Fe-Al System Research Articles

Atomistic simulation of the diffusion behavior in Al-Fe

• As Al block was attached to Fe block, Al atoms penetrated Fe block and vice versa on simulation. • Al atoms diffused massively into the Fe lattice, whereas Fe atoms moved deeper inside Al block. • The diffusion coefficient of Al was 2 times the diffusion coefficient of Fe. • Activation energy is 0.83 and 0.72 eV for Al and Fe, respectively. • Pre-exponentials is 1.03 × 10 −6 m 2 /s for Al and 5.83 × 10 −8 m 2 /s for Fe. The diffusion behavior of the Al-Fe system was investigated by a classical molecular dynamics simulation for simulating the Al coating process on Fe. Two bulks were built as the model: one bulk contained Al atoms and the other was made from Fe atoms. The diffusion was studied at four different temperatures for 6 ns by utilizing a MEAM potential. The mean square displacement (MSD) and potential energy of Al and Fe atoms were recorded during the simulation. Fe atoms penetrated inside the Al lattice in low quantities and at a slower rate compared with the fast and large number of diffusing Al atoms that did not penetrate inside the Fe lattice. The diffusion coefficient was estimated by the fitting of the linear region from the MSD and time curves. The Arrhenius equation was used to find the activation energy and the frequency of attempts. The activation energy of Al was 0.83 eV, whereas that of Fe was 0.72 eV. The frequency of attempts for the Al and Fe atoms were 1.03 × 10 - 6 and 5.83 × 10 - 8 m 2 /s, respectively. The diffusing mechanisms were studied, and it was found that the Fe atoms diffused into the Al lattice by the first-neighbor hopping mechanism. The potential energy of the Fe atoms increased as the Fe atoms penetrated the Al lattice.

Mechanisms for Forming Iron-Containing Intermetallics Prepared by Aluminothermy and the Effect of Special Treatment Methods on their Properties

Scientists around the world are conducting research in the production of new materials and alloys with a good set of physicomechanical properties with the aim of their prospective application in a wide variety of industries. Today, researchers in this field are faced with the problem of improving known and creating new methods for producing heat-resistant, thermally stable, and wear-resistant materials. For example, alloys based on iron aluminides have good anti-corrosion properties and oxidation resistance due to formation of aluminum oxide, as well as low cost. Iron aluminides belong to a class of especially light promising structural materials and are used in mechanical engineering, metallurgy and electrical engineering. Preparation of Fe–Al aluminides for the production of materials and coatings is currently being accomplished using isostatic pressing and sintering in a vacuum, arc and plasma spraying, electroslag remelting, and self-propagating high-temperature synthesis, which do not fully meet contemporary requirements, since the production processes for preparing these alloys using known methods are multi-stage. Development of simple and productive technology for producing high-quality intermetallic compounds in the Fe–Al system is an urgent scientific and technical task. So far the most feasible approach is one that provides preparation of iron aluminides by combined aluminothermic reduction of the original metal oxides using SHS-metallurgy in one stage. Mechanical and operating properties of compounds of the Fe–Al system are largely determined by lattice parameters and structural features. All intermetallic compounds of the Fe–Al system exhibit a brittle fracture pattern. In order to adjust the physicomechanical and operating properties various elements, such as chromium, niobium, carbon, molybdenum, tungsten, etc., are added to an alloy composition based on the Fe–Al system. These elements are introduced into the alloy by assembling special charge materials in which the elements are present in pure form or in the form of compounds, including oxides, in various combinations above, up to, and equal to the stoichiometric ratio. The starting components of charge mixtures are cheap low-cost materials, including waste from engineering and metallurgical enterprises. Studies of the properties of the experimental alloys obtained, in particular chemical composition, phases formed, microstructure, strength, hardness, wear resistance, corrosion and oxidation confirm their suitability for operation in high temperature and corrosive environments. At the same time, it is possible to correct further the properties by treating the resulting alloys with the methods of deformation and heat treatment, as a result of which the latter not only increase in strength and yield strength, but also increase in elongation associated with a change in grain size and shape. Development of new alloys based on iron aluminides, combining a set of the required properties and chemical composition, allows them to be used as independent structural materials, and as modifiers in smelting various alloys. At the same time, it is possible to expand the field of application of alloys based on iron aluminide with wider use in the aerospace industry, where these materials may replace expensive nickel aluminides, titanium alloys, etc.

