Fe-Al Alloys Research Articles

FeAl/MgO/FeAl MTJ with enhanced TMR and low resistance area product for MRAM: A first principle study

A first principle analysis of Magnetic Tunnel Junction (MTJ) having electrodes of Iron–Aluminum (Fe–Al) alloy separated by MgO (barrier) is presented. In Fe–Al alloy, narrowing of d bands in Fe atoms occur due to hybridization between 3p orbital of Al and 3d orbital of Fe. This increases electronic scattering rate resulting in reduction of propagation of Δ2, Δ2' and Δ5 symmetries of Bloch states through barrier of MTJ. As a result, tunneling magneto resistance (TMR) of MTJ is very high around 5000% for 0.4–1 V. Moreover, it has been found that spin injection efficiency and spin transfer torque (STT) both increase, thereby, improving switching speed of MTJ.

RETRACTED: Laser Welding of UNS S33207 Hyper-Duplex Stainless Steel to 6061 Aluminum Alloy Using High Entropy Alloy as a Filler Material

The high entropy alloy (HEA) filler used during the fabrication method determines the reliability of HEAs for steel-aluminum dissimilar alloy configuration. HEAs have a direct impact on the formation of intermetallic compounds (IMC) formed by the interaction of iron (Fe) and aluminum (Al), and influence the size of the joint’s interaction zone. A novel welding process for Fe-Al alloy joints was developed to prevent the development of a brittle iron-aluminum interface. This research involved investigation of the possibility of using HEA powdered filler. Fe5Co20Ni20Mn35Cu20 HEAs was used as a filler for the laser joining lap configuration joining hyper-duplex stainless steel UNS S33207 to aluminum alloy 6061. This HEA has unique properties, such as high strength, good ductility, and high resistance to corrosion and wear. A tiny portion of the stainless-steel area was melted by varying the welding parameters. The high-entropy alloy (HEA) with slow kinetic diffusion and large entropy was employed to aid in producing solid solution structures, impeding the blending of iron and aluminum particles and hindering the development of Fe-Al IMCs. The weld seam was created without the use of Fe-Al IMCs,. The specimen broke at the HEAs/Al alloy interface with a tensile-shear strength of 237 MPa. The tensile-shear strength achieved was 12.86% higher than for the base metal AA 6061 and 75.57% lower than for the UNS S33207 hyper-duplex stainless steel.

Microstructure and stress analyses in nano-structured alumina layers developed on Fe-Al single crystals

In the present work low index single crystal surfaces of a binary Fe-Al alloy were oxidized in atmospheric air at 700 °C. The oxide layer composition, microstructure and texture were investigated by XPS, TEM and XRD. The oxidation stresses were determined in situ by synchrotron XRD. The results revealed the presence of a dual layered oxide scale, consisting of an inner layer of α-Al2O3 and an external layer of α-Fe2O3 and α-Al2O3. Differences in crystal orientation led to variations in the internal stress distribution in the oxide scales, with compressive stress values α-Al2O3 following (110) > (111) > (100).

Synthesis of Co2FeAl alloys as highly efficient electrocatalysts for alkaline hydrogen evolution reaction

The development of cost-effective non-precious metal electrocatalysts is a major challenge for water splitting applications, but it is important for the realization of renewable energy systems. Alloying has proved an effective way to design metal-based electrocatalysts, and by controlling the annealing temperature, the surface morphology and crystallinity of the alloy can be tuned to control the hydrogen evolution reaction (HER) performance. In this work, with a simple coprecipitation method, we have prepared Co 2 FeAl alloys at different annealing temperatures (550 °C–670 °C), which exhibit excellent crystallinity and electrocatalytic performance for HER in alkaline solution. Among all conditions, the Co 2 FeAl alloys prepared at 620 °C shows the better crystallinity and the higher purity, and it could achieve a low overpotential of 149 mV at 10 mA cm −2 in alkaline solution. The overpotential demonstrates persistent stability with only 3 mV change after over 1000 cycles. Both density functional theory (DFT) calculations and experimental results revealed that alloying optimizes the electronic structure near the Fermi surface of the system, improving the electron transport efficiency and enhancing the catalytic activity. These Co 2 FeAl alloys are appealing candidates for high-performance alkaline HER electrocatalytic electrodes in water electrolysis due to their outstanding electrocatalytic properties. We demonstrate that the efficient electrocatalytic activity is due to high temperature annealing, along with the synergistic effect of alloying, lead to the surface structure and electronic structure of the alloy have changed. This strategy enables the Co 2 FeAl alloy electrocatalyst to achieve a low overpotential of 149 mV at 10 mA cm −2 in alkaline solution. • Co 2 FeAl Alloy is prepared by facile coprecipitation method. • High temperature annealing to adjust the crystal plane orientation of alloys. • It could achieve a low overpotential of 149 mV at 10 mA cm −2 in alkaline solution. • It shows highly efficient electrocatalytic activity for HER while remaining stable/durable. • DFT calculations revealed that it optimizes the electronic structure near the Fermi surface.

