FeAl Phase Research Articles

Multi-phase ELAStic Aggregates (MELASA) software tool for modeling anisotropic elastic properties of lamellar composites

We introduce a new web-based tool called MELASA (Multi-phase ELAStic Aggregates), open-access available at https://melasa.cerit-sc.cz, for computations and visualizations of anisotropic elastic properties of lamellar (nano-)composites. MELASA implements a linear-elasticity method by Grimsditch and Nizzoli (1986), originally developed for superlattices of any symmetry. Our tool may be used for computation of anisotropic elastic properties of a specific type of periodically separated lamellar (nano-)composites using matrices of elastic stiffnesses of co-existing phases as an input. Elastic properties are visualized in the form of directional dependencies of selected elastic characteristics (Young’s modulus and linear compressibility). MELASA further generalizes the Grimsditch–Nizzoli approach, which was originally formulated for only two phases, to multiple-phase composites. Additionally, our implementation allows for treating internal rotations of local coordination systems corresponding to the natural set of coordinates that match directional vectors of unit cell defining crystal lattice within the co-existing phases. Fe–Al-based superalloy nanocomposites are employed as a numerical example of superlattices with the input and output elastic stiffnesses determined by quantum-mechanical calculations. In particular, three different atomic configurations of interfaces in superlattices containing the ordered Fe3Al phase and a disordered Fe–Al phase with 18.75at.%Al (modeled by a special quasi-random structure, SQS) are considered. They differ by relative positions of sublattices in Fe3Al (an antiphase-like shift) and/or atomic planes in Fe-18.75at.%Al with respect to the interface (a circular/cyclic shift). Program summaryProgram title: MELASAProgram files doi:http://dx.doi.org/10.17632/rzc2yd2rvc.1Licensing provisions: MIT licenseProgramming language: JavaScriptNature of problem: Computations and visualizations of anisotropic elastic properties of lamellar (nano-)composites/superlatticesSolution method: Implementation of a linear-elasticity method by M. Grimsditch and F. Nizzoli [1], originally derived for superlattices of any symmetry. MELASA computes anisotropic elastic properties of a specific type of periodically separated lamellar (nano-)composites using matrices of elastic stiffnesses of co-existing phases as input. Elastic properties are visualized in the form of directional dependencies of selected elastic characteristics (Young’s modulus and linear compressibility).Additional comments including restrictions and unusual features: MELASA generalizes the Grimsditch–Nizzoli approach, which was originally formulated for only two phases, to multiple-phase composites. Additionally, our implementation allows for treating internal rotations of local coordination systems corresponding to the natural set of coordinates that match directional vectors of unit cell defining crystal lattice within the co-existing phases.

Crystallization and Structure of AlSi10Mg0.5Mn0.5 Alloy with Dispersion Strengthening with Al–FexAly–SiC Phases

The paper characterizes a composite with dispersion phases cast via the use of stir casting method on an aluminum matrix. A mixture of aluminum with FexAly and SiC powders was achieved in the process of mechanical alloying and self-propagating high temperature synthesis (ASHS). Chemical composition of agglomerates was chosen in such a way that the strengthening components made up 25% of the mass of the AlSi10Mg0.5Mn0.6 (EN AC-43400) alloy matrix. The characteristic temperatures of crystallization of the tested alloy were measured by thermal analysis ATD (analysis thermal derivative). A change of chemical and phase composition was confirmed in the elements of the intermetallic phase FeAl in the aluminum matrix. A silumin casting structure was achieved, with the matrix including micro-areas of ceramic phases and intermetallic phases, which are characteristic for hybrid strengthening. A refinement of dendrites in solid solution α was found, together with a transition from a binary plate eutectic composition α(Al) + β(Si) into modified eutectic composition.

