Fe-Al Alloys Research Articles

Evaluation of Structure and Corrosion Behavior of FeAl Alloy after Crystallization, Hot Extrusion and Hot Rolling.

The paper presents the results of tests on the corrosion resistance of Fe40Al5Cr0.2TiB alloy after casting, plastic working using extrusion and rolling methods. Examination of the microstructure of the Fe40Al5Cr0.2TiB alloy after casting and after plastic working was performed on an Olympus GX51 light microscope. The stereological relationships of the alloy microstructure in the state after crystallization and after plastic working were determined. The quantitative analysis of the structure was conducted after testing with the EBSD INCA HKL detector and the Nordlys II analysis system (Channel 5), which was equipped with the Hitachi S-3400N microscope. Structure tests and corrosion tests were performed on tests cut perpendicular to the ingot axis, extrusion direction, and rolling direction. As a result of the tests, it was found that the crystallized alloy has better corrosion resistance than plastically processed material. Plastic working increases the intensity of the electrochemical corrosion of the examined alloy. It was found that as-cast alloy is the most resistant to corrosion in a 5% NaCl compared with the alloys after hot extrusion and after hot rolling. The parameters in this study show the smallest value of the corrosion current density and corrosion rate as well as the more positive value of corrosion potential.

Microstructural and mechanical properties of oxide dispersion strengthened iron aluminides produced by mechanical milling and hot extrusion

Abstract Yttria dispersed Fe3Al alloy with a nominal composition of Fe–13Al–5Cr-0.18Ti-0.35 Y2O3 was produced by high energy ball milling followed by hot extrusion. The extruded and heat treated ODS Fe3Al exhibited both elongated and fine equi-axed grain structure in longitudinal direction, whereas, equi-axed grain structure was observed in transverse direction. Even though, both prealloyed as well as milled powder showed only FeAl phase, D03 structured Fe3Al along with Y3Al5O12 and TiO phases existed in ODS Fe3Al. Presence of fine (7–25 nm corresponding to Y3Al5O12) and coarse (>25 nm, TiO) particles were observed in ODS Fe3Al. The material exhibited yield and ultimate tensile strengths of 1104 and 1308 MPa with 8% elongation. The improved strength and elongation are due to the presence of dispersoids and fine grained structure.

Interpretation of Fe-rich part of Fe–Al phase diagram from magnetic properties of A2-, B2-, and DO3-phases

Iron-rich Fe–Al binary phase diagram in the composition range of 23–26 at% Al shows a complex structure partly due to magnetic properties of the disordered A2-phase, the ordered B2-phase and the ordered DO 3 -phase. In this study, the disorder-order transformations between the constituent phases have been investigated through magnetization measurements of Fe- x Al alloys ( x = 22.0, 24.0, 24.3, 24.7, 26.5 at%). It is found that spontaneous magnetization of the B2-phase is larger than that of the DO 3 -phase and smaller than that of the A2-phase. The former relation disagree with previous reports but was further confirmed as the decrease of the B2-DO 3 transformation temperature under magnetic field (−1.58 K/T). It is also found that the Curie temperature of the B2-phase (836 K for Fe-24.7 at%Al alloy) coincides with that of the A2-phase; furthermore, these temperatures agree with the phase boundary between B2-region and (A2+B2)-region. • Temperature dependence of spontaneous magnetization was evaluated for the A2-, B2- and DO3-phases of Fe24.7at%Al alloy, and found that the value decreases in this order at any temperature. • Magnetic field dependence of B2-DO3 transformation temperature was evaluated for several Fe-Al alloys, and confirmed that it decreases as magnetic field increases. • Critical behavior for the magnetic transition was analyzed for several Fe-Al alloys and revealed that Curie temperature of the B2-phase almost coincides with that of the A2-phase.

Methods of electron transport in ab initio theory of spin stiffness

We present an ab initio theory of the spin-wave stiffness tensor for ordered and disordered itinerant ferromagnets with pair exchange interactions derived from a method of infinitesimal spin rotations. The resulting formula bears an explicit form of a linear-response coefficient which involves one-particle Green's functions and effective velocity operators encountered in a recent theory of electron transport. Application of this approach to ideal metal crystals yields more reliable values of the spin stiffness than traditional ill-convergent real-space lattice summations. The formalism can also be combined with the coherent potential approximation for an effective-medium treatment of random alloys, which leads naturally to an inclusion of disorder-induced vertex corrections to the spin stiffness. The calculated concentration dependence of the spin-wave stiffness of random fcc Ni-Fe alloys can be ascribed to a variation of the reciprocal value of alloy magnetization. Calculations for random iron-rich bcc Fe-Al alloys reveal that their spin-wave stiffness is strongly reduced owing to the atomic ordering; this effect takes place due to weakly coupled local magnetic moments of Fe atoms surrounded by a reduced number of Fe nearest neighbors.

