Fe-based Alloys Research Articles

Affable thermal treatment process to overcome the trade-off relation via interface engineering in an Fe-based amorphous film

As pre-eminent soft magnetic materials, Fe-based amorphous alloys have been extensively studied due to adjustable composition, low cost, and low iron core loss. The soft magnetic properties could be further improved after thermal annealing, which achieve a low coercive force (Hc) due to the low magnetic anisotropy and a high saturation magnetic flux density (Bs) on account of the precipitation of soft magnetic nanocrystalline phases. However, it is a key difficulty to control the nucleation and growth procedures of nanocrystals during annealing, resulting in rapid deterioration of Hc. Here, a soft magnetic Fe76Si8B13Nb3 film with ultra-fine amorphous/crystalline (a/c) core–shell structure is achieved from an amorphous precursor with the nanoscale phase separation. The pre-existing nanoscale phase separation provides vast nucleation sites and interphase boundaries, which could generate high concentration of nanocrystals and depresses the subsequent coarsening behavior even for long-time heat treatment. In consequence, the a/c core–shell soft magnetic film breaks the general trade-off relation in the soft magnetic material family with the highest Bs and lowest Hc simultaneously. This work provides a new perspective to design a/c alloys by amorphous precursor with dual phase structure, and importantly, it supplies effortless thermal treatment requirement to conveniently regulate the microstructures and soft magnetic properties of metallic glasses.

Phase Evolution and Glass Formation in an Fe-Based Alloy

Phase Evolution and Glass Formation in an Fe-Based Alloy

Shear capacity investigation of RC concrete beams using self-prestressing Fe-based shape memory alloys strips

Shear failure is a sudden and brittle failure, which causes human and economic losses. Hence, enhancement of shear capacity is critical for shear-deficient members of existing structures. In this study, the effectiveness of using Shape Memory Alloy ‘SMA’ strips on the shear capacity of reinforced concrete (RC) beams was investigated in a series of experiments. The experimental work included the study of six RC beams with a 200 × 300 mm cross-section considering shear parameters such as transverse shear reinforcement and the effect of prestressing. Beams were strengthened in U configuration using Fe-SMA strips 30 mm wide and anchored by one expansion anchor (M10-Hilti). The testing was performed in a simply supported condition where each beam was tested twice. The purpose of testing specimens twice was to confirm the results. The activation of the strips was achieved by heating the strips using a custom-made heater up to 200°. The method was proven effective, with an increase in shear capacity of up to 32–45% and 24–25% for specimens strengthened with passive strengthening (non-activated strips) and specimens strengthened by activated SMA strips, respectively. However, the active strengthening improved serviceability conditions by delaying the appearance of cracks and reducing the crack width. The occurrence of the main crack was delayed by 12.5–19.2%, the width of the crack was reduced by more than 65% compared to the reference beam, and the angle of the main crack increased compared to the reference beam as a result of activation. Beams containing internal transverse reinforcement performed better than the beams without shear reinforcement.

High compressive loading performance of a complex multi-phase hard-facing alloy explained through a highly elastic silicide phase

Hard-facing alloys in nuclear applications must remain resistant to deformation and wear, whilst also minimising transmutation to problematic elements during service. To this end, the Fe-based alloy RR2450 has been developed to potentially replace Co-based hard-facing alloys. RR2450 is a complex multi-phase stainless steel alloy showing an unusually high strength. To understand the possible root cause for such favourable mechanical behaviour, the phase specific response was recorded in this material during mechanical loading using neutron diffraction and electron microscopy based high-resolution digital image correlation in combination with electron backscatter diffraction (EBSD). The detailed analysis shows that despite the high-volume fraction of hard phases expected to impose constraint on the relatively soft ductile ferrite and austenite phases, the latter still deform plastically first. The in-situ loading experiment using neutron diffraction revealed that the hard π-ferrosilicide phase assumes large elastic strains whilst at the same time showing significant diffraction peak broadening. Additional electron microscopy-based strain mapping on compressed samples confirmed an almost pure elastic response of the π-ferrosilicide phase. The possible effect of lattice cell angular distortion of the π-ferrosilicide phase on diffraction peaks was modelled using crystal structure analysis, demonstrating that small changes (<1°) in angular lattice cell parameters can account for the apparent broadening observed by neutron diffraction. Such reversible elasticity by angular distortion of the unit cell is expected to provide a significant pull-back effect during unloading resulting in improved galling wear resistance, an important performance factor for hard-facing alloys intended for nuclear applications.

