FeSi Particles Research Articles

Optimizing of hardness, microstructure and adhesive strength of plasma-sprayed FeSiAl coatings using orthogonal analysis

The traditional high-efficiency absorber FeSiAl has gradually achieved the attention at high temperature. The paper focuses mainly on the preparation and characterization of plasma-sprayed FeSiAl coatings. The plasma-sprayed FeSiAl coatings were prepared through the Praxair 100HE high enthalpy plasma spray gun on stainless steel 316 substrate by orthogonal experiment. The cross-section and properties of sprayed coatings were analyzed. The results reveal that the best parameters of sprayed coatings can be represented by C3B2A3D2 for microhardness, i.e., 30 SCFH, 140 mm, 50 KW, 3 PRM. The optimal parameters can be expressed as C3D1B3A3 for adhesive strength, i.e., 30 SCFH, 2 PRM, 200 mm, 50KW. The cross-section of sprayed coatings is composed of fattening FeSiAl particles (pale gray) and oxidation phase of FeSiAl (dark). The percentage of disorder structure reduces in FeSiAl coatings.

Behavior of Electrodeposited Fe/FeSi Composite in High Magnetic Fields

Fe-Si composite coatings were prepared through composite electrodeposition in high magnetic fields. The results indicated the magnetic field modified the surface morphology and particle content of composite coatings significantly. Many striped structures arranged perpendicular to the direction of magnetic field on the coating surface for the Fe-Si particles with relatively high silicon content when in longitudinal electrode system, and the silicon content in the composite coatings significantly increased with the increase of magnetic field intensity. However, hill-shaped structures along with the decrease of silicon content appeared on the coating surface when in an horizontal electrode system. Further, with the increase of current density, the silicon content in composite coatings reached a maximum when at 2 A·dm−2 in the longitudinal electrode system both without and with an 8 T magnetic field, whereas that for the horizontal electrode system decreased. The modification of the surface morphology and particle content during electrodeposition under the magnetic field may be attributed to the magnetohydrodynamic(MHD) flow and gradient magnetic force(GMF).

Effects of the Mg/Si Ratio on Microstructure, Mechanical Properties, and Precipitation Behavior of Al⁻Mg⁻Si⁻1.0 wt %-Zn Alloys.

Aluminum alloys are widely used as first-choice materials for lightweight automotive applications. It is important that an alloy have a balance between strength and formability. In this study, the alloys were melted, cast, hot rolled, and cold rolled into 1 mm-thick sheets. The microstructure, mechanical properties, and precipitation behavior of Al–Mg–Si–1.0 wt %-Zn alloys with Mg/Si ratios of 0.5, 1, and 2 after solution treatment were studied using optical and electron microscopy, a tensile test, the Vickers hardness test, and differential scanning calorimetry. The results showed that a high density and number of Al–Fe–Si particles were observed in the matrix, thus causing the formation of more homogeneous and smaller recrystallized grains after treatment with the solution. In addition, a higher volume fraction of cubeND and P-types texture components formed during solution treatment. Also, a high r value and excellent deep drawability were achieved in the medium-Mg/Si-ratio alloy. The formation of denser strengthening precipitates led to a better paint-bake hardening effect in comparison with the other two alloys. Furthermore, the precipitation kinetics were enhanced by the addition of Si, and the addition of Zn did not alter the precipitation sequence of the Al–Mg–Si alloy. The dual-phase strengthening effect was not achieved in the studied alloys during paint-bake treatment at 175 °C.

Comparative investigation of microstructure and properties of Ni-coated FeSiAl soft magnetic composite coatings produced by cold spraying and HVOF

In this work, the techniques of cold spray (CS) and high velocity oxygen-fuel (HVOF) were employed to fabricate Ni/FeSiAl soft magnetic composite (SMC) coatings by using Ni-coated FeSiAl composite powder. The microstructural features were characterized in terms of scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses. The tribological and magnetic properties of the Ni/FeSiAl SMC coatings were also comparatively studied. Results showed that the CS coating exhibited higher particle deformation and much higher density, whereas the HVOF coating showed more visible defects and slightly higher oxide content. Both CS coating and HVOF coating resulted some loss of FeSiAl particles during deposition, while a higher content of FeSiAl particles was achieved in the HVOF composite coating, indicated a higher deposition efficiency of FeSiAl particles during HVOF deposition. According to the XRD analysis, both SMC coatings had no obvious oxidation and phase transformation during deposition processes. The EDS analysis proved partially melted particles during HVOF deposition. Tribological tests revealed a better wear performance of the CS coating as a result of the enhanced plastic deformation and microhardness. The HVOF coating showed a better magnetic performance, with a lower coercivity and a higher saturation magnetization compared to those of CS coating. This can be explained by a higher retainability of FeSiAl particles and a smaller strain stress generation during HVOF deposition.