Valmet Oyj, Finland

Hydrogen is becoming important clean energy while zerovalent iron (ZVI) and ferroferric oxide are of great interest to many applications including environmental remediation and chemical catalysis. Here, we report production of hydrogen, zerovalent iron and ferroferric oxide octahedron by etching Al–Fe alloys using NaOH solutions. The rate of hydrogen generation increased with increasing NaOH concentration and the alloy's particle size and decreasing the alloy's Fe concentration. Alkaline etching Al–Fe alloy particles of 425–850 μm produced 19–53 μm ZVI particles, which had paralleled ravines of 0.2–0.3 μm wide on the surface and possessed specific surface areas of 30–70 m2/g. The microscale ZVI was highly active for the removal of a model pollutant acid orange 7 from water. After 3–6 h ageing in the alkaline etching solution, the microscale ZVI particles were transformed to octahedral ferroferric oxide with saturation magnetization of 68.2 emu/g and residual magnetization of 13.2 emu/g and a coercive force of 330 Oe. This study provides a new approach for a facile synthesis of highly active ZVI and octahedral ferroferric oxide along with on-board generation of hydrogen from Al–Fe alloys.

Aluminum cluster size effects in the phase diagram of disordered Fe-Al alloys

A spin-1/2 Ising model, with nearest-neighbor exchange and next-nearest-neighbor superexchange interactions, is proposed to describe the phase diagram of disordered Fe p -Al q (p + q = 1) alloys in the body centered cubic lattice. The size of the aluminum clusters have been taken into account in order to induce a superexchange interaction among the Fe atoms. Extensive Monte Carlo simulations have been employed by using a hybrid algorithm consisting of Metropolis spin flip and Wolff cluster algorithm, together with single histograms techniques. A good fit to the experimental phase diagram has been achieved, including the anomalous region for Al concentration in the range q ≤ 0.2.

Direct Synthesis of Fe-Al Alloys from Elemental Powders using Laser Engineered Net Shaping.

The laser engineered net shaping (LENS®) process is shown here as an alternative to melting, casting, and powder metallurgy for manufacturing iron aluminides. This technique was found to allow for the production of FeAl and Fe3Al phases from mixtures of elemental iron and aluminum powders. The in situ synthesis reduces the manufacturing cost and enhances the manufacturing efficiency due to the control of the chemical and phase composition of the deposited layers. The research was carried out on samples with different chemical compositions that were deposited on the intermetallic substrates that were produced by powder metallurgy. The obtained samples with the desired phase composition illustrated that LENS® technology can be successfully applied to alloys synthesis.

Calcium Modification of Inclusions via Slag/Metal Reactions

This paper examines the consistency between experiments and thermodynamic predictions of the modification of non-metallic inclusions by dissolved Ca in liquid Fe-Al alloys. Current thermodynamic predictions made with FactSage (version 7.2) were found to overestimate the amount of dissolved Ca and the Ca in non-metallic inclusions. This was demonstrated in two ways. First, Al-deoxidized Fe was held in CaO-3 pct ZrO2 crucibles for 100-136 minutes at 1873 K (1600 °C) and then reoxidized to precipitate dissolved Ca as oxide inclusions. The amount of Ca in the inclusions after reoxidation was quantified and considered equal to the dissolved Ca in the liquid Fe prior to reoxidation. Although experimental data were limited, the results suggested that the dissolved Ca was low and that the thermodynamic behavior of Ca could be best described by excluding Ca-O interaction. The assumption of no Ca-O interaction was compared with the associate solution model employed in FactSage by simulating the evolution of inclusion compositions in Fe—2, 1, 0.5, 0.1 wt pct Al alloys exposed to CaO (sat.)-MgO (sat.)-Al2O3 slags. The assumption of no Ca-O interaction led to predictions that were much closer to experimental results. More work is needed to ensure dissolved Ca behavior is accurately described and to ensure the sources for Ca modification of inclusions in industrial samples are properly identified.

