Fe-Al System Research Articles

The influence of different additives on the kinetics of self-propagating high-temperature synthesis during the sintering process of Fe and Al elemental powders

The influence of small additions of Mg, Ti, and their hydrides on the kinetics of the Self-propagating High-temperature Synthesis (SHS) reaction during sintering of iron and aluminum elemental powders was investigated using the DSC technique and XRD analysis. It was observed that the additives have a significant effect on the SHS reaction parameters. The start of the SHS reaction in a Fe–Al system containing additives (especially with Mg and MgH 2) is shifted to lower temperatures as compared with that of an undoped Fe–Al system. The influence of these additives is also visible from changes in the Avrami exponent and the activation energy value of specific phase formation from the Fe–Al equilibrium system. Furthermore, additives cause a change of intensity of the SHS reaction, which should allow control of the degree of sintering porosity.

A Study of Point Defects in the B2-Phase Region of the Fe–Al system by Mössbauer Spectroscopy

In this work, we employed the Mössbauer spectroscopy in a study of point defect formation in intermetallic phases of the B2 structure from the Fe-Al system as a function of Al concentration. We present the values of the 57Fe isomer shift and quadruple splitting for the components describing the point defect in the local environment of a Mössbauer nuclide. The concentration of the Fe vacancies and Fe atoms substituting Al (Fe-AS) are determined. The results shown that an increase in Al content causes an increase in vacancy and Fe-AS

The effect of Ti addition on alloying and formation of nanocrystalline structure in Fe–Al system

In this work, the effect of Ti addition on alloying and formation of nanocrystalline structure in Fe–Al system was studied by utilizing mechanical alloying (MA) process. Structural and morphological evolutions of powder particles were studied by X-ray diffractometry, microhardness measurements, and scanning electron microscopy. In both Fe75Al25 and Fe50Al25Ti25 systems MA led to the formation of Fe-based solid solution which transformed to the corresponding intermetallic compounds after longer milling times. The results indicated that the Ti addition in Fe–Al system affects the phase transition during mechanical alloying, the final crystallite size, the mean powder particle size, the hardness value and ordering of DO3 structure after annealing. The crystallite size of Fe3Al and (Fe,Ti)3Al phases after 100 h of milling time were 35 and 12 nm, respectively. The Fe3Al intermetallic compound exhibited the hardness value of 700 Hv which is significantly smaller than 1050 Hv obtained for (Fe,Ti)3Al intermetallic compound.

Modified embedded-atom method interatomic potential for the Fe–Al system

An interatomic potential for the Fe–Al binary system has been developed based on themodified embedded-atom method (MEAM) potential formalism. The potential can describevarious fundamental physical properties of Fe–Al binary alloys—structural, elastic andthermodynamic properties, defect formation behavior and interactions between defects—inreasonable agreement with experimental data or higher-level calculations. The applicabilityof the potential to atomistic investigations of various defect formation behaviors and theireffects on the mechanical properties of high aluminum steels as well as Fe–Al binary alloysis demonstrated.

Investigation of the ε phase in the Fe–Al system by high-temperature neutron diffraction

In the central part of the Fe–Al system between about 58 and 65 at.% Al, a high-temperature phase denoted as e occurs with a hitherto unknown crystallographic structure. The phase is stable between 1231°C and 1095°C. In order to study the crystallographic structure of the e phase, in situ high-temperature neutron time-of-flight diffraction experiments have been performed at the HIPPO instrument at the Los Alamos Neutron Science Center (LANSCE). The e phase was found to have the formula Fe5Al8 with a body-centred cubic structure of the Hume–Rothery Cu5Zn8 type (I\(\bar{4}3\)m (No. 217), Z=4, cI52) and 52 atoms in the unit cell. Its lattice parameter is a=8.9756(2) A at 1120°C, which is 3.02 times that of cubic FeAl (B2) at the same temperature. We report here the evolution of the crystallographic parameters over the temperature range between 1080°C and 1120°C.