Ab initio investigations of point and complex defect structures in B2-FeAl

We study single-site and two-site defect structures in B2-type Fe-Al alloys by means of density functional theory supercell calculations. The defect formation energies are calculated as functions of the chemical potential, which are used to obtain the dependence of the defect concentrations on Al content at different temperatures. We also examine the converging behavior of the formation energies with respect to the supercell size to study the corresponding limit of dilute defects. The effect of magnetism is investigated by considering nonmagnetic, ferromagnetic, and paramagnetic states, calculations for the latter showing that the magnitude of the local magnetic moments strongly impacts the defect formation energies. The methodological studies are used to provide explanations for the wide spread of defect formation energies reported by experiments and other theoretical investigations. Based on these insights, the stability of the B2-FeAl structure as a function of Al concentration is obtained and discussed.

Effects of Sc and Zr addition on the solidification and mechanical properties of Al–Fe alloys

The effects of Sc and Zr on the microstructure and properties of Al–3Fe alloys were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and mechanical property testing. The results show that the Al 3 (Sc, Zr) phases with a L1 2 structure are formed with the addition of Sc and Zr, which promotes the heterogeneous nucleation, reduces the segregation and improve columnar grains. In the process of iron-rich phase nucleation and growth, Sc and Zr atoms are adsorbed around iron-rich phases, which prevents the growth of iron-rich intermetallics and makes the needle-like primary Al 3 Fe phases gradually change to short rod-like, butterfly-like and flower-like morphologies. Additionally, the fibrous eutectic Al 6 Fe phases are also observed. With increasing the Sc and Zr contents from 0 to 0.35 wt% and 0 to 0.14 wt%, respectively, the strength of the alloy increases and the elongation decreases. The Al–3Fe alloy with the addition of 0.16 wt% Sc and 0.06 wt% Zr has a tensile strength of 160.8 MPa and a yield strength of 132.4 MPa. During aging process, fine, dispersed and coherent nanoscale secondary Al 3 (Sc, Zr) (L1 2 structure) phases are formed in the α-Al matrix to promote precipitation strengthening. When the addition of Sc and Zr is 0.35 wt% and 0.14 wt%, respectively, the refinement effect on the macrostructure and the second phase is most obvious. After aging, the tensile strength reaches 233 MPa and the yield strength reaches 200 MPa.

Nitriding behaviour of the intermetallic alloy FeAl

Abstract An iron-based intermetallic FeAl alloy was gas nitrided under well-defined conditions, and the influences of the process parameters, i. e., time, temperature, and nitriding potential on the layer formation, were investigated. Microstructural, morphological, and chemical characterization of the nitride layer was performed by means of glow discharge optical spectroscopy, electron probe microanalysis, scanning electron microscopy, X-ray diffraction, internal-stress measurement, hardness– depth profiles, and indentation fracture mechanics. Pin-on-disk tests were carried out to investigate the load-bearing capacity and wear resistance of the nitride layers. The formation of hexagonal AlN during the nitriding treatment leads to an increase in hardness of about 920 – 980 HV 0.025 and to a significant improvement of the wear resistance. Additional annealing tests proved the thermal stability of the nitride layer up to 950 °C.

