FeAl Phase Research Articles

Mesoscale hetero-deformation induced (HDI) stress in FeAl-based metallic-intermetallic laminate (MIL) composites

Single-phase intermetallic FeAl layered material is synthesized using a layered foil approach to study the fracture mechanisms of FeAl-based metallic-intermetallic laminate (MIL) composites containing a similarly fabricated structure. The mechanical properties and crack evolution of the single-phase FeAl are investigated via incremental compression testing. Microstructure and composition assessment confirm a similar intermetallic layer laminate microstructure of single-phase FeAl and FeAl-based MIL composites. When compressed perpendicular to the layers, both materials fail by the axial splitting of the FeAl phase along the loading direction. Mesoscale hetero-deformation induced (HDI) stress, which is tensile on the FeAl layers of MIL composites, accelerates crack nucleation and crack propagation, eventually inducing failure. The HDI stress evaluated via finite element analysis (FEA) simulation provides an explanation for the difference between 430SS-FeAl and 304SS-FeAl MIL composites, which posses similar microstructure and composition, but very different strengths. When compressed parallel to the layers, mesoscale HDI stress is expected to be negligible, whereas the geometrically necessary dislocation (GND) pile-up induced HDI stress can enhance the performance of the composites. Fracture toughness is characterized via four-point bend testing, and the results demonstrate improvement of the FeAl-based MIL composites over the single-phase FeAl material.

Microstructure and Deformation Behaviour of Austenitic Low-Density Steels: The Defining Role of B2 Intermetallic Phase

The feasibility of significant weight reduction in conjunction with the superior strength-ductility combination makes Fe-Mn-Al-C-based steels the candidate material for automotive and structural applications. The alloy chemistry and processing conditions influence the microstructure in low-density steels (LDS); however, their role in deformation behaviour is not fully understood. In the present study, three different austenitic LDS grades viz. Fe-28Mn-9Al-0.9C, Fe-28Mn-9Al-5Ni-0.9C and Fe-15Mn-9Al-5Ni-0.9C alloys in hot-rolled conditions were used for evaluating the role of secondary phases, especially B2 ordered Fe(Ni)Al phase on deformation characteristics. Ni-free LDS microstructure consisted of the γ-matrix with fine κ-carbides, whereas Ni containing low Mn alloy possessed coarser κ-carbides along with B2 in both bamboo-like stringer and polygonal particle morphology in the γ-matrix. The B2 containing alloy exhibited higher strength with reduced tensile ductility than the B2-free alloy. Hardness of the γ-matrix and B2 phase were similar with B2 grains exhibiting distinct pop-in events in the nanoindentation curves indicating incipient plasticity. The γ-matrix and B2 co-deform near yield, and a favourable orientation relationship (OR) between the γ-matrix and B2 facilitated easy slip transfer, while the non-favourable OR controlled ductility by strain accumulation and B2-cracking. The differences in the strain hardening behaviour of B2-free and B2 containing alloys were elucidated based on the changes in dislocation substructure evolution examined by an automated crystal orientation mapping in electron microscopy.

Mechanical Parameters Response on Micro-Friction Stir Welding of AA6061 and SS304 Sheets

Friction stir welding is a contact welding process that uses the heat generated by friction to fuse two different materials. This work is focused on the development of micro-friction stir welding which is carried out for very thin sectioned materials of thickness 1000[Formula: see text][Formula: see text]m or less. Friction welded butt-joints were successfully produced for 0.8[Formula: see text]mm thin AA6061 and SS304 sheets on a semi-automated vertical milling machine using a zero-pin length tool. A mild steel backing plate is used as fixture mechanism to hold the welding sheets on machine. Tool-rotational speed and Tool-travel speed are the weld-parameters examined on mechanical responses such as tensile behavior, micro-hardness and surface-roughness across the nugget-weld zone interface. The maximum tensile strength is obtained at lower weld-parameters. Tensile strength properties of AA6061-T6/SS304 joints were approximately found to be 25% lower than that of the AA6061-T6 alloy base metal. Maximum hardness value of 93HV and minimum roughness value of 2.808[Formula: see text][Formula: see text]m are observed for higher tool speeds at nugget-weld zone interface due to the formation of intermetallic phases. Microstructural behavior is studied on weld-parameters using scanning electron microscope and energy dispersive X-ray analyzer. Very thin intermetallic layers (consisting of Fe2Al5, FeAl3 and FeAl2 phases) were observed in stainless steel/aluminum interface.

