Binary Fe-Al Alloys Research Articles

Quantitative x‐ray fluorescence analysis of Fe—Al and Cu—Fe binary alloys using selective excitation

AbstractThree excitation modes for Fe—Al binary alloys were compared using an energy‐dispersive spectrometer system. A set‐up with an appropriate secondary target to achieve selective excitation of aluminium proved to be a good solution for the determination of aluminium with a precision of ±0.2 at.% Al for concentrations between 40 and 60 at.% and an extrapolated lower limit of detection (LLD) of 0.04 wt.% (0.08 at.%) for Al in Fe. Experimental data were compared with theoretical calculations and showed good agreement. The geometry of the irradiation chamber improved the peak‐to‐background ratio due to polarization effects. The method was also applied for the analysis of Cu—Fe binary alloys with low Fe concentrations (1 at.%) with similarly good results, and an extrapolated LLD in the ppm range for Fe in Cu. A non‐destructive analysis was required as the samples were needed for Mössbauer spectrometric experiments in later investigations.

Effects of minor alloying elements on the welding behavior of FeAl alloys for structural and weld-overlay cladding applications

This paper reports that recent properties studies of FeAl alloys for high-temperature structural applications have been expanded to include improved weldability. a base FeAl (B2-phase) binary allow composition of Fe-36 at. % Al appears to offer a nearly optimum combination of oxidation/corrosion resistance and mechanical behavior. FeAl alloys show outstanding oxidation resistance to temperatures of [gt] 1100[degrees]C, corrosion resistance in sulfidizing environments at 800-900[degrees]C, and excellent resistance to corrosion in molten nitrate salts at 650[degrees]C (1-3). While binary FeAl alloys generally have poor room-temperature ductility, and are weak above about 600[degrees]C, alloying effects can significantly improve their mechanical properties at room- and high-temperatures. Furthermore, studies of room-temperature brittleness of FeAl alloys have shown that hydrogen released at crack-tips from moisture in air causes low ductility at room-temperature, so that these alloys are not inherently brittle, but are sensitive to environmental effects. Results of systematic studies of minor element alloying effects have shown that small additions of molybdenum (0. 2 at. %) improve oxidation resistance at 1000[degrees]C, combined additions of small amounts of zirconium and boron (0. 05 at. % and 0. 24 at. %, respectively) produce room-temperature ductility [gt] 10%, and small additions of molybdenum (0. 2 at. %) improvemore » tensile and creep-rupture strength at 600[degrees]C, especially when combined with Zr + B or chromium plus boron. However, preliminary results show that such alloys hot-crack during welding. Because there is almost no data on welding of FeAl alloys, this study was undertaken to: identify the alloying elements associated with the hot-cracking, and attempt to minimize or eliminate hot-cracking during welding by controlling the minor alloying additions.« less

Stiffness constants and dislocation line energies and tensions of binary and ternary iron-rich FeAlSi alloys

The adiabatic stiffness constants C ik of binary and ternary Fe 3Al xSi y alloys, 0 ⩽ x,y ⩽ 1.3, 0.6 ⩽ x + y ⩽ 1.3 have been measured in the temperature range 90–360 K. The stiffnesses were derived from the velocities at which ultrasonic pulses propagated in single crystals. Prior to the measurements of the C ik, the specimens had been quenched from successively lower temperatures: 1273, 1073 and 723 K. According to the current phase diagrams, the state of order of most of the present binary alloys changes in the quoted temperature range. In most cases this affects the C ik. For binary FeAl alloys there is a strong ΔE effect. From the stiffnesses, the dislocation line energies and tensions have been calculated within the framework of the linear anisotropic theory of elasticity.

DO3-B2-α phase relations in Fe-Al-Ti alloys

A transmission electron microscopic investigation has been conducted to determine the phase relations, transformation temperatures, and microstructures in Fe-Al-5 at. pct Ti alloys with Al content varying from 18 to 25 at. pct. As compared to the binary Fe-Al alloys, the effects of Ti addition are (i) a significant expansion of the (α + DO3) phase field, (ii) increased transition temperatures, and (iii) a tendency of the DO3 thermal anti-phase domain boundaries to exhibit anisotropy with a preference to lie on {100} planes.

