Binary Fe Alloys Research Articles

Study of gradient eutectic structure changes and mechanical-corrosion properties of Zr–Fe binary alloys

In order to create a cost-effective Zr alloy with superior overall characteristics, Zr-xFe (x = 0, 2, 4, 6, 8, 10 at.%) binary alloys were prepared by a vacuum arc furnace system. The microstructure of these alloys was examined utilizing various techniques such as optical microscope, X-ray diffractometer, scanning electron microscopy, and transmission electron microscopy. The results showed that the addition of Fe effectively refined α-Zr slats, and the Zr3Fe compound phase was dispersed throughout the alloy. However, the composition line of the alloying elements in the phase diagram intersected with the Zr2Fe and β-Zr eutectic lines when the Fe content exceeded 6 at.%. Zr–Fe alloys were transformed from monocrystalline-eutectoid to eutectic-eutectoid reactions. The Zr3Fe compound phase accumulated inside the grain and at the grain boundary as a result of the eutectic reaction, which stabilized the microstructure of the Zr–Fe alloys. This seriously affected the mechanical and corrosion properties of the alloys. The mechanical and corrosion properties of the alloys were assessed by universal testing machine, dynamic microhardness tester, Vickers hardness tester, and electrochemical workstation. The mechanical and corrosion properties of Zr–2Fe were excellent due to the coupling effect of Zr3Fe and grain refinement. The surface of the Zr–Fe alloy was analyzed by X-ray photoelectron spectroscopy, revealing the presence of passivation film components ZrO2 and Fe2O3.

Evaluation and Modeling of the Rate of Formation of Lath Martensite in Fe-C Alloys, Extracted from Ultra-Rapid Quenching Experiments

Isothermal information is rarely available for the formation of martensite in Fe or Fe alloys due to a very high rate of transformation compared to the rate of heat conduction. Such information has now been extracted for lath martensite in some sets of Fe alloys from available information on ultra-rapid quenching but only at a single temperature for each alloy, related to its two MS temperatures. The temperature dependence could, thus, be studied only on binary sets of alloys. Those results have been applied to mathematical models based on the Arrhenius equation and illustrated with Arrhenius plots. For three sets of binary Fe alloys, a large group of rates came close to the rate of an almost pure and carbon-free Fe-C alloy. It illustrated that Cr, Ni, and Ru in low contents have relatively small effects on the rate of formation of lath martensite in Fe. It also demonstrated that the present measurements have considerable reproducibility. In contrast, a set of Fe-C alloys did not give a straight line in the Arrhenius plot. Using a new mathematical model based on the concept of the Arrhenius equation to express the effect of carbon, it was possible to predict the rate of formation of lath martensite for Fe-C alloys with fixed C content and their temperature dependencies which are not available experimentally due to the very high rate of formation.

Clarification of origin of positive excess volume of Pd–Fe binary alloys by using first-principles calculations and HAXPES

Disordered Pd–Fe alloys show a positive excess-volume effect, contrary to the predictions of the Iida–Guthrie model. The effect becomes larger at a composition of approximately Pd0.5Fe0.5. The origin of the positive excess-volume effect was investigated by using first-principles calculations to study the electronic structures in the ordered and disordered states of Pd–Fe alloys with two different compositions, i.e., Pd0.53Fe0.47 and Pd0.75Fe0.25. The calculated partial density of states for the disordered state in Pd0.53Fe0.47 indicates weakening of Pd metallic bonds because of fully occupied 4d majority-spin states with enhanced anti-bonding characteristics, which cause an increase in the volume. In addition, the magneto-volume effect, which minimizes the increase in the electronic kinetic energy caused by exchange splitting, contributes to the positive excess volume. The calculated electronic states and those obtained from hard X-ray photoelectron spectra were consistent with each other.