Influence of iron content in Fe-based amorphous alloy catalysts on degradation of azo dyes by fenton-like process

Degradation of organic pollutants in industrial wastewater has become one of the biggest problems that are threatening the environment, and correspondingly it is a priority for scientists to find a solution. In this work, we study the effect of the iron content in Fe-based amorphous ribbon catalysts (Fe78+xSi9B13-x, x = 0, 1 and 2) in degradation of Direct Blue 6 (DB 6) azo dye by Fenton-like process. We evaluated the catalytic efficiency by changing experimental conditions with the aim to optimize the degradation performance. The amorphous Fe80Si9B11 ribbon showed the highest catalytic activity with its ability to degrade DB 6 by 94.65% within 15 min Fe80Si9B11 ribbon provides more reactive sites than what generates the most hydroxyl radicals (. OH) and thus increases the degradation reaction. Degradation efficiency can be improved by increasing the reaction temperature and ribbons dosage, a correct amount of H2O2 but decreases with increasing initial pH value and concentration of DB 6. Fe80Si9B11 amorphous ribbons can be reused up to 12 times in optimal conditions, which confirms a good reusability. The excellent performance in catalytic activity and reusability of Fe-based amorphous alloy catalysts will contribute to wastewater treatment.

Structure and physical properties changes of Fe-based amorphous alloy induced by Joule-heating

Structure and physical properties changes of Fe-based amorphous alloy induced by Joule-heating

Electrochemical Treatment of Emulsified Oil Wastewater Using Fe-Si-B Amorphous Alloy Technology

As Fenton reagents, Fe-based amorphous alloys have achieved good results in the treatment of dye wastewater. However, it is rarely reported how to exert the high activity and high adsorption capacity of those amorphous alloys to treat the oily wastewater with more complex components. In this article, Fe78Si8B14 amorphous ribbon was used as the anode and graphite as the cathode to degrade a kind of emulsified oil wastewater by the electro-Fenton (EF) method. The catalytic degradation under such processing parameters as current density, pH values, and H2O2 concentration was investigated. The catalytic performance of the Fe-Si-B amorphous ribbon was characterized by using the degradation efficiency of the emulsified oil wastewater. The water samples before and after degradation by Fe-Si-B amorphous ribbons were examined by infrared spectrophotometry and gas chromatography-mass spectrometer (GC-MS), respectively. The results show that the degradation efficiency of 99.91% is obtained under optimum process conditions of the current density of 30 mA/cm2, pH value of 3, and H2O2 concentration of 20 g/L. Furthermore, all the long-chain organic compounds in the emulsified oil wastewater are decomposed into short-chain organic substances within 40 min of the reaction. Therefore, the EF method with amorphous alloy as anode and graphite as cathode has a good prospect for the degradation of emulsified oil wastewater. Moreover, the obtained results provide a theoretical basis and guidance for the application of amorphous alloy catalysts in practical wastewater remediation applications.

Effects of heat treatment on the structural properties and magnetic hyperfine parameters of Fe72Cr8Si8B12 amorphous ribbons

Fe-based amorphous alloys are extensively used in power electronics and other industries due to their high magnetic permeability, low coercivity and exceptional soft magnetic properties, which are closely related to their microstructure. In this study, the microstructure and hyperfine parameters of Fe72Cr8Si8B12 amorphous ribbons annealed at different temperatures were investigated using X-ray diffraction, scanning electron microscopy, Mössbauer spectrometry, and vibrating sample magnetometer. The results show that the crystallization process is due to the formation of α-Fe(Si), Fe2B and Fe23B6 phases. The measured 57Fe Mössbauer spectra were calculated by the superposition of several crystalline magnetic components for each annealing temperature (800, 825, 850 and 875 K), and the calculated values of the hyperfine fields for each component reflect a crystallization of the sample. Furthermore, the average nanograin size as well as the Curie temperature (TC) increase as annealing temperature increases. The simulation of the M(T) curve agrees well with the experimental data.