Phase decompositions of Fe-Si-Al ordered alloys

Stable structures of Fe-Si-Al ternary alloys and Fe-Si and Fe-Al binary alloys containing up to about 40 at% solute atoms were investigated by means of transmission electron microscopy. The following results were obtained. Two types of phase separation, B2+DO3 andα + DO3 were observed in the alloys whose compositions lie in a narrow band connecting Fe-10 to 14 at% Si with Fe-20 to 25 at % Al and also in the neighbourhood of a Fe-30 at%Al-3 at% Si alloy. Such compositions of the alloys are located in the phase boundary of B2 and DO3 single phases orα and DO3 single phases. The phase separation in the Fe-Si-Al and Fe-Si alloys produce the 〈100〉 modulated structure which differs from the morphology formed by the phase separation of the Fe-Al system.

Determination of the long-range order parameters of Fe3Al alloys by Mössbauer spectroscopy and X-ray diffraction technique

Binary Fe-Al alloys in the range (21–25.2) at.% Al were investigated with use of Mossbauer spectroscopy and X-ray diffraction technique. A linear correlation between the hyperfine field Hhf and the isomer shift IS was found for ordered and disordered alloys. The results of Mossbauer investigations are compared with those obtained by X-ray diffraction technique.

A Review of Recent Developments in Iron Aluminides

AbstractThis paper presents a review of recent research conducted at the Air Force Wright Aeronautical Laboratories (AFWAL)/Materials Laboratory to develop iron-aluminides as elevated temperature structural materials. The research consisted of investigations on the microstructure, tensile behavior, deformation, and fracture mechanisms of the DO3 and B2 ironaluminides. Binary Fe-Al alloys with a wide range of Al contents, solidsolution ternary alloys and precipitation- and dispersion-strengthened two-phase alloys have been investigated. It is shown that iron-aluminides have a potential to be structural materials at least up to 650°C.

Anodic Polarization Behavior of Iron-Aluminum Alloys in Sulfuric Acid Solutions

Abstract Potentiostatic anodic polarization behavior of annealed, high purity Fe and 6 binary Fe-Al alloys containing up to 16 Wt% Al was investigated in hydrogen saturated, 1, 5, and 10N sulfuric acid solutions at 22 ± 1 C. All specimens exhibited active, passive, and transpassive behavior in all acid environments. Tafel lines for anodic dissolution in the active potential region shifted in the active potential direction with increasing aluminum content and increasing pH. Tafel lines for oxygen evolution in the transpassive potential region shifted in the noble potential direction with decreasing pH and appeared to be independent of the aluminum content. Tafel slopes for anodic dissolution and oxygen evolution varied, respectively, from 0.040 to 0.078 and 0.060 to 0.105 volt per decade of current density, and both appeared to be composition and pH independent. Corrosion potentials (Ecorr) for pure Fe and the Fe-Al alloys were linear functions of pH over the pH range −1.12 to +1.29. Slope dependency of th...

Structure and properties of nitrided binary Fe-Al, Fe-V, and Fe-Ti alloys

1. The formation of phases with nitrogen in the diffusion layer of binary alloys of iron with aluminum, vanadium, and titanium after nitriding at 500° for 1h occurs in the conformity with the Fe-N phase diagram. 2. With increasing amounts of aluminum in the alloy the amount of e phase decreases, while the amount of γ′ phase increases and it extends into the grains in the form of whiskers. 3. Aluminum has a slight effect on the hardness of the α solid solution; titanium and vanadium substantially increase the hardness after nitriding at 500°. 4. Sectioning and electron microscopic and electron diffraction analysis of the diffusion layer on nitrided Fe-Al alloys showed that the surface consists of e phase, with γ′ phase alloyed with aluminum beneath it. The sublayer contains two excess nitride phases-Fe4N and Fe16N2. 5. Besides e and γ′ phases on the surface of nitrided Fe-Al alloys, we observed separate crystals of Al2O3. 6. No precipitates of stable hcp AlN were observed on the surface of Fe-Al alloys after nitriding. 7. The diffusion sublayer of Fe-V and Fe-Ti alloys nitrided at 500° contains a second nitride phase-Fe16N2 — that is isomorphous with the matrix, in addition to precipitates of γ′ phase. The effect of diffusion scattering is noticeable on the matrix reflections in the form of streaks, indicating the formation of coherent GP zones.