Analysis of Magnetic Losses and Complex Permeability in Novel Soft Magnetic Composite With Ferrite Nanofibers

This paper investigated the magnetic properties of novel soft magnetic composite (SMC) with ferrite nanofibers. Material consists of FeSi powder covered by resin and different amounts of Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ferrite nanofibers. We prepared SMC with very high specific electrical resistivity. FeSi/resin (0.49 wt% ferrite) sample exhibits the highest electrical resistivity (6.05 Ω·m) due to low interparticle contacts. The image analysis of SEM pictures was used for the evaluation of effective area, in which local eddy currents are flowing. The FeSi/resin (0.49 wt% ferrite) sample displays the lowest total losses in the measured frequency range due to the highest specific electrical resistivity and appropriately covered FeSi particles. Loss separation and the analysis of movable magnetic objects were performed for all studied materials.

Cold spraying of thermally softened Ni-coated FeSiAl composite powder: Microstructure characterization, tribological performance and magnetic property

The low retainability of reinforcing particles in functional composite coatings fabricated by cold spray (CS) is a major problem in maximizing coating properties. In this work, the Ni-coated FeSiAl composite powders were used to fabricate soft magnetic composite (SMC) coatings via CS. The feedstock particles were preheated prior to the entrance of nozzle to improve the retainability of FeSiAl particles and the coating properties. Our results showed that the dense Ni/FeSiAl coatings containing the uniformly-dispersed and crack-free FeSiAl particles were produced. The thermal softening effect of Ni layer, as a result of particle preheating, can effectively increase the volumetric content of FeSiAl particle (from 24.3% to 46.2%) in the composite coating. Particle preheating also conducted to the significant improvement of coating thickness due to enhanced deposition efficiency. Dry-sliding test showed that the tribological performance of SMC coating with particle preheating weakens, owing to lowered microhardness. Enhanced magnetic property was achieved with higher soft ferromagnetic characteristic and decreasing coercivity value at higher particle preheating temperatures. The study on coating formation mechanism highlighted that thermal softening effect can give rise to adiabatic shear instability of Ni layer. This results in the significantly improved retainability of FeSiAl particles and soft magnetic performance.

A novel approach for fabricating Ni-coated FeSiAl soft magnetic composite via cold spraying

Currently, soft magnetic composites (SMCs) have attracted increasing attention due to their outstanding magnetic properties, and various methods have been developed and applied for their fabrication. As an emerging additive manufacturing technique, cold spraying (CS) can fabricate bulk material via solid-state deposition by avoiding oxidation and phase change. In this work, SMCs coating was first fabricated by Ni-coated FeSiAl composite powder via CS. Two groups of Ni-coated FeSiAl composite particles (40 μm and 57 μm) were used as feedstocks for deposition under different processing parameters. No phase transformation can be detected from XRD analysis. The coating thickness increased with the increasing of propelling gas temperature and pressure. Higher deformation of FeSiAl particles and higher micro-hardness of the composites fabricated from the powders with larger size were obtained due to the enhanced in-situ peening effect of the rebounded particles during deposition. The magnetic property of cold sprayed SMCs showed a soft ferromagnetic characteristic with a coercivity of about 60 Oe. The investigation on the coating formation mechanism was carried out by single particle deposition, and the results showed that the Ni bonding layer with sufficient plastic deformation plays a significant role during the deposition of the composite coating.

Aligning flaky FeSiAl particles with a two-dimensional rotating magnetic field to improve microwave-absorbing and shielding properties of composites

In order to enhance the microwave-absorbing and shielding properties of the composites, the flaky FeSiAl particles embedded in an epoxy polymer were aligned with a two-dimensional rotating magnetic field. The morphologies, electromagnetic (EM) characteristics, and microwave-absorbing and shielding properties of the unaligned and aligned FeSiAl/epoxy composites were investigated. The results showed that after alignment treatment, the flaky FeSiAl particles tend to orient uniformly in the rotating magnetic field, and the permittivity and permeability of the aligned composites were increased in the frequency range of 1–18 GHz compared with that of randomly distributed composites. The calculated microwave-absorbing properties indicated that the peak value of the return loss (RL) of the aligned composites can reach 8.8 dB, compared with 5.8 dB of the unaligned composites of 2.5 mm in thickness (60 wt%); and the bandwidth with RL value more than 6 dB is in a wider frequency range from 1 to 2.8 GHz. And the calculated shielding effectiveness (SE) of the aligned composites is 1.1–3 times higher than that of unaligned one in every thickness, and the maximum SE of the aligned one is 31.8 dB at 18 GHz with a thickness of 2.5 mm.