Plasma coatings made of mechanically synthesized composite powders based on the «iron-aluminum» system

Theregularitiesof the formation of plasma coatings obtained from powders based on the Fe-Al system synthesized by the reaction mechanical alloying method are established. The influence of the processing modes of the compositions in the mechanoreactor on the properties of coatings is revealed. An effective method for controlling the porosity of coatings from developed powders based on a change in the power consumed by the installation is proposed.Plasma coatings have a nonequilibrium phase composition, which, in contrast to the equilibrium one, contains a wide range of metal oxides of the base and alloying elements formed during the spraying. The coating retains submicra – microcrystalline type of structure of powders with a highly developed grain and subgrain boundary. The basis of the coating is intermetallic FeAl. The role of hardening phases is played by ultrafine compounds of intermetallics and oxides.Powder annealing has a significant effect on the structure and properties of coatings and, first of all, on layers from compositions with complex alloying with oxides. Heat treatment increases the density and hardness of coatings and reduces porosity. The study of coating samples after high temperature indicates high heat resistance and the preservation of the microcrystalline type of structure of their bases.

Investigating steel tool life in the RFSSW process

Abstract Refill Friction Stir Spot Welding (RFSSW) has demonstrated capability in joining thin sheets of aluminum with dissimilar thickness, alloy, and composition. The process remains to be implemented on a wide scale in the automotive and aerospace industries, partially due to the relatively short number of welds producible by a toolset, prior to needing cleaning. In the following work, an investigation was conducted to better understand this limitation. First, the effective tool life of a steel toolset was quantified. Experiments showed that less than 60 consecutive welds could be made before the toolset seized and required cleaning. To better understand the conditions contributing so such a short tool life, thermocouples were used in subsequent experiments, to measure the temperatures achieved at various locations in the weld. Peak weld temperature increased with longer cycle times and decreased with shorter cycle times. During the experiments, it was noted that weld temperatures in excess of 500 °C were observed at weld center. At these high temperatures, the authors anticipate that intermetallic compounds (IMCs) are able to grow on tool surfaces. A rough, existing model of IMC growth in an Fe-Al system predicted IMC growth on the same order of magnitude of the tool clearances, supporting the anticipation that IMC growth is a factor in the observed, short tool life between cleanings. Following this analysis, future evaluation of less re-active tool materials is recommended.

Preparation and characterization of novel Ti(Al)–TiB2/Ti3Al metallic-intermetallic laminated composites

In this paper, we designed and prepared Ti(Al)–TiB2/Ti3Al laminated composites consisting of alternating Ti(Al) layers and TiB2/Ti3Al layers, which were realized by using Ti foils and TiB2/Al composite foils as raw materials, stacking, and reaction annealing. Phase transformation and microstructure evolution of laminated composites during reaction annealing were systematically investigated by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). Formation mechanism of laminated structure was elucidated in details. The results showed that Ti(Al)–TiB2/Ti3Al laminated composites exhibited a significant increase in ductility while maintaining or even improving the tensile strength, in comparison with monolithic Ti3Al. It is expected that the design strategy can be extended to other brittle intermetallic compounds, such as Ni–Al and Fe–Al systems.

Electromigration effect in Fe-Al diffusion couples with field-assisted sintering

The electromigration effect in spark plasma sintering (SPS) (a.k.a. field assisted sintering) is quantitively analyzed in the Fe-Al diffusion couple system. In SPS, the samples are heated by a applied voltage and electric current, which can lead to an electromigration effect. Finite element analysis is utilized to determine the voltage applied to the Fe-Al diffusion couple, which is found to be order of magnitudes smaller than the overall system voltage, indicating the electron wind force would be the dominant mechanism for electromigration in SPS. Additionally, the simulation suggests the temperature and current density distribution is uniform across the metallic diffusion couple, which makes quantitative measurement feasible. A mathematic algorithm that allows diffusivity and electromigration coefficients to be solved, is developed for the Fe-Al, where multiple intermetallic phases coexist. At temperatures below aluminum melting, Fe2Al5 is the single intermetallic phases formed in Fe-Al system, for which electromigration is negligible. At temperatures above aluminum melting, FeAl2, FeAl and α-Fe solid solution phases coexist. Among them, the electromigration effect is noticeable in FeAl phase and is significant in the FeAl2 phase. The corresponding electromigration enhancement constants are calculated.

