Fe Ni Powders Research Articles

Application of mechanical separation method with filtration for nanodispersed FeNi powders with carbon coating

It was shown that the method of mechanical separation with filtration could be used to separate metal nanoparticles in a carbon shell. The method was used for separation of FeNi nanoparticles with a carbon shell, previously isolated from carbon condensate by boiling in acids. The particles had a crystalline structure and magnetic characteristics (Mr/Ms = 0.30, Hc = 270 Oe). Method of mechanical separation with filtration made it possible to separate the sample into particles coated with a carbon shell (particles size 40–50 nm, size of the metal core 10–15 nm), and into metal particles with a diameter of 6–15 nm, dispersed in a carbon matrix. The work shows that the samples have similar magnetic properties (Mr/Ms = 0.27, Hc = 236 Oe) and chemical composition (Ni ∼ 10 wt.%, Fe ∼ 12 wt.%, C ∼ 57 wt.%). However, the samples differ in structure, one contains FeNi(220), FeNi(200), FeNi(111) and C(002) phases, while the other contains only FeNi(200) and C(002) phases.

Effect of Compaction Pressure on Core Loss in Fe–Ni Powder Cores for High-Frequency Applications

Effect of Compaction Pressure on Core Loss in Fe–Ni Powder Cores for High-Frequency Applications

Laser Melting of Mechanically Alloyed FeNi: A Study of the Correlation between Microstructure and Texture with Magnetic and Physical Properties.

The current study attempts to establish the interrelation between microstructure and magnetic properties induced during laser melting of the FeNi alloy. This study demonstrates the optimization of laser parameters for defect-free, uniform, and chemically homogeneous FeNi alloy synthesis. Mechanically alloyed FeNi (50-50 atom %) powders obtained after 12 and 24 h milling, with average particle sizes of 15 and 7 μm, were used as starting materials. It was found that the optimum range of laser power density for synthesis of dense and defect-free solids is between 1 and 1.4 J/mm2. For laser melting under similar conditions, 12 h milled FeNi powder produces a larger grain (∼100 μm) with a preferred texture of (001), compared to 25 μm grain size in 24 h milled FeNi, with random texture. Smaller grain size is correlated with higher resistance to domain wall movement, resulting in higher coercivity and remanence in the laser-melted samples prepared from 24 h of milled powder. The presence of microtexture in laser-melted samples prepared from 12 h milled powder is related to a higher anisotropy.

Soft magnetic properties of Fe-Ni powder cores in the high frequency range

Fe-Ni cores are excellent candidates for switching regulator inductors, transformers, reactors and in-line noise filters. Herein the influence of the phenol binder content on the microstructure and magnetic properties of Fe-50 wt% Ni powder cores in the high frequency range is investigated. Regardless of the binder content, all cores form a disordered A1 phase. The saturation magnetization (4πMs) and initial permeability increase as the binder content decreases. The core with a binder content of 0.5 wt% shows a relatively high 4πMs of 1.38 T and the highest permeability value of 70.9. Moreover, the total core loss (Pcv) with frequency ranges from 5 kHz to 1 MHz under a magnetic flux density of 10 mT depending on the binder content. A binder content of 3.0 wt% significantly reduces Pcv in the high frequency range above 100 kHz. At a frequency of 500 kHz, the Pcv values are 154.9, 128.7, and 133.8 kW/m3 for the cores with binder contents of 0.3, 0.5, and 1.0 wt%, respectively, but the value drastically decreases to 60.5 kW/m3 for a binder content of 3.0 wt%. Thus, the binder, which acts as an insulator layer between particles, affects the eddy current and consequently, Pcv. These results demonstrate that Fe-Ni powder cores exhibit excellent soft magnetic properties at various frequencies and suggest that a binder content of 3.0 wt% may realize optimal properties for future high frequency applications.

