Powder Cores Research Articles

Study on FeSiAl magnetic powder core coated with nano-Y2O3 and its influence on magnetic properties

The microstructure and magnetic properties of the FeSiAl /phosphoric acid/nano-Y2O3/kaolin soft magnetic composites were investigated in this article. The morphology and structure were characterized by SEM, EDS, XRD, DSC, and XPS. The surface of FeSiAl powder particles was densely and uniformly coated with a phosphoric acid/nano-Y2O3/kaolin insulating coating. It was discovered that nano-Y2O3 played a dominant role in the coating process. Using a precision magnetic analyzer and lossy power tester, the effective permeability, quality factor, DC bias performance, and the core loss of the FeSiAl/phosphoric acid/nano-Y2O3/kaolin SMCs after pressing and annealing were computed and examined. The results show that nano-Y2O3 can improve the quality factor and DC bias performance of the powder core, but leads to a reduction in magnetic permeability and the core loss is also a little high. This behavior may be caused by the competition mechanism: nano-Y2O3 lowers the magnetic coupling between FeSiAl particles, resulting in a decrease in permeability and an increase in the core loss. When the content of nano-Y2O3 is 5 wt%, the comprehensive magnetoelectric performance is good (ue=21.04, at f =100 kHz; Pcv = 1555.13 mW/cm3, at f = 50 kHz; Q = 150.25, at f = 70 kHz; at Bm = 1000 Gs). The effects of nano-Y2O3 coating on the permeability and the loss of FeSiAl SMCs will be a major focus of future research and development.

Structure evolution of Fe-based nanocrystalline soft magnetic powder cores with excellent properties

The effect of heat treatment temperature on the structural evolution and soft magnetic properties of FeSiBNbCu soft magnetic powder cores (SMPCs) was systematically investigated. The comprehensive magnetic properties of the SMPCs first increased and then decreased with an increase in temperature. At 600 °C, the SMPCs grain size was approximately 8.8 nm, presenting a concentrated nanocrystalline structure, and showing the best soft magnetic properties, including low core loss of 135.6 mW/cm3 (50 mT, 100 kHz), stable effective permeability of 49.1 up to 10 MHz and high DC bias performance of 60.3% at 100 Oe. This study provides an effective solution for the preparation of Fe-based nanocrystalline SMPCs with excellent performance and validates the application prospects under working conditions of different frequencies and ripple currents.

Preparation and electromagnetic performances of Finemet nanocrystalline soft magnetic composites with flake and spherical powders

Nanocrystalline soft magnetic composites (n-SMCs) with excellent soft magnetic properties are widely used in medium and high frequency electronic devices. However, the production of n-SMCs with high frequency stability and low core losses (Pc) remains a challenge. In this work, we balanced electromagnetic performances and frequency properties of Finemet n-SMCs by tuning the mass ratio of flake and spherical powders. The morphology, phase structures, electromagnetic performances or frequency characteristics of powders and n-SMCs were systematically investigated. Scanning electron microscope was employed to prove that the addition of spherical powders (SPs) can improve the matching degree of powders and density of n-SMCs. As the mass ratio of SPs increased, the Pc and the hysteresis losses (Ph) of magnetic powder cores first decreased and then increased, while the eddy current losses (Pe) showed the monotonic downward trend. What’s more, owing to the excellent insulation coating performances of SPs, quality factor (Q), DC-bias characteristics and frequency stability were significantly improved after mixing SPs with FPs. The n-SMCs with the mass ratio of 2:3 between SPs and FPs exhibited the best comprehensive performances with the effective permeability of μe = 43 (f = 100 kHz), the quality factor of Q = 78, the core losses of Pc = 294 mW/cm3 (Bm = 50 mT, f = 100 kHz), and the DC-bias characteristics of 56%. This work endows Finemet n-SMCs with a potential application for inductance components at high frequency.