Effect of carbon addition on the single crystalline magnetostriction of Fe-X (X=Al and Ga) alloys

The effect of carbon addition on the magnetostriction of Fe–Ga and Fe–Al alloys was investigated and is summarized in this study. It was found that the addition of carbon generally increased the magnetostriction over binary alloys of Fe–Ga and Fe–Al systems. The formation of carbide in the Fe–Ga–C alloys with a composition near D03 phase region decreased the magnetostriction drastically. Fe–Al–C and Fe–Ga–C alloys responded differently to thermal treatments; the magnetostriction in the quenched Fe–Al–C alloys is equal to or slightly lower than that of the slow cooled as is observed in binary Fe–Al alloy; in contrast, the magnetostriction is generally higher in quenched Fe–Ga–C alloys than slow cooled condition, consistent with the behavior of binary alloys of Fe–Ga. A significant increase in magnetostriction between 25% and 165% depending on the phase region in Fe–Ga–C alloys by quenching was observed in the A2+D03 two-phase region and D03 single phase region.

A Study of Point Defects in the B2-Phase Region of the Fe-Al System by Mössbauer Spectroscopy

In this work, Mössbauer spectroscopy and X-ray powder diffraction (XRD) are used in a study of point defect formation in intermetallic phases of the B2 structure of the Fe-Al system as a function of Al concentration. The results are compared with the concentrations of point defect determined from positron annihilation data. In the Mössbauer effect, two types of samples are investigated: Fe-Al alloys with few additives obtained by induction melting and Al-rich metallic powders produced by the self-decomposition method and intensive grinding of high energy in the electro-magneto-mechanical mill. The work presents the values of the 57Fe isomer shift and quadruple splitting for the components describing the point defect in the local environment of a Mössbauer nuclide. The concentration of the Fe vacancies and Fe atoms substituting Al (Fe-AS) are determined. The results show that an increase in Al content causes an increase in vacancy and Fe-AS concentration.

Positron annihilation study of vacancies in Fe–Al based alloys

In the present contribution, high-resolution positron lifetime and coincidence Doppler broadening spectroscopies are used to characterize defects in Fe 76Al 24 and Fe 72Al 28 alloys. In order to facilitate defect identification, we also perform a theoretical study of basic vacancy-like defects in three phases of the Fe–Al system: ordered, short-range ordered, and disordered. Positron characteristics, like positron lifetime, positron binding energy to defects, high-momentum parts of Doppler broadening curves and specific trapping rates, are calculated for various defect configurations. The results are discussed in the context of experimental data obtained here and available in literature.

Isothermal section of the Er–Fe–Al ternary system at 800 °C

Abstract Physico-chemical analysis techniques, including X-ray diffraction and Scanning Electron Microscope–Energy Dispersive X-ray Spectroscopy, were employed to construct the isothermal section of the Er–Fe–Al system at 800 °C. At this temperature, the phase diagram is characterized by the formation of five intermediate phases, ErFe 12− x Al x with 5 ≤ x ≤ 8 (ThMn 12 -type), ErFe 1+ x Al 1− x with −0.2 ≤ x ≤ 0.75 (MgZn 2 -type), ErFe 3− x Al x with 0.5 x ≤ 1 (DyFe 2 Al-type), Er 2 Fe 17− x Al x with 4.74 ≤ x ≤ 5.7 (TbCu 7 -type) and Er 2 Fe 17− x Al x with 5.7 x ≤ 9.5 (Th 2 Zn 17 -type), seven extensions of binaries into the ternary system; ErFe x Al 3− x with x 3 Cu-type), ErFe x Al 2− x with x ≤ 0.68 (MgCu 2 -type), Er 2 Fe x Al 1− x with x ≤ 0.25 (Co 2 Si-type), ErFe 2− x Al x with x ≤ 0.5 (MgCu 2 -type), ErFe 3− x Al x with x ≤ 0.5 (Be 3 Nb-type), Er 6 Fe 23− x Al x with x ≤ 8 (Th 6 Mn 23 -type), and Er 2 Fe 17− x Al x with x ≤ 4.75 (Th 2 Ni 17 -type) and one intermetallic compound; the ErFe 2 Al 10 (YbFe 2 Al 10 -type).