Effects of rare earth modification on microstructure refinement and mechanical properties of Al-2 wt%Fe alloys

The microstructure and mechanical properties of Al-2 wt%Fe alloys after mixed RE modification, homogeneous annealing and cold rolling have been studied using OM, XRD, SEM and mechanical testing. Results showed that during traditional casting, the α-Al grain and Al3Fe/Al6Fe intermetallic could be effectively refined by the mixed RE in Al-2 wt%Fe alloy. The average grain size of primary α-Al with 0.5 wt% RE addition is half smaller than that without RE. The addition of mixed RE makes the mechanical properties of alloys initially increased and then decreased. The RE elements that enriched in front of the solid/liquid interface formed Al8Fe2Ce at grain boundaries of α-Al. An addition of 0.7 wt% mixed RE lead to the preferential formation of the granular Al11Ce3, which the La were dissolved in. However, the formation of Al11Ce3 weakened the refining effect of mixed RE on the microstructure, also deteriorated the mechanical properties of the alloy. Homogeneous annealing decomposes lamellar Al-Fe phase into short rods, and cold rolling process makes the second phase dispersively and uniformly distributed in the primary α-Al matrix. The elongation and tensile strength of alloy with 0.5 wt% mixed RE addition are increased by 50.14% and 10.67% respectively compared with those of unmodified alloy in cold rolled state.

Revealing the Nuclei Formation in Carbon-Inoculated Mg-3%Al Alloys Containing Trace Fe.

In this study, Fe-bearing Mg-3%Al alloys were inoculated by combining carbon with or without Ca. Both processes can significantly refine the grain size of Mg-3%Al alloys. The highest refining efficiency can be obtained by carbon combined with Ca. The synergistic grain refining efficiency can be attributed to the constitutional undercooling produced by the addition of Ca. Two kinds of carbon-containing nuclei with duplex-phase particles and cluster particles were observed in the carbon-inoculated alloys. A thermodynamic model was established to disclose the formation mechanisms of the duplex-phase particles and Al4C3 cluster particles. This thermodynamic model is based on the change of Gibbs free energy for the formation of these two kinds of particles. The calculated results show that these two particles can form spontaneously, since the change of Gibbs free energy is negative. However, the Gibbs free change of the duplex-phase particle is more negative than the Al4C3 cluster particle. This indicates that the adsorption process is more spontaneous than the cluster process, and tiny Al4C3 particles are preferred to form duplex-phase particle, rather than gathering to form an Al4C3 cluster particle. In addition, the addition of Ca can reduce the interfacial energy between the Al4C3 phase and the Al–Fe phase and promote the formation of duplex-phase particles.

An experimental investigation of phase transformations in the Al-rich corner of the Al–Cr–Fe system

This paper presents a comprehensive investigation of the aluminium-rich corner of the Al–Cr–Fe phase diagram within the solidification interval, using X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and electron probe microanalysis (EPMA). Liquidus and solidus surfaces were constructed. The nature of the phase equilibria and invariant reactions observed between the phases were different from those recently reported in the literature. It was determined that over the composition range ∼80–100 at.% Al, the liquidus surface is characterized by primary solidification fields of two ternary compounds Al76Cr16Fe8 (O) and Al82.5Cr11.5Fe6 (H), four solid solutions based on binary phases Al4Cr, Al11Cr2, Al13Cr2 and Al13Fe4 and one solid solution based on aluminium. The solidus surface over the composition range ∼75–100 at.% Al is characterized by three three-phase fields (Al) + Al13Fe4 + Al13Cr2, Al13Fe4 + Al13Cr2 + H and Al13Fe4 + Al11Cr2 + H, which result from invariant four-phase equilibria of transition type at 770, 680 and 654 °C respectively. It was also found that only Al13Cr2 and Al13Fe4 phases coexist in equilibrium with the aluminium solid solution.

Formation mechanism of multilayer aluminide coating on 316L stainless steel by low-temperature pack cementation

In this study, the aluminide coating was prepared by a combined process. The coating thickness and phase structure at different aluminizing temperatures and times were investigated. In addition, the thermodynamics and kinetics of the pack cementation aluminizing process were studied. The aluminizing temperature had influence on the coating phase structure. As the temperature and time increased, the coating thickened. In the process of pack cementation aluminizing, the Fe2Al5 phase was formed first, followed by the FeAl and FeAl3 phases. As the temperature was lowered to below 422 °C, the Fe3Al phase began to form. The kinetic study showed that the low-temperature aluminizing process had a low activation energy value of 164.78 kJ/mol. This research provided a theoretical basis for the parameter selection of low-temperature pack cementation aluminizing process.

