Fe-Al System Research Articles

Controlling the composition and properties of deposited alloys of the iron–aluminium system

The formation of coatings based on alloys of the Fe–Al system by deposition of aluminium and steel is investigated. A calculation–experimental method for calculating the conditions of argon-shielded arc surfacing with a consumable electrode and an aluminium filler wire is proposed. The method can be used for controlling the chemical composition and properties of the deposited layers. The experimental results are used to determine the effect of the deposition conditions on the chemical composition of the weld metal and the service properties of deposited layers.

Kinetics study on the SHS reaction in massive samples with high heating rate in the Fe–Al system

This paper presents the results of studies on the SHS reaction kinetics in massive Fe–Al samples. Three different chemical compositions (Fe30Al, Fe40Al, and Fe50Al (at.%)) were heated up to 800°C with three different heating rates (70, 150, and 220°C/min) under a uniaxial load of 65MPa. During the processes, the temperature changes were measured by five thermocouples placed evenly on the diameter of the sample. Based on the temperature measurements, the following parameters were calculated: the heating rate and temperature gradient through the diameter of the sample just before starting the SHS reaction, the SHS reaction ignition temperature, the rate of SHS temperature increase, and the combustion velocity [mm/s]. The kinetics of the SHS reaction are presented as an animation in video files. The results give new insight into the direct reaction of iron with aluminum leading to the formation of Fe–Al intermetallic alloys on close-to-real scale.

Laser in situ synthesis of gradient aluminides in metal matrix composite during DMD process

The suitability of direct metal deposition process of exothermic powders (Ni-Al, Ti-Al, Fe-Al systems), traditionally used in the self-propagating high-temperature synthesis technology, is described. Owing to the synthesis of new intermetallic phases, the overlapping of laser in situ synthesis and layerwise deposition processes makes it possible both to obtain more durable parts of complex shape, and to enlarge the functional resource of these functional-graded structures. Besides, relationships between the main laser deposition parameters and the intermetallic phase structures of the built-up objects were studied. In our research we applied optical microscopy, X-ray analysis, microhardness measurement and SEM with EDX analysis of the laser-fabricated intermetallics.

Control of WC grain sizes and mechanical properties in WC–FeAl composite fabricated from vacuum sintering technique

This work addressed on size control of WC grains in WC–FeAl composite fabricated from vacuum sintering techniques. Carbide additives and oxygen were candidates for the size controller of WC grains. The carbide additives such as VC and Cr3C2 suppressed the WC grain growth, which was similar to WC–Co system. As a result, they improved Vickers hardness, but degraded transverse rupture strength. On the other hand, some amount of oxygen included in the composite also suppressed the WC grain growth but improved both the hardness and the strength. It is concluded that oxygen is one of the most effective size controller of WC grains in the WC–FeAl system.

Study of the iron atom clustering in mechanically alloyed Al-rich Fe-Al mixture

Structural changes in the Fe-Al system modified by high-energy ball milling were studied using Mossbauer spectroscopy and X-ray diffraction. Pure Fe and Al powders were mixed in compositions with 0.5, 1.5, and 5 at.% Fe and milled for various times using the Fritsch Pulverisette planetary mill. The formation of iron clusters was observed when the percentage of paramagnetic iron was higher than 0.5 at.%. It was found that the arrangement of Fe atoms in iron clusters is similar to that observed in FeAl n (n≥2) intermetallic compounds.

Low-Density Steels: The Effect of Al Addition on Microstructure and Properties

Density reduction of automotive steels is needed to reduce fuel consumption, thereby reducing greenhouse gas emissions. Aluminum addition has been found to be effective in making steels lighter. Such an addition does not change the crystal structure of the material. Steels modified with aluminum possess higher strength with very little compromise in ductility. In this work, different compositions of Fe-Al systems have been studied so that the desired properties of the material remain within the limit. A density reduction of approximately 10% has been achieved. The specific strength of optimal Fe-Al alloys is higher than conventional steels such as ultra-low-carbon steels.