Effect of annealing on magnetic properties of iron-based soft magnetic composites with iron oxide insulator

This study introduces a closed oxidation system for forming an oxide insulating film on the surface of pure-iron powder, using an oxygen concentration analyzer to monitor the progress of the reaction. The closed system is designed such that all the supplied oxygen completely reacts to form an oxide film at 500 ℃. It is established that the oxide-film thickness can be controlled by the quantity of oxygen supplied. XRD analysis indicates that the oxide film is mostly composed of the Fe3O4 phase. The TEM oxygen mapping image shows that the oxide film is uniformly and completely formed on the surface of pure-iron powder. Further, toroidal cores are fabricated by compacting the pure-iron powder coated with an oxide insulating film. To relieve the strain generated during compaction, annealing is performed in the 400–700 ℃ range. At annealing temperatures below 550 ℃, the change in the core loss is not considerable (85.0 W/kg at room temperature (23 ℃) and 94.8 W/kg at 550 ℃). However, above 550 ℃, sudden increase in the core loss is observed (505.9 W/kg at 700 ℃). The Fe3O4 in the oxide film reacts with the Fe phase to form FeO above 570 ℃, which is the eutectoid temperature. This phase transformation damages the insulation of the oxide film, resulting in a sharp increase in the eddy current loss. The hysteresis loss decreases from 71.2 W/kg to 43.9 W/kg with the increase in the annealing temperature. It is determined that the pure-iron powder core coated with an oxide insulating film is heat-resistant up to a temperature of 550 ℃.

Influence of sintering temperature on heterogeneous-interface structural evolution and magnetic properties of Fe–Si soft magnetic powder cores

Ceramic oxides have attracted considerable research attention as ideal coating layers for novel Fe-based soft magnetic powder cores (SMPCs). However, maintenance of the integrity and uniformity of Fe-based/MOx core–shell heterostructures is challenging. The mechanism underlying the evolution of the core–shell heterostructure is a key determinant of the performance of Fe-based SMPCs. Herein, the laws governing the evolution of the core–shell structure of and heterogeneous interface in Fe–Si/SiO2 SMPCs with temperature and the influence of this evolution on SMPCs performance were investigated. The results revealed that at the sintering temperature of 1093–1183 K, the core–shell heterostructure gradually integrated, while SiO2 insulating coatings underwent amorphous-to-crystalline state transformation. When the sintering temperature was >1243 K, Fe–Si particles melted partially, and the core–shell heterostructure collapsed owing to the overheating induced by the gradient temperature field during the hot-pressing sintering process. When the sintering temperature was 1153 K, the core–shell heterostructure was intact, and the Fe–Si/SiO2 SMPCs had a saturation magnetisation of 245.5 emu/g, resistivity of 0.42 mΩ cm, and total loss of 923.2 kW/m3 at 10 mT and 100 kHz. When the core–shell heterostructure was destroyed, the resistivity dropped drastically, and the total loss increased by approximately 36.7% and 41.8%. Based on these results, the relationship among the core–shell heterostructure of Fe–Si/SiO2 SMPCs, sintering temperature, and magnetic properties was established, which is instrumental in achieving high power density, high efficiency, and miniaturisation in SMPCs.

High-frequency loss analysis and related magnetic properties of Fe-based amorphous soft magnetic composites with different granularity matches

The regulation mechanism of comprehensive soft magnetic properties for the Fe-based amorphous powder cores with different granularity match schemes used in high-frequency applications was investigated in detail. Herein, the FeSiBCCr amorphous particles with three different average particle diameters of 2.20 (P1), 12.52 (P2), and 27.65 μm (P3) were employed. Based on the establishment of the loss separation model, the total core loss (Pcv, at 25–900 kHz, 0.1 T) was divided into hysteresis loss Ph, eddy current loss Pe, and residual loss Pr. The particle size matching, which can directly affect the core's density under constant parameters, has a significant impact on the magnetic properties of powder cores. With the increase in the density induced by varying granularity match scheme, the real part of complex permeability μ′ increases, while Pcv, Ph, Pr, and DC-bias property of powder core show a reducing trend. This is attributed to the decrease in air gap in the composites, which is closely related to the pinning of domain movement and coercivity. The powder core with the granularity match scheme of 30:60:10 for P1%:P2%:P3% exhibits the excellent comprehensive magnetic properties including a stable μ′ of 41.2 up to 3 MHz, high DC-property of 74.3%@100 Oe, and low Pcv of 10389.5 kW/m3 at 900 kHz, 0.1 T. This work offers insights into regulating magnetic properties for the powder core toward high-frequency applications, particularly referring to the granularity matching.