Determination of the crystal structure of the ɛ phase in the Fe–Al system by high-temperature neutron diffraction

The crystal structure of the high-temperature ɛ phase of the Fe–Al system has been determined by in-situ high-temperature neutron diffraction for the first time and the crystallographic parameters have been established by Rietveld refinement of the data. The ɛ phase was found to have a body-centered cubic structure of the Hume-Rothery Cu 5Zn 8-type (space group I 4 ¯ 3 m (No. 217), Z = 4, Pearson symbol cI52, Strukturbericht designation D8 2). Accordingly, the ε phase has the formula Fe 5Al 8. Its lattice parameter is a = 8.9757(2) Å at 1120 °C, which is 3.02 times that of cubic FeAl (B2) at the same temperature. All fractional atomic coordinates, site occupation factors and interatomic distances were determined and it was examined how this phase can meet the rules for Hume-Rothery-type phases.

Thermodynamic Description of the Al-Mo and Al-Fe-Mo Systems

The Al-Mo and Al-Fe-Mo systems were critically assessed using the CALPHAD technique. The solution phases (liquid, fcc and bcc) were described by a substitutional solution model. The non-stoichiometric compound AlMo3 was described by a two-sublattice model (Al,Mo)(Al,Mo)3 in the Al-Mo binary system and (Al,Fe,Mo)(Al,Fe,Mo)3 in the Al-Fe-Mo ternary system. Other compounds Al63Mo37, Al8Mo3, Al3Mo, Al4Mo, Al17Mo4, Al22Mo5, Al12Mo and Al5Mo in the Al-Mo system were treated as stoichiometric compounds in the binary system and as line compounds Alm(Fe,Mo)n in the Al-Fe-Mo ternary system. The compounds μ and Fe2Mo in the Fe-Mo system were treated as (Al,Fe)7Fe2(Fe,Mo)4 and (Fe,Mo)2(Al,Mo) in the Al-Fe-Mo system, respectively. Compounds Al5Fe4, Al2Fe, Al5Fe2 and Al13Fe4 in the Al-Fe system were treated as (Al,Fe,Mo), Al2(Fe,Mo), (Al,Fe)5(Al,Fe,Mo)2 and (Fe,Mo)0.235Al0.6275(Al,Va)0.1375 in the Al-Fe-Mo system, respectively. Ternary compounds τ1 and τ2 were treated as Al8(Al,Fe)Mo3 and (Al,Fe,Mo)(Va)3, respectively. A set of self-consistent thermodynamic parameters of the Al-Fe-Mo system was obtained.

Thermodynamic assessment of the Fe–Al–Zr phase diagram

The thermodynamic assessment of the Fe–Al–Zr ternary system was performed using the CALPHAD technique. The four published isothermal sections at 1073, 1173, 1273 and 1423 K, together with the proposed liquidus surface and the corresponding invariant reaction scheme, were taken into account. The reliability of the previous binary assessments was checked for the systems of interest, namely, for the Fe–Zr, Zr–Al and Fe–Al systems. Reassessment of the C15 Laves phase of the Fe–Zr system has been done to obtain a better description of the phases in the ternary system. The solution phases, including liquid, α -Fe, γ -Fe, α -Zr, β -Zr and γ -Al, were modelled as substitutional solutions, while the new ternary phases ( τ 1 , τ 2 and τ 3 ) were modelled as linear and stoichiometric compounds, respectively. The C14 and C15 Laves phases have been assessed using a two-sublattice model. Any ternary solubility of the other binary phases was not taken into account in the ternary assessment. The liquidus projection and several isothermal sections were calculated, and they agreed reasonably well with the reported experimental data.

Structure and plasticity in hot deformed FeAl intermetallic phase base alloy

This paper constitutes part of research conducted on the possibility of forming alloys based on intermetallic phases from the Fe–Al system via thermoplastic processing. Insufficient plasticity, which is an inhibitor of further development of these intermetallics as construction materials, makes the range of their applications limited. In the paper, an analysis is conducted of the influence of deformation parameters on the structure of an alloy of Fe–Al with the B2 type structure. Axi-symmetric compression tests were carried out at temperatures ranging from 600 °C to 1200 °C and at a deformation rate from 0.001 s 1 to 10 s − 1 . Structural examination was carried out using light microscopy and transmission electron microscopy. A quantitative evaluation of the structure was made with the use of “Met-Ilo”. The results obtained will be used for the development of mathematical models determining the influence of deformation parameters on the alloy structure.