Computational study of atomic mobility for bcc phase in Ti–Al–Fe system

Experimental diffusion data were critically assessed to develop the atomic mobility for the bcc phase of the Ti–Al–Fe system by using the DICTRA software. Good agreements were obtained from comprehensive comparisons made between the calculated and the experimental diffusion coefficients. The developed atomic mobility was then validated by well predicting the interdiffusion behavior observed from the diffusion-couple experiments in available literature.

Solid-State Diffusion Reaction and Formation of Intermetallic Phases in the Fe-Al System

The solid-state diffusion reaction between Fe and Al was studied using bulk diffusion couples in the temperature range 450°C to 600°C for annealing durations up to 240 h. The Al-rich intermetallic phase Fe2Al5 formed in the diffusion zone at all annealing temperatures. However, for diffusion couples annealed at and above 600°C, additional intermetallic phases Fe3Al, FeAl, and FeAl2 appeared in the diffusion zone. The existence of these phases at and below 640°C and the composition range of their existence were investigated, and these results provided better insight into the existing Fe-Al phase diagram. It was observed that Fe2Al5 is the dominant phase in the diffusion zone, and the formation of this phase was rationalized based on the modified effective heat of formation model. Both kinetic and diffusion parameters were evaluated for Fe2Al5, and the activation energy for interdiffusion of this phase was found to be 146.8 kJ/mol; these results were compared with previously published work.

Effect of Mn on Fe containing phase formation in high purity aluminium

In this study, the effect of varying Mn additions on Fe phase formation in high purity Al and its corresponding effect on the resulting mechanical properties have been investigated. Thermodynamic simulations have shown that in the Al–Fe–Mn ternary system two intermetallic phases (namely Al6(Fe,Mn) and Al13Fe4) form. Findings indicated that a relatively high amount (>1 wt-%) of Mn was required to achieve Al6(FeMn) phase formation which was congruent with experimental results. Both the Al–Fe and Al–Fe–Mn phases observed displayed fibre/platelet type morphologies and were found to exist at α-Al grain/cell boundaries. Results indicate that the Fe phases coarsen with increasing Mn content. In the Al–Fe system the Mn addition improves yield strength (YS) and ultimate tensile strength (UTS) but reduces elongation beyond the reduction resulting from the Fe addition. The further decrease in elongation with Mn was attributed to the increase in volume fraction of the intermetallic phases.

The Structure of Coatings Obtained in the Zn-31Al-3Mg Bath on High-Silicon Steel

Coatings obtained in Zn-Al-Mg baths on steel plates by using the continuous method provide effective protection against corrosion. They have greater corrosion resistance than traditional zinc coatings. Even though Zn-Al-Mg coatings have many advantages, they are not made on galvanized products by use of the batch hot dip method. For products galvanized by use of the batch hot dip method coating growth mainly depends on the content of silicon in the steel. An increase in coating thickness is particularly intense in the case of high-silicon steel. In the paper the results of tests on obtaining Zn-Al-Mg coatings on high-silicon steel by use of the batch hot dip method have been presented. The growth kinetics of coatings obtained in the Zn-31Al-3Mg bath on steel with Si content of 0.27% has been defined. The structure has been developed and the chemical composition of particular structural components of the coating has be established. It has been determined that coatings obtained in the Zn-31Al-3Mg bath are continuous and they have uniform thickness. The structure of the coating is compact and the chemical composition points to the presence of phases of the Fe-Al system. The presence of silicon in the steel limits steel reactivity in the tested bath. The course of growth kinetics of the coating is close to parabolic.

Intermetallics Synthesis in the Fe–Al System via Layer by Layer 3D Laser Cladding

Intermetallide phase formation was studied in a powdered Fe–Al system under layer by layer laser cladding with the aim of fabricating the gradient of properties by means of changing the Fe–Al concentration ratio in the powder mixture from layer to layer. The relationships between the laser cladding parameters and the intermetallic phase structures in the consecutively cladded layers were determined. In order to study the structure formation an optical microscopy, X-ray diffraction analysis, measurement of microhardness, scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) spectroscopy analysis were used after the laser synthesis of intermetallic compounds.