Comparative investigation of insulation techniques based on APTES for different structures and magnetic properties of soft magnetic composites

FeNi powders were insulated with APTES by solution method and solidification method, respectively. Different coating mechanisms have been systematically studied according to analysis on microstructure, surface charge state, thermal stability of magnetic powders and magnetic properties of corresponding soft magnetic composites (SMCs). It was found that a slight amount of polysiloxane and amorphous silica would be deposited on FeNi powders in solution method, resulting in an ultra-thin insulation layer. In contrast, continuously increasing concentration of polysiloxane in reaction zone gives rise to a thick and smooth SiO2 layer in solidification method. Owing to unique growth mechanisms of solidification method, it is easy to control the thickness of SiO2 layer by adjusting the concentration of APTES, which is in favor of improving insulation quality. Accordingly, FeNi SMCs prepared in solidification method own much higher resistivity, lower μ″ and lower tanδ (particularly at high frequency), compared with samples obtained by solution method with the same volume of APTES. Besides, increasing volume of APTES in solidification method leads to the decrease of both μ′ and μ″. This work may not only provide novel insights into APTES-based insulation process, but also offer powerful technique for fabricating high-frequency SMCs.

Migration of N element and evolution of microstructure in spark plasma sintered bulk γ′-Fe4N

Magnetic bulk γ′-Fe4N alloys were successfully fabricated by spark plasma sintering (SPS) using high purity γ′-Fe4N powder at 500 °C and 550 °C under 100 MPa and 150 MPa, respectively. The density of the bulk γ′-Fe4N was 7.092 g/cm3 with 98.8 % of the theoretical density, which exhibit the high saturation magnetization 199.6 emu/g. The morphology, microstructure, sintering process and magnetic properties of the bulk samples is explored. It is found that the resistivity and hardness which closely corresponds to the density at the center and margin of the bulk sample are different for the temperature and pressure distribution. With the temperature and pressure increases in the SPS process, N element gradually migrates from the central region of high temperature and high pressure to the margin region of low temperature and low pressure, resulting in the appearance of pores and the decreased density. Moreover, ε-Fe3N phase in the margin region is higher than that in the central region. The phase distribution in the SPS process and the related electrical properties provide insight into the formation and evolution of the phase in the SPS sintering process, which can help to obtain bulk samples with good properties and uniform composition in practical applications.

Fe-based sintered matrix for diamond tools: microstructure, mechanical performance and crack initiation and propagation characteristics

To design Fe-Cu-Sn-Ni metal binders for diamond tools and optimize the performance of binders, Fe-based binders were prepared by hot-press sintering method using Fe powder, Cu powder, Sn powder and Ni powder as the raw materials. The phase constitution, microstructure, mechanical properties and crack formation were evaluated. Results showed that Fe-based matrixes are composed of Cu3Sn intermetallic compounds and several solid solutions, such as α-Fe, γ(Fe,Ni), and Cu13.7Sn. The relative high Sn content can increase the hardness of the sintered bulk samples and significantly reduce the bending strength. With the increase of Ni content, the hardness increases gradually, while the bending strength increases firstly and then decreases. The cracks initiate from brittle Cu3Sn intermetallic phases and quickly propagate in the brittle phases or along the interface between Cu3Sn intermetallic compounds and γ(Fe,Ni) phases. The propagation of crack can be impeded by Cu13.7Sn solid solution.

Prediction of Structural and Magnetic Properties of Nanocrystalline Mechanically Alloyed Fe-Ni Powders Using Multi-Gene Genetic Programming Approach

In this paper, a theoretical model based on multi-gene genetic programming (MGGP) approach has been applied to predict the structural and magnetic properties in nanocrystalline Fe–Ni powders prepared by mechanical alloying (MA) using a planetary ball mill. The MGGP model was used to correlate the input parameters (milling speed, chemical composition, and milling time), to output parameters (crystallite size and coercivity) of nanocrystalline Fe–Ni powders. The model obtained was tested with additional data to demonstrate its performance and prediction ability. The MGGP model is a robust and efficient method to find an accurate mathematical relationship between input and output data. A sensitivity analysis study was applied to determine the most influential milling parameters on the crystallite size and coercivity.

Phase Stability of Iron Nitride Fe4N at High Pressure-Pressure-Dependent Evolution of Phase Equilibria in the Fe-N System.

