Fe-based Alloy Powders Research Articles

A facile route to insulate an Fe-based nanocrystalline alloy powder for magnetic composite cores

We tested a facile surface coating procedure using 3-aminopropyltriethoxysilane (APTES) as a coating reagent to insulate the surface of Vitroperm 800. Both Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the presence of iron oxides on the surface of the Vitroperm. The higher oxidation state of Fe3+ (Fe2O3) was preferably formed over the Fe2+ state (Fe3O4) when the organosilane concentration was increased. XPS revealed that a coating solution concentration >5 mM was required to obtain an insulating silicon oxide layer similar to SiO2. The presence of these oxides on the surface of Vitroperm elevated the surface resistivity into the 106 Ω-cm range without having a detrimental impact on the direct current (DC) magnetic flux density or alternating current (AC) permeability. The insulating coating slightly decreased the DC coercivity, which is related to hysteresis loss. However, the increase in surface resistivity should decrease eddy current losses.

Progress in materials and processes of multilayer power inductors

Passive components have continuously improved in recent years in miniaturization, multi-functionality, performance, and energy efficiency. The requirements of portable devices, home appliances, automobiles, industrial equipment, and other products demand these improvements. The passive components used in these products have had to continuously become smaller and thinner to meet ever-higher performance requirements. During the last several years, the demand for power inductors with high-rated current has increased rapidly due to the diversification and reduction in operating voltage in portable electronic devices. The low-temperature firing NiCuZn ferrites and Fe-based alloy powders for inductors have attracted much attention in recent years, while the review of the materials and processes for multilayer power inductors has not been described in the open literature to our best knowledge. Therefore, this article is aimed to deliver an overview on the progress of the multilayer power inductors, from materials and processes' point of view.

Laser additive manufactured high-performance Fe-based composites with unique strengthening structure

Steel matrix composites (SMCs), reinforced by ceramic particles, have received a consistent attention in recent years. Using conventional methods to prepare SMCs is generally challenging, and the mechanical properties of conventionally fabricated SMCs are limited. In this study, we successfully fabricated high-performance SMCs by laser powder bed fusion (LPBF) of a composite powder consisting of Fe-based alloy powder and submicron-sized WC particles. The effect of laser energy density on the phase formation, microstructural evolution, overall density and resulting mechanical properties of LPBF-fabricated composites was investigated. The present results show that a novel Fe2W4C carbidic network precipitates in the solidified microstructure entailing segregations along the boundaries of cellular sub-grains. The presence of this carbidic network hampers the growth of sub-grains even at elevated temperatures, and hence, stabilizes the grain size though prepared at a broad range of different energy densities. The exact distribution of the Fe2W4C carbides depends on the employed laser energy densities, as for instance they are more uniformly distributed at higher energy input. The density of LPBF samples reaches the maximum value of 99.4 % at 150 J/mm3. In this parameter set, high microhardness of ∼753 HV, compression strength of ∼3350 MPa and fracture strain of ∼24.4 % are obtained. The enhanced mechanical properties are ascribed to less metallurgical defects, higher volume fraction of the martensitic phase and increasing pile-up dislocations resulting from the pinning effect by Fe2W4C carbide.

Development of Fe-based high Bs nanocrystalline alloy powder

We developed nanocrystalline powders with high Fe contents through methodological and compositional innovations. The Fe-Cr-Cu-Si-B-Sn powders exhibit high Bs of 1.55 T–1.60 T and core losses of 4800–8000 kW/m3 at 2 MHz under 30 mT, P0.2/3M. The Cu clusters provide a high number density of nucleation sites, leading to the formation of powders with nanocrystalline structures. It is found that high number density of Cu clusters are realized by distribution of sub-nanometer Sn clusters, especially near the surface. The addition of Sn enables the maintenance of a stable supply of nucleation sites regardless of powder diameters i.e., a wide variety of quenching rates is accepted.

