Papers by Keyword: Fe-Al Alloy

Abstract: The alloys based on intermetallic phases involving Al belong to a new group of heat-resistant materials. Their physico-chemical and mechanical properties allow to apply them in the operating conditions in corrosive environment and elevated temperature. Research conducted for many years has shown that these materials can work at temperature up to 1100°C without degradation of their occurrence in the environment containing oxygen and sulphur. Heat resistance of these materials is provided by forming the Al₂O₃ passive layer on the surface. This layer is a protective barrier, which hinders the oxygen diffusion into the surface. This paper presents the morphology of passive Al₂O₃ layer depending on the temperature of its formation. The study allows to define the surface condition for corrosion products carried out using scanning electron microscopy together with EDS X-ray microanalysis.

Abstract: Nanocrystalline powders of iron aluminum alloy of the Fe82Al18 nominal composition were prepared under air, hydrogen and nitrogen atmospheres from the Fe and Al elemental powders by mechanical alloying and also from the conventionally cast Fe82Al18 alloy by the high-energy ball milling. The intensive plastic deformation during high-energy mechanical treatment has introduced high concentrations of open volume defects and contributed to a rapid decrease in the crystallite size down to a nanoscopic range.The hydrogen atmosphere was found to be the most efficient for the Fe-Al mechanical alloying since it has resulted into the fully alloyed Fe82Al18 after 30 h of milling. On the other hand, the nitrogen and air atmosphere have slightly prevented mechanical alloying and after the same milling time the pure iron particles were still detected in the powder mixtures. This partial suppression of the mechanical alloying process is explained by a formation of thin iron nitride and/or oxide layers on the surface of Fe particles preventing mutual inter-diffusion of Fe and Al atoms.

Abstract: Surfacing of Fe-Al alloy layer is achieved on the surface of Q235 steel plate by using the twin wire consisting of one aluminum welding wire and one steel welding wire in the shielding of pure argon. When the ER1100 aluminum welding wire of Φ1.6mm and ER50-6 steel welding wire of Φ1.2mm are selected as the master wire and slave wire respectively, with preheating and interlayer temperature reaching 350°C by controlling filling volume of aluminum and steel , the Fe-Al alloy layer featured by well-formed welding line is thus gained with no macroscopic defect. As the mechanical performance testing shows, the shear strength of surface combining surfacing layer and steel substrate is higher than 270MPa. The rupture position is located in surfacing layer and it turns out to be brittle fracture; the micro-hardness of surfacing layer ranges from 320HV to 420HV. Abrasion resistance testing indicates that abrasion resistance of surfacing layer is better than that of base material. According to micro-structure observation, the welding line is a coarsening columnar structure with a great deal of precipitated phase. According to EDAX, the aluminum content of precipitated phase in surfacing layer ranges from 24% to 32% (at), and the steel content ranging from 76% to 68% (at) - it is thus considered a Fe3Al structure through XRD.

Abstract: Employing NH3/H2 gas mixtures, Fe-4.65at% Al alloy specimens were nitrided to assess how the presence of Al, originally dissolved in the ferrite matrix, influences the development of γ-Fe4N1-x phase in the surface adjacent region. The nitrided specimens were characterized by light microscopy, X-ray diffraction, Electron Backscatter Diffraction and Electron Probe Micro Analysis. Surprisingly, formation of ε-Fe2N1-x was observed, although, for the applied nitriding parameters (nitriding potential and temperature), only the formation of γ-Fe4N1-x would be expected in case of nitriding pure ferrite. An unusual plate-type morphology of γ-Fe4N1-x was observed, contrasting with the usual continuous layer-type growth observed upon nitriding iron, Fe-Cr and Fe-V alloys. These unexpected phenomena may be explained as consequences of the need to realize a very high nitrogen supersaturation in the ferrite matrix in order to initiate the precipitation of AlN.

