Fe Si Research Articles

Microstructure and magnetic domain structure of additively manufactured Fe–Si soft magnetic alloys with 3 and 9 wt.-% Si

Electrical steels are numerously used in engineering applications. Nowadays, future challenges related to climate change and e-mobility push the boundaries to higher efficiency also in electrical parts. A promising material group to reduce electrical losses are electrical steels with high silicon contents. However, such steels are difficult to process with conventional methods and, thus, additive manufacturing came into focus in recent years. The present study investigates the processability, crack sensitivity, microstructure evolution and magnetic domain structures of laser powder bed fused Fe–Si alloys with 3 and 9 wt.-% Si. It is shown that specimens, which are built using appropriate process parameters, are dense and free of cracks. Still, Fe–9Si is characterized by a higher crack susceptibility at low temperatures of the build platform. A checkerboard like microstructure with elongated grains alongside build direction evolved. Global magnetic properties from ring core measurements showed lower losses for the Fe–9Si ring. Moreover, it was found that the magnetic domain structures are directly influenced by the crystallographic orientations present in the specimen volumes. The findings elaborated will contribute to advanced possibilities in tailoring the magnetic properties of electrical steels for an increase of the efficiency of envisaged applications.

Effect of Nb addition and annealing treatment on structural and magnetic properties of Fe–Si–B–P–Cu alloy ribbons

Thermal and magnetic properties of Fe85-xSi2B8P4Cu1Nbx (0 ≤ x ≤ 4) alloy ribbons of different microstructures were systematically investigated. Increase in Nb content raised the first crystallization onset temperature from 646 to 701 K suggesting improved thermal stability. XRD results on the as-spun ribbons also suggested the role of Nb increasing the thermal stability and glass-forming ability by showing fully amorphous patterns for all alloys with Nb addition. However, Nb addition turned out to decrease the saturation magnetic flux density from 1.74 to 1.17 T. To further optimize the properties, annealing treatment was carried out to find the optimized condition as Fe84Si2B8P4Cu1Nb1 processed at 793 K for 10 min resulting in nanocrystalline microstructure with a high saturation magnetic flux density of 2.03 T. Transmission electron microscopy confirmed the formation of nanocrystalline α-Fe phase in the annealed ribbons.

The fundamental research on suspended dross in hot dip Al–Zn galvanising process

In this research, supergravity enrichment experiment was conducted to determine compounds in suspended dross and to analyse density of the suspended dross in the hot-dip Al–Zn (ZA) melt. It was found that the suspended dross was composed of Al–Fe–Si–Zn intermetallic compounds (IMCs), mixtures of Fe2Al5Zn0.4 and Alx–Fe3–Siy with various Al and Si contents. The density of suspended dross was small compared with the molten hot-dip ZA liquid. After being quenched in water, the morphology of the suspended dross was confirmed as polygonal granular structures. Thermodynamics was applied to explain why there were various morphological structures of the suspended dross in the solidified hot-dip ZA melt. This research had also demonstrated that it was technically feasible to separate the suspended dross from the molten hot-dip ZA melt in a supergravity field.

Cu-based metastable microstructural template and its role in the heat flux application

The present paper focuses on developing an optimised strength-conductive alloy in Cu–Fe–Si system. We present the effect of a cost-effective rapid-casting route on modifying the microstructure. The non-equilibrium phase transformation events are tracked and the evolution sequences of metastable phases in the microstructure are elucidated. The metastable phase transformation of the precipitates from DO19- to L12-ordered structure and its role in enhancing thermal conductivity are presented. A density functional theory (DFT)-based calculation also complements the experimental evidence of the relative stability of the evolved metastable phases. One of the key findings is the evolution of L12-ordered precipitates via face centred cubic (FCC)-based interfacial matrix template.