ОСОБЛИВОСТІ ВЗАЄМОДІЇ КОМПОНЕНТІВ У РІДКИХ СПЛАВАХ ПОТРІЙНИХ СИСТЕМ Al-Ge-3d-Me (Me = Mn, Fe, Ni, Cu)

The features of the component interaction in liquid alloys of ternary Al-Ge-3d-Me systems (Me = Mn, Fe, Ni, Cu) are described. A joint analysis of the concentration dependences of the enthalpies of mixing of liquid alloys previously obtained by the authors via high-temperature calorimetry, and also of the phase diagrams of the constituent binary systems was carried out. The relationship between the enthalpy values and the type of short-range ordering in liquid alloys of the studied systems was established. The visual similarity of the topology of the projections of ΔmH isolines of the Al-Ge-Fe (Ni, Cu) liquid alloys and a completely different course of the isolines of the enthalpies of mixing for the liquid Al-Ge-Mn alloys are established. The changes in the absolute values of the ΔmHmin from system to system are observed. The enthalpies are approximately the same for the Al-Ge-Mn and Al-Ge-Fe systems (about -20 kJ⋅mol-1), they increase significantly from Al-Ge-Fe to Al-Ge-Ni (-50 kJ⋅mol-1), and then decrease substantially towards the Al-Ge-Cu system (-15 kJ⋅mol-1). For the Al-Ge-Mn (Fe, Ni, Cu) liquid alloys the lines of extreme interaction are located near the 3d-corner of the concentration triangle. These lines connect the compositions of the most stable intermetallic compounds in binary Al(Ge)-Mn(Fe, Ni, Cu) systems. It has been shown that the thermodynamic properties of Al-Ge-Fe (Ni, Cu) liquid alloys are mainly determined by the pair interaction of the components of the constituent binary Al-Fe(Ni, Cu) and Ge-Fe(Ni, Cu) systems, the influence of Al-Fe(Ni, Cu) systems being prevailed. For the Al-Ge-Mn system, the interaction of components in the Ge-Mn binary system gives the main contribution to the thermodynamic properties of the ternary system. The Al-Ge-Mn (Fe, Cu) systems are characterized by significantly lower absolute values of the heats of alloy formation compared to the Al-Ge-Ni one. The specified characteristics of component interaction in the ternary systems under consideration and different values of the enthalpies of mixing are determined by the peculiarities and regular changes of the electronic structure of 3d metals across the 3d series from Mn to Cu.

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.

Characterization and Wear Properties of Fe3Al and (Fe,Ti)3Al Intermetallic Claddings Produced by GTAW Process

In this study, Fe3Al and (Fe,Ti)3Al intermetallic coatings were applied on the surface of CK45 steel by GTAW process. For this purpose, Fe3Al and (Fe,Ti)3Al intermetallic powders were synthesized by mechanical alloying. Phase analysis of powders and coatings was carried out by X-ray diffractometery. The microstructure of the coatings was evaluated by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The wear behavior of the coatings was characterized by reciprocal wear test. It was found that Fe3Al and (Fe,Ti)3Al coatings were deposited successfully on the surface of substrate. The addition of Ti into Fe–Al system enhanced the hardness of the coating due to the dissolution of Ti in lattice and therefore distortion of crystal structure. In FA2 coating (Fe75Al25, 2 weldings) synergic effect of abrasive and adhesive wear mechanisms increased the wear of coating as compared with FAT2 coating (Fe50Al25Ti25, 2 weldings), while the main wear mechanism of FAT2 coating was microcutting abrasive wear.

The phase composition, structure and properties of high-temperature-based powders of the system iron-aluminum obtained by the technology of the reaction-mechanical alloying. Foundry production and metallurgy

The regularities of the formation of powders based on the Fe-Al system, obtained by the method of mechanical alloying and intended for the deposition of thermal spraying coatings were established. The morphology, structure, phase composition and properties of materials are investigated. After mechanical synthesis, the powders have an average particle size of 30–100 µm, submicrocrystalline structures, and nonequilibrium phase composition. Annealing of powders causes to an increase in the hardness of particles up to 80%, the value of which is largely preserved after prolonged heating to 1170 K, which indicates the presence of heat-resistant materials.