Effect of Annealing Process on Microstructure and Magnetic Properties of FeSiBPCNbCu Nanocrystalline Soft Magnetic Powder Cores

In this work, the effect of the annealing process (heating rate (HR) and holding time (HT)) on microstructure and magnetic properties of FeSiBPCNbCu nanocrystalline soft magnetic powder cores (NPCs) are systematically studied. NPCs annealed under the HR of 100 K/min and HT of 30 min exhibit a finely uniform nanocrystalline structure with a concentrated grain size distribution and a small average grain size of 18.71 nm and show a modified magnetic domain structure where the domain walls move easily with the changes in the external magnetic field. The optimized microstructure leads to outstanding soft magnetic properties, including the low coercivity of 10.5 A/m (50 mT, 500 kHz), low core loss of 751 mW/cm3 (50 mT, 500 kHz), and highly effective permeability of 64.7 (100 kHz). We believe that the annealing process regulation can contribute to the industrial production of high-performance NPCs, which can meet the performance requirements of high-end electronic components such as molding chokes used in power supplies, mobile phones, and other terminal equipment.

Enhancing the Properties of FeSiBCr Amorphous Soft Magnetic Composites by Annealing Treatments

Fe-based amorphous powder cores (AMPCs) were prepared from FeSiBCr amorphous powders with phosphate–resin hybrid coating. The high-frequency magnetic properties of AMPCs annealed at different temperatures were systematically studied. After annealing at low temperatures, the effective permeability and core loss improved due to the internal stress of the powder cores being released. The sample annealed at 480 °C exhibits the lowest hysteresis loss of about 29.6 mW/cm3 at 800 kHz as well as a maximum effective permeability of 36.4, remaining stable until 3 MHz, which could be useful for high-frequency applications.

Effect of Polyimide-Phosphating Double Coating and Annealing on the Magnetic Properties of Fe-Si-Cr SMCs.

Fe-Si-Cr soft magnetic powder cores (SMCs), with high electrical resistivity, magnetic permeability, saturation magnetic induction, and good corrosion resistance, are widely applied to inductors, filters, choke coils, etc. However, with the development of electronic technology with high frequency and high power density, the relative decline in the magnetic properties limits the high-frequency application of SMCs. In this paper, the phosphating process and polyimide (PI) insulation coating is applied to Fe-Si-Cr SMCs to reduce the core loss, including hysteresis loss and eddy current loss. The microstructure and composition of Fe-Si-Cr powders were analyzed by SEM, XRD, and Fourier-transform infrared spectra, respectively. The structural characteristics of the Fe-Si-Cr @ phosphate layer @ PI layer core–shell double coating were studied, and the best process parameters were determined through experiments. For SMCs with 0.4 wt% content of PI, the relative permeability is greater than 68%, and the core loss is the lowest, 7086 mW/cm3; annealed at 500 °C, the relative permeability is greater than 57%, and the core loss is the lowest, 6222 mW/cm3. A 0.4 wt% content of PI, annealed at 500 °C, exhibits the ideal magnetic properties: μe = 47 H/m, P = 6222 mW/cm3.

Microstructure and magnetic properties of FeSiCr soft magnetic powder cores with a MgO insulating layer prepared by the sol-gel method

In this study, the electromagnetic properties of FeSiCr soft magnetic powder cores (SMPCs) were optimized by providing a novel insulation process. Magnesium acetate tetrahydrate and oxalic acid dihydrate were used as raw materials for the sol-gel method. The powder was then heat-treated at 700 °C so that it was evenly coated by an insulating layer. Thermogravimetric analysis-differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy, and energy dispersive spectroscopy were used to demonstrate that the layer heat-treated at 700 °C was the ideal MgO layer and was uniformly coated on the surface of the FeSiCr powder. Additionally, the potential reactions and growth mechanism of the MgO layer were analyzed. The effects of the magnesium acetate tetrahydrate content on the soft magnetic properties of the FeSiCr@MgO SMPCs were investigated. The optimal soft magnetic performance (Pcv = 248.48 mW/cm3, measured at 2500 kHz and 10 mT) was achieved at a magnesium acetate tetrahydrate content of 0.50 wt%, yielding a direct current-bias performance of up to 92.3% at 100 Oe. In addition, the FeSiCr@MgO SMPCs effectively improved the heat dissipation performance, which is necessary to avoid high-temperature damage, thereby enhancing their applicability in high-frequency and high-current environments.

