Papers by Keyword: Iron Aluminide

Abstract: Fe3Al intermetallic compounds and several (Fe,Cr)3Al alloys with Cr content from 3 to 25 % have been studied using isothermal mechanical spectroscopy. The Zener relaxation caused by reorientation of pairs of substitute atoms in Fe is observed in all studied alloys and used to evaluate the activation parameters of Al (Cr) atom jumps in Fe. The second internal friction peak at higher temperatures was observed only in Cr containing alloys. Isothermal mechanical spectroscopy (employed frequency from 10-4 to 102 Hz) gives some advantages as compared with ordinary techniques, i.e. study of anelasticity as a function of temperature. It allows to avoid transient effects and to measure materials in a state close to equilibrium. This allows to distinguish clearly between Al atom diffusion in Fe3Al in B2 and D03 states (activation energies for Fe – 26 Al in the B2 range the HB2 ≈ 235 kJ/mol, and in the D03 ordered range the HD03 ≈ 286 kJ/mol). Effect of chromium on the Zener relaxation is analysed.

Abstract: Fracture behaviour of two intermetallic alloys based on FeAl and Fe3Al was studied. On the alloys Fe-40Al-1C (at%) and Fe-29.5Al-2.3Cr-0.63Zr-0.2C (at%) (FA06Z), a basic characterization, the fracture toughness tests and fractographic analysis were carried out. Tensile tests and fracture toughness tests were performed at 20, 200, 400 and 600°C. The fracture toughness values range from 26 MPa.m1/2 at 20°C to 42 MPa.m1/2 at 400°C. In addition, Jintegral dependence on
a obtained by potential method was measured. The fractographic analysis showed that samples fractured at 20, 200 and 400°C in the tensile or fracture toughness tests exhibit transgranular cleavage fracture, while at 600°C the ductile dimple fracture predominates.

Abstract: The characteristics of Al-coating materials on low carbon steel sheets during high temperature oxidation process were investigated. The phases’ evolution and growth were systematically evaluated by SEM/EDS and XRD. The hardness distribution from the surface to the steel substrate was measured to check the brittleness of iron aluminides coating layers. The oxidation properties of coating materials were investigated using weight gain method. Intermetallic compound recognized as FeAl3 was initially formed on the interface between steel substrate and coating materials. After exposing the specimens at elevated temperature, FeAl3 layer was gradually transformed into Fe2Al5, FeAl2, and FeAl+Fe3Al. Oxidation rate increased fastly after α-Al in the coating completely transformed at 650 °C. The brittle FeAl3 and Fe2Al5 have the lower resistance to oxidation because the easier cracking during intermetallic reaction.

Abstract: In this study, the distribution of colloidal nano-gold particles on the nanoporous surfaces of FeAl single crystals was investigated. Colloidal nano-gold particles were dropped onto the nanoporous surface, and their distribution was observed by TEM. Some of nano-gold particles located at the edges of nanopores. A few additional attempts to improve the wettability of the surfaces were made using surface treatments. As a result, the frequency of nano-gold particles put into nanopores was achieved up to 98.3%.

Abstract: Aqueous corrosion behaviors of Fe3Al-based iron aluminides were investigated. From the result of cyclic anodic polarization tests conducted in 3.5 wt.% NaCl solution at 25, 48, 72 and 95°C, as the temperature increased, the resistance to pitting corrosion decreased significantly, especially over the range of 25~48°C. From the result of crevice corrosion tests, no crevice corrosion occurred on FAL-Mo in the lower chloride-containing solution (200 ppm Cl-), however, FAL-Mo did not perform as well as the 304L SS in the higher chloride-containing solution (3.5 wt.% NaCl). From the result of anodic polarization tests performed in sulfur-compound solutions, additions of Cr and Mo to the Fe3Al-based iron aluminides tend to improve the aqueous corrosion resistance. Aqueous corrosion behaviors with different Al content evaluated by cyclic anodic polarization test in the chloride-containing solution exhibited the more stable passive behavior and the higher pitting resistance as Al contents increased.