Coating properties, energy consumption, and cost analysis of the induction cladding process

Induction cladding may provide an innovative approach for repairing or remanufacturing grey cast iron components. A complete analysis of the induction cladding technology is important for promoting practical applications. Three commonly used alloy powders were chosen for the research, and the induction cladding technology was thoroughly investigated from three aspects: the coating properties, energy consumption, and unit cost. The porosity, microhardness, and frictional performance were defined as the coating properties. An energy consumption measurement system was set up to quantitatively assess the energy consumption during the induction cladding process. Finally, the unit costs of alloy powders used for the induction cladding were assessed. The results suggest that the Ni-based coating possesses the best coating properties except for a porosity that is relatively high (but still lower than that of coatings fabricated using other surface coating technologies). The microhardness values of Ni-based and Fe-based coatings are higher than that of the Co-based coating, and the Ni-based coating has the lowest coefficient of friction and smallest wear volume. The energy consumptions per unit coating of the three alloy powders are similar, although that of the Fe-based coating is slightly lower. The unit cost of the Co-based alloy powder is approximately three times higher than that of Ni-based and Fe-based alloy powders. Therefore, based on comprehensive assessment, the Ni-based alloy coating shows the best performance.

Mössbauer spectroscopy studies on the particle size distribution effect of Fe–B–P amorphous alloy on the microwave absorption properties

An Fe-based nanocrystalline alloy powder is important for application in microwave absorption, and the particle size has a critical impact on the electromagnetic microwave parameters. Therefore, it is necessary to study further the effects of the particle size on such parameters and improve the microwave absorption performance of Fe-based nanocrystalline powers. In this study, Fe–B–P particles were prepared through a synthetic approach consisting of an aqueous chemical reduction and a ball milling treatment. We investigated the effects of ball milling on the microstructure and electromagnetic properties of Fe–B–P particles. The experimental results indicate that the Fe–B–P particles synthesized through an aqueous chemical reduction are amorphous spheres. Fe–B–P particles with an original particle size of 200–1200 nm can be milled into an irregular shape with the size reduced to < 500 nm after 0.5 h of ball milling, and subsequently, the particles become smaller with increases in the milling time, with traces of Fe2O3 generated on the particle surface. The results of the Mossbauer spectra show that a portion of the small particles demonstrate a superparamagnetic property. The volume proportions of the superparamagnetic component increase from 13.1 to 15.8% as the treatment time increases. We measured the permittivity and permeability spectra of Fe–B–P particles within the frequency range of 2–18 GHz. The reflection loss (RL) is − 10 dB for an absorber thickness of 1.7–5.0 mm. The RL is − 20 dB for an absorber thickness of 1.9–2.7 mm. The microwave absorption properties of samples with the same thickness are improved with an increase in the treatment time and are shifted to a higher frequency, which will broaden the bandwidth of the absorption as well.

Numerical Investigation of In-Flight Behavior of Fe-Based Amorphous Alloy Particles in AC-HVAF Thermal Spray Process

Computational fluid dynamics is used to investigate the in-flight behavior of particles of Fe-based amorphous alloy powder in an activated combustion high-velocity air fuel spray process. The continuity, momentum, energy, and species equations are solved with a renormalization group k–e turbulence model to predict the flow fields. A one-step chemistry model and eddy-dissipation model are used to simulate the combustion reaction. The processing of the Fe-based amorphous alloy particles in the gas flow is modeled based on the Lagrangian approach. The predictions show that the static pressure and flame temperature of the combustion products in the combustion chamber can reach up to 515,000 Pa and 1600 K, respectively, under the conditions considered in this study. Both the temperature and velocity of the alloy particles are strongly affected by the powder particle size. The particle injection position also has a great influence on the particle temperature. The greater the deviation of the injection point from the centerline, the higher the particle temperatures. The nitrogen flow rate and particle size were projected as two important parameters to avoid nozzle clogging, revealing that high gas flow rates and large particles favor expansion of the particle stream in the radial section during the spray process.