Optimizing soft magnetic properties by reducing internal defects and residual stress of Fe85-xSi9.6Al5.4Snx soft magnetic composites

In this work, Fe85-xSi9.6Al5.4Snx (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) Soft magnetic powder cores (SMPCs) were prepared by Sn doping, and the effects of the doping on the microstructures and soft magnetic properties were systematically investigated. With the increase of Sn content, the dislocation density of SMPCs decreases from 0.53 × 1014 m−2 to 0.29 × 1014 m−2, so does the degree of lattice distortion and the residual stress. These changes optimize the soft magnetic properties of Fe85-xSi9.6Al5.4Snx SMPCs. Based our experiments, the effects of the crystal grain size, grain orientation, and magnetic domain motion on the magnetic properties are also discussed. At last, the best soft magnetic performance was obtained, when Sn doped with 0.8 wt.%. Fe85-xSi9.6Al5.4Snx SMPCs designed by Sn doping have excellent soft magnetic properties, which expands their application advantages in the field of power electronics, the composition design also provides an effective method for the optimization of soft magnetic properties of FeSiAl SMPCs.

Microstructure and magnetic properties of novel powder cores composed of iron-based amorphous alloy and PTFE

Microstructure and magnetic properties of novel powder cores composed of iron-based amorphous alloy and PTFE

Great reduction in pressure by particle grading for Fe-Si-Al SMCs with good low-frequency magnetic properties

Gas-atomized Fe-Si-Al powder cores with optimized particle grading are successfully prepared at various pressures much lower than those of conventional ungraded powder cores (UGCs). The influences of the particle grading and the pressure on the frequency dependence of μ’, μ’’ and tanδ and DC-bias performance are studied in detail. The optimized discontinuous particle size distribution based on the powder’s tape density is found to improve the core’s density effectively and thus reduce the demagnetizing field. This helps to realize high μ' with good frequency stability, low μ'' and small tanδ in low-frequency range below 10 kHz, close to those of conventional UGCs, without adopting high-pressure pressing. Besides, good anti-saturation ability, similar to that of conventional UGCs, is also achieved in the graded cores (GCs) because no annealing treatment retains internal stress introduced by the pressing process. This suggests that the utilization of particle grading makes it possible to realize good low-frequency magnetic performance in powder cores pressed at greatly reduced pressures. For such a particle grading, the downside that needs further improvement is the great decrease of the core’s volume resistivity, which leads to a high eddy current within the GCs and thus deteriorates the frequency stability of the permeability and the core loss in high-frequency range above 20 kHz.

Microstructure and Magnetic Properties of Grain Boundary Insulated Fe/Mn0.5Zn0.5Fe2O4 Soft Magnetic Composites.

Mn0.5Zn0.5Fe2O4 nano-powder was coated on Fe microparticles by mechanical ball milling combined with high-temperature annealing. The effects of milling time on the particle size, phase structure and magnetic properties of core–shell powder were studied. Scanning electron microscopy (SEM), energy-dispersive spectroscopy and X-ray diffraction showed that the surface of the milled composite powder was composed of thin layers of uniform Mn0.5Zn0.5Fe2O4 insulating powder. SEM also revealed a cell structure of Fe particles, indicating that the Fe particles were well separated and isolated by the thin Mn0.5Zn0.5Fe2O4 layers. Then, Fe/Mn0.5Zn0.5Fe2O4 soft magnetic composites were prepared by spark plasma sintering. The amplitude permeability of Fe/Mn0.5Zn0.5Fe2O4 SMCs in the Fe/Mn0.5Zn0.5Fe2O4 soft magnetic composites was stable. The resistivity decreased with the increase in sintering temperature. The loss of the composite core was obviously less than that of the iron powder core. Hence, the preparation method of Mn0.5Zn0.5Fe2O4 insulating iron powder is promising for reducing core loss and improving the magnetic properties of soft magnetic composites.

Fabrication of Fe-Si-B Based Amorphous Powder Cores by Spark Plasma Sintered and Their Magnetic Properties

Mechanical ball milling was used to coat SiO2 nanopowder on a Fe-Si-B amorphous powder in this study. The Fe-Si-B/SiO2 core–shell amorphous composite powder was obtained after 6h of ball milling. At 490 °C, the amorphous powder is thermally stable. Discharge plasma sintering was used to create a Fe-Si-B/SiO2 magnetic powder core (SPS). At a sintering temperature of 420 to 540 °C, the phase composition and magnetic characteristics of the magnetic particle core were investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to examine the structural features of the magnetic particle core. A precision resistance tester and a vibrating sample magnetometer were used to assess the resistivity and magnetic characteristics of the magnetic particle core. The findings showed that Fe3Si and Fe2B are the phases generated during spark plasma sintering. High-frequency power loss increases as density rises. However, at the measured frequency, the magnetic permeability of the magnetic particle core changes slightly and has excellent frequency characteristics, making it appropriate for use in high-frequency components.