Although the general instability of the iron nitride γ′-Fe4N with respect to other phases at high pressure is well established, the actual type of phase transitions and equilibrium conditions of their occurrence are, as of yet, poorly investigated. In the present study, samples of γ′-Fe4N and mixtures of α Fe and γ′-Fe4N powders have been heat-treated at temperatures between 250 and 1000 °C and pressures between 2 and 8 GPa in a multi-anvil press, in order to investigate phase equilibria involving the γ′ phase. Samples heat-treated at high-pressure conditions, were quenched, subsequently decompressed, and then analysed ex situ. Microstructure analysis is used to derive implications on the phase transformations during the heat treatments. Further, it is confirmed that the Fe–N phases in the target composition range are quenchable. Thus, phase proportions and chemical composition of the phases, determined from ex situ X-ray diffraction data, allowed conclusions about the phase equilibria at high-pressure conditions. Further, evidence for the low-temperature eutectoid decomposition is presented for the first time. From the observed equilibria, a P–T projection of the univariant equilibria in the Fe-rich portion of the Fe–N system is derived, which features a quadruple point at 5 GPa and 375 °C, above which γ′-Fe4N is thermodynamically unstable. The experimental work is supplemented by ab initio calculations in order to discuss the relative phase stability and energy landscape in the Fe–N system, from the ground state to conditions accessible in the multi-anvil experiments. It is concluded that γ′-Fe4N, which is unstable with respect to other phases at 0 K (at any pressure), has to be entropically stabilised in order to occur as stable phase in the system. In view of the frequently reported metastable retention of the γ′ phase during room temperature compression experiments, energetic and kinetic aspects of the polymorphic transition are discussed.

Bending Strength and Cutting Performance of WB-Coated-Diamond/Fe-Ni Composites

Diamond particle with tungsten boride (WB) coating was synthesized by the molten salt method. Three different diamond/Fe-Ni composites made from pristine diamond, B4C coated diamond and WB coated diamond with Fe-Ni powders were prepared by powder metallurgy. The composition and microstructure of the tungsten boride coating were investigated. Both bending strength and cutting performance of the composites were investigated. Addition of the WB coating provided an increased bending strength (871.2 MPa) and relative density (93.54%), compared with the composites consist of uncoated diamond and Fe-Ni (746.8 MPa, 92.81%). Three different Fe-Ni-based impregnated diamond drill bits contained 20 vol.% pristine diamond, B4C coated diamond and WB coated diamond were manufactured by powder metallurgy, respectively. Drilling rate of bits was measured by XY-4 geological core drill on granite. The test results show that the drilling rate of bits with WB coated diamond (2.42 m/h) was 40% higher than that with pristine uncoated diamond (1.72 m/h).

Nanocrystalline Powder Cores for High-Power High-Frequency Applications

Soft magnetic composites (SMCs) based magnetic cores are attractive in high-frequency inductor design. The desired overall core permeability of SMC core can be achieved by adjusting the powder size, addition of insulation material and phosphoric acid, and pressure during the preparation process to reduce the air gap loss and ease the inductor design. The nanocrystalline alloy (Fe-Cu–Nb–Si–B) is an emerging SMC with high saturation flux density and low hysteresis loss, showing potential suitability for SMC-based magnetic cores. To date, nanocrystalline alloys are mostly used in form of laminated ribbon for magnetic cores, and nanocrystalline powder SMCs have been seldom used in practice. Also, neither experimental validation nor comparison with other commercialized and commonly used SMC cores has been reported. In this article, the structure and manufacturing process of nanocrystalline powder cores are introduced. The calculation of core loss is defined for the nanocrystalline powder core. The characteristics and performance of the nanocrystalline powder toroidal core are compared with those of existing commercial SMC cores, such as Fe–Si powder (X flux), Fe–Ni powder (High flux), Fe–Si–Al powder (Kool Mμ), and Fe-Ni–Mo powder (MPP). Experimental results are conducted at frequencies from 100 to 600 kHz to verify the loss calculation and feasibility of this new nanocrystalline powder core.