Microstructure and property of laser clad Fe-based composite layer containing Nb and B4C powders

In present study, Fe-based composite layers were fabricated on steel substrate by laser cladding with or without the addition of Nb and B4C in Fe-based alloy powders. The phase composition, microstructure evolution, microhardness and wear properties of Fe-based composite layers were studied. The results showed that the phases in the Fe-based composite layer were mainly α-Fe, Fe2B, Cr7C3 and Cr23C6. The addition of Nb and B4C resulted in the in-situ formation of NbC phase, an increase in the amount of Fe2B phase, and the refinement of the microstructure in the Fe-based composite layer. The microhardness of the Fe-based composite layer was increased by 269.5 HV0.5 and the wear resistance was improved to about 1.5 times the original wear resistance when the 5% Nb and 5% B4C powders were added. The wear mechanisms of both two Fe-based composite layers were abrasive wear and adhesive wear.

Novel Method for Making Surface Insulation Layer on Fe-Based Amorphous Alloy Powder by Surface-Modification Using Two-Step Acid Solution Processing

By introducing the SiC/GaN power devices, the high-frequency switching dc–dc converters are expected to have higher efficiency and lightweight. This paper focuses on the Fe-based amorphous alloy powder (Fe–Si–B–Cr–C based) used in the metal composite bulk magnetic core for high-frequency power inductor and transformer. In terms of eddy-current loss at MHz band or beyond, iron-based metal composites are required to have fine magnetic particles with surface insulation layer. In this paper, the finest amorphous powder with a median diameter of 2.57 $\mu \text{m}$ made by water atomization process was used. In order to fabricate the amorphous powder with surface insulation layer, a surface-modification scheme through the two-step acid solution processing using phosphoric acid and hydrochloric acid was introduced. As a result, the surface-modification scheme enabled to make a single-phase silica thin layer on the surface of the amorphous powder, and the silica thin layer was considered to be derivable from the silicon element in the amorphous (Fe–Si–B–Cr–C based) powder.

Fabrication and Evaluation of Composite Magnetic Core Using Iron-Based Amorphous Alloy Powder With Different Particle Size Distributions

The authors proposed the iron-based metal composite bulk magnetic core for high efficient and lightweight MHz switching DC–DC converter using SiC/GaN power devices. Although the iron-based metal composite bulk magnetic core exhibited a lower core loss than that of Ni-Zn ferrite in MHz frequency band, its relative permeability was low around 10. In this paper, in order to increase the permeability of such composite magnetic core with low core loss, we investigated an effect of mixing amorphous alloy powder having different particle size distributions. This method estimated increasing volume fraction of amorphous alloy powder and decreasing the demagnetization field of the composite magnetic core. From the experimental results, the composite magnetic core with an optimal mixing ratio of 2.4 $\mu \text{m}$ and 12.8 $\mu \text{m}$ median diameter Fe-based amorphous alloy (Fe-AMO) powders exhibited a relative permeability of 20.5 which was 2.4 times higher than that of composite magnetic core using 2.4 $\mu \text{m}$ median diameter Fe-AMO powders. And its core loss was 555 kW/m3 at 1 MHz in frequency and under 20 mT in maximum flux density.

Microstructure and Wear Resistance of 62Cu-38Zn Brass with Bionic Coupling Units Treated by Laser Cladding

In order to improve the wear resistance of 62Cu-38Zn brass, bionic coupling units were fabricated by laser cladding using Ni-based, Fe-based and Co-based self-fluxing alloy powders. The microstructures, chemical composition and mechanical properties of the units were studied in this paper. Wear resistance of samples was examined by dry sliding wear. Good metallurgical bonding between the unit and substrate was obtained, and fine dendritic microstructure was resulted in the unit zone, which proved marked availability of laser cladding on brass. Laser cladding treatments with different self-fluxing alloy powders were beneficial to reinforcing the surface of brass and then improved its wear resistance with various results. The Ni-based alloy powders led to the best wear resistance amongst the all samples.

