Intermetallic FeAl Research Articles

Effect of Fe-Al intermetallics on fatigue properties of aluminum to steel dissimilar spot welds

Lightweight structures made of aluminum alloys and high strength steels are increasingly used for improving vehicle fuel efficiency. One barrier for joining aluminum and steel is the formation of brittle Fe-Al intermetallics that can have deleterious effects on joint ductility and strength under static loading conditions. However, it is unclear how the intermetallics affect the joint fatigue properties. In this study, the effect of intermetallics on fatigue properties of dissimilar metal joints between a 6xxx aluminum alloy and a high-strength steel is investigated on welds created by ultrasonic interlayered resistance spot welding (Ulti-RSW). Joint efficiency calculations are used to normalize the peak load so the fatigue properties of Ulti-RSW are compared with a wide range of joining processes in the literature. During fatigue testing the failure mode transitions from interfacial or button pull-out failure during low cycle fatigue loading (below 100,000 cycles) to through-thickness failure during high cycle (above 100,000 cycles). Based on the stress intensity factors calculated using a simple 2D fracture mechanics model, the transition in failure mode is attributed to the plastic deformation near the notch tip. Overall, this study shows that the intermetallics have little effect on the high-cycle fatigue properties of dissimilar spot joints.

Detonation coatings produced by spraying of alloyed powders based on Fe–Al intermetallics

Detonation coatings produced by spraying of alloyed powders based on Fe–Al intermetallics

Superior corrosion resistance of a slurry FeAl coating on 316LN stainless steel in 550 ℃ liquid lead-bismuth eutectic

An intermetallic Fe-Al coating was successfully produced on 316LN austenite stainless steel by slurry Aluminizing. The coating greatly enhanced the corrosion resistance of substrate in LBE (lead-bismuth eutectic) containing low (10−7 wt%) and high (1.8 ×10−3 wt%) oxygen concentrations at 550 ℃ and the coating was mostly intact after 1500 h exposure test. The high corrosion resistance results from the formation of a uniform layer of alumina oxide on the coating which can be achieved when the dissolved oxygen is above 10−18 wt%. This FeAl coating maybe a promising option for protecting structure material in the fourth LBE-cooled fast reactor.

INVESTIGATION OF CORROSION BEHAVIOR OF AISI 304 AND AISI 316L STAINLESS STEELS COATED WITH FeAL AND NiAL INTERMETALLICS USING ELECTRO-SPARK DEPOSITION METHOD

Due to their superior corrosion resistance at high temperatures, stainless steels have a wide range of applications in numerous industries (including chemistry, the petrochemical industry, the paper industry, and nuclear engineering), it is also utilized in the medical industry as an implant material. To enhance the outstanding qualities of stainless steel such as high temperature corrosion, surface coating methods are also used. Boronizing, nitriding, thermal spray coating, physical vapor deposition, chemical vapor deposition, and electro-spark deposition procedures are used to apply these coating processes to steel surfaces. The electro-spark deposition (ESD) coating technology is one of the most promising approaches in this area. Using high-frequency and high-current electric pulses, the ESD micro-welding procedure bonds electrode material to the surface of a metallic substrate. In this study, AISI 304 and AISI 316L stainless steels were coated with FeAl and NiAl intermetallics using the ESD method. First, suitable experimental parameters for ESD coating were established. Second, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the microstructures and phases that formed on the coated surfaces. Then, the surface hardness of the resulting layers was determined. Finally, the corrosion properties of intermetallic-coated stainless steels were determined using electrochemical methods and compared with each other. As a result, both the hardness values and corrosion resistances of both stainless steel sheets have increased with intermetallic coatings.

Influence of carbon content on static recrystallization behavior of 50% cold-rolled Fe-18Mn-9Cr-2Al-xC steels

Recrystallization behavior during annealing at various temperatures was investigated for 50% cold-rolled Fe-18Mn-9Cr-2Al-xC steels with C contents varying between 0 and 0.5 wt%. Nucleation of recrystallization occurred near randomly in the carbon-free steel, whereas increasing the carbon contents promoted preferential nucleation at carbides formed along the grain boundaries through the particle stimulated nucleation mechanism. New grains in the carbon-free steel grow freely at the expense of deformed grains until the end of recrystallization during which migration of recrystallization front was blocked by the elongated δ-ferrites. For the carbon-added steels, on the other hand, (Cr,Mn)23C6 carbides and FeAl intermetallics formed during annealing and pre-existing carbides at grain boundaries pinned the recrystallization front, and thereby suppressing the growth of new grains and developing a distinct necklace structure. Recrystallization of the carbon-added steels completed only after carbides were dissolved at higher temperatures around 900 °C. It is noteworthy that it is not the carbon atom itself in solid solution but carbides that promotes nucleation of recrystallization and subsequently suppressed growth of new grains. It was also found that tensile properties of the cold-rolled steels restored nearly to those prior to cold rolling, i.e., in as-annealed state. It is concluded that recrystallization kinetics, special distribution of new grains, and texture of the cold-rolled Fe-18Mn-9Cr-2Al-xC steels are significantly affected by the carbon contents. In addition, restoration of tensile properties of cold-rolled steels by recrystallization suggests that many repetitive thermomechanical processing are applicable to the steels for forming into a desire shape.