Microwave loss percolation effect and microwave self-healing function of FeNip/PP nanocomposites

Based on the study of microwave loss percolation effect of FeNip/PP nanocomposites, the microwave healing technology of FeNip/PP nanocomposites was proposed and its mechanism was studied. There is a unique microwave loss percolation characteristic between the microwave loss factor (tanδ) of FeNip/PP nanocomposites and the content of FeNi powders (0–20 wt%), and the percolation area is the range of 2–10 wt%. The microwave healing technology can realize the self-healing property of the PP-based composites. When the composites received the microwave signal, the magnetic nanopowders generate heat effect to heat the resin matrix, which forms a mobile phase. The mobile phase, melted PP matrix with some magnetic nanopowders, moved toward the microcracks, thereby healing or reducing microcracks inside the composite. The optimum time for microwave treatment was 15 min. After microwave healing, the microcracks of the composites were closed, and the tensile strength of FeNip/PP nanocomposites can be restored to 90% of that before damage.

Synthesis of γ’-Fe4N powder in liquid nitrogen

A novel synthesis approach is developed to prepare nanocrystalline γ’-Fe4N in this paper. High energy cryomilling approach in liquid nitrogen is used to prepare the sample. A FexN amorphous state with a degree of metastable supersaturation of N into Fe is obtained. The crystalline size after higher energy cryomilling approach is characterized to be 40 ∼ 80 nm. A post-annealing among 200 ∼ 300 °C for 10 minutes results in phase transformation from α-iron into γ’-Fe4N. Its magnetic properties and structures are characterized, showing good soft magnetic material with ultralow coercivity (0.7 Oe). It shows high electrical resistivity (375 μΩ·m) at room temperature. The feasibility of the ball milling synthesis approach in liquid nitrogen is verified, suggesting a novel approach for the soft magnetic material preparation.

Study on Preparation and MD Simulation of Nano Fe4N

Nano Fe4N powder has been successfully prepared by the combination between high pressure combined method of reduction and nitriding and molecular dynamics (MD) simulation. The phase, composition, morphology, and magnetic properties have been preliminarily characterized by XRD, TEM, and VSM to investigate the influence of temperature, time, ammonia hydrogen ratio, and pressure during reaction process on the preparation. The results indicate that the preferable nano Fe4N powder of the average size around 35[Formula: see text]nm could be obtained nitriding at 0.4[Formula: see text]MPa and 673[Formula: see text]K for 2.5[Formula: see text]hours with the ammonia hydrogen ratio being 3:1. The results of magnetic detection show that the nano Fe4N produced here is a fairly desirable soft magnetic material with Ms[Formula: see text][Formula: see text][Formula: see text]169.70[Formula: see text]emu/g. This process could reduce the reaction temperature and shorten the reaction time, which is of important significance to the industrial production of nano Fe4N powder.

Preparation and microwave absorbing property of porous FeNi powders

Porous FeNi powders with particle size of 1μm were successfully prepared by two steps in this paper. First, Fe0.5Ni0.5C2O4·2H2O particles with uniform size distribution and morphology were obtained by an oxalate precipitation process. Second, the porous FeNi powders were prepared by thermal decomposition of the oxalate precursor at 450°C for 30minina N2/H2mixedatmosphere. The electromagnetic (EM) parameters of FeNi (30wt%)/paraffin composite were measured in 2–18GHz, and the reflection loss (RL) values were calculated based on the transmission line theory. The results show that the bandwidth of RL<−10dBreaches 2.57GHzwhen the composite thickness is 2.0mm, and the minimum RL reaches −52.58dBat 6.82GHzwith a composite thickness of 3mm.