Optimizing laser additive manufacturing process for Fe-based nano-crystalline magnetic materials

Fe-based amorphous magnetic alloys offer new opportunities for magnetic sensors, actuators and magnetostrictive transducers due to their high saturation magnetostriction (λs = 20–40 ppm) compared with that of amorphous Co-based alloys (λs = −3 to −5 ppm). Due to the conventional production limitations of Fe-based glassy alloys, including dimensional limitations and poor mechanical properties, this has led to a search for novel fabrication techniques. Recently, the laser powder bed fusion (LPBF) technique has attracted attention for the production of Fe-based magnetic bulk metallic glasses (BMGs) as it provides high densification, which brings about excellent mechanical properties, and high cooling rate during the process. Optimization of process parameters in the LPBF technique have been studied using the volumetric energy input (E), which includes the major build parameters; laser power (P), scan speed (v), layer thickness (t) and hatch spacing (h). This study investigates how the major process parameters influence the physical and magnetic properties of LPBF-processed Fe-based amorphous/nanocrystalline composites ((Fe87.38Si6.85B2.54Cr2.46C0.77 (mass %)). Various process parameter combinations with P (90, 100, 120 and 150 W) and v (700, 1000 and 1300 mm/s) were applied with t of 30, 50 and 70 µm and h of 20, 30, 40, 50 and 60 µm. It was found that bulk density improves as P and t increases, v and h decreases, i.e., high E is necessary, however, 99.45% of bulk density was achieved with E of 61.22 J/mm3 (P = 150 W, v=700 mm/s, h=50 µm and t = 70 µm), which indicates the importance of understanding how parameters affect the specific materials. In addition, the magnetic properties differ significantly due to the nanocrystalline phases present in the microstructure, with their size depending on the process parameters considerably. Owing to the laser scanning nature, the microstructure evolves as molten pools (MP) and heat affected zones (HAZ) due to the high thermal gradient that occurred between laser tracks. MP form around the scans, containing α-Fe(Si) nanograins mainly, whereas HAZ generally contains Fe2B and Fe3Si nanocrystalline clusters. The size and quantities of those nanocrystallites determine the magnetic properties. With the same E (60 J/mm3), v (1000 mm/s) and t (50 µm), only changing P and h caused samples to have different saturation magnetization; 206 emu/gr (P: 90 W and h: 30 µm) and 150 emu/gr (P: 150 W and h: 50 µm). In general, the saturation magnetisation, Ms of LPBF-processed samples changes between 130 and 206 emu/gr, which is much higher than that of feedstock powder (102 emu/gr) due to their nanocrystalline structures. The coercivity (Hc) is in the range of 14.55 and 34.68 Oe, which is considered high for soft-magnetic behaviour (Hc ≤ 12.5 Oe), resulting from the larger crystallite size and the presence of defects (pores and cracks) in the microstructure.

The role of Cr, P, and N solutes on the irradiated microstructure of bcc Fe

The objective of this study is to understand irradiation-induced and assisted defect evolution in binary body center cubic (bcc) Fe-based alloys. The broader class of bcc ferritic alloys are leading candidates for advanced nuclear fission and fusion applications, in part due to their exceptional void swelling resistance. However, their irradiated microstructure evolution is sensitive to solute species present, since these solutes can act as traps for irradiation-induced defects due to the surrounding tensile or compressive stress fields. Here, three alloys (Fe-9.5%Cr, Fe-4.5%P, and Fe-2.3%N) are selected for study because they systematically exhibit varying solute sizes and solute positions (i.e., substitutional or interstitial). Ex situ and in situ ion irradiations reveal that Fe-P has a considerably finer and denser population of irradiation-induced defects than Fe-Cr and Fe-N at the same irradiation conditions, which is attributed to strong defect trapping at undersized substitutional P, consequently hindering the development of extended defects. Meanwhile, oversized substitutional solutes (e.g., Cr) and interstitial solutes (e.g., N) may also suppress dislocation loop development due to weak solute-defect trapping.