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

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

Synthesis and stability of quasicrystalline phase in Al-Cu-Fe-Si mechanically alloyed powders

The effect of Si addition on a quasicrystalline phase formation in Al-Cu-Fe-Si alloys prepared by mechanical alloying has been investigated using X-ray diffraction and scanning and transmission electron microscopy. Two compositions containing 10 at.% of Si were selected to verify the influence of the e/a ratio on a sequence of phase formation during milling: Al58.5Cu18Fe13.5Si10 (e/a = 1.98) and Al53.5Cu19.5Fe17Si10 (e/a = 1.75). A quasicrystalline icosahedral phase (i-phase) was found in both alloys after 10 h of milling in the form of nano-quasicrystallites with the size of 10–20 nm. Addition of Si stabilized the quasicrystalline phase being dominant after prolonged milling time, contrary to the reference ternary Al65Cu20Fe15 powder, which apart of the quasicrystalline phase contained the cubic β-Al(Cu, Fe) phase. Thermal stability of the quasicrystalline phase in the powders milled for 10 h was examined after annealing at 800 °C for 4 h. The i-phase was preserved partially in Al53.5Cu19.5Fe17Si10 and reference Al65Cu20Fe15 powders (both with a ratio e/a = 1.75), which coexisted with β-Al(Cu, Fe) and Al13Fe4 phase or α-Al55Si7Cu25.5Fe12 and Al2Fe3Si3 phases in Al65Cu20Fe15 and Al53.5Cu19.5Fe17Si10, respectively. For the Al58.5Cu18Fe13.5Si10 powders (e/a = 1.98), the annealing led to complete transformation of the i-phase to the cubic α-Al55Si7Cu25.5Fe12.5 approximant, forming crystallites with a size of 100–300 nm.Graphical abstract

Effect of Mg on the Formation of Periodic Layered Structure during Double Batch Hot Dip Process in Zn-Al Bath

The article presents the results of studies on the influence of Mg on the formation of the periodic layered structure of the Zn-AlMg coatings. These coatings were produced by the double batch hot dip method in a Zn bath and then in a Zn-Al(Mg) bath with a content of 15, 23, 31 wt.% Al and 3, 6 wt.% Mg. The microstructure of the coatings (OM, SEM) was revealed and the phase composition (XRD) obtained in two-component Zn-Al baths and Zn-AlMg baths were determined. The periodic layered structure was found to consist of alternating FeAl3 phase layers and a bath alloy (Zn + Al + Mg). Moreover, it was observed that the addition of 3 wt.% Mg reduces the thickness of the coating in baths containing 23 and 31 wt.% Al. However, the addition of 6 wt.% Mg causes complete disappearance of periodic layered structure in a bath with 23 wt.% Al. In a bath with a content of 31 wt.% Al the addition of 6 wt.% Mg creates a compact layer consisting of the FeAl3 phase containing the precipitation of the MgZn2 phase and Fe2Al5 phase. Such a structure of the coating transition layer limits the growth of the periodic layered structure in the coating.

Porous FeAl alloys via powder sintering: Phase transformation, microstructure and aqueous corrosion behavior

This study investigates the phase transformation and microstructure of porous FeAl parts sintered from elemental powder mixtures using in-situ neutron diffraction and in-situ thermal dilatometry. A single B2 structured FeAl phase was determined in the sintered FeAl alloy. The combined effects of the Kirkendall porosity, transient liquid phase, and phase transformations associated with powder sintering all contribute to the swelling phenomenon of the final sintered part. The aqueous corrosion test indicates that the corrosion products include iron oxides in the porous FeAl parts. The accumulation of corrosion products blocks the pore channel and decreases pore size and permeability over the soaking time.