Phase Transformation of a Dual Phase Al–Fe Alloy Prepared by Mechanical Alloying

Abstract A metastable Al90Fe10 (at.%) alloy, composed of a supersaturated solid solution of face-centred cubic (fcc) Al(Fe) and an amorphous phase matrix, was prepared by mechanical alloying of a mixture of Al and Fe elemental blends. The thermally induced microstructural evolution in the dual phase alloy was characterized by X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and magnetothermal analysis. On continuous heating two stages of solid state phase transformation occurred: (i) a polymorphous crystallization of the amorphous phase to a metastable crystalline Al6Fe that structurally stabilizes over a temperature range of about 200 K, and (ii) a eutectoid decomposition of the crystalline Al6Fe into the equilibrium phases of Al13Fe4 and fcc Al(Fe). Thermodynamic and kinetic analyses of the observed phase transformation processes were given. The formation of the dual phase alloy in the as-milled state and the phase transitions can be illustrated by a hypothetical free energy diagram, implying the dual phase structure facilitates the polymorphous crystallization of Al6Fe.

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.

Magnetostriction and damping of forced vibrations in Fe-Cr-Mo-Al alloy

The magnetostriction, damping capacity and mechanical properties of a Fe-Cr-Mo-Al alloy are studied and compared with binary Fe-Cr and Fe-Al alloys. Synchronous change in magnetostriction and damping in Fe-16Cr-0.6Mo-0.6Al alloy: the maximum magnetostriction strain and damping capacity are obtained after annealing at 900 °C followed by air cooling. Frequency dependence of damping in subresonance range is analyzed and interpreted in terms of variations in relaxation time and stiffness of DMA.

Point defects, precipitates and the strength anomaly in ordered Fe–Al alloys

AbstractThe strength of B2-ordered Fe60Al40has been investigated with respect to the influence of vacancies and interstitial impurities. Preconditioned states with different ratios of the concentration of vacancies and interstitial impurities have been established, which then were recovered by subsequent annealing treatments. The evolution of the recovered states with temperature has been monitored by measuring the strength (ultra-microhardness) at room temperature as a function of the annealing temperature. The observed dependencies are discussed on the basis of the resistance of vacancies and impurities to dislocation motion, of vacancy – interstitial interactions and also of the possible formation and dissolution of precipitates (primarily perovskites). The yield stress maximum which, independent of the stoichiometry, appears near 800 K is found to be controlled by vacancy migration in combination with strain ageing by interstitial agglomerates and by the formation of precipitates.

Phase decomposition and precipitation of metastable A2 phase in B2 ordered Co–Al–Fe alloys

Abstract Phase decomposition in rapidly solidified Co–Al – Fe B2 alloys during isothermal ageing at 923 K has been investigated by means of X-ray diffraction and transmission electron microscopy. At the early stage of ageing, A2 disordered particles precipitate inside B2 matrix grains, being aligned along the <100> direction of the matrix, and equilibrium A1 phase (α-Co) is also formed mostly on grain boundaries. With further ageing, the plate-like A2 particles increase in size. On the other hand, the A1 phase on grain boundaries increases in size and also spreads into the B2 grain like tree branches as so-called Widmanstätten precipitate. Finally, the A2 phase disappears. The A1 phase remains on grain boundaries and also inside the B2 grains as spherical particles. Using the composition gradient method, the metastable precipitation limit of the A2 phase, that is the metastable phase boundary B2/(A2 + B2), was experimentally determined at 923 K. It extends smoothly into the stable A2 + B2 two-phase field on the Co–Fe side of the ternary Co–Al –Fe system.

Density and molar volumes of liquid alloys of iron with C, B, Si, P, Cu, Al, Ni, Cr and Mn

The paper discusses density and molar volume of liquid alloys of iron with C, B, Si, P, Cu, Al, Ni, Cr and Mn. Liquid alloys of iron with other metals are considered as substitutional solutions using the hard-sphere model. Deviations of molar volumes of Fe-Cu and Fe-Al alloys from the ideal solutions were analysed using relationship between excess volume and entropy. Alloys of iron with Ni, Cr and Mn are close to the ideal solutions. Calculated volumes are in agreement with experimental data. Alloys of Fe with C, B, Si and P are considered as interstitial solutions using P. Gaskell�s model developed for amorphous alloys of transition metals with metalloids. Calculated partial molar volumes of C, B, Si and P in dilute binary solutions at 1823 K are (cm3/mol): 1.59, 3.37, 7.06 and 6.26 respectively. The model correctly describes the liquid alloys of iron with metalloids as interstitial solutions.