Investigation of the Microstructure and Wear Properties of Conventional Laser Cladding and Ultra-High-Speed Laser Cladding Alloy Coatings for Wheel Materials

In this paper, Fe-based and Co-based alloy powders were chosen to perform laser cladding on wheel materials through conventional laser cladding (CLC) and ultra-high-speed laser cladding (UHSLC) processes, respectively. The microstructures, element distribution, phase composition and hardness of the Fe-based alloy and Co-based alloy coating layers using the CLC and UHSLC processes were compared and analysed. The results show that the CLC and UHSLC alloy coatings were dense and free of defects such as pores and cracks. Compared with the CLC alloy coating, the grain size of the UHSLC alloy coating was smaller, the coating composition was close to the powder design composition, and the distribution of Cr within and between the grains was more uniform. The Fe-based coating was mainly composed of (Fe, Ni) and Cr7C3, and the Co-based coating was mainly composed of γ-Co and Cr23C6. It was found that the cooling rate of the CLC alloy coating was smaller than that of the USHLC, and the hardness of the CLC alloy coating was less than that of the USHLC. The average hardness of the UHSLC Fe-based and Co-based alloy coatings was 709 HV and 525 HV, respectively. The average hardness of the CLC Fe-based and Co-based alloy coatings was 615 HV and 493 HV, respectively. The rolling friction and wear tests were carried out with the CLC-treated and UHSLC-treated wheel specimens on the GPM-30 rolling contact fatigue testing machine. The results showed that the wear rate of the UHSLC alloy coating on the wheel specimens was significantly lower than that of the CLC alloy coating on the wheel specimens. The wear rates of the UHSLC Fe-based and Co-based alloy coatings on the wheel specimens were reduced by 40.7% and 73.8%, respectively. It was demonstrated that the wear resistance of the USHLC alloy coatings was better than those of the CLC alloy coatings. The CLC alloy coating exhibited more severe fatigue damage with small cracks. Furthermore, the damage of the UHSLC alloy coating was relatively minor, with slight spalling. The Co-based alloy coating exhibited superior wear properties with the same laser cladding process.

Wire and arc additive manufacturing of Fe-based shape memory alloys: Microstructure, mechanical and functional behavior

Shape memory alloys (SMA) are a class of smart materials with inherent shape memory and superelastic characteristics. Unlike other SMAs, iron-based SMAs (Fe-SMA) offer cost-effectiveness, weldability, and robust mechanical strength for the construction industry. Thus, applying these promising materials to advanced manufacturing processes is of considerable industrial and academic relevance. This study aims to present a pioneer application of a Fe–Mn–Si–Cr–Ni–V-C SMA to arc-based directed energy deposition additive manufacturing, namely wire and arc additive manufacturing (WAAM), examining the microstructure evolution and mechanical/functional response. The WAAM-fabricated Fe-SMAs presented negligible porosity and high deposition efficiency. Microstructure characterization encompassing electron microscopy and high energy synchrotron X-ray diffraction revealed that the as-deposited material is primarily composed by γ FCC phase with modest amounts of VC, ε and σ phases. Tensile and cyclic testing highlighted the Fe-SMA's excellent mechanical and functional response. Tensile testing revealed a yield strength and fracture stress of 472 and 821 MPa, respectively, with a fracture strain of 26%. After uniaxial tensile loading to fracture, the γ → ε phase transformation was clearly evidenced with post-mortem synchrotron X-ray diffraction analysis. The cyclic stability during 100 load/unloading cycles was also evaluated, showcasing the potential applicability of the fabricated material for structural applications.