Treatment of dairy wastewater by electrocoagulation process: Advantages of combined iron/aluminum electrodes

ABSTRACT The objective was to assess the efficiency of electrode material in an electrocoagulation (EC) process for wastewater treatment by comparing the efficiency of aluminum (Al–Al), iron (Fe–Fe) and combined Fe–Al electrodes. The treatment of synthetic dairy wastewater, characterized by high levels of 5-day biological oxygen demand (BOD5) and chemical oxygen demand (COD), was used to compare electrode materials. Experimental results showed that all electrodes materials achieved the same final removal yield in the range of current studied (55% COD, 60% total organic carbon, 90% total nitrogen, and nearly 100% turbidity) when equilibrium was achieved. But at fixed current density and initial concentration of dairy waste, the Al–Al assembly exhibited the fastest elimination, whereas the slowest removal rate was observed with the Fe–Fe electrodes, even though adsorption was always the main removal mechanism. Finally, an Fe–Al system using an Fe anode with an Al cathode emerged as a techno-economic trade-off because of the low price of iron: both metals contributed to the removal of dairy waste, and the treatment time to achieve equilibrium values was closer to the Al–Al assembly at fixed current density. Moreover, experimental results proved the additivity of the mechanisms reported for Al–Al and Fe–Fe systems with Fe–Al.

Thermodynamic investigations in the Al–Fe system: Thermodynamic modeling using CALPHAD

AbstractThe Al–Fe system has been modeled and optimized with the CALPHAD approach. Heat capacity values from three intermetallic phases (stoichiometric compositions: Al2Fe, Al5Fe2 and Al13Fe4) were experimentally determined and implemented into the Gibbs energy descriptions, thus the estimated heat capacity from Neumann–Kopp is substituted. From these results together with new literature values, a revised dataset of the binary Al–Fe system is presented. Based on the Compound Energy Formalism, the homogeneity range of the Al2Fe and Al5Fe2 phase is represented using a two-sublattice model. In addition, the Al8Fe5 phase has been modeled with a four-sublattice model and the number of sublattices of the Al13Fe4 phase has been changed from a three-sublattice model to a two-sublattice model. The critically assessed parameters provide a consistent thermodynamic dataset and represent most of the relevant thermochemical data as well as phase diagram data within their experimental uncertainties.

An Ab Initio Study of Vacancies in Disordered Magnetic Systems: A Case Study of Fe-Rich Fe-Al Phases.

We have performed quantum-mechanical calculations to examine the impact of disorder on thermodynamic, structural and electronic (magnetic) properties of Fe-Al systems with vacancies. A series of supercells was used and their properties were computed employing density-functional theory (DFT) as implemented in the VASP package. Our case study is primarily aimed at a disordered solid solution FeAl but we have compared our results also with those obtained for the ordered FeAl intermetallic compound for which experimental data exist in literature. Both phases are found in Fe-Al-based superalloys. The Fe-18.75at.%Al solid solution was simulated using special quasirandom structures (SQS) in three different disordered states with a different distribution of Al atoms. In particular, we have considered a general disordered case (an A2-like variant), the case without the first nearest neighbor Al-Al pairs (a B2-like distribution of atoms) and also the case without both the first and second nearest neighbor Al-Al pairs (the D0-like variant, in fact, an Fe-rich FeAl phase). The vacancy formation energies as well as the volumes of (fully relaxed) supercells with vacancies showed a large scatter for the disordered systems. The vacancy formation energies decrease with increasing concentration of Al atoms in the first coordination shell around the vacancy (an anti-correlation) for all disordered cases studied. The computed volumes of vacancies were found significantly lower (by 25–60%) when compared with the equilibrium volume of the missing atoms in their elemental states. Lastly, we have analyzed interactions between the vacancies and the Fe atoms and evaluated vacancy-induced changes in local magnetic moments of Fe atoms.

Электропроводный материал на основе порошковой меди с повышенными механическими свойствами

The methods of pressing, rolling, and sintering in hydrogen at 800°C have been applied to production of powdered materials based on copper of the Cu–Fe–Al system. The influence of single components and their blends on compaction, structure, and main functional properties of composite materials—electrical conductivity, hardness, and strength (yield stress)—has been analyzed as a function of process variables: compacting pressure of 200–700 MPa, deformation by rolling of 40–85%, dispersity of iron powders having particle sizes <50 and 63–100 μm, contents of iron powder of 5–10 wt % and Fe2Al5 intermetallic powder of 2.5–5 wt %. The best combination of physicomechanical properties has been found for composite material with the composition (wt %) 92.5 Cu + 2.5 Fe2Al5 + 5 Fe, together with iron particle sizes of 63–100 μm. It has been demonstrated that dispersion strengthening of copper by Fe2Al5 particles and filling of its structure with iron fibers formed by rolling provides high relative density of 98–99% and subsequent strength properties of the composite material: hardness HB of 980 MPa, yield stress of 150 MPa at electrical conductivity of 71% of copper conductivity.