Preparation of FeNi powders/ butyl rubber nanocomposite film and its force sensitive characteristic

Firstly, the spherical Fe50Ni50 powders, particle size about 100 nm, were prepared by liquid phase reduction method, and then were mixed with butyl rubber (IIR) dispersed in liquid. Fe50Ni50 powders/IIR nanocomposite films, powder mass fraction was 65 wt%, were harvested through being mixed and milled lastly. The force sensitive properties of the films were studied under the condition of that the loading/unloading speed of the stress was 0.10 mm/min controlled by the LYYL-500N high-grade microcomputer controlling compression-testing machine, and the test frequency of impedance (Z) was 1 kHz tested with the TH2816B LCR digital electric bridge. Results show that Fe50Ni50 powders can be dispersed uniformly as nanometer scale in this nanocomposite by liquid phase mixing method. And the Fe50Ni50 powders/IIR nanocomposite film, thickness 185 μm, has excellent force–sensitive properties when the stress is between 0.20Mpa and 0.90Mpa. The impedance ∼ stress curve appears approximately linear decline, and stress sensitivity |k| value is stable in 40–60, stability S value is about 1∼ 2 kΩ, and the film enters into a steadily sensitive stage responding to stress.

Investigation of the Absorption Properties of the Alloys Fe-Ni and Fe-Ni-Cr Prepared by Mechanical Alloying

The microwave-absorption properties and microstructures of Fe-Ni and Fe-Ni-Cr alloys prepared by mechanical alloying were investigated in the frequency range 2–18 GHz. Other properties were studied by scanning electron microscopy, x-ray diffractometry, vibrating sample magnetometry, and transmission line theory. Dependence of reflection loss (RL), electromagnetic properties (permeability μ and permittivity e), magnetic and dielectric loss tangent, impedance matching, and absorber thickness (d) on milling time is discussed. The alloy powders had excellent microwave-absorption properties in the frequency range 7 to 14 GHz. The minimum RL, the frequency at which the RL is minimum, and the bandwidth (RL < −10 dB) all depend on milling time and d. Introduction of Cr affected the RL of the powders, especially the minimum RL of −19.8 dB at 7.2 GHz for Fe-Ni-Cr powder milled for 90 h (compared with −22 dB at 9.9 GHz for Fe-Ni powder milled for the same time), suggesting that the Fe-Ni-Cr alloy could be a promising candidate as a microwave-absorbing filler at low frequencies. This may help broaden the range of microwave-absorbing materials.

Preparation and magnetic properties of novel hybrid magnetic powder cores

Magnetic powder cores are an important kind of soft magnetic materials that are widely used in various electrical and magnetic devices. In this work, high performance hybrid magnetic powder cores have been prepared by compacting silicon resin coated soft magnetic composite (SMC) powders. The SMC powders are obtained from mixing suitable proportions of FeSi and FeNi powders uniformly with pure iron powders. A high density of over 7·27 g cm−3 can be obtained in hybrid magnetic powder cores. The core loss of the magnetic cores prepared from mixing 90 wt-%Fe and 10 wt-%FeSi powders measured at a frequency of 50 Hz and an induction level of 1 T is 7·5 W kg−1, which is much lower than that of pure iron powder cores (8·4 W kg−1), and their magnetic induction measured at an induction level of 10 kA m−1 is 1·38 T, which is higher than that of pure iron powder cores (1·34 T).

Structural and microstructural properties of nanocrystalline Cu–Fe–Ni powders produced by mechanical alloying

A nanostructured disordered copper–iron–nickel alloy having the (Cu60Fe40)70Ni30 composition was prepared through the mechanical alloying of the elemental powders in a high-energy ball mill under an argon atmosphere. The structural and morphological evolutions during mechanical alloying were investigated by X-ray diffraction and scanning electron microscopy. The patterns obtained were analyzed using the MAUD program. The transformation of the phase depended on the alloying time. The final product of the mechanical alloying process was nanocrystalline double-phase FCC-Cu(Fe,Ni) and BCC-Fe(Ni) solid solutions with a mean crystallite size in the range of few nanometers. The dislocation densities were found to be 6×1015m−2, and the strain hardening caused by high-energy mechanical alloying was consistent with the concept of dislocations.

New Fe-Ni and Fe-Mn Powders Used in Manufacturing Diamond Tools

The work attempts substitution of very expensive, wear resistant Co-WC powders, that are commonly used in the production of sintered diamond tools, with cheap iron-base counterparts manufactured by ball milling. It has been shown that ball milled Fe-Ni and Fe-Mn powders can be consolidated to a virtually pore-free condition by hot pressing at 900°C. The as-consolidated materials are characterised by high hardness and resistance to 3-body abrasion.