Abstract: Iron aluminides exhibit good resistance to high-temperature oxidizing and sulphidizing environments and have potential for structural applications at high temperatures under corrosive environments. In this study, an Fe-Al intermetallic compound was prepared by multi-layered roll-bonding of elemental Fe and Al foils. The process consisted of the accumulative roll-bonding (ARB) for making a laminated Fe/Al sheet and the subsequent heat treatment promoting a solid-phase reaction in the laminated Fe/Al sheet. Accumulated foils were rolled and bonded at room temperature or 573 K. A pulsed electric current sintering (PECS) process was used for the subsequent heat treatment. The microstructures produced at each processing stage were characterized by optical microscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). Vickers microhardness testing was used for hardness determination. A homogeneous intermetallic compound of Fe3Al or FeAl could be obtained after the subsequent heat treatment for 1.8 ks at 873 K and for 3.6 ks at 1173 K.

Abstract: Mechanical properties of thermomechanically fabricated D03 Fe-33Al and B2 Fe-38Al intermetallic alloys containing Zr were investigated by means of tensile test and microhardness measurement. The Zr-added ternary alloys showed fine-grained microstructure containing large (Fe,Al)12Zr τ1 phase particles, while the binary alloy showed a single-phase microstructure consisted of coarse recrystallized grains. By introducing the large τ1 phase particles to Fe-Al matrix, tensile strength at room temperature as well as at high temperature (873K) was enhanced but tensile ductility at both temperatures decreased. On the other hand, it was found that vacancy hardening which was significant in the alloys with high contents of Al (i.e., Fe-38Al) was reduced by the large τ1 phase particles.

Abstract: The pseudoelastic behavior of Fe3Al single crystals doped with an extra element (e.g. Ti, V, Cr, Mn, Co, Ni, Si, Ga, Ge) was investigated. In binary Fe-23.0at.%Al crystals with the D03 structure, 1/4[111] superpartial dislocations moved independently dragging the nearest-neighbor anti-phase boundaries (NNAPB) during loading. During unloading, the NNAPB pulled back the superpartials decreasing its energy resulting in a giant pseudoelasticity of which the recoverable strain is about 5 %. Addition of a third element significantly affected the pseudoelastic behavior of Fe3Al single crystals. Mn- or Ga-doped crystal demonstrated a giant pseudoelasticity. In particular, Ga-doping was found to be effective in the enhancement of the pseudoelasticity. On the other hand, the amount of strain recovery decreased upon doping of the other elements. The frictional stress of the superpartials, the back stress of the NNAPB and ordered domain structure in the crystals changed upon doping, which was closely related to the pseudoelastic behavior.

Abstract: Structure investigation results for MASHS powder Fe40Al/Al2O3 are presented. The powder structure formation proceeds via two stages. On the first step (mechanical activation) aluminothermal reaction takes plays in the system Fe+Al+Fe2O3, leading to formation of nanocomposite precursor Fe-Al-Al2O3. On the second step (SHS), iron and aluminum reacts, forming intermetallic FeAl. As-synthesized composite powder completely inherits the precursor structural morphology in spite of the phase transformations taking place during the production process. Such a production route provides the formation of intergrowth nanocomposite material structure with improved interfacial strength.

Abstract: The paper examines the phase evolution in blends consisting of different proportions of stainless steel (SS316) and Al (0, 25, 65 and 85 wt. %) powders during high-energy ball milling by x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy. An attempt has also been made to study the mechanical property of the bulk samples obtained by hot pressing the ball milled powder blend at suitable a temperature and pressure. The results of microstructural changes and mechanical property and the ability of consolidation of the amorphous/nanocrystalline powders by high-pressure techniques to develop engineering components has been discussed and highlighted.