Improving the comprehensive mechanical property of the rheo-extruded Al-Fe alloy by severe rolling deformation

Al-3Fe alloy was prepared by the method of continuous rheo-extrusion, and the effect of rolling deformation on the microstructure and the property of the rheo-extruded Al-3Fe alloy was studied by means of scanning electron microscope (SEM), transmission electron microscopy (TEM) and tensile test. The rheo-extruded pure Al was also prepared for comparison. The results showed that the rolling deformation could further refine the grain size of the rheo-extruded Al-Fe alloy, and reduce the size of the Al-Fe phase. Due to the present of nanosized and sub-micron sized Al3Fe phase, the strength of rheo-extruded Al-Fe alloy is significantly higher than that of rheo-extruded pure Al, and this advantage has been maintained during subsequently rolling deformation. Moreover, the strength and the elongation are simultaneously increased when the rolling reduction exceeds 60% for Al-Fe alloy and pure Al. Both of Al-Fe alloy and pure Al have the best comprehensive mechanical property when the rolling reduction reaches 90%. The main contribution is attributed to the grain refinement and the formation of high fraction substructure.

An Ab Initio Study of Magnetism in Disordered Fe-Al Alloys with Thermal Antiphase Boundaries.

We have performed a quantum-mechanical study of a B2 phase of FeAl alloy with and without antiphase boundaries (APBs) with the {001} crystallographic orientation of APB interfaces. We used a supercell approach with the atoms distributed according to the special quasi-random structure (SQS) concept. Our study was motivated by experimental findings by Murakami et al. (Nature Comm. 5 (2014) 4133) who reported significantly higher magnetic flux density from A2-phase interlayers at the thermally-induced APBs in FeAl and suggested that the ferromagnetism is stabilized by the disorder in the A2 phase. Our computational study of sharp APBs (without any A2-phase interlayer) indicates that they have moderate APB energies (≈0.1 J/m) and cannot explain the experimentally detected increase in the ferromagnetism because they often induce a ferro-to-ferrimagnetic transition. When studying thermal APBs, we introduce a few atomic layers of A2 phase of FeAl into the interface of sharp APBs. The averaged computed magnetic moment of Fe atoms in the whole B2/A2 nanocomposite is then increased by 11.5% w.r.t. the B2 phase. The A2 phase itself (treated separately as a bulk) has the total magnetic moment even higher, by 17.5%, and this increase also applies if the A2 phase at APBs is sufficiently thick (the experimental value is 2–3 nm). We link the changes in the magnetism to the facts that (i) the Al atoms in the first nearest neighbor (1NN) shell of Fe atoms nonlinearly reduce their magnetic moments and (ii) there are on average less Al atoms in the 1NN shell of Fe atoms in the A2 phase. These effects synergically combine with the influence of APBs which provide local atomic configurations not existing in an APB-free bulk. The identified mechanism of increasing the magnetic properties by introducing APBs with disordered phases can be used as a designing principle when developing new magnetic materials.

Preparation and properties of FeAl/Al2O3 composite tritium permeation barrier coating on surface of 316L stainless steel

In fusion reactors, preparing barrier coatings on the surface of steel structures is one of the most effective ways to reduce the penetration of hydrogen and its isotopes. An FeAl/Al2O3 composite tritium permeation barrier is a good choice for the current tritium permeation prevention technology because it has low enthalpy permeability, small thermal mismatch, good compatibility with lithium lead, and metallurgical bonding. In this study, FeAl/Al2O3 composite tritium permeation barrier coating was successfully prepared on the surface of 316L stainless steel by embedding method combined with in-situ thermal oxidation. By using test methods, such as TEM, SEM, EDS, and XRD, we found that the FeAl alloy transition layer was successfully formed on the surface of the aluminized matrix, thereby effectively relieving the thermal mismatch between the Al2O3 coating and the substrate. The results showed that the thickness of the aluminum-rich layer and the FeAl transition layer on the surface of the substrate were approximately 32 μm and 8 μm, respectively. In addition, α-Al2O3 layer formed on the surface of the aluminum-rich layer after oxidation was approximately 4 μm thick. According to the scratch test, the bond strength of the coating showed that the adhesion of the FeAl/Al2O3 composite coating was 52.4 N. The hydrogen permeation test results showed that the FeAl/Al2O3 composite coating remarkably improved the hydrogen barrier properties of the 316L stainless steel matrix.