The Effect of Fe Addition on Microstructure, Mechanical Properties and Electric Conductivity of the As-Cast Al-Mg-Si Alloys.

Fe is considered as one of the most harmful trace elements among impurities in aluminum and its alloys due to its influence of the mechanical properties especially in elongation. It is therefore essential that the Fe content is controlled to improve quality and the toughness of aluminum alloy castings. Since demand for high strength aluminum alloy casting was significantly increased in electro materials and devices, automotive and airplane industries, it is necessary to characterize the effect of Fe and set the tolerable amount of Fe content in aluminum alloys. Al6061 alloys were prepared with compositions of 0.36, 0.45, 0.58, 0.65, 0.75, 0.81 and 0.91 wt.% Fe. Solidification characteristics were analyzed by CALPHAD (Pandat software) method. Mechanical properties such as hardness, tensile strength, elongation and fatigue strength were evaluated and compared with different Fe contents. Al13Fe₄ phase increased with increasing as Fe content, however, other phases, α-AlFeSi and Mg₂Si, showder a slight decrease. The higher the Fe content, the lower the electrical conductivity of the alloy due to the severe distortion of the Al matrix. As Fe content was more than specification of Al6061 alloy, 0.7 wt.%, the mechanical properties, especially, hardness and elongation were greatly influenced. The hardness is attributed to the poor densification and angular-shaped Al13Fe₄ phases unevenly distributed in the α-Al matrix.

Phase Composition of Al-Si Coating from the Initial State to the Hot-Stamped Condition.

The chemical and phase composition of the coating and the coating/substrate interface of an Al-Si-coated 22MnB5 hot stamped steel was investigated by means of SEM-EDS, XRD, micro-XRD and electron diffraction. Moreover, the surface profile was analyzed by XPS and roughness measurements. The XPS measurements showed that the thickness of the Si and Al oxide layers increased from 14 to 76 nm after die-quenching, and that the surface roughness increased as well as a result of volume changes caused by phase transformations. In addition to the FeAl(Si) and Fe2Al5 phases and the interdiffusion layer forming complex structures in the coating, electron diffraction confirmed the presence of an Fe2Al5 phase, and also revealed very thin layers of Fe3(Al,Si)C, Fe2(Al,Si)5 and Al-bearing rod-shaped particles in the immediate vicinity of the steel interface. Moreover, the scattered nonuniform layer of the Fe2Al8Si phase was identified in the outermost layer of the coating. Despite numerous studies devoted to researching the phase composition of the Al-Si coating applied to hot stamped steel, electron diffraction revealed very thin layers and particles on the coating/substrate interface and outermost layer, which have not been analyzed in detail.

First-principles study of tensile and shear strength of an Fe2Al5//Fe interface

The interfacial strengths of a low misfit Fe2Al5//Fe interface structure found at aluminum-steel joints has been studied using density functional theory. An interface between Fe and Fe2Al5 was selected based on a criteria of low lattice misfit and number of atoms. Through virtual tensile testing of bulk Fe2Al5 and the interface structures we show that the energy-displacement curve can be well described by including extra polynomial terms in the Universal Binding Energy Relation (UBER). It is shown that the Fe2Al5//Fe interface has a higher tensile strength than the bulk Fe2Al5 phase. We also find that the shear deformation process potentially can be initiated from an Fe-terminated interface.

Influence of Compositionally Graded Interface on Microstructure and Compressive Deformation of 316L Stainless Steel to Al12Si Aluminum Alloy Bimetallic Structures.