Biocorrosion and biocompatibility of Zr–Cu–Fe–Al bulk metallic glasses

Owing to their unique chemo‐physical and structural characteristics, amorphous bulk metallic glasses (BMGs) are of great demand for fabrication of variety of advanced and innovative products including surgical and biomedical tools and devices. In this study, a series of Ni‐free Zr‐based BMGs in Zr–Cu–Fe–Al system are fabricated using copper‐mold casting technique, and their biocorrosion and biocompatibility are evaluated with respect to their corrosion behavior in the phosphate buffered saline (pH = 7.4) solution. Anodic polarization curves, scanning electron microscopy combined with energy‐dispersive X‐ray, and wettability analyses are conducted to characterize the surfaces of BMG samples. The biocompatibility of the BMG and control samples is studied by comparing cell–substrate interactions among different samples. It is found that Zr60Cu20Fe10Al10 displays a higher passive region compared with that of Zr60Cu22.5Fe7.5Al10, but both BMGs exhibit lower corrosion resistance compared with Ti–6Al–4V alloy. By addition of titanium to Zr–Cu–Fe–Al system (Zr60Ti6Cu19Fe5Al10), a significant increase in the passive region of the polarization curve is detected. The cell culture experiments reveal that the number of attached and grown cells is significantly higher on the surface of the treated BMGs as compared with Ti–6Al–4V substrates and the culture plate as controls. There is no noticeable difference in cellular morphology among the BMG samples, and no cytotoxicity is detected. We speculate that the interaction of water molecules and matrix proteins with the surfaces of BMGs plays an important role in cell–substrate interactions and improved cell response. Copyright © 2013 John Wiley & Sons, Ltd.

Analysis of Structure and Abrasion Resistance of the Metal Composite Based on an Intermetallic FeAl Phase with VC and TiC Precipitates

Abstract Metal alloys with matrix based on an Fe-Al system are generally considered materials for high-temperature applications. Their main advantages are compact crystallographic structure, long-range ordering and structural stability at high temperatures. These materials are based on an intermetallic phase of FeAl or Fe3Al, which is stable in the range from room temperature up to the melting point of 1240°C. Their application at high temperatures is also beneficial because of the low cost of production, very good resistance to oxidation and corrosion, and high mechanical strength. The casting alloy the structure of which includes the FeAl phase is, among others, highaluminium cast iron. This study has been devoted to the determination of the effect of vanadium and titanium on the transformation of the high-aluminium cast iron structure into an in-situ FeAl-VC composite.

Vacancy-induced hardening in Fe-Al alloys

Hardness of Fe-Al alloys shows a non-trivial dependence on chemical composition and thermal treatment of samples and cannot be fully explained by consideration of intermetallic phases formed according to the equilibrium phase diagram of Fe-Al system. Hardening in Fe-Al alloys caused by quenched-in non-equilibrium vacancies was studied in this work. Non-equilibrium vacancies introduced into the alloys by quenching from 1000 °C were detected by means of positron annihilation spectroscopy. The concentration of quenched-in vacancies was found to strongly increase with increasing Al content from ≈ 10−5 at.−1 in the alloy with cAl = 18 at. % up to ≈ 10−1 at.−1 in the alloy with cAl = 45 at. %. Comparison of the vacancy concentration and the Vickers microhardness revealed that hardening is proportional to square root of concentration of quenched-in vacancies.

Study of Point Defects in Fe-Al System by Mössbauer Spectroscopy and XRD Method

In this work, the Mössbauer spectroscopy employed 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 concentration.