Numerical Determination of Intrinsic Diffusion Coefficient of Aluminide Coatings on Metals

This paper presents a numerical method to determine the composition dependent diffusivities and to predict the concentration profile during the interdiffusion process. The intrinsic diffusion coefficients in diffusion aluminide coatings (Fe-Al) were determined at 1000oC. The obtained diffusion coefficient for iron in Fe3Al or FeAl is in the range 10-10 to 10-9 cm2.s-1. The aluminum diffusion coefficient varies from 10-11 to 10-7 cm2.s-1 in the same phases.The present approach also permits to model the reactive diffusion in the Fe-Al systems.

An assessment of the entire Al–Fe system including D0 3 ordering

The Al–Fe system is important for many alloys and the new interest in iron aluminides makes it necessary to improve the modeling of the different ordered forms on the body-centered cubic lattice in this system. This has now been done using a four-sublattice model based on the compound energy formalism, which can describe disordered A2 and the B2, D 0 3 and B32 ordering. The chemical and ferromagnetic ordering transitions can be both first and second-order and they have a strong interaction. Almost all available experimental and theoretical data for all phases in the system have been fitted within estimated uncertainties.

Thermodynamic re-assessment of the Fe-Al-C system based on the Fe-rich experimental data

The influence of C and Al content on phase transformation temperatures, i.e., the A1 and A3 of Fe-rich alloys is investigated by dilatometric analysis. With the new set of experimental data, an updated thermodynamic description of the Fe-Al-C system is presented, by using the thermodynamic data of the Fe-C, Fe-Al and Al-C systems, as well as the parameters for the Fe-Al-C ternary system optimized in this study. The good compatibility of the thermodynamic parameters with experimental data is demonstrated by several calculated vertical sections. A well reproduced vertical section of the Fe-Mn-Si-Al-C system is also presented according to the thermodynamic description of the lower order systems.

Structural Defects Formed in Alloy Layers of Fe–Al System by Diffusion in Air

The aluminizing process is performed in air at 1173K after the aluminum has been bonded to a carbon steel S45C surface by hot dipping or pressure bonding, Al-rich alloy layers are first formed by diffusion of Al into the steel, but as the diffusion progresses, these layers become Fe-rich. However, each of the alloy layers is found to contain structural defects. In this work, the nature of these defects has been studied by EPMA and XRD analysis. It was found that void-like defects formed during the early stages of diffusion were mainly a combination of Al2O3 with voids and Al2O3, and that the band-like defects formed at later stages in the boundary region between FeAl and αFe were mainly composed of Al2O3. These Al2O3 formations are most likely the result of oxygen penetrating into Kirkendall voids and subsequently reacting with Al.

A Study of Point Defects in the B2-Phase Region of the Fe-Al System by Mössbauer Spectroscopy

A Study of Point Defects in the B2-Phase Region of the Fe-Al System by Mössbauer Spectroscopy

Point defect structure in B2-ordered Fe–Al alloys

In this work, Mössbauer spectroscopy and X-ray powder diffraction (XRD) have been employed to study various types of the point defect formation in B2-structured intermetallic phases of the Fe–Al system as a function of Al concentration. We present the values of the 57Fe isomer shift and quadruple splitting for the components describing the point defect in the local environment of a Mössbauer nuclide. The concentrations of Fe vacancies and anti-site Fe atoms substituting Al (Fe-AS) are determined. The results show that an increase in Al content causes an increase in vacancy and Fe-AS concentrations.

Magnetic moment of iron atoms in Fe-Al body-centered cubic alloys as a function of the nearest environment

The Fe-Al systems in the concentration range from 29 to 44 at. % Al are investigated in terms of the density functional theory. It is shown that, in the system under consideration, there can exist three magnetic states with close energies. Two of these three magnetic states have collinear magnetic moments (the ferromagnetic and antiferromagnetic states), and the third is a spin-spiral state. In collinear magnetic structures, the local magnetic moments are determined by the nearest chemical environment and, in the antiferromagnetic state, the iron atoms surrounded by a large number of aluminum atoms in their environment have a negative magnetic moment. The results obtained substantiate the applicability of modified models of the Jaccarino-Walker type for the interpretation of the experimental data obtained for Fe-Al alloys. The results of the calculations also indicate a significant role of Stoner excitations in the formation of magnetic order in these alloys.