Identifying intrinsic factors for ductile-to-brittle transition temperatures in Fe–Al intermetallics via machine learning

The determination of ductile-to-brittle transition temperatures (DBTT) in intermetallic compounds is crucial for assessing their practical applications. In this study, we investigate the intrinsic factors influencing the DBTT of Fe–Al intermetallic compounds through feature engineering. We developed and evaluated two machine learning strategies for this task. Comparing the strategy that incorporates all features, including alloy compositions and atomic features, with the strategy utilizing selected features, it is found that the latter demonstrates superior computational efficiency and reduces overfitting. Specifically, surrogate models based on two selected features, namely cohesive energy and ionization energy, enable accurate prediction of the DBTT of Fe–Al intermetallics, achieving an accuracy of 95%. Additionally, through symbolic regression, we derived a functional expression that captures the relationship between variations in the DBTT and the selected features of intermetallic compounds. These findings have the potential to serve as a valuable guide for optimizing intermetallic compounds.

Fabrication of a Porous Fe–Al Intermetallic Alloy with Ultrahigh Open Porosity

Herein, a porous Fe–Al intermetallic material with ultrahigh open porosity is prepared via the multistep sintering process using a Fe–Al–Mn powder mixture as the raw material. The microstructure, phase composition, Mn sublimation, and open porosity of the sintered Fe–Al–Mn compacts are investigated. The compacts sintered at temperatures ≤700 °C are composed of the newly formed Fe/Mn‐based solid solutions, intermetallic phases, and the original elemental particles without the sublimation of Mn. The open porosities of the 650‐ and 700 °C‐sintered compacts are ≈39.83 and ≈47.19 vol%, respectively. After sintering at 1250 °C, Mn is rarely left in the porous body, and a single Fe–Al intermetallic phase with an even chemical composition is generated. The open porosity of the 1250 °C‐sintered compacts is ≈66.67 vol%, superior to other reported porous Fe–Al materials, and its strength is ≈22.5 MPa, which is competitive as well. This work may open a new strategy to design and optimize the high‐quality porous Fe–Al alloy in future.

Effect of APS Spraying Parameters on the Microstructure Formation of Fe3Al Intermetallics Coatings Using Mechanochemically Synthesized Nanocrystalline Fe-Al Powders

The present paper presents a study of the behaviour of Fe3Al intermetallic powders particles based on 86Fe-14Al, 86Fe-14(Fe5Mg), and 60.8Fe-39.2(Ti37.5Al) compositions obtained by mechanochemical synthesis at successive stages of the plasma spraying process: during transfer in the volume of the gas stream and deformation at the moment of impact on the substrate. The effect of the change in current on the size of powder particles during their transfer through the high-temperature stream and the degree of particle deformation upon impact with the substrate was determined. It was found that during transfer through the plasma jet, there was an increase in the average size of sputtering products by two-three times compared to the initial effects of mechanochemical synthesis due to the coagulation of some particles. In this case, an increase in current from 400 to 500 A led to a growth in average particle size by 14-47% due to the partial evaporation of fine particles with an increase in their heating degree. An increase in current also led to a 5-10% growth in particle deformation degree upon impact on the substrate due to the rising temperature and velocity of the plasma jet. Based on the research, the parameters of plasma spraying of mechanically synthesized Fe3Al intermetallic-based powders were determined, at which dense coatings with a thin-lamellar structure were formed.

Buttering for FSW: Enhancing the fracture toughness of Al-Fe intermetallics through nanocrystallinity and suppressing their growth

The formation of intermetallic compounds (IMCs) is an inevitable phenomenon during friction stir welding (FSW) of dissimilar metals. Majority of approaches that have ever been used to control the IMC thickness during FSW have been process-based. In the present study, the objective was to develop a novel metallurgical approach to control the growth and microstructure of AlFe IMCs during FSW. To do so, the faying surface of a structural carbon steel (CS) was buttered with stainless steel (SS) prior to the FSW process. The joints were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to study the intermetallic compounds. Tensile specimens with holes in the joint area were prepared and tested. The fracture surfaces of the specimens were studied by SEM. The analyses showed that the buttering caused the tensile strength and the fracture elongation to increase by 60 % and 250 %, respectively. SEM and TEM results revealed that there were two mechanisms responsible for this improvement. First, the thinning of the IMC layer and second, the nano-crystallinity of the IMC. The underlying physical phenomenon in controlling the IMCs thickness by this approach is discussed, highlighting the mechanisms by which the mechanical properties are enhanced. The alloying elements Cr and Ni introduced by the buttering technique were found to play the major role in controlling the thickness and nano-crystallinity of the IMC layers in the FSW of Al to St. It was found that the harmful intermetallic compounds in FSW of dissimilar metals can be effectively controlled by the alloying elements imparted through buttering before FSW.