Microstructure and soft magnetic properties of nanocrystalline Fe–Si–B–Cu–Nb soft magnetic alloy by laser annealing

The impact of laser annealing on the nanocrystalline Fe–Si–B–Cu–Nb soft magnetic alloy has been investigated. The experimental results showed that the microstructure of nanocrystals produced by laser annealing is comparable to that of furnace annealing. However, the annealing time plays a crucial role in determining the grain size and crystalline fraction evolution, thereby affecting both the coercivity and saturation magnetization. Nonetheless, the volume crystalline fraction of the laser annealed samples is lower than that of the furnace annealed ones due to the ultrahigh heating and cooling rate, which hinders the growth of nanocrystals and crystallization region. In addition, laser annealed samples demonstrate no distinct crystallization at high scanning speeds, even with noticeable changes in soft magnetic properties. Furthermore, the correlation between coercivity and grain size is examined, revealing a progressive decline in coercivity with a decrease in grain size. It is also found that the rule Hc ∝ D6 is also valid in laser annealing for relatively larger grains, whereas the rule becomes Hc ∝ D3 for smaller grains.

Transforming detrimental intermetallics by accumulative thermal and strain energies in the Al–Fe–Si alloy

Transforming detrimental intermetallics by accumulative thermal and strain energies in the Al–Fe–Si alloy

Formation process and characteristics of an amorphous SiO2 ceramic coating on 6061 aluminum alloy by plasma electrolytic oxidation in organosilicon electrolyte

An amorphous silica ceramic coating with thicknesses exceeding 100 μm (adjustable thickness) was prepared on 6061 aluminum alloy by plasma electrolytic oxidation in organosilicon electrolyte. To investigate its formation process and structural characteristics, the digital microscope system, SEM, X-ray diffractometer and microhardness tester were used to characterize morphology, structure and hardness at different voltages and times. The results show that it thickens rapidly after the voltage is raised to 480–500 V, and its surface begins to roughen and the micropores appear to enlarge. In organosilicon electrolyte, unlike conventional electrolytes, the coarse Al–Fe–Si second phase particles in the matrix do not negatively affect the PEO treatment. The produced coatings increase the surface hardness of 6061 aluminum alloy by more than 6 times and are stable in common acid solutions such as HCl and HNO3. Furthermore, the energy consumption rate of PEO treatment can be significantly reduced to 0.24–0.31 kJ cm−2 μm−1. The potentiodynamic polarization curves measured in 1 mol L−1 HCl solution show that the ceramic coating can reduce the corrosion current density of 6061 aluminum alloy from 3.74 × 10−2 A cm−2 to 2.24 × 10−6 A cm−2. And its corrosion resistance can be further improved by adding a 2nd low-voltage PEO treatment.

Tailoring microstructure and mechanical properties of Al-Mg-Si-Cu alloy with varying Mn and/or Cr additions

Introducing and maintaining the subgrain structure during thermomechanical processes is an effective approach to mitigate the strength-ductility contradiction of Al-Mg-Si-Cu alloys, which holds significant importance for their engineering application. The objective of this work is to explore the effects of individual and synergistic additions of two dispersoid-forming elements, Mn and Cr, on microstructure and associated mechanical properties of an Al-Mg-Si-Cu alloy. The results show that when compared to alloys with individual addition of either Mn or Cr, their synergistic incorporation leads to an improved dispersoid precipitation with reduced size. For instance, the 0.7Mn0.4Cr alloy exhibits a number density of 10.26 μm-2, which is twice that of the sum of 0.7Mn and 0.4Cr alloys. In response to that, the 0.7Mn0.4Cr alloy attains enhanced resistance to recrystallization, leading to a well-maintained recovery structure and exceptional mechanical properties. But an excess addition of Cr will result in the formation of primary Al45Cr7 phase, which significantly deteriorate the mechanical properties of the alloy. While notably, the 0.4Cr alloy surprisingly exhibits better recrystallization resistance compared to the 0.7Mn alloy, despite having larger dispersoid size and lower number density. This can be attributed to the coherent interface between the α-Al(Cr,Fe)Si dispersoids and matrix, providing higher pinning force that effectively impede the recrystallization.