Magnetic behavior of ordered DO3-type Fe3Al Heusler alloy

Fe3Al alloy is synthesized in a vacuum arc-melting furnace under an argon atmosphere. The prepared ingot is annealed in a vacuum furnace at 800 °C for 1hr, further at 500 °C for 48 hrs to facilitate the re-crystallization. The alloys are crystallized in a cubic DO3 structure. The magnetic properties are derived from M−H, and M−T measurements and the thermal properties like transition temperature (Tc), heat flow, and heat capacity (Cp) are measured from DSC. We have observed the magnetic transition at a temperature of 925°K with an applied magnetic field of 5000 Oe. The saturation magnetization (Ms) is found to be 188 emu/g, and remanence magnetization (Mr) of 0.78 emu/g. From M−T and DSC measurements it appears that the samples have ferromagnetic ordering with second-order phase transition. The critical exponent is derived by applying mean-field, 3D-Heisenberg, 3D-Ising, and tricritical models.

Microstructural Patterns, Microsegregation, Porosity, and Mechanical Properties of Hypoeutectic Al-Fe Alloy, and its Dependency with Solidification Thermal Parameters

Al-Fe alloys are usually used as packaging and structural materials, but in the recent years, there have been considered for possible applications in aerospace field. The solidification sequence in pure aluminum containing 1 wt.% Fe is described in term of the formation of macrostructure, microstructure, microsegregation, porosity and mechanical properties. This material was studied in the upward unidirectional solidification system under transient heat flow conditions. Differences in microstructure, microsegregation, porosity and mechanical properties such as ultimate tensile strength, elongation and microhardness, due to the thermal parameter effects were observed and discussed. Experimental growth laws relating cellular spacing to the cooling rate and solidification speed have been determined, indicating that the increase in thermal parameter have induced a refinement effect on cell morphology. Microsegregation profiles of Fe solute were experimentally determined from the central region of the cell to the intercellular region under different solidification speeds. The Fe microsegregation determined from central region of the cell (FS = 0) to the intercellular region (FS = 1) show a growing profile, in any case considered. However, the profiles move upward with the increase in solidification speed, which indicates that Fe solubility in solid, increases with the increase in solidification speed. The effect of the solidification thermal parameters and cellular spacing on the porosity content were experimentally investigated. The value of porosity content increased along the casting. These results have pointed out that porosity content is affected by solidification parameters and cellular patterns. Further, measurable effects of the thermal parameters, cellular spacing and porosity content on the mechanical properties were experimentally determined. It stands out among experimental results the influence of porosity on the mechanical properties of as-cast material. In any case analyzed, mechanical properties increase with decreasing porosity content.

A stable and high-energy aqueous aluminum based battery.

Aqueous aluminum ion batteries (AAIBs) have received growing attention because of their low cost, safe operation, eco-friendliness, and high theoretical capacity. However, one of the biggest challenges for AAIBs is the poor reversibility due to the presence of an oxide layer and the accompanying hydrogen evolution reaction. Herein, we develop a strongly hydrolyzed/polymerized aluminum–iron hybrid electrolyte to improve the electrochemical behavior of AAIBs. On the one hand, the designed electrolyte enables aluminum ion intercalation/deintercalation on the cathode while stable deposition/stripping of aluminium occurs on the anode. On the other hand, the electrolyte contributes to the electrochemical energy storage through an iron redox reaction. These two reactions are parallel and coupled through an Fe–Al alloy on the anode, thus enhancing the reversibility and energy density of AAIBs. As a result, this hybrid-ion battery delivers a specific volumetric capacity of 35 A h L−1 at the current density of 1.0 mA cm−2, and remarkable stability with a capacity retention of 90% over 500 cycles. Furthermore, the hybrid-ion battery achieves a high energy density of approximately 42 W h L−1 with an average operating voltage of 1.1 V. This green electrolyte for high-energy AAIBs holds promises for large-scale energy storage applications.