Experimental study of phase equilibria on Co–Fe-rich side of Co–Al–Fe system

Despite various studies on Co–Al–Fe ternary system, its phase equilibria are still in doubt. Phase equilibria, magnetic transition and bcc_A2/bcc_B2 order–disorder transformation at the Co–Fe-rich side of the Co–Al–Fe alloys were carefully investigated by means of electron probe microanalysis (EPMA), X-ray diffraction (XRD) and differential scanning calorimetry. The equilibrium phases and their compositions were determined by 18 alloy samples annealed at 900, 1000, 1100 and 1200 °C for 528, 336, 168 and 96 h, respectively, followed by quenching. However, by adopting the above traditional method, bcc_A2 and fcc_A1 phases are difficult to be distinguished through XRD analysis at room temperature due to the martensitic transformation of fcc_A1 phase during quenching. For this reason, high-temperature in situ XRD technique was utilized to correctly establish the phase relationships among bcc_A2, bcc_B2 and fcc_A1 phases. The phase transformation between bcc_A2 and B2 phases was determined to be second order instead of first order at temperatures higher than 900 °C. The equilibrium phases and compositions were further confirmed by fabricating 16 diffusion couples together with EPMA. Meanwhile, using three-dimensional differential scanning calorimetry method, bcc_A2/B2 and ferro-/paramagnetic transitions were determined with high accuracy.

Study Experimental and Numerical Simulations of the Micro-hardness Tests in AL-FE alloy in Different Laser Beam Scanning

In the Al–2.0 wt.%Fe alloy the laser surface remelting (LSR) treatment was executed to investigate the treated and untreated layers areas, at different laser beam scanning, among them, 80, 100 and 120 mm/s, to respect, was presented and discussed about microstructural characteristics using the FEG and EDS techniques, and numerical experiments of pyramidal indentations of the LSR-treated systems were conducted using the FEM method. In the sample-treated cross-sectional area, the microstructure presented a columnar growth characteristic, a lot of nano-porosities and large size of the molten pool geometry in low laser beam scanning, however, in high laser beam scanning, the microstructure consisted of a cellular arrangement or fine-grained microstructure, the nano-porosities concentration and the molten pool geometry are slightly decreased. Besides, the micro-hardness in the LSR-treated area increased slightly as a function of increase of the laser beam scanning, but, the micro-hardness was much higher than the untreated sample. Meanwhile, modeling of indentation on COMSOL of the LSR-treatment by finite element method of the micro-hardness was successfully calculated. Therefore, a good agreement was found between experimental and simulated data.

Finding a New B1-Type Phase in Single Crystals of Fe–Al and Fe–Ga Soft Magnetic Alloys

The atomic structure of Fe–Al (7 and 9 at % Al) and Fe–Ga (18 at % Ga) alloys is studied by X‑ray diffraction using a laboratory four-circle diffractometer. After refining annealing, single-crystal alloy samples were annealed in the ferromagnetic state (T TC), was quenched in room temperature water. Earlier, the authors reported on the peculiarities of the ordering of alloying atoms in B2 and D03 phase structures in quenched and annealed samples of these alloys. Here, we present and discuss the results of our observations in these alloys of a new phase with a face-centered cubic (fcc) lattice (B1-type structure with NaCl prototype and unit cell parameter ~5.2 nm). The fcc phase appears in the Fe–Al alloy as the aluminum concentration increases from 7 to 9 at %; it is observed in the Fe–18 at % Ga alloy, and its volume fraction increases after annealing in the ferromagnetic state in comparison with a quenched alloy sample. In these alloys (9 at % Al) and (18 at % Ga), different ways of embedding fcc crystals in the bcc phase of single crystals are realized; i.e., the axes of the fcc lattice are directed in four different ways relative to the axes of the bcc lattice.

Preliminary study on hydrogen storage for fuel of fuel cell using Fe3Al metal hydride system

Fe3Âl alloy for hydrogen storage was successfully synthesized from Fe (70 wt%) and Al (30 wt%) through ball-mill method in 5 hours milling and Ball to Powder Ratio (BPR) 10:1 to produced mechanical alloy. The results was confirmed by XRD diffraction pattern at 2¸ = 44.791° (10) which is characteristic peak of Fe3Al. The material was applied on hydrogen storage to form metal hydride in which at various temperature and pressure. The Fe3Al alloy performance for hydrogen storage for fuel cell application was indicated from the capacity of hydrogen adsorption and the ability to supply hydrogen for fuel cell. Characterization by using SEM-EDX on adsorption used alloy showed that Fe3Al Alloy has homogeneous surface and no cracks revealed. XRD pattern of alloy after being used to adsorb hydrogen showed a typical pattern at 2¸ = 44.667° (11). Based on the results it can be concluded that hydrogen storage capacity increases with increasing temperature and pressure, and the average adsorption capacity were 58%. Hydrogen storage by the metal hydride method has met the storage criteria established by the US Department of Energy (DOE) as clean and efficient urban energy for the future.