Anodic leaching plus chronopotentiometric aging of Ni2Fe ingot for sustainable oxygen evolution and urea oxidation reactions

A Ni–Fe binary alloy ingot, prepared by conventional vacuum smelting, was adopted as substrate in this work to fabricate the anode for water splitting. To improve the surface roughness of anode surface, the electrode was firstly subjected to anodic leaching in a simple KSCN solution. The as-leached electrode was subsequently activated through linear sweep voltammetry in 1 M KOH solution with or without 0.33 M urea addition to finish the final step for electrode preparation. The as-prepared anode delivers the 10 mA cm−2 current density at an overpotential of 284 mV for oxygen evolution reaction (OER) and at 1.361 V (RHE) for urea oxidation reaction (UOR), respectively. No apparent change of OER and UOR performance was observed after chronopotentiometric aging. The more complex UOR behavior was analyzed to elucidate the synergy among all constituents functioning through direct or indirect mechanisms for the half-reaction on this binder-free, self-supporting and substrate-rejuvenating anode.

Wear properties of aluminum alloys fabricated by laser powder bed fusion

The production of an aluminum alloy using the laser powder bed fusion (LPBF) process results in a unique microstructure that differs from that of the same alloy when cast; this microstructure is advantageous for wear resistance. This study compared the wear resistance of Al-12Si and Al-2.5Fe (mass%) binary alloys produced by LPBF process with their cast equivalents, to analyze their suitability for lightweight wear-resistant parts. The wear resistance of the LPBF-produced alloys was significantly improved owing to the increase in hardness induced by the rapid cooling rate of the LPBF process and the dense dispersion of the fine secondary phase. Thus, Al alloys fabricated using LPBF can provide excellent wear resistance and possess the potential for application as industrial materials.

High spin polarization and spin signal enhancement in non-local spin valves with Co–Fe alloy injectors and detectors

For applications such as spin accumulation sensors for next-generation hard disk drive read heads, and for fundamental research, it is desirable to increase the spin signal in metallic non-local spin valves, which are central devices in spintronics. To this end, here, we report on the integration of high-spin-polarization Co–Fe binary alloy ferromagnetic injectors and detectors in Al-based non-local spin valves. Room-temperature deposition on amorphous substrates from an alloy target is shown to generate smooth, polycrystalline (110-textured), solid-solution body-centered-cubic Co75Fe25 films, which we characterize by energy dispersive x-ray spectroscopy, x-ray diffraction, x-ray reflectivity, atomic force microscopy, and electronic transport. Simple integration into transparent-interface Al non-local spin valves is then shown to realize up to a factor of ∼5 enhancement of the spin signal relative to Co, with full quantitative analysis yielding strikingly temperature-independent current spin polarizations exceeding 60%. We make a detailed quantitative comparison of these values with prior literature, concluding that Co–Fe alloys present a remarkably facile route to higher spin polarization and spin signals in non-local spin valves, with minimal barrier to adoption.

Effects of Mn and Cu Additions on Solidification Microstructure and High-Temperature Strength of Cast Al–Fe Binary Alloy

In order to investigate the effects of Mn and Cu additions on solidification microstructure and high-temperature strength of cast Al–Fe alloys, we have fabricated various Al–Fe-based alloys with compositions of Al–1%Fe, Al–1%Fe–1%Mn, Al–1%Fe–1%Cu, and Al–1%Fe–1%Cu–1%Mn (mol%) solidified at different cooling rates (0.3 K·s−1 and 145 K·s−1). In the Al–1%Fe binary alloy, the coarsened θ-Al13Fe4 phase with a needle-shaped morphology was often observed in the furnace-cooled sample (0.3 K·s−1), whereas the cast sample (145 K·s−1) exhibited several elongated α phases surrounded by fine α/Al6Fe eutectic microstructure. Such a solidification microstructure was observed in the cast Al–1%Fe–1%Cu alloy, whereas the Al23CuFe4 phase was locally formed in the finally solidified zone in the furnace-cooled sample. In the Al–1%Fe–1%Mn alloy, the Al6(Fe, Mn) phase was formed regardless of the cooling rate. Finer α/Al6(Fe, Mn) two-phase eutectic microstructure was almost entirely occupied in the cast sample. The fine eutectic microstructure was observed in the cast Al–1%Fe–1%Cu–1%Mn alloy as well. Compression tests for cast alloy specimens revealed that the Al–1%Fe–1%Cu–1%Mn alloy exhibited the highest strength level among the studied alloy specimens, indicating the combined addition of Mn and Cu elements could be effective in improving the high-temperature strength of the cast Al–Fe alloys.