Quantum criticality features in the Co,Fe doped MnSi

An universal line revealing an independence of spin fluctuation contributions to the heat capacity on impurity content and its nature is discovered in the helical phase of Mn(Co,Fe)Si. This situation declares an invariance of the heat capacity of spin subsystem under doping, which probably arises as a result of relative stiffness of the helical spin structure in respect to the impurity spins. On the other hand the situation drastically changes at the helical fluctuation region when no long range spin order exists. At low temperatures the spin fluctuation contributions to the heat capacity for a whole set of compositions of Mn(Co,Fe)Si are described by a single power expression with an exponent less then unity, which implies divergence of the ratio Cp/T at T→0. The current data are revealing that a singular quantum critical point does not exist in the system under study. In its place, one can see some sort of a quantum critical cloud covering a significant range of dopant concentrations.

Enhanced soft-to-hard magnetic switching ratio in grain-oriented Fe–Si cores induced by helical anisotropy

The non-segmented shifted design of magnetic cores made of grain-oriented electrical steels, which induces the helical anisotropy, has been highly effective in reducing magnetic losses and minimizing acoustic noise in rotating machines. In order to address the challenges associated with precise theoretical modeling of complex underlying magnetization process, we have introduced angle-dependent first-order reversal curve diagrams. These diagrams offer significant insights into the microscopic properties of magnetization switching. By analyzing the distribution of coercive and interaction fields, we can identify distinct features that correspond to different domain wall processes and local coercivities, highlighting the magnetic behavior's heterogeneity. Through experimental measurements and theoretical analysis, we have gained quantitative understanding of the competing contributions from 90° and 180° domain wall processes in shifted structures. At shifting angles near the location of the hard magnetization axis, a notable transition in the magnetization process is observed by promoting the activation of the softer 180° domain wall processes. Among the different shifting angles tested, the structure with a shifting angle of 90° exhibits the highest ratio of soft-to-hard magnetization switching.

Accumulative coarse-graining of simple structural descriptors enables accurately predicting the dynamics of metallic liquids

The typical dynamic mode of liquids is often marked by a long-time α relaxation which is accompanied by heterogeneous dynamics. However, the explicit structural origin of the α relaxation is ongoing debated. Recent advances in graph neural networks (GNN) have shown promise in this area, with an intuitive approach that can be simplified as an iterative coarse-graining (CG) to update atomic features based on neighboring atoms. Here, we propose a new CG strategy called accumulative CG, which aggregates the spherically averaged and deviated features to generate a robust representation of atomic arrangement over a broad range. This can enhance the direct visibility of the center atom among all its surrounding atoms, as opposed to being limited to its nearest-neighbors and relying on iterative message passing to indirectly observe further neighbors. Starting with two descriptors (local energy and volume), the augmented features derived from accumulative CG along with machine learning (ML) can accurately predict the atomic-level dynamics of multi-component liquids, as indicated by the inverse of α-relaxation time. We performed atomistic simulations of multi-component Al–Fe-(Si, Y) liquids with a set of deep-learning interatomic potentials to demonstrate the feasibility of the accumulative CG approach. By injecting physical inspirations from liquid dynamics theories into data-driven ML model, we interpret the structural origin of dynamic heterogeneity, particularly the bimodal behavior of Si atoms in Al–Fe–Si liquids.

Significant improvement of slag corrosion resistance and thermal shock resistance of corundum‐based dry vibratable refractory by addition of Fe–Si3N4

AbstractFe–Si3N4 was introduced to improve the service performance of corundum‐based dry vibratable refractories in the casting industry, specifically enhancing their thermal shock resistance and resistance to slag corrosion. The study analyzed the effects of Fe–Si3N4 powder content on the refractories’ mechanical properties, phase compositions, slag corrosion resistance, and microstructures. The addition of Fe–Si3N4 facilitated the production of magnesium aluminate spinel in the refractory matrix, while also decreasing the wettability between the molten slag and refractory. Increasing the Fe–Si3N4 content resulted in accelerating the replacing Mg2+ (0.072 nm) with Al3+ (0.053 nm) in the spinel. Simultaneously, Fe3+ (0.055 nm) was effectively dissolved into the alumina crystals. The bulk density, compressive strength, and slag corrosion resistance of the refractories were improved. However, the thermal shock resistance initially increased but then decreased. In industrial tests, a corundum‐based dry vibratable refractory with a 1 wt.% Fe–Si3N4 content effectively prolonged the lifespan of an induction melting furnace when used as a lining refractory. Importantly, the refractory did not spall or generate cracks in the matrix after induction melt furnace industrial test.