Diffusion bonding of Q345 steel to zirconium using an aluminum interlayer

The microstructure, interface reactions and mechanical properties of the Q345 steel/Al/Zr bonding interface were investigated. The thicknesses of the reaction layer in both Al/Fe and Al/Zr interfaces are temperature-dependent, with a higher temperature yielding a larger thickness. Both experimental results and thermodynamic calculation confirmed that the diffusion transition regions near the Al/Fe and Al/Zr interfaces mainly consist of Al5Fe2 and Al3Zr with thin Al3Fe and Al3Zr2 transitional phases, respectively. The growth kinetic equations of Al5Fe2 and Al3Zr as a function of temperature were investigated. The fitted curves from the equations well agree with the experimental results. The hardness of Al5Fe2 is higher than Al3Zr and the base materials. The propagation of shear crack occurs within Al5Fe2. Optimized shear strength can be obtained by controlling the thickness of reaction layer. The grain growth and fracture mechanisms of Al5Fe2 and Al3Zr at the interfaces were also discussed based on electron back scattering diffraction (EBSD) analysis of both reaction layers and fracture morphology.

Microstructural investigations on the hot-dip aluminized AISI 321 stainless steel after diffusion treatment

The microstructure of the hot-dip aluminized AISI 321 stainless steel was studied after diffusion treatment at 900 °C for 3 h. The microstructural characterization was carried out by scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. The microstructure of the as aluminized steel consisted of two regions, viz.; aluminum topcoat and aluminide layer. During the diffusion treatment, the coating transformed into a layered structure consisting of four layers. The Fe2Al5 phase was formed in the outermost layer and the presence of Al13Fe4 quasicrystalline approximant phase was observed. The innermost layer adjacent to the base metal transformed to ferrite phase with NiAl precipitates. Next, to this layer, a disordered FeAl phase was observed. The lattice parameter of the disordered FeAl phase was found to be larger than that of the ordered B2 FeAl phase. The layer between outer Fe2Al5 phase and disordered FeAl phase consists of a mixture of three phases, namely Fe2Al5, disordered FeAl and a new phase with the simple cubic structure. The phase with simple cubic structure shares cube on cube crystallographic orientation relationship with the disordered FeAl phase.

Influence of crystalline structure on diffusion barrier property of electroless Ni–Fe–P coatings in Zn–Al solder interconnects

The rapid growth of interfacial Cu–Zn intermetallic compounds (IMCs) at Zn–Al/Cu solder interfaces significantly deteriorates their integrity due to the physical mismatch of interface materials. Thus, a robust interlayer to inhibit the interactions between solder and substrate at elevated temperature is urgently required. In this work, ternary Ni–Fe–P coatings with various crystalline structure were electroless plated on Cu substrates to investigate their interfacial reactions and diffusion barrier properties in Zn–Al solder interconnects. It was found that Ni–Fe–P coatings can significantly suppress the growth of interfacial IMCs in Zn–Al solder interconnects during liquid-solid reaction. Moreover, crystalline structure of Ni–Fe–P coatings played a vital role in the interfacial reactions and microstructural evolutions at the Zn–Al/Ni–Fe–P interfaces. The Ni–Fe–P coating with mixed structure (amorphous + crystalline) exhibited the best diffusion barrier properties among three types of the coatings for the thinnest and void-free Al3Ni2 layer, while crystalline Ni–Fe–P coating is the worst due to not only the rapidly growth of Al3Ni2 and Fe2Al5 phases but also the spalling phenomenon of Al3Ni2 particles.