Investigation of pre-existing particles in Al 5083 alloys

Pre-existing particles formed in Al 5083 alloys (H131 and H116) have been investigated using scanning transmission electron microscopy(STEM), energy-dispersive X-ray spectroscopy(EDS), atom probe tomography (APT), and small angle neutron scattering (SANS). Three types of pre-existing particles, Al6Mn, Mg2Si, and α-Al(Mn,Fe)Si, were observed in Al 5083 alloys, and their relative fraction was obtained from EDS results. The average size, number density, and interfacial area of pre-existing particle were calculated using STEM and SANS results. In addition, an extra layer rich in Mg and Si was found on a pre-existing Mg2Si particle, and an Al6Mn layer was identified on an α-Al(Mn,Fe)Si particle. Thermodynamic calculations were also applied to investigate the possible pre-existing particles formed in the alloys, which can be used to explain the extra layers formed on Mg2Si and α-Al(Mn,Fe)Si particles.

Properties of FeSiAl-based soft magnetic composites with AlN/Al2O3 and hybrid phosphate–silane insulation coatings

FeSiAl soft magnetic composites (SMCs), which are widely used in electromagnetic applications, can be described as FeSiAl particles surrounded by electrical insulating layers. In general, good insulation is required to minimize eddy currents within SMCs in high frequency applications. In this work, FeSiAl-based SMCs with uniform single insulation layer of AlN/Al2O3 were prepared by high-temperature selective nitridation and oxidation. For comparison, SMCs with double layers of phosphate-resin or phosphate-silane were produced by traditional chemical process. Their magnetic properties were systematically studied. The results revealed that the core insulated by AlN/Al2O3 with high electrical resistivity had much better stability in the real part of permeability μ′ than double layer insulated cores with respect to frequency in the range of 100 kHz to 28 MHz. In addition, the FeSiAl-AlN/Al2O3 core had higher quality factor Q at higher frequency than other cores. The investigation of the effects of annealing process up to 600 °C on the cores indicated that the magnetic properties of FeSiAl-AlN/Al2O3 cores were strongly improved in terms of μ′, Q, total core loss Ptot and coercivity HC mainly on account of the hysteresis loss reduction by stress relaxation and defects elimination. By contrast, annealing treatment had less positive effects on the properties of the cores with double insulating layer. In addition, the microstructure, composition and thermal stability of the AlN/Al2O3 insulated particles were characterized by Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction, X-ray Photoelectron Spectroscopy and Derivative Thermogravimetric Analysis, respectively.

Soft magnetic composites based on hybrid coated Fe-Si nanocrystalline powders

The preparation and characterisation of soft magnetic composite compacts based on hybrid coated nanocrystalline Fe-Si powder are presented. The Fe-Si powder was prepared by mechanical milling of Fe-Si electrical steels sheets up to 20h. The hybrid coating consists in an electrically insulating phosphate and a polymer layer that covers the Fe-Si particles. The influence of phosphating duration on the particles surface was investigated by SEM, EDX, XRD, and FTIR investigations. The saturation magnetisation of the powders phosphated for 60s decreases with 17% as compared to the uncoated powder. The influence of the compaction pressure, as well as the phosphating duration, on initial relative permeability and power losses of the compacts was investigated. It was found that increasing the compaction pressure leads to the increase of the compact's permeability and a decrease of the hysteresis losses. A shorter phosphating duration leads to a partial coating with phosphate of the Fe-Si particles and to compacts with higher density characterised by high magnetic permeability.