Influence of the combined additions Mn, Cr or Ni on the formation of dispersoids and mechanical properties of Al–Mg–Si–Cu alloys

The effect of individual and combined additions of different transition metals (TMs), Mn, Cr, and Ni, on the precipitation of dispersoids and the final mechanical properties of Al–Mg–Si–Cu alloys was systematically studied by scanning electron microscopy, transmission electron microscopy and tensile testing. The various TM additions examined are found to induce notably different dispersoid precipitation behaviors. The combined addition of Mn, Cr produces the highest number density of dispersoids among the three TM-added alloys examined, due to the incorporation of Cr promoting the precipitation of the α-Al(Mn, Cr, Fe)Si dispersoid. By contrast, the combined addition of Mn, Ni slightly suppresses the precipitation of the α-Al(Mn, Ni, Fe)Si dispersoid compared with individual Mn addition. The presence of a fine dispersoid microstructure can moderately increase the strength, and strongly increase the elongation, especially for the case of the combined Mn, Cr added alloy, where the elongation is increased almost threefold compared with the base alloy. An excellent strength-elongation combination, with an ultimate tensile strength of 421.9 ± 2.2 MPa and an elongation of 18.2 ± 3.6, is achieved for this alloy. This property is superior to most reported 6xxx alloys. The main reasons for this result are the presence of a high number density of dispersoids promoting grain refinement, providing high Orowan hardening, and reducing stress concentration on the grain boundary. The findings of this work are expected to provide guidance for developing new Al–Mg–Si–Cu alloys with excellent comprehensive mechanical properties.

Modifying C/C–SiC brake pads with different Fe–Si alloy phases to improve the wear resistance of full-carbon/ceramic brake pair

The full-carbon/ceramic brake pair is designed to meet the increased demands for reliable braking at high speeds, heavy loads and complex service environments for vehicle and power machinery. In this paper, braking performance of different Fe–Si modified C/C–SiC composites have been studied using laboratory scale dynamometer. The phase composition/microstructure and mechanical properties of the material were studied. By mating with C/C–SiC brake disc, the effect of Fe–Si alloy modification on the friction and wear performance of full carbon/ceramic brake pair was investigated. The results indicated that the Fe–Si modification can effectively improve the wear resistance of both C/C–SiC disc and pads, and the disc/pads will have the least amount of wear only when the appropriate type of Fe–Si alloy and the suitable amount of Fe–Si alloy phase are introduced. When FeSi75 was used as the fusion infiltration material, the wear of disc/pad was 115.4 and 13.3 mm, respectively. Compared to the unmodified C/C–SiC disc/pad, the wear of Fe–Si modification disc/pad was reduced by 72.7 % and 87.2 %, respectively.

Anodic Dissolution Behavior of Al Alloys Containing Al6Fe or β-AlFeSi in EmImCl–AlCl3 Electrolyte During Electrorefining

To produce over 99.9% of high-purity Al from Al alloys containing Al6Fe or β-AlFeSi through electrorefining, their anodic dissolution and cathodic electrodeposition characteristics should be clarified. In this study, the anodic dissolution and cathodic electrodeposition behavior of Al–Fe binary and Al–Fe–Si ternary alloys were investigated in an EmImCl–AlCl3 ionic liquid electrolyte at 323 K. Anodic polarization measurements, constant potential electrolysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission SEM (FE-SEM), and energy dispersive spectroscopy (EDS) were used to study the anode and electrodeposits on the cathode. Constant potential electrolysis showed that Fe dissolved from Al6Fe in the Al–Fe anode at 0.7 V vs Al/Al(III) and from β-AlFeSi in the Al–Fe–Si anode at 1.4 V and was co-deposited with Al on the cathode. Notably, Si did not dissolve from β-AlFeSi at either potential. A combination of controlled anodic dissolution potential and the use of the Al alloy containing β-AlFeSi further suppressed the dissolution and cathodic co-deposition of Fe, affording high-purity Al on the cathode. This suggests that Al alloys with intermetallic compounds that are less likely to dissolve Fe at the anode are optimal for obtaining over 99.9% of high-purity Al from Al alloys containing Fe in the electrorefining method.