Microstructure evolution during laser cladding Fe-Cr alloy coatings on ductile cast iron

Ductile cast iron illustrates well cast characteristics and abrasive resistance, excellent corrosion resistance and good mechanical properties. Fe-based alloys were always used to repair invalid ductile cast iron components owing to their cheapness in price. But it is difficult to eliminate defects like pores and chilled structure for the remanufacturing of ductile cast iron without preheating and post heat treatment. In this research work, a kind of Fe-based alloy powders were used as the cladding material for the laser cladding process on ductile cast iron, and different cladding procedures had been successfully completed. The microstructure and phase evolution in the partially melted zone (PMZ) and heat affected zone (HAZ) had been investigated. Mechanical properties also had been studied. Scanning electron microscopy (SEM), energy dispersive microanalysis (EDS), X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to determine the microstructure and phase composition of the cladding layers and transition zones. The result revealed that distinct phases were formed during a single pass and multi-layer cladding process. Different kinds of pearlite structures formed in the transition zone during cladding process. Element migration was not apparent near the interface. The wear resistance of the cladding layers was not higher than that of the substrate.

Effect of Nano-Y2O3 on Microstructure and Crack Formation in Laser Direct-Deposited In Situ Particle-Reinforced Fe-Based Coatings

In situ hard-particle-reinforced Fe-based composite coatings were prepared on Q235 steel substrates by direct laser deposition using Fe-based alloy powders containing 2 wt.% B, 3 wt.% Si and 1-3 wt.% nano-Y2O3. The microstructures, phase compositions, hardnesses and wear resistances of the deposited coatings with different nano-Y2O3 contents were studied using metallographic microscopy, scanning electron microscopy, x-ray diffraction, transmission electron microscopy, microhardness tests and pin-on-disk abrasion tests (MMW-1A), respectively. The results showed that the appropriate addition of Y2O3 played a role in grain refinement and in decreasing the number of brittle phases and impurity elements in the grain boundaries. Consequently, the number of cracks in the laser-deposited coating also decreased. The Fe-based composite coatings were mainly composed of α-Fe, γ-Fe and in situ-produced reinforced particle phases, such as Cr23C6, Cr7C3, (Cr, Fe)7C3, Fe2B, and CrFeB. When the content of nano-Y2O3 was 2 wt.%, a Fe-based composite coating with a thickness of 4 mm that was free of cracks was obtained, and its surface hardness reached 650HV. Moreover, the wear resistance of the coating with 2 wt.% nano-Y2O3 was the best among the samples studied. The presence of nano-Y2O3 increased the solubility of Cr and Si in the solid solution, which eliminated the residual austenite region, and as a result, the phase transformation from γ-Fe to α-Fe was restrained and the transformation stress was also limited, thereby decreasing the probability of cracks in the coatings.

Characteristics of Fe-based powder coatings fabricated by laser metal deposition with annular and four stream nozzles

The present work focuses on performing a comparative study in the field of Laser Metal Deposition (LMD) analyzing the obtained clads in terms of geometry and quality when vertically using a discrete coaxial nozzle or an annular one. A Fe-based alloy powder (Eutroloy 16606A.04) was used for the study, a heat treatable alloy, with high wear-resistant to abrasion and fatigue stress, typically employed for coating applications. The possibility of controlling the coating process with a non-coaxial thermographic camera has also been evaluated.

Pressure controlled micro-viscous deformation assisted spark plasma sintering of Fe-based bulk amorphous alloy

In this paper, the theoretical framework of viscous flow deformation is presented as a model to investigate the inherent role of applied pressure in the densification of Fe-based amorphous alloy powder during spark plasma sintering. The proposed model revealed that the evolution of the structural geometry of the powder compact resulted in an amplification of the applied pressure to a larger contact pressure. The resulting pressure controlled compressive viscous flow deformation of the particles exhibited the contribution of increased applied pressure towards enhancement of densification and thus confirmed the validity of the present model for analyzing pressure-assisted sintering of amorphous alloy powder. The application of this theoretical model correctly predicted the trend of increasing final density of the compacts with pressure while further improvement on its accuracy can be attained upon establishment of the relative contribution of mass flow and deformation of powder particles towards their consolidation.