The Specific Heat Capacity and Oxidation Kinetics of NiAl, FeAl and TiAl Alloys

The specific heat capacity was calculated by DSC and the kinetics of oxidation was determined for alloys from the NiAl, FeAl and TiAl phase equilibrium system. The Ti48Al alloy contained an addition of 2 at.% of chromium and niobium. The highest value of heat capacity had the Ti-Al and Fe-Al alloys. At temperatures above 673K, the Ti48Al alloy showed an anomaly, that is, a lower value of the heat capacity. The change in heat capacity was related with an exothermic reaction. The oxidation of alloys was running according to either parabolic or cubic law. Alloys characterised by high thermal capacity showed a higher gain in weight. The slowest to oxidise was the Ni3Al intermetallic phase.

Mössbauer probe spectroscopy of the initial stage of mechanical alloying in a binary Mg-Fe system in comparison to Al-Fe and Si-Fe systems

This work compares the results from investigating a Mg-57Fe binary system with a 99: 1 atomic ratio to previously obtained data for systems based on Al and Si. It is shown that the necessary conditions of the process are the formation of a nanostructure state and the penetration of Fe atoms into the boundaries of the grains of the basic elements. Substantial differences are observed in the kinetics of nanostructure state formation and the consumption of Fe in the Mg → Al → Si series, due to the determining role of the chemical interaction of Mg (Al, Si) with Fe.

Microstructure and mechanical properties of titanium aluminide compositions containing Fe

Six titanium aluminide alloys, based on the Ti–Al–Fe system, in the composition space defining the limits of the three-phase (γ+α2+β/B2) field have been prepared. The effects of heat treatment temperature (1000°C and 1200°C) and cooling rate (water quenching and air cooling) on the microstructure and room temperature mechanical behaviour (as determined by a shear punch test) are reported. It is shown that additions of Fe between 1.4at% and 2.8at% to the binary Ti–44Al alloys may improve room temperature ductility without sacrificing strength. The presence of the disordered bcc phase, rather than the ordered B2 phase, is required to achieve higher room temperature ductility. The preferred microstructure contains β-phase between 15% and 20%, together with a fraction of lamellar (γ+α2) colonies between 30% and 70%. The remainder of the microstructure is γ-phase.

Determination of Thermal Diffusivity and Influence of Defect Structure in Alloys Based on the Fe-Al System

Alloys of the Fe-Al system are interesting due to occurrence of long-range order and many thermal vacancies at high temperature, which lead to not only significant hardening, but also cause changes of physical properties. High temperature diffusion is conditioned by structural defects in solids, such as vacancies, foreign atoms and dislocations influencing thermal characteristics of a solid solution, among others the thermal diffusivity coefficient. Measurement of thermal diffusivity was performed at room temperature using the laser flash method. For characterization of the defect structure, positron annihilation lifetime spectroscopy was used. The data were presented for alloys with 28 and 38 at.% aluminium without chromium and containing 5 at. % Cr addition. The results showed that thermal diffusivity decreased with aluminium content and deviation from stoichiometry. In the studies, different structural defects in the alloys were observed.

Experimental Investigation of the Al-Fe-Gd System at 773 K

The phase equilibrium of the Al-Fe-Gd plays an important role of development of bulk amorphous alloys and magnetocaloric materials. The entire isothermal section of the phase diagram for Al-Fe-Gd ternary system at 773 K has been investigated by means of x-ray powder diffraction, scanning electron microscopy with energy dispersive analysis, and optical microscopy. The existences of 13 binary compounds for the Al-Fe, Al-Gd, and Fe-Gd binary systems were confirmed. The binary phases, i.e., Al2Gd, Fe2Gd, and α-Fe17Gd2 present appreciable ternary solubility. Three ternary compounds: τ1-Al10Fe2Gd, τ2-Al8+xFe4-xGd (0 ≤ x ≤ 2), and λ-Al2−xFexGd (0.951 ≤ x ≤ 1.245) were determined. The isothermal section consists of 19 single-phase regions, 40 binary-phase regions, and 20 ternary-phase regions.