Abstract: The influence of heat treatment on the amplitude dependence of internal friction in Fe - 11 at. % Al alloys with carbon contents in the range 0.005 - 0.2 at. % has been studied using an inverted torsion pendulum in the temperature range 300 – 950 K and a vibrating reed apparatus at room temperature. The specimens were annealed at 1273 K in vacuum and cooled down with different cooling rates in order to obtain different degrees of order. It was found that ordering is hardly avoidable in Fe - Al alloys with Al contents > 11 at. %. Ordered alloys are characterised by lower damping capacity due to higher coercivity caused by additional pinning of magnetic domain walls by antiphase boundaries. X-ray diffraction investigations indicate that water-cooling suppresses ordering in Fe - 11 at. % Al alloys while cooling in air or in furnace provokes D03–type ordering. Slowly cooled specimens are characterised by higher damping capacity due to lower coercivity than water cooled or plastically deformed specimens. The amplitude dependent magneto-mechanical damping was determined as the difference between amplitude dependent damping without and with saturating magnetic field (~ 20 kA/m). Magneto-mechanical damping was found to be proportional to the strain where the amplitude dependent damping is maximum and reciprocal to the coercivity and saturation polarisation. Cold rolling increases the coercivity and therefore decreases the magneto-mechanical damping. An increase of the grain size in the investigated samples by heat treatment leads to a qualitatively expected decrease of coercivity and therefore to an increase of magneto-mechanical damping.

Abstract: Industrial high damping steels based on the Fe - Al metallic system have been studied. The optimization of the crystalline structure of the industrial damping steels has been shown to be very important for the achievement of high mechanical properties including high fatigue resistance. In the same time the achievement of high damping properties strongly depends on the magnetic domain structure of the material and, consequently, on the heat treatment procedure.

Abstract: High damping Fe - Cr and Fe - Al alloys have been studied in two different states: in the high damping state and in the suppressed damping capacity state. It has been shown that magnetic domain structures of Fe - Cr and Fe - Al alloys are fundamentally different in the high damping state and in the state with the suppressed damping. Magnetic domain structure corresponding to the high damping state can be characterized by an enhanced volume fraction of the easy movable 90o-domain walls, but the state with the suppressed damping capacity can be characterized by the enhanced volume fraction of the 180o-domain boundaries.

Abstract: The corrosion behavior of pre-treated Fe–Al alloy in a sulfuric acid solution and chloride-containing solution was studied. Alumina layer formed at 1073–1173 K on the surface of Fe–Al alloy improves the corrosion resistance of the alloy, whereas that at 1273 K does not improve it. This was explained by the defects of Al2O3 layer, the fraction of Al2O3 in the oxides, crystallity of Al2O3, and residual stress in the oxide layer. On the other hand, TiO2 layer produced by dip coating and subsequent annealing at 523–773 K slightly improved the corrosion resistance of the alloy. The effect of the oxide layer on the aqueous corrosion was discussed focusing on the quality of the oxide.

Abstract: The laminated composite of Fe–Al alloy and CrMo steel was fabricated by clad rolling to provide additional properties to the steel such as corrosion resistance, strength, and light weight. Three layered composite consisting of alloy/steel/alloy was succesfully fabricated using the process condition to satisfy the criteria for simultaneous deformation of different materials. The fabricated composite could be cold rolled to 120 μm thickness (99.8 % reduction), and wound to a coil without damage. The corrosion resistance of the composite in a sulfuric acid solution was comparable to that of monolithic CrMo steel, and it depends on the aluminium content of the Fe–Al alloy. The aluminium content dependence of the corrosion behavior is explained by the corrosion potential (Ecorr) of the Fe–Al alloy derived from the polarization curves in the solution. In order to improve the corrosion resistance of the composite, pre-oxidation treatment was conducted to form Al2O3 layer to protect the substrate. Analyses by XPS and SIMS show that the Al2O3 oxide fraction increases with the oxidization temperature and Al content of the alloy. The pre-oxidation treatment improved the corrosion resistance of the composite in a sulfuric acid solution. It is concluded that the effect of oxidation on the corrosion resistance is due to the formation of Al2O3 oxide and the Al2O3 fraction in the oxides.

Abstract: It is shown that industrial high damping steels based on the Fe-Al metallic system are characterized by a very high level of internal dissipation of elastic energy. The specific damping capacity of industrial steels exceeds 40 % and their damping properties are close to those of highpurity damping alloys based on the Fe-Al system. Mechanical properties of damping steels are similar to those of conventional construction steels. High level of properties of damping steels can be explained by their specific crystalline and magnetic structure.