Design and preparation of Al-Fe-Ce ternary aluminum alloys with high thermal conductivity

Ce element was introduced to modify Al-2%Fe (mass fraction) binary alloy. The microstructures, crystallization behavior, electrical/thermal conductivities and mechanical properties of these alloys were systematically investigated. The results indicated that the appropriate Ce addition decreased the recalescence temperature and growth temperature of Al-Fe eutectic structure, improved the morphology and distribution of Fe-containing phase, and simultaneously increased the conductivity and mechanical properties. The annealed treatment improved the thermal conductivity of these alloys due to the decreasing concentration of point defects. Rolling process further broke up the coarser Fe-containing phases into finer particles and made the secondary phases uniformly distributed in the α(Al) matrix. After subsequent annealing treatment and rolling deformation, the thermal conductivity, ultimate tensile strength and hardness of the Al-2%Fe-0.3%Ce (mass fraction) alloy reached 226 W/(m·K), (182±1.4) MPa and HBW (49.5±1.7), respectively.

High-temperature strength sustained by nano-sized eutectic structure of Al–Fe alloy manufactured by laser powder bed fusion

This study investigated the high-temperature strength of a hypereutectic Al–Fe binary alloy (Al–15%Fe) additive-manufactured by laser powder bed fusion (L-PBF). The L-PBF Al–15%Fe alloy exhibited superior yield strength to the other existing L-PBF processed alloys due to α-Al/Al6Fe eutectic structure with a nanoscale cellular morphology. The present results demonstrated the feasibility of using L-PBF processed Al–Fe alloys as high-temperature lightweight materials.

Change in microstructural characteristics of laser powder bed fused Al–Fe binary alloy at elevated temperature

• Al–Fe alloys built via laser powder bed fusion show high microstructural stability. • As-built samples showed multi-semi-cylindrical patterns corresponding to melt pools. • Metastable nanoscale Al 6 Fe phases were uniformly dispersed inside melt pools. • Stable θ-Al 13 Fe 4 phases were locally formed and coarsened upon exposure to 300 °C. • Dispersed fine particles showed a pinning effect on grain-boundary migration. The present study addressed the change in the microstructure of Al–2.5 wt% Fe binary alloy produced using laser powder bed fusion (L-PBF) technique by thermal exposure at 300 °C, and the associated mechanical and thermal properties were systematically examined as well. Multi-semi-cylindrical patterns corresponding to melt pools in the microstructure were macroscopically observed for the as-manufactured sample. No change in the melt-pool morphology was observed after thermal exposure for 1000 h. Inside the melt pools, a large number of the nanoscale metastable Al 6 Fe phase particles were uniformly distributed inside columnar grains of the α-Al matrix containing concentrated solute Fe in supersaturation. The sequential formation and coarsening of stable θ-Al 13 Fe 4 phases were observed upon exposure to a 300 °C environment, but a considerable amount of nano-sized metastable Al 6 Fe phases remained even after 1000 h. Furthermore, the thermal exposure continuously reduced the concentration of solute Fe atoms in the α-Al matrix. No significant grain growth was found in α-Al matrix after 1000 h owing to the pinning effect of the dispersed fine particles on grain boundary migration. These results demonstrate a sluggish change in microstructural morphologies of the Al–2.5 wt% Fe alloy. The quantified microstructural parameters addressed dominant strengthening contributions by the solid solution of Fe element and Orowan strengthening mechanism by fine Al–Fe intermetallics in the L-PBF-produced alloy. The high strength level was sustained even after being exposed to 300 °C for long periods. The superior balance of mechanical properties and thermal conductivity can be achieved in the experimental alloys by taking advantage of the various microstructural parameters related to the Al–Fe intermetallic phases and α-Al matrix.