Bimetallic structures offer properties that can be customized based on applications, manufactured in one operation. Such manufacturing options are fascinating, as joining two metallic materials, especially for two dissimilar metals without significant defects, is challenging. In this study, 316L stainless steel (SS) to Al12Si aluminum alloy structures were processed, tailoring the compositionally graded interface on a SS 316 substrate using a directed energy deposition (DED)-based additive manufacturing (AM) process. Applying such a compositionally graded transition for joining two dissimilar metals could mitigate the mismatch of mechanical and thermal properties. This study's objective was to understand the processing parameters that influence the properties of AM processed SS 316L to Al12Si bimetallic structures. Two different approaches were used to fabricate these bimetallic structures. The results showed no visible defects on the as-fabricated samples using four layers of Al-rich mixed composition as the transition section. The microstructural characterization showed a unique morphology in each section. The microstructural variation was caused due to various processing parameters such as laser power, powder feed rate, and laser scan speed. FeAl, Fe2Al5, and FeAl3 intermetallic phases were formed at the compositionally graded transition section. After stress relief heat treatment of the bimetallic samples, diffused intermetallic phases were seen at the compositionally graded transition. At the interface, as processed bimetallic structures had a microhardness value of 834.2 ± 107.1 HV0.1, which was a result of the FeAl3 phase at the compositionally graded transition area. After heat treatment, the microhardness value reduced to 578.7 ± 154.1 HV0.1 because of a more Fe-dominated FexAly phase formation. Compression test results showed that the non-HT and HT SS 316L/Al12Si bimetallic structures had a similar maximum compressive strength of 299.4 ± 22.1 MPa and 270.1 ± 27.1 MPa, respectively. These results demonstrated that the applied heat treatment conditions only had a minor impact on samples' compression strength.

Influence of Cr, Mn, Co and Ni Addition on Crystallization Behavior of Al13Fe4 Phase in Al-5Fe Alloys Based on ThermoDynamic Calculations.

Alloying is an effective method to refine coarse grains of an Al13Fe4 phase and strengthen Al-Fe alloys. However, the grain refinement mechanism remains unclear in terms of the thermodynamics. Herein, the influence of M-element, i.e., Cr, Mn, Co and Ni, addition on the activity of Al and Fe atoms, Gibbs free energy of the Al13Fe4 nucleus in Al-Fe melt and the formation enthalpy of an Al13Fe4 phase in Al-Fe alloys is systematically investigated using the extended Miedema model, Wilson equation, and first-principle calculations, respectively. The results reveal that the addition of different M elements increases the activity of Fe atoms and reduces the Gibbs free energy of the Al13Fe4 nucleus in Al-Fe melt, where the incorporation of Ni renders the most obvious effect, followed by Mn, Co, and Cr. Additionally, the formation enthalpy decreases in the following order: Al78(Fe23Cr) > Al78(Fe23Mn) > Al13Fe4 > Al78(Fe23Ni) > Al78(Fe23Co), where the formation enthalpy of Al78(Fe23Ni) is close to Al78(Fe23Co). Moreover, the presence of Ni promotes the nucleation of the Al13Fe4 phase in Al-Fe alloys, which reveals the mechanism of grain refinement from a thermodynamics viewpoint.

Fe addition influence on the mechanical and thermophysical behaviours of PM Alumix 431 alloy

We investigated Alumix 431 alloy powder mixed with Fe element with a ratio of 2.5, 5 and 10 (wt%) using powder metallurgy method (PM) and sintered at 610°C temperature for an hour under N2 gas atmosphere. The structural and morphological properties of Alumix 431-2.5, 5 and 10 Fe (wt%) mixtures determined using x-ray diffraction (XRD), optical microscope (OM), and scanning electron microscopy (SEM). XRD data showed that dominant α-Al phases mixed with increasing Fe content and resulted in a peak shift in the alloy. SEM images revealed Al/Al-rich areas and intermetallic phases such as Fe-Al, Al13Fe4, Fe2Al5, and Al7Cu2Fe mixtures as well as cracks and grain boundaries. The mechanical and thermophysical properties of the alloys studied and maximum hardness value obtained with a mixture of 10% Fe mixture as 28.46 HB. Maximum bulk density, minimum porosity, and water adsorption values of mixtures were obtained on the Alumix 431-10% Fe mixtures which are 2.50 g/cm3, 7.60%, and 3.03%, respectively. The maximum specific heat capacity and enthalpy values were found to be 1.94 J/g°C at 400°C temperature for the Alumix 431-2.5% Fe and 886.48 J/g at 595°C for Alumix 431-10% Fe mixtures. These results showed that the mixture of the Alumix 431-Fe alloy improved the mechanical and thermophysical properties due to PM method, Al-based and Al-Fe phase formations such as Al7Cu2Fe and Al2CuMg phases.

