated using an X-ray diffractometer (XRD), Mössbauer spectroscopy (MS), differential scanning calorimeter (DSC) and vibrating sample magnetometer (VSM). The changes in the surface morphology were observed by a changed atomic force microscope (AFM). The XRD patterns and the Mössbauer spectrums show the formation of nanocrystallites of α-Fe(Si), Fe-B, Fe₃C and Fe₃Si of different grain sizes when annealed at different temperatures. The nanocrystallization kinetics of the Fe₈₁B_13.5Si_3.5C₂ ribbon are described by an Avrami growth curve with an exponent values of 1.34 and 1.01 for the isothermal annealing at 425 and 495 °C, respectively. AFM topography pictures and surface image show that the density of the microstructure and the size of the grain increase as higher annealing temperatures are used.     

Nanocrystalline structure and initial permeability of annealed Fe73.5Cu1M03Si13.5B9 alloy

Abstract

The nanocrystalline structure of annealed Fe_73.5Cu₁M0₃Si_13.5B₉ alloy was investigated using X-ray diffraction and transmission electron microscopy. The relationship between the initial permeability and the microstructural parameters of the annealed alloy is discussed in this paper. The crystalline phase in annealed Fe_73.5Cu₁M0₃Si_13.5B₉ alloy is the α-Fe(Si) phase with a D0₃ superstructure. The volume fraction, silicon content, and degree of order of the α-Fe(Si) phase increased with an increase in the annealing temperature. In the temperature range of 460–560°C, the α-Fe(Si) phase had a grain size of 14 nm, and its grain number increased as the annealing temperature was increased. The D0₃ ordered region in the α-Fe(Si) grain was approximately spherical and its size increased as the annealing temperature increased. The size of the D0₃ ordered region was 14.0 nm at a temperature of 560°C, which is close to that of the α-Fe(Si) grain. There was an obvious change in the microstructure of the residual amorphous phase during annealing, the nearest atomic distance and the short range order of residual amorphous phase reaching a maximum and minimum respectively at 520°C. The initial permeability of annealed Fe_73.5Cu₁M0₃Si_13.5B₉ alloy was not only dependent on the microstructure of the α-Fe(Si) phase but was also related to the microstructural state of the residual amorphous phase.     

Fine Fe16N2 powder prepared by low-temperature nitridation

α-Fe was prepared by reduction of a fine γ-Fe₂O₃ powder under hydrogen at 500 °C for 8 h. The α-Fe fine powder, about 100 nm in crystallite size, was then nitrided under an ammonia flow at 130 °C for 100 h. X-ray single-phase Fe₁₆N₂ was obtained with a magnetization value of 225 emu/g at room temperature under a magnetic field of 15 kOe. The Mössbauer spectrum at room temperature could be resolved into three sets of hyperfine fields with an average magnetic moment of 2.52 μ_B. An additional paramagnetic component was present in the spectrum with an area ratio of 19%.     

Characteristics of NixFe100−x films deposited on SiO2/Si(1 0 0) by DC magnetron co-sputtering

Ni_xFe_100−x films with a thickness of about 200 nm were deposited on SiO₂/Si(1 0 0) substrates at room temperature by DC magnetron co-sputtering using both Fe and Ni₈₀Fe₂₀ targets. Compositional, structural, electrical and magnetic properties of the films were investigated. Ni₇₆Fe₂₄, Ni₆₅Fe₃₅, Ni₆₀Fe₄₀, Ni₅₅Fe₄₅, Ni₄₉Fe₅₁ films are obtained by increasing the sputtering power of the Fe target. All the films have a fcc structure. Ni₇₆Fe₂₄, Ni₆₅Fe₃₅, Ni₆₀Fe₄₀ and Ni₅₅Fe₄₅ films grow with crystalline orientations of [1 1 1] and [2 2 0] in the direction of the film growth while the Ni₄₉Fe₅₁ film has the [1 1 1] texture structure in the direction of the film growth. The lattice constant of the film increases linearly with increasing Fe content. All of the films grow with thin columnar grains and have void networks in the grain boundaries. The grain size does not change markedly with the composition of the film. The resistivity of the film increases with increasing Fe content and is one order of magnitude larger than that of the bulk. For all the films the magnetic hysteresis loop shows a hard magnetization. The Ni₇₆Fe₂₄ film has the lowest saturation magnetization of 6.75×10⁻² T and the lowest saturation field of 8.36×10⁴ A/m while the Ni₄₉Fe₅₁ film has a largest saturation magnetization of 9.25×10⁻² T and the largest saturation field of 1.43×10⁵ A/m.     