Fe–Si Powder Nitriding Control System

Fe–Si Powder Nitriding Control System

Effects of Different Quenching Rate on the Various Properties of Fe–Si–B Amorphous Alloy Prepared by Melt Spinning Method

Effects of Different Quenching Rate on the Various Properties of Fe–Si–B Amorphous Alloy Prepared by Melt Spinning Method

Thermodynamic assessment of La–Fe–Si systems

The phase equilibria of the La–Fe–Si system were investigated using a combination of experimental and thermodynamic modeling methods. The isothermal cross-section of the La–Fe–Si ternary system in the (Fe, Si)-rich region at 1373 K was experimentally investigated using electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Based on the experimental results and literature reports of the La–Fe–Si system, the thermodynamic model parameters of the system were optimized using the CALPHAD method. The intermediate compounds in the La–Si binary system and ternary compounds in the La–Fe–Si ternary system were described via sublattice models. The calculated thermodynamic and phase equilibria data were in good agreement with the experimental data, providing a foundation for the development of a multi-component thermodynamic database for LaFeSi-based alloys.

High-performance Fe–Si soft magnetic composites with controllable silicate/nano-Fe composite coating

The design of magnetic insulation coating structure has always been a challenge for high-performance soft magnetic composites (SMCs). In this work, we prepared Fe–Si SMCs with silicate/nano-Fe composite coating successfully by in-situ oxidation method combined with spark plasma sintering (SPS). The formation mechanism of the composite coating and its effect on the electro-magnetic properties of Fe–Si SMCs were investigated. The results showed that a uniform Fe2O3 coating can be obtained by reactions between Fe and H2O/O2 during in-situ oxidation process, and became thicker with the increased oxidation time. After sintering, the oxide coating was transformed into a composite coating composed of Fe2SiO4 with excellent insulation and nano-Fe with high ferromagnetism, which resulted from the interfacial reaction between Fe2O3 coating and Fe–Si core. The increased oxidation time led to the gradually thicker composite coating, and resulted in a linear decrease in saturation magnetization, indicating good controllability of the coating. However, excessive oxidation time led to the increased eddy current loss as well as the core loss due to the weakened resistivity. Thus, the Fe–Si SMCs exhibited high saturation magnetic induction (1.66T) and very low core loss (643.9 kW/m3 at 0.1 T/50 kHz) especially when the oxidation time was 1 h.

Air surface crystallization with quenched-in Fe crystallites and associated magnetomechanical properties in Fe–Si–B amorphous ribbons

The effect of surface crystallization on the magnetomechanical properties is studied for amorphous ribbons with a nominal composition of Fe80Si9B11 that are prepared with the single roller melt-spinning method. Our results indicate that the magnetomechanical power efficiency of surface crystallization ribbons is twice as higher as that of its amorphous counterpart. The surface configuration for such ribbons has been investigated through a prism of microstructures and chemical compounds. The surface crystallization with quenched-in α-Fe(Si) crystallites is confirmed by means of x-ray diffraction measurements and the surface polishing process, inducing irregular in-plane domain patterns, which are observed by magneto-optical Kerr effect microscopy. The vibrational absorption peak for polymerized B–O bonds is observed by means of a Fourier transform infrared spectrometer, being ascribed to the presence of pre-precipitated boron atoms from the crystalline film, which is confirmed by x-ray photoelectron spectroscopy. The mechanism that enhances the magnetomechanical power conversion efficiency in FeSiB ribbons with quenched-in crystallites is quite different from the ones with annealing induced “surface-interior” configurations in the previous investigations.