Preparation of gas-atomized Fe-based alloy powders and HVOF sprayed coatings

High-pressure gas atomization was employed to prepare the Fe-based Fe50Cr24Mo21Si2B3 alloy powder. The effect of flow rate of atomizing gas on the median powder diameter was studied. The results show that the powder size decreased with increasing the flow rate of atomizing gas. Fe-based alloy coatings with amorphous phase fraction was then prepared by high velocity oxygen fuel spraying (HVOF) of gas atomized Fe50Cr24Mo21Si2B3 powder. Microstructural studies show that the coatings present dense layered structure and low porosity of 0.17% in about 200 μm thickness. The Fe-based alloy coating exhibits an average hardness of about 1230 HV. Our results show that the HVOF process results in dense and well-bonded coatings, making it attractive for protective coatings applications.

Development and application of Fe-based soft magnetic bulk metallic glassy inductors

The characteristics and application fields of core inductors made of Fe-based glassy alloy powders have been reviewed based on the data of Fe-based bulk metallic glasses developed for the last two decades. Fe-based glassy alloys in Fe-Cr-(B,Si,P,C) and Fe-Cr-Nb-(B,P) systems have been used as core inductors in various electronic-magnetic devices. The commercialization is attributed to a bulk glass-forming ability in conjunction with good soft magnetic properties, high mechanical strength, high corrosion resistance and high thermal stability during annealing at the high temperature near glass transition temperature (Tg). Besides, the possibility whether or not the application can be made even for Fe-based amorphous alloys without glass transition as well as bulk glass-forming ability is also discussed on the basis of fundamental properties for recently developed Fe-Cr-Nb-(B,Si,P) and Fe-Mo-(B,Si,P) amorphous alloys. It is concluded that the success of mass production application to magnetic core inductors is attributed to the utilization of Fe-based glassy type alloys with high glass-forming ability, high degree of magnetic softness (low coercivity, high effective permeability and low core losses), high mechanical strength and high corrosion resistance.

Prediction of heating rate controlled viscous flow activation energy during spark plasma sintering of amorphous alloy powders

The viscous flow behavior of Fe-based amorphous alloy powder during isochronal spark plasma sintering was analyzed under the integrated theoretical background of the Arrhenius and directional structural relaxation models. A relationship between viscous flow activation energy and heating rate was derived. An extension of the pertinent analysis to Ti-based amorphous alloys confirmed the broad applicability of such a relationship for predicting the activation energy for sintering below the glass transition temperature (Tg) of the amorphous alloy powders.

Initial stage densification during spark plasma sintering of Fe-based amorphous alloy powder: Analysis of viscous flow

Understanding the mechanism of densification of amorphous alloy powders is important for determining the parameters during sintering of these materials. In this paper, we report on the analysis of densification of Fe48Cr15Mo14Y2C15B6 amorphous alloy powder during spark plasma sintering. Sintering up to 1000 °C resulted in two clearly distinguishable stages of densification: stage I from 320 °C to 740 °C and stage II from 830 °C to 1000 °C. The maximum densification rate during stage I was attained at 585 °C up to which the sample remained fully amorphous. During the entire stage II, the sample was fully crystalline, and the maximum densification rate attained at 935 °C was much lower than that observed during stage I. Viscous flow during stage I was analyzed, yielding an estimate of the activation energy to be 94.0 ± 0.2 kJ mol−1 in the temperature range from 525 °C to 580 °C.

Enhancement in the corrosion resistance of WC coatings by adding a Fe-based alloy in simulated seawater

In this study, a composite coating was formed by adding Fe-based alloy powder to WC powder using a high velocity oxygen fuel thermal spraying process. The microstructure, wear, and corrosion properties of the single WC coating and composite coating were studied in detail. It was observed that the composite coating displays a partial amorphous character and closely adheres to the WC matrix. The composite coating exhibited an extremely dense structure with a porosity of 1.5%. Polarization tests demonstrated that the composite coating exhibited better corrosion resistance than a single WC coating in simulated seawater. The reasons for the observed enhanced corrosion resistance have been discussed from the perspective of structure and the elemental composition of the alloys.