Temperature Dependence of Powder Cores Magnetic Properties for Medium-Frequency Applications

Soft magnetic powder cores are attractive because of their loss at medium frequency. However, the performance of electrical equipment is affected by temperature increase by the heat of core losses. In this article, the magnetic properties of nanocrystalline powder core, amorphous powder core, X-Flux (Fe-Si), Sendust (Fe-Si-Al), and ferrite are measured and compared in the range of 25 °C–125 °C from 20 to 100 kHz. The discussed magnetic properties include the temperature-dependent coercive field, initial permeability, inductance factor, saturation flux density, and core loss. The results show that magnetic properties depend on temperature and frequency. In comparison, the nanocrystalline powder core has the best temperature stability and relatively low core loss among the five materials, so it can be well used at broad temperature and medium frequency.

Effects of the substitution of Si with P on the glass forming ability, crystallization behavior, and magnetic properties of FeCuNbSiBP atomized powder

Soft magnetic nanocrystalline Fe80Cu1Nb2Si11−xB6Px (x = 0, 1, 2, 3, 4, 5, 6) alloy powders with nearly spherical shape were produced by gas-water combined atomization. Effects of the substitution of Si with P on the glass forming ability, crystallization behavior, magnetic properties of the powders, and the properties of magnetic powder cores made of these powders were studied. The P addition enhances the glass forming ability of the powders, facilitates the nucleation of α-Fe (Si) grains, and refines the grain size during annealing. Coercivity (Hc) and the saturation magnetic polarization (Js) of the powders decrease with the increase of P content. The Fe80Cu1Nb2Si6B6P5 powder annealed under 773 K exhibits better overall properties with grain size of 20.3 nm, Hc of 98 A/m, and Js of 1.42 T. The magnetic powder cores prepared from the Fe80Cu1Nb2Si6B6P5 powder have an effective permeability of 23.3 and a relative permeability of 90.5% under a DC magnetic field of 7.96 kA/m, and the core loss of 495 mW/cm3 at f = 100 kHz and Bm = 0.05 T.

Evolution of magnetic loss with annealing temperature in FeSiAl/carbonyl iron soft magnetic composite

ABSTRACT The evolution of magnetic loss of FeSiAl/carbonyl iron powder cores annealed at different temperatures was investigated. The experimental results reveal that the magnetic permeability of FeSiAl/carbonyl iron core increases as the annealing temperature increases, but it almost remains constant when annealing temperature higher than 650°C. The magnetic loss of the core first decreases with the increase of the annealing temperature, reaches a minimum at about 640°C, and then starts to increase with further annealing temperature increasing. It is found in loss separation that both hysteresis loss and excess loss decrease with the increase of annealing temperature before 640°C, which can be attributed to the reduction of effective anisotropy caused by stress relief. However, the eddy current loss increases with annealing temperature increasing when it is higher than 650°C, which may be the result of the degradation of the surface insulation layer caused by the high temperature annealing.

DC bias characteristic enhancement of the powder core by using densified submicron sized FeNi particles through spray pyrolysis

High-density submicron-sized FeNi particles prepared by a spray pyrolysis route exhibit high magnetic characteristics and enhance the powder core performance indicated by the improvement of the DC bias characteristic value.

Effects of trace Mn and B on microstructure and memory properties of additive manufacturing Cu-Al-Fe alloy

In this paper, the Cu-13Al-4Fe alloy was selected as the object, and the powder core wire with the “skin coated powder” damage-resistant structure was selected as the material for additive manufacturing. Three kinds of alloys: Cu-13Al-4Fe, Cu-13Al-4Fe-0.6Mn, and Cu-13Al-4Fe-0.2B were prepared by wire arc additive manufacturing technology. An optical microscope observed the as-deposited and quenched microstructures of the alloys before and after adding trace fourth phase elements. Their shape recovery rates under different pre-strain amounts (4%, 6%, and 8%) were tested by the bending deformation method, and the results were obtained. The mechanism of action of the fourth phase elements is discussed. The results show that the addition of trace amounts of Mn and B not only refines the microstructure of additively manufactured Cu-Al-Fe alloys but also improves the memory properties of Cu-13Al-4Fe alloys. Especially the Cu-13Al-4Fe alloys with trace amounts of B added. the shape recovery rate is 100% under the pre-strain of 4% and 6%, and the shape recovery rate is still 98.39% under the pre-strain of 8%.