Iron Aluminides

The iron aluminides discussed here are Fe–Al-based alloys, in which the matrix consists of the disordered bcc (Fe,Al) solid solution (A2) or the ordered intermetallic phases FeAl (B2) and Fe3Al (D03). These alloys possess outstanding corrosion resistance and high wear resistance and are lightweight materials relative to steels and nickel-based superalloys. These materials are evoking new interest for industrial applications because they are an economic alternative to other materials, and substantial progress in strengthening these alloys at high temperatures has recently been achieved by applying new alloy concepts. Research on iron aluminides started more than a century ago and has led to many fundamental findings. This article summarizes the current knowledge of this field in continuation of previous reviews.

Effect of cooling rate on microstructure and mechanical properties of an Al-5.0Mg-3.0Zn-1.0Cu cast alloy

This study examines the effect of cooling rate (specifically at 2.3, 3.4, 9.8 and 24.1 K/s as) on the microstructure and mechanical properties of an Al-5.0Mg-3.0Zn-1.0Cu (wt.%) alloy casted through a step-like iron mold. This study was performed in as-cast and T6-treated (470 °C × 24 h + 150 °C × 16 h) conditions. An examination of the as-cast microstructure shows that when the cooling rate increases from 2.3 to 24.1 K/s, the average secondary dendrite arm spacing decreases from 43.0 to 19.0 μm, and that the average width of the T-Mg32(AlZnCu)49 phase also decreases from 6.7 to 4.0 μm. The solution treatment has an impact on dissolving most of the T phases and aging treatment results in the formation of fine precipitates in matrix. The examinations of precipitates under different cooling rates show that a higher cooling rate promotes the transformation from the GP II zone to η′ phase and also keeps a higher concentration of Mg and Zn suspended in the alloy matrix. The results of tensile tests show that the strength and elongation of as-cast alloys are improved slightly by applying a higher cooling rate, and that of T6-treated alloys improved more significantly, especially for elongation (from 6.1% to 10.6%) and yield strength (from 402.5 to 441.9 MPa). The refinements of α-Al and Al3Fe phases are attributed to the significant increase of elongation for T6-treated alloys. Moreover, cooling rate regulates the yield strength by mainly affecting precipitation strengthening and the relative mechanisms are discussed. Overall, these results show that Al-5.0Mg-3.0Zn-1.0Cu cast alloy can exhibit a strength of 450 MPa, a high ductility of 10%, and can become one of high performance cast aluminum alloys.

The resistance of an aluminide coating on a high-strength ASTM A29 steel subjected to a temperature of 850 °C

An ASTM A29 steel was coated with aluminide by dipping in a molten Al bath at 700 °C for 16 s. The resistance of ASTM A29 steel to high-temperature oxidation drastically decreased upon oxidation at 850 °C for 12 h, whereas the oxidation resistance of the aluminised steel subjected to hot dipping was higher (by 25-fold). The external part of the aluminide layer, which consists of Fe2Al5, FeAl2, and FeAl(Cr, Si) phases scattered in the Fe2Al5 phase, was formed through the outward diffusion of Al and inward diffusion of Fe. The Fe2Al5 phase played an important role as a reservoir of Al atoms that form the alumina (Al2O3) scale, while Cr and Fe from the FeAl(Cr, Si) particles and accelerated the conversion of the metastable θ-Al2O3 phase to a stable α-Al2O3 phase. Consequently, the parabolic rate constants of aluminised steel decreased with extended oxidation time.

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.

Effect of high-frequency micro-vibration on microstructure and properties of laser cladding aluminum coatings

Successful fabrication of AlSiTiNi coatings has been achieved by laser cladding assisted by high-frequency micro-vibration. Under the high-frequency micro-vibration, the dendrites in the coating are fractured and fine structure is formed. A typical bimodal structure is found in the coatings. The bimodal structure could improve the comprehensive properties of the coatings. The partially melted particles are found to be embedded in the fully melted structure at the vibration frequency of 551 Hz. The XRD and EDS investigations show that the coatings mainly consist of FeAl and FeNi phase. The composition distribution of the coatings is uniform due to the intensified convection in the molten pool during laser cladding. The micro-hardness of the coatings shows that the highest hardness of the coating reaches 781 HV0.2 and the average hardness is 725.2 HV0.2 when the vibration frequency is 551 Hz. The friction coefficient of the coating increases slightly and the running-in period decreases. In addition, the friction coefficient is stable and the stable wear time is also prolonged. Moreover, the main wear form of the coating is abrasive wear with slight adhesive wear. The tearing layer of the grinding defect and the wear loss of the coatings fabricated under the high-frequency micro-vibration are both decreased.