Processability and Optimization of Laser Parameters for Densification of Hypereutectic Al–Fe Binary Alloy Manufactured by Laser Powder Bed Fusion

Centimeter-sized samples of hypereutectic Al–15 mass% Fe alloy were manufactured by a laser powder bed fusion (L-PBF) process while systematically varying laser power (P) and scan speed (v). The effects on relative density and melt pool depth of L-PBF-manufactured samples were investigated. In comparison with other Al alloys, a small laser process window of P = 77–128 W and v = 0.4–0.8 ms−1 was found for manufacturing macroscopically crack-free samples. A higher v and P led to the creation of macroscopic cracks propagating parallel to the powder-bed plane. These cracks preferentially propagated along the melt pool boundaries decorated with brittle θ-Al13Fe4 phase, resulting in low L-PBF processability of Al–15%Fe alloy. The deposited energy density model (using P·v−1/2) would be useful for identifying the optimum L-PBF process conditions towards densification of Al–15%Fe alloy samples, in comparison with the volumetric energy density (using P·v−1), however, the validity of the model was reduced for this alloy in comparison with other alloys with high thermal conductivities. This is likely due to inhomogeneous microstructures having numerous coarsened θ–Al13Fe4 phases localized at melt pool boundaries. These results provide insights into achieving sufficient L-PBF processability for manufacturing dense Al–Fe binary alloy samples.

Microstructure of Al-2.5Fe Binary Alloy Fabricated by Laser Powder Bed Fusion

In the present study, microstructural and crystallographic features of an Al-Fe binary alloy with a near eutectic composition (Al-2.5wt%Fe) fabricated by laser powder bed fusion (LPBF) process were examined. The LPBF processing for the Al-Fe alloy powder was conducted at room temperature using a 3D Systems ProX 200 operating at a laser power of 204 W and a laser scan speed of 0.6 m/s and 0.8 m/s to fabricate cube samples with high relative density above 99 %. The fabricated sample exhibited characteristic microstructure consisting of a number of melt pools in which the regions had locally melted and rapidly solidified by laser irradiation during the LPBF process. Numerous fine particles of Al-Fe intermetallics with a mean size below 100 nm were found within the α-Al matrix in the observed melt pools, whereas relatively coarsened particles were localized around melt pool boundaries. Electron backscatter diffraction (EBSD) analyses revealed a number of columnar a-Al grains with a mean size of approximately 10 μm. The LPBF-fabricated Al-Fe alloy exhibits a high hardness of approximately 90 HV, which is more than twice higher than the conventionally casted Al-Fe alloy.

Managing both high strength and thermal conductivity of a laser powder bed fused Al–2.5Fe binary alloy: Effect of annealing on microstructure

Abstract The microstructure of Al–2.5Fe (wt%) binary alloy samples additively manufactured by laser powder bed fusion (L-PBF) was systematically characterized, and its change due to subsequent annealing at 300 °C and 500 °C was examined. The as-fabricated samples featured homogeneous distribution of numerous fine particles of the metastable Al6Fe phase in the solidification microstructure where melt pools formed, and a relatively coarsened cellular structure was observed around the boundaries between the melt pools formed at different locations (melt pool boundaries). After the annealing at 300 °C, a slight growth of the nano-sized Al6Fe phase occurred, and coarsened plate-like θ-Al13Fe4 phases were locally formed in the cellular structure at melt pool boundaries. Annealing at 500 °C induced a pronounced transformation of the metastable Al6Fe phase to the stable θ-Al13Fe4 phase in the microstructure where melt pools formed, although no significant change in the microstructure of the α-Al matrix was detected. The thermal conductivity and tensile properties of as-fabricated and subsequently annealed specimens were measured. The as-fabricated specimens exhibited a high tensile strength of ~320 MPa and a thermal conductivity of ~150 W m−1 K−1. Annealing at 300 °C improved the thermal conductivity to ~185 W m−1 K−1 without a loss of tensile strength, whereas annealing at 500 °C significantly decreased the tensile strength. These results are utilized to discuss a balance between mechanical properties and thermal conductivity, which provided novel insights for managing both high strength and thermal conductivity of L-PBF-built Al–Fe binary alloys by controlling microstructure.