Effect of high-temperature heat treatment on electrochemical corrosion behavior of laser cladding Fe-based alloy coating in H2SO4 solution

Double-layer Fe-based alloy coatings were fabricated on the surface of ductile cast iron using high-speed laser cladding. The electrochemical corrosion behavior of the coatings in 0.5 mol/L H2SO4 solution was analyzed after heat treatment (HT) at 950 ℃ for 1, 2, and 3 h. The results show that many fine and dispersed particles were precipitated in dendrites after 1 and 2 h HT. The precipitates in the dendrites of the 3 h heat-treated aggregated, nucleated, and grew up, forming the blocky. At the same time, the intergranular part of the long-chain structure began to dissolve and break. The corrosion rate decreased significantly with the increase in HT time. The specimen had the most-nobel self-corrosion potential (−0.15 V) and the best corrosion resistance after 3 h HT.

Magnetic properties evaluation of Fe-based amorphous alloys synthesized via spark plasma sintering

Fe77.7Si8B10P4Cu0.3 amorphous powder compacts with high relative density (ρr = 94%), high saturated magnetic induction (Bs = 1.34 T), and high permeability (μ = 163 at 20 kHz) were fabricated by spark plasma sintering. In this work, Fe77.7Si8B10P4Cu0.3 spherical amorphous powders with good amorphous forming ability were prepared by regulating the material composition and the particle size distribution by gas atomization at first. The effect of sintering temperature (Ts) on the structure and magnetic properties of powder compacts was systematically investigated. The powder compacts sintered at Ts of 696–712 K were found to remain amorphous structure and exhibit optimal structural and magnetic performance, due to the high temperature and high pressure employed in SPS with high heating rate. These results are promising for the applications of Fe-based amorphous powder alloys in soft magnetic devices requiring tens of kilo-hertz frequency.

Corrosion behaviors of Ni-based and Fe-based alloys in supercritical water gasification with inorganic chloride salt

Supercritical water gasification (SCWG) technology is considered the most promising technology for treating oily wastewater. However, the impact of mixed inorganic salts on the reactor during the SCWG process of oily wastewater still lacks research. In this study, Fe-based alloys and Ni-based alloys were exposed to an environment of inorganic chloride salt in supercritical water. The analysis found that while Ni-based alloys have higher corrosion resistance than Fe-based alloys, in an environment of supercritical water containing inorganic chlorides, the surface corrosion of Fe-based alloys was significantly suppressed, while the surface corrosion of Ni-based alloys was exacerbated.

Fe-based amorphous alloy wire as highly efficient and stable electrocatalyst for oxygen evolution reaction of water splitting

The slow kinetics of the oxygen evolution reaction (OER) leads to low energy conversion efficiency during water electrolysis, thus it is very important to develop efficient and economical electrocatalysts. With high surface energy and rich active centers, amorphous alloys show excellent potential as self-supporting oxygen evolution catalysts for water splitting. In this work, (Fe0.8Ni0.2)71Mo5P12C10B2 amorphous alloy wire was successfully prepared, and after 5 h immersed in 0.5 mol/L HNO3, the wire surface was covered by the block metallic oxide. At a current density of 10 mA/cm2 in an alkaline electrolyte, the electrochemical results show that the overpotential is only 254 mV and the Tafel slope is 49 mV/dec. After the 194 h stability test, its oxygen evolution performance is even comparable to the commercial RuO2, which has been proven to have excellent electrochemical stability and low preparation cost. The highly efficient catalytic performance mainly originated from the synergistic effect of multi-metal elements and the unique crack surface characteristics which expose more active sites. This work provides new insight into low-metal-cost materials for efficient and durable OER electrocatalysts and their industrial applications in the future.

Effect of miscible and immiscible element microalloying on crystallization behavior and soft magnetic properties of Fe-P-C-B amorphous alloy

Microalloying is an efficient strategy to promote nano-crystallization of Fe-based amorphous alloys to improve soft magnetic properties. Here, the Fe-P-C-B amorphous alloy is selected as a typical system to investigate the effect of microalloying of immiscible elements (In and Sn) and miscible elements (Al, Ga and Ge) in Fe on crystallization behavior and soft magnetic properties of Fe-based amorphous alloys. Microalloying of immiscible elements leads to slightly increased energy barrier for α-Fe nuclei growth as evaluated by Kissinger equation, yielding fine and uniform α-Fe nanograins and low coercivity after annealing. In contrast, miscible elements cause high growth energy barrier, resulting in few huge α-Fe grains and large coercivity. This work suggests a strategy of obtaining amorphous-nanocrystalline alloys with good magnetic properties by microalloying of immiscible elements.