Aluminising of steel with a cathodic arc plasma based method

ABSTRACTSteel samples have been aluminised by cathodic arc PVD using Al cathodes and AC bias. The effect of time and temperature on the growth behaviour of iron aluminide phases under the constant flux of Al vapour was investigated. For samples processed at 1000°C for 30 min a layered structure that consisted of FeAl, followed by dual phase regions of metastable Fe3Al + FeAl and stable Fe3Al + α-Fe was observed. Increase of processing time resulted in the formation of Fe2Al5. The increase of processing temperature to 1100°C extended the diffusion zone and increased the time for formation of Fe2Al5. After 90 min processing at 1000°C and 1100°C the presence of Fe4Al13 in the Fe2Al5 phase was determined. It has been observed that the metastable dual phase structures composed of Fe3Al and FeAl can be transformed into stable Fe3Al by heat treatment at 500°C.

Inhomogeneous microstructure and mechanical properties of rotary friction welded joints between 5052 aluminum alloy and 304 stainless steel

The reaction layer of rotary friction welded 5052 aluminum alloy/304 stainless steel dissimilar joints consisted of Fe2Al5 and Fe4Al13 phases, and the distribution of intermetallic compounds (IMCs) and mechanical properties were inhomogeneous due to the inhomogeneity of heat generation along the radius direction. Almost no brittle IMCs formed in center part, while continuous and thicker IMCs formed in R/4, R/2, 3R/4 and edge locations, and the thickness of IMCs reached the maximum value in 3R/4 rather than in edge location. The joint efficiency was 99.51% in center location, higher than that in R/4, R/2, 3R/4 and edge locations. Meanwhile, the width of heat-affected zone on 304 stainless steel side decreased, but that of softened zone on 5052 aluminum alloy side increased from center to edge location. The entire joint fractured through the interface and predominantly presented brittle fracture feature. Cracks mainly propagated along the IMCs/AA5052 substrate interface for samples from center and R/4 locations, between the IMCs and the IMCs/AA5052 substrate interface alternately from R/2 and partial 3R/4 locations, and along the IMCs/304SS substrate interface from partial 3R/4 and edge locations.

An Al–7Si alloy/cast iron bimetallic composite with super-high shear strength

A new composite technology is presented consisting of the surface pretreatment of cast irons, the hot-dipping in a Zn–0.2wt.% Bi melt and the Al/Fe composite process. The shear strength of Al/Fe (Al–7Si/cast iron) bimetallic composites fabricated by the technology is up to 32MPa that is far more than the shear property obtained by composite technology reported in literatures. The super-high shear strength is mainly attributed to the formation of a peculiar concave–convex interface (CCI) structure. The addition of 0.2wt.% bismuth into the zinc melt can promote the formation of Zn-rich regions at the surface layer of cast irons, leading to the formation of Al–Fe phases at these Zn-rich regions. Reducing the amount of Al–Fe phases appearing in the ferrite–graphite interface in cast irons can benefit improving the shear property of Al/Fe bonding interface. Further analysis of the stress state confirms that the CCI can enhance the shear strength of Al/Fe bonding interface.