Improving oxidation resistance of porous FeAl-based intermetallics with high boron/yttrium alloying

The coalloying with high contents of chromium (Cr), boron (B) and yttrium (Y) for porous B2-structured FeAl intermetallics fabricated through reactive synthesis was conducted. The oxidation behaviors of porous FeAl-based materials were investigated by evaluating the pore-structure evolution, oxidation kinetics and oxide-scale configuration. The results show that with the coalloying of high contents of Cr, B and Y, the oxidation mass gains of porous FeAl materials at 600−800 °C are significantly reduced. The combination of B enriched on the surface of oxide scales and Y located at the scale−metal interface promotes the formation of thin protective nodular α-Al2O3 oxide scales. It is indicated that introducing relatively high contents of reactive elements such as B and Y can benefit the selective growth of α-Al2O3 scales at relatively low temperatures without pre-treatment.

Microstructural Constituents and Mechanical Properties of Low-Density Fe-Cr-Ni-Mn-Al-C Stainless Steels.

Metallic material concepts associated with the sustainable and efficient use of resources are currently the subject of intensive research. Al addition to steel offers advantages in view of lightweight, durability, and efficient use of high-Fe scrap from the Al industry. In the present work, Al was added to Fe-12Cr-(9,12)Ni-3Mn-0.3C-xAl (x = 0.1–6) (wt.%) stainless steels to assess its influence on microstructure and mechanical properties. According to density measurements based on Archimedes’ principle, densities were between 7.70 and 7.08 g/cm3. High-energy X-ray diffraction estimations of the lattice parameter indicated that nearly 31% of density reduction was caused by the lattice expansion associated with Al addition. Depending on Al concentration, austenitic and duplex matrix microstructures were obtained at room temperature. In the presence of up to 3 wt.% Al, the microstructure remained austenitic. At the same time, strength and hardness were slightly enhanced. Al addition in higher quantities resulted in the formation of duplex matrix microstructures with enhanced yield strength but reduced ductility compared to the austenitic alloys. Due to the ready formation of B2-(Ni,Fe)Al intermetallics in the ferrite phase of the present alloy system, the increase in strength due to the presence of ferrite was more pronounced compared to standard duplex stainless steels. The occurrence of B2 intermetallics was implied by dilatometry measurements and confirmed by electron microscopy examinations and high-energy X-ray diffraction measurements.

Synthesis of Fe–Al Intermetallic by Mechanical Alloying Process

Synthesis of Fe–Al Intermetallic by Mechanical Alloying Process

Catalytical enhancement on hydrogen production from LiAlH4 by Fe–Fe2O3 addition

Hydrogen storage technology plays an important role on the development of hydrogen fuel cell and lithium aluminum hydride is a powerful candidate for solid-state hydrogen storage materials. However, the high stability and slow dehydrogenation kinetics of LiAlH4 hinder its application. In this paper, the two-step thermal decomposition properties of LiAlH4 with and without Fe–Fe2O3 catalysts are investigated. According to the master plots, the model of mample power law (Pn) and nucleation and growth (An) are the optimal mechanism functions for the two-step decomposition of LiAlH4, respectively. After doping catalysts, the activation energies decrease significantly. The theoretical and optimized kinetic method are consistent with each other on activation energy. And the latter can also yield other kinetic parameters for a more comprehensive kinetic modelling of LiAlH4 decomposition. Furthermore, Fe–Al2O3 and Fe–Al intermetallics generated during dehydrogenation might significantly improve the hydrogen release properties of LiAlH4.

Plasma arc welding of dissimilar ultrahigh-strength steel and aluminum alloy assisted by copper transition layer

Plasma arc welding of dissimilar DP1180 ultrahigh-strength steel and 5A06 aluminum alloy assisted by copper transition layer was applied and a hybrid joint was obtained consisting of two metallurgical bonding zones. The hybrid joint consisted of the weld formed by the fusion welding of steel and copper on steel side, unmelted Cu and the Cu-Al interface layer formed by liquid phase diffusion reaction. The unmelted Cu acted as a diffusion barrier between steel and Al-alloy, and no Fe-Al intermetallics were detected in the weld. The Cu-Al interface layer composed of Cu9Al4 + CuAl2 + CuAl2/α-Al eutectic and the formation mechanism of the Cu-Al interface layer was discussed. Mechanical testing of the hybrid joints revealed that the average tensile strength was 125 MPa and all the tensile samples fractured at Cu-Al interface layer containing Cu9Al4 and CuAl2.