Tem study of nanocrystalline NdFeB

A detailed study is reported of the microstructure in a nanocrystalline alloy, Nd₄Fe₇₈B₁₈, consisting of a mixture of hard (Nd₂Fe₁₄B) and soft (Fe₃B) magnetic phases, utilizing conventional and analytical transmission electron microscopy (TEM). The nanocrystalline microstructures were fabricated by annealing the melt-spun amorphous Nd₄Fe₇₈B₁₈ ribbons by means of conventional (furnace) annealing techniques and also by the so-called flash-annealing process. Enhanced remanence and coercivity were reported previously for the flash-annealed alloys. Furnace-annealed ribbons contained 20–30 nm equiaxed grains with Fe/Nd = 17–19.6. Also observed were large (50–100 nm) equiaxed grains of α-Fe. For flash-annealed ribbons, significant amounts of Nd₂Fe₂₃B₃, a metastable cubic phase, were observed, as well as a marked difference in the second phase morphology. For the flash-annealed ribbon whose hysteresis loop showed good coupling of the magnetic phases, a refined microstructure was found and the large α-Fe grains were absent.     

Effect of heating rate on the microstructural and magnetic properties of nanocrystalline Fe<Subscript>81</Subscript>Si<Subscript>4</Subscript>B<Subscript>12</Subscript>P<Subscript>2</Subscript>Cu<Subscript>1</Subscript> alloys

The effect of heating rate on the structural and magnetic properties of the nanocrystalline Fe₈₁Si₄B₁₂P₂Cu₁ alloy has been investigated. Amorphous Fe₈₁Si₄B₁₂P₂Cu₁ alloy was annealed at 753 K for 180 s at different heating rates ranging from 0.05 to 5 K/s in protective argon atmosphere. The structural and magnetic properties of the as-quenched and annealed alloys were studied using X-ray diffractometer (XRD), differential scanning calorimeter (DSC), vibrating sample magnetometer (VSM), and B–H loop tracer, respectively. Amorphous precursor prepared by industry-grade raw materials is obtained. The increase of heating rate is found to be significantly effective in decreasing the grain size of α-Fe(Si) phase, but the grain size increases at higher heating rate. The volume fraction of α-Fe(Si) phase shows a monotonic decrease with the increase of the heating rate. The coercivity H _c markedly decreases with increasing heating rate and exhibits a minimum at the heating rate of 0.5 K/s, while the saturation magnetization, M _s, shows a slight decrease. These results suggest that the effect of heating rate on H _c and M _s is originated from the changes of grain size and the volume fraction of α-Fe(Si) phase.     

Influence of wheel speed during planar flow melt spinning on the microstructure and soft magnetic properties of Fe<Subscript>68.5</Subscript>Si<Subscript>18.5</Subscript>B<Subscript>9</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> ribbons

The structure and soft magnetic properties of Fe_68.5Si_18.5B₉Nb₃Cu₁ (at.%) alloy ribbons produced through planar flow melt spinning at different wheel speeds viz. 34, 17 and 12 m/s have been investigated using X-ray diffraction, differential scanning calorimetry, transmission electron microscopy, vibrating sample magnetometer and positron lifetime spectroscopy. Amorphous ribbons formed with different wheel speeds manifested different enthalpy and activation energy of crystallization. The volume fraction of nanocrystalline phase, saturation magnetization and permeability are found to increase whereas coercivity is found to decrease with increasing wheel speed on annealing. A detailed analysis of positron lifetime spectra obtained from the as-spun ribbons has been used to rationalize the variation in microstructure and magnetic properties. The presence of larger number of defects at higher wheel speed increases the volume fraction of nanocrystalline phase on annealing which improves the soft magnetic properties.     

Electrochemical behavior of partially crystallized amorphous Al86Ni9La5 alloys

The Al₈₆Ni₉La₅ amorphous ribbons were annealed at 503 K for different time to obtain partially crystallized alloys with the different volume fractions of α-Al phase, and the effect of the crystallization extent on the electrochemical behavior of the ribbon was investigated in 0.01 M NaCl solution. The results show that the corrosion resistance of the partially crystallized ribbons is higher than that of the as-spun ribbon with the fully amorphous structure, and the corrosion resistance of the partially crystallized alloy is strongly dependent on the volume fraction of α-Al phase. The partially crystallized ribbon containing about 20 vol% α-Al phase exhibits the highest corrosion resistance.     