Oxidation mechanism of three Fe-Al alloys with and without addition of 0.1 at% yttrium at 800 °C

The isothermal oxidation behavior of Fe-10Al, Fe-15Al, Fe-20Al alloys with and without the addition of 0.1 at% Y was studied at 800 °C under 1 × 105 Pa of flowing pure O2 for 24 h. The oxidation of three Fe-Al alloys can be divided into transient state and steady state oxidation stages. The oxidation of each stage is approximately in accordance with the parabolic law. The addition of 0.1 at% Y changes the oxidation behavior obviously and leads to a significant increase of the weight gain of Fe-10Al and Fe-15Al. The scale grown on Fe-10Al is much thicker and more complicated than that grown on Fe-20Al, which is composed of an exclusive thin layer of Al2O3 protective film. Due to the formation of a large number of nodules, the scales grown on Fe-15Al cannot provide full protection for the alloy. Scale microstructure of the three Fe-Al-0.1Y alloys is similar to their corresponding Fe-Al alloys. However, nodules with very small size still appear on the surface of Fe-20Al-0.1Y alloy. The critical Al concentration to form an exclusive Al2O3 protective layer for Fe-Al binary alloy is on the borderline between 15 at%–20 at%. For Fe-Al-0.1Y alloy, the presence of 20 at% Al is not enough to inhibit the growth of nodules.

SEM and EDAX Evaluation of Al-Fe Alloy

The scanning electron microscopy (SEM) and energy dispersive X-Ray analysis of the Al-Fe alloy revealed the formation of varying ironaluminide intermetallic compounds. The Al-Fe alloys were produced by varying the composition of Fe. The pure ‘Al’ billets were heated up to 750оc and in the molten condition of aluminium ‘Fe’ powder was added resulting in an exothermic reaction. The exothermic reaction raised the molten bath temperature to ~ 1400оc which activated the formation of intermetallic compound.

Role of dissolved Fe and Si atoms on recovery and recrystallization of Al–Fe alloys and commercially pure aluminums

Role of dissolved Fe and Si atoms on recovery and recrystallization of Al–Fe alloys and commercially pure aluminums

Microstructural and Corrosion Characteristics of Al-Fe Alloys Produced by High-Frequency Induction-Sintering Process

Al-x wt.% Fe bulk alloys were fabricated from a powder mixture of pure Al and x wt.% of Fe, where x = 2 wt.%, 5 wt.% and 10 wt.%. Initially, as-mixed mixtures were processed using a mechanical-alloying (MA) technique in an attritor for 4 h. The milling was performed in an argon atmosphere at room temperature followed by the sintering of the milled powders in a high-frequency induction furnace to produce bulk samples. Scanning electron microscopy (SEM) was used to study the morphology of the produced alloys, and X-ray diffraction (XRD) to determine the phases formed after the sintering process and their crystallite size. The corrosion behavior of the fabricated samples was studied by immerging them in a 3.5% sodium chloride (NaCl) solution at room temperature using cyclic-polarization (CP) and electrochemical-impedance-spectroscopy (EIS) techniques. The SEM results showed that Fe was uniformly distributed in the Al matrix, and XRD revealed the formation of Al and intermetallic, i.e., Al6Fe and Al13Fe4, phases in the Al-Fe alloys after sintering. The hardness of the Al-Fe alloys was increased with the addition of Fe due to the formation of intermetallic compounds. Electrochemical results showed that there was a proportional relationship between the percentage of Fe additives and corrosion potential (Ecorr) where it shifted toward a nobler direction, while corrosion current density (icorr) and corrosion rate decreased with an increasing Fe%. This observation indicates that the addition of Fe into an Al matrix leads to an improvement in the corrosion resistance of the alloys.

Effect of Solid Oxygen Source Species on the Al-Oxide Precipitation Behavior in Fe-Al Alloys by Powder Metallurgy

Effect of Solid Oxygen Source Species on the Al-Oxide Precipitation Behavior in Fe-Al Alloys by Powder Metallurgy