Friction surfacing assisted refilled friction stir spot welding of AA6061 alloy and Q235 steel

The AA6061 alloy and Q235 steel were well joined by refilled friction stir spot welding without stirring steel, as a 1 mm thick coating was deposited on the steel by friction surfacing before welding. The coating was composed of highly refined grains. The materials experienced shear deformation in the stir zones and the extrusion in hook and thermo-mechanical affected zones, resulting different predominant textures in the weld. A Fe-rich layer was depicted from the interface due to the enhanced atomic diffusion, and the layer's thickness increased as the sleeve plunged deeper during welding. Al-Fe intermetallics, including Al13Fe4, Al5Fe2, formed in the Fe-rich layer, since the solubility of Fe in Al was far lower than the measured content. The optimal shear strength reached 7.31 kN in this study. The welds fractured along the weld boundary and the Al/steel interface. The fracture initiated at the edge of the gap between AA6061 plate and coating, and propagated along the weld boundaries, resulting in the shear dimples and the faceted appearance. However, the spot weld with 2.9 mm penetration was fractured along the Al/steel interface mainly, which was attributed to the over formed intermetallics at the interface.

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.

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.

ショットライニングとレーザ照射によるアルミニウム合金の表面改質

The surface modification of aluminum alloy by shot lining and laser irradiation was investigated to form a hard Fe-Al intermetallic compound having excellent corrosion resistance. A centrifugal-type peening machine with an electrical heater was employed. The shot medium was high-carbon cast steel. The substrate was a commercial aluminum alloy. The sheet was commercially available pure aluminum, and the powder was an electrolytic iron. The shot lining process was carried out at 573 K in air using a peening machine. The top surface of the lined workpiece was melted by laser beam irradiation. The intermetallic Fe-Al layer was formed on the irradiated surface. The lined substrates exhibited a harder layer of aluminum-rich intermetallic in the irradiated part. The present method could be used for the formation of functional films on aluminum alloy.

Interfacial investigation of explosion-welded Al/steel plate: The microstructure, mechanical properties and residual stresses

This paper presents a systematic investigation of microstructure, mechanical properties and residual stress distribution of explosion-welded Al/steel plates. It was found that vortexes resulted from the trapped jetting were surrounded by highly deformed bulk materials and Fe–Al intermetallics. The microstructure-mechanical property relationship in individual phases was established using nanoindentation tests, e.g. FeAl + FeAl2 and FeAl3 having the hardness of 16.2 GPa and 11.4 GPa, respectively. The Al/steel interface showed higher microhardness values (200–300 HV0.1). The internal stresses were evaluated by a contour method, and the tensile stresses concentrated at the Al/steel interface, reaching to 170 MPa and 160 MPa in the longitudinal and transverse directions, respectively. Smoothed particles hydrodynamics (SPH) methods was used to simulate the formation of wave boundary, vortex zone, as well as the jet moving ahead of the collision point during the high-velocity oblique process. A good agreement was observed between the simulation and experiment, especially the formation of intermetallic compounds at interfacial regions and the evolution of residual stress.

Architectured lightweight steel composite: evaluation of the effect of geometrical parameters and annealing treatments on deformation behavior

Architectured lightweight steel composites were designed and fabricated through the cold roll bonding (CRB) of stacked steel-aluminum sheet layers. The effects of geometrical parameters including thickness ratio (TR) and the number of constituent layers on bond strength and tensile properties of the composites were evaluated using peeling and tensile tests. It was found that by decreasing the TR of aluminum to steel from 0.5 to 0.2, the bond strength increased in the as-rolled specimen. However, it led to a decrease in the bond strength of the annealed sample by the facilitation of the formation of Fe–Al intermetallics along the interfaces. In order to obtain a more in-depth understanding of deformation behavior at the interface of steel/aluminum layers, strain gradient at these regions was evaluated through the measurement of dislocation density using the XRD analysis. Macrotexture measurement and anisotropy analysis were also carried out to evaluate the formability of the optimized sample. Moreover, it was found that by increasing the number of layers, the bond strength decreased due to the insufficient extrusion of the virgin metals to the interface of the layers. Higher steel/aluminum interfaces as effective microstructural heterogeneities improved the elongation in five-layered and seven-layered composites by arresting the propagating cracks. Employing the concept of laminated composite led to the production of a lightweight architectured steel with density of 5.6 g.cm−3, which can be a promising structural material for automotive applications.