The influence of Al content on glass forming ability and magnetic properties of high Ms nanocrystalline FeSiBPCuAl alloy

Al content on the influence of glass forming ability and magnetic properties of nanocrystalline (Fe_83.3Si₄B₈P₄Cu_0.7)_100 − xAl_x (x = 0 ∼ 1.25 at.%) alloy was investigated in our work. Experimental results show that addition of 0.5 at.% Al is effective in improving the glass forming ability of Al-free alloy and thus amorphous precursor prepared by industry-grade raw materials can be obtained. Meanwhile, the addition of Al is beneficial in decreasing coercive force and maintaining high saturation magnetization above 180 emu/g, which makes Fe-Si-B-P-Cu-Al alloy a promising soft magnetic material in potential applications.     

The excellent soft magnetic properties and corrosion behaviour of nanocrystalline FePCCu alloys

The effects of the addition of Cu on the crystallisation behaviour, soft magnetic properties, and corrosion behaviour of Fe_84-xP₉C₇Cu_x (x = 0–1.15) alloys were investigated. The experimental results demonstrate that the glass-forming ability of this alloy was improved and the soft magnetic properties of the alloy system were enhanced by proper Cu addition. FePCCu nanocrystalline alloys with a dispersed α-Fe phase were obtained by appropriately annealing the melt-spun ribbons at 693 K for 2 min. The Fe_83.25P₉C₇Cu_0.75 nanocrystalline alloy exhibited a high saturation magnetic flux density, B _s , of 1.64 T; a low coercivity, H _c , of 3.9 A/m; and a high effective permeability, μ _e , of 21,000 at 1 kHz. These characteristics are superior to corresponding properties of FePC alloys. Furthermore, the corrosion resistance of this nanocrystalline alloy increases when elevating the annealing temperature and was confirmed to be improved with respect to the corresponding amorphous alloy. These results indicate that this alloy is a promising soft magnetic material.     

Bulk α-Fe/Nd2Fe14B nanocomposite magnets prepared by the phase transition of amorphous Nd9Fe81Co3Nb1B6 under high pressure

In the present study, the authors succeeded in preparing the bulk α-Fe/Nd₂Fe₁₄B nanocomposite magnets with a nearly full density by the phase transition of amorphous Nd₉Fe₈₁Co₃Nb₁B₆ powders under 1 GPa at a temperature of 750 °C. Compared to the magnets prepared from partly amorphous or nanocrystalline powders, the magnets show quite homogeneously distributed nanocrystals with a small grain size, 28 nm for the α-Fe phase and 35 nm for the Nd₂Fe₁₄B phase, which results in enhanced magnetic properties.     

Effect of addition of aluminum on the evolution of microstructure in HITPERM class Fe44Co44Zr7B4Cu1 alloy

The paper reports the effect of the addition of small amount of Al on the microstructure and properties of HITPERM class rapidly solidified Fe₄₄Co₄₄Zr₇B₄Cu₁ glassy alloy. Using three dimensional atom probe measurements we present evidence for the formation of Cu clusters on annealing in the metallic glass matrix of the Al containing alloy Fe₄₃Co₄₃Al₂Zr₇B₄Cu₁. Such clusters are otherwise absent in the parent alloy under similar conditions. The Cu clusters provides heterogeneous nucleation sites for the formation of bcc α′-FeCo phase leading to an increase in number density of this nanocrystalline phase and thereby enhancing the magnetic properties.     

Method to improve high-frequency magnetic characteristics of Fe80Ni20-O alloy films by introducing low-dose oxygen

In this letter, we propose a method to fabricate Fe₈₀Ni₂₀-O film with improved static and high-frequency, magnetic and electrical properties. Fe₈₀Ni₂₀-O alloy films were prepared by direct current magnetron sputtering at room temperature. The results show that the in-plane uniaxial magnetic anisotropy fields can be adjusted in a broad range by solely adding a very low dose of oxygen into Fe₈₀Ni₂₀ alloy films without applying any inducing field on substrates during deposition. By increasing the oxygen flow ratio from 0.75% to 3%, Fe₈₀Ni₂₀-O alloy films could be achieved with an adjustable ferromagnetic resonance frequency f_r (from 2.2 to 5.9 GHz), a large saturation magnetization 4πMs (from 16.7 to 15.2 kG), and a high resistivity ρ (from 56.7 to 108 μΩ cm).     