Механические свойства, электропроводность и термостабильность проволоки из сплавов системы Al–Fe, полученных литьем в электромагнитный кристаллизатор

The development and production of new aluminum-based materials is a critical task of the up-to-date industry. Particularly, new materials are necessary to produce light, strong, and thermally-stable wires and cables for household usage, transport, and power sphere. The paper presents the results of the study of the microstructure and physical and mechanical properties of Al–0.5Fe and Al–1.7Fe alloys (wt. %), produced by continuous casting into an electromagnetic crystallizer (EMC). The authors carried out a comparative analysis of alloys under the study and commercial alloys. During this analysis, the authors produced a wire with the diameter of 3 mm from the primary cast blanks by the cold drawing method (CD). The microstructure analysis showed that as a result of casting into an electromagnetic crystallizer, the particles of metastable modification Al2Fe phase appear during the crystallization process that have sizes close to the nanometric range. The use of the cold drawing method led to the substructure formation in both alloys and the refinement of intermetallic particles, which ensured the significant hardening of alloy specimens. After cold drawing, the intermetallic particles were grinded and distributed along the boundaries of grains/sub-grains. The ultimate tensile strength of the Al–0.5Fe alloy was 204 MPa, while in the Al–1.7Fe alloy, it reached 295 MPa. The electrical conductivity level of the Al–0.5Fe and Al–1.7Fe alloys wire was 58.4 and 52.0 % IACS, respectively. The study showed that the Al–Fe alloys wire with ferrum concentration of up to 1.7 wt. % demonstrated thermal stability at the level of thermally-stable Al–Zr and Al–REM conductive alloys.

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.

B2-ordered NiAl content on microstructure, mechanical and oxidation properties of FeAl intermetallic compounds

B2-ordered FeAl based materials with 0, 10, 20, 30, 40, 50 and 60 wt.% B2-ordered NiAl reinforced phase were prepared by mechanical alloying with subsequent hot-pressing sintering. The microstructure, mechanical properties and oxidation resistance were investigated. The results showed that after adding NiAl, the main phase was composed of B2-ordered NiAl, B2-ordered FeAl phase, a small amount of AlFe3C0.5 and α-Al2O3. With the increase of NiAl content, the hardness and compressive strength of NiAl/FeAl composites first increased and then decreased. When the content of NiAl increased to 30 wt.%, the hardness and compressive strength of NiAl/FeAl composite reached the maximum value of 50.30 HRC and 2053.43 MPa, which was 35.2% and 40.8% higher than FeAl alloy. Besides, with the increase of NiAl content, the formation of dense oxide film on the surface was easier and faster, and the oxidation resistance was gradually improved. When the content of NiAl increased to 60 wt.%, the oxidation weight gain of NiAl/FeAl composite was 0.19 mg/cm2. Compared with FeAl alloy, the oxidation resistance of 60 wt.% NiAl/FeAl was increased by 81%, and the thickness of oxide layer was reduced from 1.527 μm to 0.253 μm. At this time, the oxide on the surface of the oxidized sample was mainly composed of α-Al2O3, α-Fe2O3 and a small amount of NiO.

Corrosion behaviors at different temperature based on the ultrafine-grained structure of Al-Fe alloy

Electrochemical tests and immersion experiments were employed to investigate the corrosion behaviors of the Al-Fe alloy (AA8176) processed by equal channel angular pressing (ECAP) in 3.5 wt% NaCl solution at different temperature (25 °C and 0 °C). It was worked out that after ECAP, with the reduction of grain size, the fragmentation and uniform distribution of precipitated phases increased the number of pitting corrosion but reduced its size, the increase of grain boundary density and the reduction of precipitated phase aggregation decreased the degree of intergranular corrosion. AA8176 changed from local corrosion to uniform corrosion, which provides a new idea to improve the corrosion resistance of Al-Fe alloys.