Formation of multiple intermetallic phases in a hypereutectic Al–Fe binary alloy additively manufactured by laser powder bed fusion

An attempt was made to additively manufacture an Al–Fe binary alloy sample with a hypereutectic composition of 15 wt% Fe using a laser powder bed fusion (LPBF) process. The LPBF-built Al–15Fe alloy sample exhibited a microstructure consisting of a number of melt pools in which regions had locally melted and rapidly solidified due to scanning laser irradiation during the LPBF process. The α-Al (fcc) matrix consists of a number of elongated grains with a mean size of approximately 10 μm. These microstructural features correspond well to previous results of Al alloys additively manufactured by the LPBF process. It was found that relatively coarsened stable θ-Al13Fe4 phases with a length of a few micrometers were localized along the melt pool boundaries. Numerous spherical particles of a metastable Al–Fe intermetallic phase were finely distributed within the nanoscale eutectic microstructure consisting of α-Al and metastable Al6Fe phases inside the melt pools. The metastable phase formation corresponds well to the previous results on the rapidly solidified Al–Fe alloys. The refined multiple intermetallic phases produced by the LPBF process contribute to a high hardness of approximately 200 HV. The refined microstructure appeared stable at an elevated temperature of 300 °C. The high microstructural stability would sustain sufficient strength in a hostile environment for long-term periods of service at elevated temperatures above 200 °C. The present results were utilized to discuss the formation sequence of multiple Al–Fe intermetallic phases in rapid solidification by the LPBF process.

Laser powder bed fusion of a near-eutectic Al–Fe binary alloy: Processing and microstructure

•This study focused on additive manufacturing (AM) of the Al–Fe binary alloy samples with a near-eutectic composition of 2.5 mass% Fe using the laser powder bed fusion (LPBF) process. The melt pool depth, relative density, and hardness of LPBF-fabricated Al–2.5Fe alloy samples under different laser power (P) and scan speed (v) conditions were systematically examined. The results provided optimum laser parameter sets (P = 204 W, v ≤ 800 mm s−1) for the fabrication of dense alloy samples with high relative densities >99%. Additionally, Pv-1/2, which is based on the deposited energy density model, was found to be a more appropriate parameter for additively manufacturing Al–2.5Fe alloy samples, and using it to simplify the relative densities of the samples made the determination of a threshold value for the laser parameters required to fabricate dense alloy samples. The microstructural and crystallographic characterization of the LPBF-built Al–2.5Fe alloy samples revealed a characteristic microstructure consisting of multi-scan melt pools that resulted from local melting and rapid solidification owing to laser irradiation during the LPBF process. Furthermore, a number of columnar grains with a mean width of ∼21 μm elongated along the building direction were also observed in the α-Al matrix. Numerous nano-sized particles of the metastable Al6Fe intermetallic phase with a mean size <100 nm were finely dispersed in the α-Al matrix. The hardness of the refined microstructure produced by the LPBF process was high at ∼90 HV, which is more than twofold higher than that of conventionally casted alloys that contain the coarsened plate-shaped Al13Fe4 intermetallic phase in equilibrium with the α-Al matrix.

Predicting magnetization of ferromagnetic binary Fe alloys from chemical short range order

Among the ferromagnetic binary alloys, body centered cubic (bcc) Fe-Co is the one showing the highest magnetization. It is known experimentally that ordered Fe-Co structures show a larger magnetization than the random solid solutions with the same Co content. In this work, based on density functional theory (DFT) studies, we aim at a quantitative prediction of this feature, and point out the role of the orbital magnetic moments. Then, we introduce a DFT-based analytical model correlating local magnetic moments and chemical compositions for Co concentrations ranging from 0 to 70 at.%. It is also extended to predict the global magnetization of both ordered and disordered structures at given concentration and chemical short range orders. The latter model is particularly useful for interpreting experimental data. Based on these models, we note that the local magnetic moment of a Fe atom is mainly dictated by the Co concentration in its first two neighbor shells. The detailed local arrangement of the Co atoms has a minor effect. These simple models can fully reproduce the difference in magnetization between the ordered and disordered Fe-Co alloys between 30% and 70% Co, in good agreement with experimental data. Finally, we show that a similar model can be established for another bcc binary Fe alloy, the Fe-Ni, also presenting ferromagnetic interactions between atoms.