Structure and Selected Properties of Arc Sprayed Coatings Containing In-Situ Fabricated Fe-Al Intermetallic Phases

The paper presents the results of research on the production by means of arc spraying of composite coatings from the Fe-Al system with participation of in-situ intermetallic phases. The arc spraying process was carried out by simultaneously melting two different electrode wires, aluminum and steel. The aim of the research is to create protective coatings with a composite structure with a significant participation of FexAly as an intermetallic phases reinforcement. The synthesis of intermetallic phases takes place during the (in-situ) spraying process. Currently most coatings involving intermetallic phases are manufactured by different thermal spraying methods using coating materials in the form of prefabricated powders containing intermetallic phases. The obtained results showed the local occurrence of intermetallic phases from the Fe-Al system, and the dominant components of the structure have two phases, aluminum solid solutions in iron and iron in aluminum. The participation of intermetallic phases in the coating is relatively low, but its effect on the properties of the coating material is significant.

High-Efficiency UHF Radio-Absorbing Composites Based on Iron Alloys

The use of pure iron in UHF radio-absorbing composite fillers is appraised. A method is proposed for selecting iron-based alloys with improved properties. Experiments confirm that the Fe–Al system with 10–14% Al is the most promising filler for such systems. The main trends in the use of such alloys as broadband fillers for radio-absorbing composites are noted.

Experimental and computational study of diffusion mobilities for the bcc phase in the Fe-Al-(Si, Mn) systems

The electrical steel has attracted considerable attention due to the excellent soft magnetic properties, which can be improved by the addition of alloying elements such as Al, Si and Mn. To increase element contents, the hot-dipping and diffusion-annealing method has been developed. The method requires detailed insight on the diffusion behavior of the alloy system. In the present work, the re-assessment of the diffusion mobilities for the bcc phase (including both bcc_A2 and bcc_B2 phases) in the Fe-Al system were firstly performed based on the critical evaluation of the available experimental data. By applying the diffusion-couple method, the interdiffusion coefficients in bcc_A2 Fe-Al-Si alloys were determined and used to optimize the diffusion mobilities. The bcc_A2 Fe-Al-Mn diffusion couples were also designed to verify the diffusion mobilities. Comparison between the model-predicted and experimental diffusion data such as diffusion coefficients, concentration profiles and diffusion paths confirms the reliability of the present mobility parameters.

Experimental investigation and thermodynamic assessment of the Al-Fe system

The heat capacity of ε (Fe5Al8) was determined between 1395 and 1455 K by DSC measurements. The homogeneity ranges of the intermetallic phases ζ (FeAl2), η (Fe2Al5) and θ (Fe4Al13) in the temperature range between 1073 and 1435 K were determined using WDS measurements on annealed and quenched samples in the composition range between 56.0 and 75.3 at.% Al. The solidus and liquidus temperatures of all samples were determined using DTA. A CALPHAD-type assessment of the Al-Fe system was done based on latest experimental results on heat capacity of the intermetallic phases.

Thermodynamic investigations in the Al-Fe system: Heat capacity measurements of three intermetallic phases

For a comprehensive understanding of the Al-Fe systems' thermodynamics further experimental investigations are required, especially for the Al-rich side. Intermetallic phases in the Al-Fe system have been produced by arc-melting (stoichiometric compositions: Al2Fe, Al5Fe2 and Al13Fe4). The samples were heat treated at elevated temperatures and characterized using scanning electron microscopy, X-ray diffraction and inductive coupled plasma - optical emission spectrometry. Heat capacities were measured using independent heat flux differential scanning calorimeters in the temperature range from 223 K up to 1370 K. In general, the obtained data are lower than the estimations based on the Neumann-Kopp rule over a large temperature range. The heat capacity functions of the three intermetallic phases are represented by regression functions over the complete measured temperature intervals.

Phase Composition of Mechanically Alloyed Titanium and Iron Aluminides

Aluminides belong in these days group of materials, which can be used as a good replacement of stainless steels, for whom they owe attractive mechanical properties, or nickel superalloys, which are too heavy. These materials are used in aerospace industry as well as in automotive industry. Good corrosion and oxidation resistance and high specific strenght even up to high temperatures predict them to be also used for high temperature applications. In this paper, mechanical alloying was used. During mechanical alloying differences between TiAl and FeAl systems were seen. Iron aluminide formed single phased structure, whereas titanium aluminide formed preferentially two-phase structure.