Stress distribution around Fe5Si3 and its effect on interface status and mechanical properties of Si3N4 ceramics

AbstractSi3N4 ceramics with different amount of Fe5Si3 were prepared by adding FeSi2. Residual thermal stress distribution and elastic energy around Fe5Si3 particles in various depths were calculated. The interface status between second phase particles and matrix was analyzed in terms of stress and energy. High tangential compressive stresses and low radial tensile stresses were generated along the surface of the ceramics. Elastic strain energy caused by unit interface was high around big particles in deep area of the ceramics. Microcracks are observed around the big Fe5Si3 particles. Furthermore, accord to our calculation, microcracks are easily generated around particles in superficial layer of matrix when second phase particles have lower thermal expansion coefficient than the matrix, while microcracks tend to be generated in deep layer of matrix preferentially when the thermal expansion coefficient of second phase particles is higher than matrix. Residual stresses and microcracks around Fe5Si3 particles greatly influenced mechanical properties. Fracture toughness of Si3N4 ceramics with similar Si3N4 particle size distribution increased with the amount of Fe5Si3, and fine Fe5Si3 particles could enhance the strength of Si3N4 ceramics. Si3N4 ceramics exceeding 1.2 GPa strength were prepared.

Effects of Annealing Temperature and Compaction Pressure on Magnetic Properties of Fe–Si Powder Cores Fabricated by an Improved Bluing Method

Fe-6.5wt%Si soft magnetic powder cores were prepared by using an improved bluing insulation method. A high-quality oxide insulation layer with good temperature stability was found to distribute continuously in the intervals between the Fe–Si particles. The effects of the annealing temperature and the compaction pressure on the core’s magnetic properties were investigated in detail. It was found that high temperature and low compaction pressure are beneficial to decrease the core’s inner stress and high compaction pressure is helpful to reduce the air gap. All the variations of the magnetic performance for the powder cores discussed in this paper were explained reasonably by considering these two factors. From the point of view of low loss, 760 °C and 2090 MPa were confirmed to be the relatively best annealing temperature and compaction pressure, respectively. The μ e , the % μ e at 100 Oe, and the loss at 50 kHz/1000 Gs for the core prepared under these two conditions are 63.57, 72.82%, and 547.66 mW/cm3, respectively.

The Preparation of Soft Magnetic Composites Based on FeSi and Ferrite Fibers

Abstract The fields of soft magnetic composites and powder metallurgy technologies have a powerful potential to redesign the way of electric motor preparation, and will continue to grow for years to come. A design of the novel soft microcomposite material composed of spherical FeSi particles and Ni0.3Zn0.7Fe2O4 ferrite nanofibers is reported together with a characterization of basic mechanical and electrical properties. The needle-less electrospinning method was used for a preparation of Ni0.3Zn0.7Fe2O4 ferrite nanofibers, which has a spinel-type crystal structure as verified by XRD and TEM analysis. The dielectric coating was prepared by mixing of nanofibers with glycerol and ethanol because of safe manipulation with fumed fibers and homogeneous distribution of the coating around the FeSi particle surface. The final microcomposite samples were prepared by a combination of the traditional PM compaction technique supplemented with a conventional sintering process of the prepared green compacts. The composition and distribution of the secondary phase formed by the spinel ferrite fibers were examined by SEM. It is demonstrated that the prepared composite material has a tight arrangement without any significant porosity, which manifest itself through superior mechanical properties (high mechanical hardness, Young modulus, and transverse rupture strength) and specific electric resistivity compared to the related composite materials including resin as the organic binder.

Structure and electromagnetic properties of FeSiAl particles coated by MgO

FeSiAl particles with a layer of MgO surface coating have excellent soft magnetic and electromagnetic properties. In order to obtain the FeSiAl/MgO composites, Mg(OH)2 sol prepared by sol-gel process was well-mixed with FeSiAl flake particles, and then treated by calcination at 823K in vacuum. The microstructural, morphological and electromagnetic parameters of FeSiAl/MgO particles were tested. Accordingly, the electromagnetic wave reflection loss in the frequency range of 0.5–18GHz was calculated. The results show that the surface coating increases coercivity Hc and decreases complex permittivity, leading to a good impedance matching. When the coating amount was 7.5%, reflection loss of the composite particles can reach to −33dB.

New route to improve the fracture toughness and flexural strength of Si3N4 ceramics by adding FeSi2

Silicon nitride (Si3N4) ceramics were pressureless sintered with 0.2wt% FeSi2 at 1780°C for 2h in nitrogen with Al2O3 and Y2O3 as sintering aids and found to have high toughness and strength. During the sintering process, β-Si3N4 crystal seeds and Fe5Si3 reinforcing particles were in situ generated by FeSi2. Abnormal growth of Si3N4 grains was promoted by β-Si3N4 crystal seeds. High thermal expansion coefficient of Fe5Si3 particles induced residual stresses in the ceramics matrix, which deflected the crack. Ultimately, the fracture toughness and flexural strength of Si3N4 ceramics reached 9.8±0.5MPa·m1/2 and 1086±48MPa respectively.