Roles of the semisolid heating on the microstructure of a hypereutectic Al\u2013Fe\u2013Cu alloy

A hypereutectic Al–Fe–Cu alloy with a high-volume fraction ferro-aluminum second phase (AlFe phases for short) was reheated in the solid–liquid region and the microstructure evolution was investigated. During semisolid heating, the high-melting AlFe phases in the Al–Fe–Cu alloy were demonstrated to stunt the grain growth and to block the liquid coalescing and the solid moving. Consequently, the grain sizes in the alloy increased rapidly and then slowly with increasing holding time, and the grains increased gradually with increasing temperature. Smaller grain grew into the large grain but it did not continually grow into the larger grain with increasing temperature or holding time. The shape factor (SF) of the alloy increased gradually and then decreased quickly with increasing temperature or holding time. The major alloying elements in addition to magnesium in the hypereutectic Al–Fe–Cu alloy were finally enriched at the grain boundaries or around the AlFe phases. Besides dissolving in the grains or AlFe phases, copper also diffused between the grains or around AlFe phases, resulting in the formation of diverse Cu-enriched zones. Cu constituents in the inter-grains are outnumbered in the intra-grains. The coarsening kinetics of the alloy was controlled by grain boundary diffusion. The coarsening rate constants K in the initial stage of heating (5–20 min) were several times larger than that in the later stage of heating (20–60 min), indicating the blocking effect of AlFe phases on coarsened grain being obvious.

Growth dynamics of faceted Al13Fe4 intermetallic revealed by high-speed synchrotron X-ray quantification

High-speed synchrotron tomography was used to investigate the nucleation and growth dynamics of Al13Fe4 intermetallic during solidification of an Al-5wt%Fe alloy, providing new insights into its formation process. The majority of Al13Fe4 intermetallics nucleated near the surface oxide of the specimen and a few nucleated at Al13Fe4 phase. Al13Fe4 crystals grew into a variety of shapes, including plate-like, hexagonal tabular, stair-like and V-shaped, which can be attributed to the crystal structure of this compound and its susceptibility to twinning. Hole-like defects filled with aluminium melt were observed within the intermetallics. Oriented particle attachment mechanism was proposed to explain the formation of the Al13Fe4 intermetallic, which needs further experiments and simulation to confirm.

Effect of the upset pressure on Microstructure and Properties of Friction Welded Joints of 6082 aluminum alloy/304 stainless steel

The dissimilar connection between 6082 aluminum alloy and 304 stainless steel was realized by continuous drive friction welding. Microstructures of the joint were studied by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffractometry (XRD). In the process of continuous drive welding, the intermetallic compounds (IMCs) Fe2Al5 phase was observed at the interface, the formation mechanism of IMC was discussed, and the corresponding analysis model was established. When the upset pressure in the range of 6–10 MPa, the element diffusion distance increases with the increase of upset pressure. The tensile strength of the joint increased firstly and then decreased with the increase of upset pressure. The joint’s maximum tensile strength can reach 234 MPa, and tensile fracture of the joint exhibited brittle-tough mixed fracture characteristics.