Effects of Cu and Ag Elements on Corrosion Resistance of Dual-Phase Fe-Based Medium-Entropy Alloys.

The effect of adding elements to promote phase separation on the functional properties of medium-entropy alloys has rarely been reported. In this paper, medium-entropy alloys with dual FCC phases were prepared by adding Cu and Ag elements, which exhibited a positive mixing enthalpy with Fe. Dual-phase Fe-based medium-entropy alloys were fabricated via water-cooled copper crucible magnetic levitation melting and copper mold suction casting. The effects of Cu and Ag elements microalloying on the microstructure and corrosion resistance of a medium-entropy alloy were studied, and an optimal composition was defined. The results show that Cu and Ag elements were enriched between the dendrites and precipitated an FCC2 phase on the FCC1 matrix. During electrochemical corrosion under PBS solutions, Cu and Ag elements formed an oxide layer on the alloy's surface, which prevented the matrix atoms from diffusing. With an increase in Cu and Ag content, the corrosion potential and the arc radius of capacitive resistance increased, while the corrosion current density decreased, indicating that corrosion resistance improved. The corrosion current density of (Fe63.3Mn14Si9.1Cr9.8C3.8)94Cu3Ag3 in PBS solution was as high as 1.357 × 10-8 A·cm-2.

Supersaturation and dissolvable α-Cr phase enable superior oxidation resistance in FeCrNi medium-entropy alloys

Increasing Cr content in Fe-based alloys is expected to improve oxidation and corrosion resistances, but its effectiveness always degrades because of the over-doping induced precipitation of harmful σ-FeCr and Cr23C6 phases. In this study, the precipitation and oxidation behaviors of FexCrNi alloys were systematically investigated. It is found that the precipitation behavior could be controlled by adjusting the Cr content. The α-Cr phase precipitates at 800 °C in supersaturated FeCrNi medium-entropy alloy (MEA), while it is absent in Fe3CrNi alloy due to the lower Cr content. FeCrNi MEA shows much better oxidation resistance than Fe3CrNi, the oxidation rate constant of FeCrNi is two to three orders lower than that in the Fe3CrNi alloy. The oxidation activation energy of FeCrNi (545 kJ/mol) is much higher than that of the Fe3CrNi alloy (80 kJ/mol), which can be attributed to the synergistic effects of α-Cr dissolution, high configuration entropy and Cr supersaturation. Unlike σ-FeCr and Cr23C6 in stainless steels, the metastable α-Cr phase can be controllably introduced in FeCrNi as a “Cr resource”, and will dissolve during long-term oxidation to provide the required Cr element for the stabilization of the Cr2O3 scale. These discoveries shed new insights into the innovative design of stainless materials for heat-resistance structural applications.

Temperature field simulation and microstructure evolution of Fe-based coating processed by extreme high-speed laser cladding for re-manufacturing locomotive axle

With the rapid development of Chinese railway network in the last decade, the number of scrapped locomotive axles is increasing year by year due to various damages. Re-manufacturing is an effective way to save resources and reduce carbon footprint for developing an environmental-friendly society. In the present work, Fe-based alloy powder was deposited on the surface of a 25CrMo4 steel using extreme high-speed laser cladding (EHLA). The optimum processing parameters were determined through range analysis, and the thermal effect to the substrate was studied by numerical simulation. The depth of heated-affected zone (HAZ) was obtained by both experimental method and numerical simulation approach, and the results showed good agreement. The microstructure evolution, phase composition, and mechanical properties of the cladding layer were investigated systematically. The cladding layer was mainly consisted of austenite, ferrite, and carbides. The microstructure evolution exhibited a gradient variation from the interface to the top of cladding layer, which was similar to conventional laser cladding (CLA). Furthermore, the quenching effect to the substrate changed the microstructure from sorbite to martensite, leading to the formation of hardening layer beneath the cladding layer. The cladded sample exhibited higher tensile strength but lower elongation compared with 25CrMo4 substrate, which was detrimental to the service life of locomotive axles.