Determination of ferrosilicon medium rheology and stability

Ferrosilicon (FeSi) has a fast settling rate in dense suspension, attributed to its very high solids density, coarse particle size, more spherical particle shape and low medium viscosity. The fast-settling nature in dense suspension is a challenge to acquire reliable rheological data. A testing rig was set up to maintain a constant medium density during the rheology measurement by circulating the medium to keep FeSi particles well suspended. A rotational rheometer with a modified concentric bob-cup measuring system was incorporated in the testing rig. Taylor number (Ta) was calculated and a threshold Ta=41.3 was used to identify the onset of unstable laminar flow owning to the Taylor vortices and turbulence formation in the measuring system. The data with Ta>41.3 were excluded in the determination of rheological flow curves. Evaluation of the modified measuring system with Newtonian silicone oils of known viscosities confirmed that the system can produce true flow curves over the entire tested shear rate range for a stable laminar flow (Ta<41.3). This data reduction procedure was applied to the FeSi medium rheology measurement. It demonstrates that FeSi medium exhibits a pseudoplastic trend with a yield stress. The apparent viscosities were calculated at two shear rates, 10s−1 that is assumed to be a typical shear rate in dense medium bath separators and 75s−1 for dense medium cyclones. A characteristic curve between apparent viscosity and medium density was established, which can be used in FeSi selection for dense medium separation. Medium stability was determined from the FeSi sedimentation rate measurement. It shows that medium stability was closely correlated with medium viscosity. A trade-off between stability and viscosity for optimal dense medium separation should be established.

Effect of pre-annealing on microstructure evolution of TRC AA3003 aluminum alloy subjected to ECAP

An AA3003 aluminum alloy prepared by twin-roll casting was modified by a small amount of zirconium. Annealing at 450 °C led to precipitation of coherent Al3Zr phase and a simultaneous co-precipitation of Mn-rich α-Al(Mn, Fe)Si phase. Severe plastic deformation by equal channel angular pressing resulted in the grain refinement and increase of microhardness. Observation by electron back-scatter diffraction and in-situ transmission electron microscopy revealed influence of pre-annealing on microstructure changes during post-deformation heat treatment. Dislocation recovery and precipitation of α-Al(Mn, Fe)Si particles preceded recrystallization at 450 °C in material which was not annealed before deformation. The pre-deformation annealing enabled dynamic recovery during deformation as it depleted the solid solution from Mn atoms. Recrystallization was enhanced by Al3Zr precipitates.

Core–shell structured FeSiAl/SiO2 particles and Fe3Si/Al2O3 soft magnetic composite cores with tunable insulating layer thicknesses

Abstract FeSiAl/SiO2 core–shell particles and Fe3Si/Al2O3 composite cores with tunable insulating layer thicknesses have been synthesized via a modified Stober method combined with following high temperature sintering process. Most of the conductive FeSiAl particles could be coated by insulating SiO2 using the modified Stober method. During the sintering process, the reaction 4Al + 3SiO2 2α - Al2O3 + 3Si took place and the new Fe3Si/Al2O3 composite was formed. The Fe3Si/Al2O3 composite cores displayed more excellent soft magnetic properties, better frequency stability at high frequencies, much higher resistivity and lower core loss than the raw FeSiAl core. Based on this, several types of FeSiAl/SiO2 particles and Fe3Si/Al2O3 composite cores with tunable insulating layer thicknesses were selectively prepared by simply varying TEOS contents. The thickness of Al2O3 insulating layer and resistivity of Fe3Si/Al2O3 composite cores increased with increasing the TEOS contents, while the permeability and core loss changed in the opposite direction.

Grain Refinement in Al-Mn-Fe-Si Alloys by Severe Plastic Deformation

Aluminium alloys are widely used materials and their properties are constantly being improved. The enhanced properties can be achieved, for instance by alternation of chemical composition or processing route. Severe plastic deformation leads to an increase of strength due to a grain size reduction. Two Al-Mn-Fe-Si alloys differing in Zr content were subjected to four passes of equal channel angular pressing. Grain size was re-duced from 100 μm to 0.5 μm. In the course of subsequent annealing to 400 ◦C the grain size rose moderate-ly; at 450 °C both materials recrystallized and new defect free grains were formed; with fraction of high angle grain boundaries nearly 1. The recrystallized grain size was comparable with the grain size after cast-ing. Moreover, high density of α-Al(Mn,Fe)Si particles precipitated during annealing in both alloys.