Effect of Manganese on Microstructure and Corrosion Behavior of the Mg-3Al Alloys

Microstructure and corrosion behavior of the Mg-3Al-xMn (x = 0, 0.12, 0.21, 0.36, 0.45) (hereafter in wt.%) alloys were experimentally investigated by electron probe microanalysis (EPMA), scanning electron microscope equipped with energy dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), electrochemical, and hydrogen evolution tests. A new self-constructed Mg-Al-Mn-Fe thermodynamic database was used to predict the solidification paths of the alloys. The addition of Mn showed no grain refinement in the cast Mg-3Al alloys. According to the microstructure observation, Al-Fe phases were observed in the non-Mn-added alloy, while Al8Mn5(LT) (Al8Mn5 in low temperature) became the main intermetallic phase in the Mn-added alloys, and the amount increased gradually with the Mn addition. The τ–Al0.89Mn1.11 phase with lower Al/(Fe + Mn) ratio was observed in the alloys with 0.36 and 0.45 wt.% Mn content. According to the electrochemical tests, all five alloys showed localized corrosion characteristics in 3.5 wt.% NaCl solution. Compared with the Mg-3Al alloy, the corrosion resistance of Mn-added alloys were significantly improved and increased gradually with the Mn addition, which was due to the variation of Al-containing intermetallic compounds. The present experimental investigations and thermodynamic calculations confirmed the mechanism that the increasing amount of Al8Mn5(LT) with Mn addition could encapsulate the B2-Al(Mn,Fe) phase with higher Fe. Therefore, it could prevent this detrimental phase from contacting magnesium matrix, thus suppressing micro-galvanic corrosion and improving corrosion resistance gradually.

Influence of Graphite Morphology on Phase, Microstructure, and Properties of Hot Dipping and Diffusion Aluminizing Coating on Flake/Spheroidal Graphite Cast Iron

The influence of graphite morphology on the phase, microstructure and properties of hot dipping and diffusion aluminizing (HDDA) coating on flake/spheroidal graphite cast iron (FC/FCD) was investigated. The microstructure and properties of the HDDA coatings on FC/FCD were determined by the graphite morphology. The outer and inner layers of the HDDA coating comprised the Fe2Al5 and FeAl phases, respectively. The outer layer of HDDA on FCD was dense and uniform; however, some pores of different sizes were found in the outer coating on FC, resulting in looser HDDA coating. Hence, the wear resistance of the HDDA coating on FC was worse than that of the coating on FCD. During oxidation, many continuous oxidation channels were formed from the coating surface to the matrix in the HDDA coating on FC, resulting in the oxidation of graphite in the HDDA coating and the matrix. However, only exposed spheroidal graphite was oxidized in the HDDA coating on FCD. Thus, the high-temperature oxidation resistance of the HDDA coating on FC was also worse than that of the coating on FCD.

Nanoindentation behavior of nanostructured bulk (Fe,Cr)Al and (Fe,Cr)Al-Al2O3 nanocomposites

The purpose of the present study was to design a new generation of FeAl-based intermetallic compounds with improved mechanical and oxidation properties. Synthesis of powders of FeAl, (Fe,Cr)Al and (Fe,Cr)Al in situ composites with 5 and 10% Al2O3 contents was reported elsewhere. In this paper the sintering behavior is reported. FeAl, (Fe,Cr)Al and (Fe,Cr)Al - Al2O3 powders were sintered by a hot-pressing method at 1600 °C and 5.5 GPa for 15 min to produce bulk specimens for mechanical and microstructural characterization. Microstructural characterization by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of theses nanocomposites disclosed uniform distribution of Al2O3 nano-particles. XRD analysis indicated the presence of FeAl, (Fe,Cr)Al and Al2O3 phases. The presence of nano-sized Al2O3 particles effectively retarded grain growth by pinning the grain boundary during hot pressing. Nanoindentation tests indicated that with increasing content of Cr and Al2O3 reinforcement, the hardness and Young's modulus increased, and the fracture toughness reaches a high value of 19.6 ± 0.4 MPa m1/2 for the (Fe,Cr)Al-10%Al2O3 composition, with a hardness value of 21.7 ± 1.8 GPa. Nanoindentation creep tests at room temperature showed that composites with Al2O3 nanoparticles had higher creep rate than FeAl and (Fe,Cr)Al. It was found that improvements in the mechanical properties of FeAl intermetallic compound can be achieved by adding Cr and uniform distribution of Al2O3 nanoparticles.