Electrospun SrRe0.6Fe11.4O19 magnetic nanofibers: Fabrication and characterization

Substituted strontium ferrite SrRe_0.6Fe_11.4O₁₉ (Re = La, Ce) nanofibers with average diameters of 200-300 nm were manufactured by electrospinning technology combined with sol-gel method. In the process, spinnability was conferred by the addition of poly(vinyl pyrrolidone) and acetic acid, which were used as a spinning aid. Structural and morphology investigations made by X-ray diffraction, SEM and TEM revealed that SrRe_0.6Fe_11.4O₁₉ polycrystalline nanofibers were hexagonal magnetic plumbite structure. The calculation using the Scherrer's equation on the base of the X-ray diffraction spectrum indicated that the average grain size was about 30-40 nm. The magnetic properties were also investigated by the means of vibrating sample magnetometer (VSM). From the magnetization hysteresis loops, by rare earth La substitution of Fe a significant decrease in intrinsic coercivity and a slight decrease in specific saturation magnetization and specific remanent magnetization were observed as compared with SrCe_0.6Fe_11.4O₁₉ nanofibers.     

NiO/SiO2 nanostructure and the magnetic moment of NiO nanoparticles

We report on the synthesis, morphology and magnetic properties of a novel NiO/SiO₂ nanostructure. The NiO/SiO₂ nanostructure was synthesized by a method based on the contribution of sol-gel and combustion processes. X-ray powder diffraction (XRPD) showed the formation of the nanocrystalline NiO phase. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) revealed perfectly spherical NiO nanoparticles with diameter of about 5 nm. Amorphous silica shell around the NiO nanoparticles was also observed by HRTEM showing NiO/SiO₂ core-shell nanostructure. Magnetic measurements show hysteretic behavior at 2 K with coercivity H_C = 700 Oe, remanent magnetization M_r = 3.9 emu/g, saturation magnetization M_S = 28.2 emu/g and huge magnetic moment m_p ≈ 1300 μ_B of the nanoparticles.     

Solid state amorphization transformation in the mechanically alloyed Fe27.9Nb2.2B69.9 powders

Mössbauer spectrometry and Rietveld analysis of X-ray diffraction patterns were used to follow the solid state amorphization transformation during the milling process of the Fe_27.9Nb_2.2B_69.9 powders. The reaction between elemental Fe, Nb and B powders leads to the formation of the Nb(B) and Fe(B) solid solutions after 1 and 10 h of milling, respectively. A mixture of α-Fe, Nb(B) and highly disordered Fe(Nb, B) solid solution is found after 25 h of milling. An amorphous structure is obtained on further milling time (100 h). From the Mössbauer spectrometry results, it is observed that the total mixing of the elemental powders, at the atomic level, is achieved after 50 h of milling and a stationary state corresponding to a full paramagnetic amorphous phase is reached after 100 h of milling. The amorphization process can be described by an Avrami parameter close to n = 1.     

Structural stability of ZnFe2O4 nanoparticles under different annealing conditions

We study the structural stability of surfactant coated ZnFe₂O₄ (ZF) nanoparticles of average particle size 10 nm annealed under different environments. The X-ray diffraction studies in oleic acid coated ZF (OC-ZF) show distinctly different phase transitions under different annealing conditions. The OC-ZF is reduced to α-Fe/ZnO phase under vacuum while it forms FeO/ZnO under argon whereas the ZnFe₂O₄ phase remains stable under air annealing. The simultaneous thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC) coupled mass spectra (MS) in OC-ZF under argon atmosphere suggests that the residual carbon removes oxygen from the lattice to reduce the ZnFe₂O₄ phase into FeO/ZnO during argon annealing. Apart from CO and CO₂ gas evolution at high temperature under argon annealing, creation of oxygen vacancies due to the random removal of oxygen under vacuum annealing, leads to direct interaction between Fe–Fe and the formation of metal Fe. It appears that the residual carbon aids the reduction of ZF and the formation of α-Fe/ZnO during vacuum annealing. After annealing at 1000 °C in vacuum, the magnetization is increased abruptly from 13.8 to 106.5 emu g⁻¹. In sharp contrast, the air and argon annealed samples show a diminished magnetization of 1 emu g⁻¹. The field cooled (FC) and zero FC magnetization of vacuum and argon annealed samples exhibit superparamagnetic and spin-glass type behavior respectively. Our results offer possibilities to switch a magnetically inactive material to an active one.