Paving the way to Fe3O4 nano- and microoctahedra by dealloying Al[sbnd]Fe binary alloys

The preparation, morphologies, and properties of Fe3O4 octahedra have attracted considerable attention, while their formation mechanism has been less investigated. In this study, Fe3O4 nano- and microoctahedra are prepared by dealloying Al–xFe (x = 5–25 at.%) alloys in NaOH aqueous solutions with different concentrations. The dealloying of Al15Fe in the 5-mol·L−1 NaOH solution provides the most regular Fe3O4 octahedra. Al13Fe4 in the precursor AlFe alloy and appropriate concentration of OH– ions are dominant factors in the formation of Fe3O4 octahedra by changing the chemical potentials and growth rates along the 〈111〉 and 〈100〉 plane directions. A low concentration of NaOH solution deteriorates the anisotropic growth of Fe3O4, while a highly concentrated solution enhances the reduction of oxides and produces α-Fe rather than Fe3O4. In addition to the experimental results, ab-initio molecular dynamics simulations are performed to reveal the evolutions of the surface energies and growth rates of different facets, depicting the formation trajectory from Fe3O4 nuclei to octahedra. This fundamental understanding provides technological guidelines for the synthesis and morphology control of Fe3O4, being of significance in the development of functional nanoparticles.

Liquid phase separation in immiscible Cu–Fe alloys

Cu–Fe binary alloys containing 20–50wt. % Fe were studied by the combination of the melt fluxing and cyclic superheating technique. The microstructural evolution of Cu–Fe alloys was investigated with scanning electron microscopy. When the undercooling was larger than the critical undercooling, the Fe-rich spheroids were embedded into a Cu-rich matrix and the metastable phase separation was observed in microstructures. The size of separated particles in the Cu-35wt.% Fe alloy was larger than that of other Cu–Fe alloys with different compositions and the size of separated droplets was related to the ΔTS, which was equal to the undercooling (ΔT) minus the critical undercooling (ΔTC). Moreover, a large undercooling tended to promote the coagulation of the separated droplets, so the size of the separated Fe-rich spheroids in the microstructure of the immiscible Cu–Fe alloys increased with the increase in the undercooling.

A Mechanistic Study of Dissolution of Pt–Fe Binary Alloys in 0.5 M H2SO4 Solution by Channel Flow Triple Electrode

A channel flow triple electrode (CFTE) was applied for the in situ detection of Fe ions (Fe(II) and Fe(III)) and Pt ions (Pt(II) and Pt(IV)) dissolved from Pt–50at%Fe (Pt–50Fe) and Pt–25at%Fe (Pt–25Fe), under potential cycling in 0.5 M H2SO4 at 298 K. These ions, dissolved from a Pt–Fe alloy working electrode set upstream in a channel, were simultaneously detected on two Au collector electrodes placed downstream by reducing or oxidizing their dissolved ions. When Pt–50Fe was potential-cycled between 0.05 and 1.4 V vs. standard hydrogen electrode, Fe dissolution was significantly enhanced in a double-layer (DL) charging region (0.25–0.85 V), probably owing to the surface diffusion of Pt atoms. In addition, the Fe dissolution was enhanced by Pt dissolution which takes place in a place-exchange potential region (1.2–1.4 V) and in the reduction potential of Pt oxides (0.9–0.5 V) in the cathodic scan. On the contrary, when Pt–25Fe was potential-cycled between 0.05 and 1.4 V, Fe dissolution was strongly suppressed by a Pt–enriched layer, especially in the potential region for the DL. The dissolution also depended on the upper limit of potential cycling (EU) and was significantly suppressed, even for Pt–50Fe, when EU was 0.6 V.

Thermodynamic of selective reduction of laterite ore by reducing gases

As the sulfide ore deposits become less economical and environmental viable as a source of nickel, increasing attention is being paid to the laterite ores. But in the pyrometallurgical process of laterite, more efforts should be paid to control the reduction of iron oxide in order to get high nickel-content nickeliferous product. For these reasons, equilibrium condition of iron oxide when laterite ore was selectively reduced by CO2/CO, H2O/H2 and CO2/H2 was studied from the perspective of iron activity with an assumption that the activities of FeO and Fe3O4 equal 1 in this work, and it well accounts for the inescapability of Fe metallization. Activity coefficient of iron in Ni–Fe binary solid alloy was calculated by Miedema model based on the known thermodynamics datum filed. According to Raoult's law, the relationship among the Fe/Ni ratio, reduction temperature and reduction gas composition was calculated when laterite ore was selectively reduced by the three different reduction systems. The calculation result was discussed and also compared with the experimental result. The trend of metal iron content in the reduction product of laterite ore varying with temperature and gas composition was well predicted by the calculation result.