Improved interface bonding of Mg/aluminized steel bimetallic castings prepared by solid–liquid compound casting process

ABSTRACT The effect of pouring temperature on microstructure and bonding properties of the Mg/aluminised steel bimetallic castings prepared by the solid–liquid compound casting process was investigated in this paper in order to improve the interface bonding of the Mg/aluminised steel bimetallic castings. The results show that the Mg/aluminised steel bimetallic castings produced with different pouring temperatures obtained a uniform interface layer that was mainly composed of the Fe2Al5, τ10-Al9Fe4Si3, FeAl3 and Al12Mg17 phases. When the pouring temperature was low, the cracks were formed between the Mg and the interface layer. With increasing pouring temperature, a compact interface bonding was achieved. The bonding properties of the Mg/aluminised steel bimetallic castings increased with increasing pouring temperature. An optimised bonding of the Mg/aluminised steel bimetallic castings was obtained with a pouring temperature of 780°C.

Nucleation and growth of Fe-rich phases in Al-5Ti-1B modified Al-Fe alloys investigated using synchrotron X-ray imaging and electron microscopy

Plate-like Fe-rich intermetallic phases directly influence the mechanical properties of recycled Al alloys; thus, many attempts have been made to modify the morphology of these phases. Through synchrotron X-ray imaging and electron microscopy, the underlying nucleation and growth mechanisms of Fe-rich phases during the solidification of Al-5Ti-1B-modified Al-2Fe alloys were revealed in this study. The results showed that the Al-5Ti-1B grain refiner as well as the applied pressure both resulted in reduction of the size and number of primary Al3Fe phases and promoted the formation of eutectic Al6Fe phases. The tomography results demonstrated that Al-5Ti-1B changed the three-dimensional (3D) morphology of primary Fe-rich phases from rod-like to branched plate-like, while a reduction in their thickness and size was also observed. This was attributed to the fact that Ti-containing solutes in the melts inhibit the diffusion of Fe atoms and the Al3Fe twins produce re-entrant corner on the twin boundaries along the growth direction. Moreover, the TiB2 provides possible nucleation sites for Al6Fe phases. The nucleation mechanism of Fe-rich phases is discussed in terms of experimental observations and crystallography calculations. The decrease in the lattice mismatch between TiB2 and Al6Fe phases was suggested, which promoted the transformation of Al3Fe to Al6Fe phases.

Síntesis y caracterización estructural del compuesto de refuerzo de Ti+Ni3Al+Al2O3 a base de Fe producido por aleación mecánica

La mezcla de polvo de Ti+Ni3Al+Al2O3 a base de Fe se alea mecánicamente en un molino de bolas Spex. Los compuestos con adición de Ti+Ni3Al+Al2O3 a base de Fe se produjeron a una temperatura de sinterización de 1000 °C durante un tiempo de 1 h. Las propiedades de estos compuestos se examinaron mediante microscopía electrónica de barrido (SEM), microscopía óptica (OM), espectroscopía de dispersión de energía (EDS), difracción de rayos X (XRD) y análisis de microdureza. El producto final producido por aleación mecánica fue una solución sólida rica en níquel nanocristalina, el tamaño promedio del cristal era de unos pocos nanómetros. El contenido de titanio en el refuerzo aumentó los valores de microdureza del composite. Los compuestos producidos incluían las fases Fe3Al, TiAl, NiAl, Al3Ni2, Al2O3 y Fe3O.

In-situ oxidation of aluminized stainless-steel to form alumina as tritium permeation barrier coating

Tritium permeation barrier (TPB) coating technology is one of the most effective methods to solve the problem of permeation and leakage of tritium through the structural materials to the coolant, environment, and other functional components in tritium breeder blanket modules (TBMs). Alumina coatings prepared by in-situ oxidation of aluminized steel shows a high permeation reduced factor (PRF) and self-healing ability. However, to eliminate the Al5Fe2 phase in the aluminizing process, the stainless-steel substrate is often heat treated under high temperature conditions for a long time which leads to the degeneration of steel. In this work, a gradient alumina TPB coating was prepared on 316 L stainless steel by aluminizing process at low temperature. The influence of Al5Fe2 on the formation of Al2O3 is studied. The mechanism for the different growth behavior of Al2O3 in the polished and unpolished samples is also discussed. Compared to the polished samples, the existence of porous Al5Fe2 layer in unpolished sample changes the diffusion behavior of Al and leads to the formation of an un-continuous and rough Al2O3 layer.