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R Balasubramaniam - One of the best experts on this subject based on the ideXlab platform.
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electrochemical impedance spectroscopy and cyclic voltammetry study of carbon alloyed Iron Aluminides in sulfuric acid
Corrosion Science, 2006Co-Authors: A K Nigam, R Balasubramaniam, S Bhargava, R G BaligidadAbstract:Abstract The electrochemical behaviour of three carbon-alloyed Iron Aluminides Fe–11.0Al–0.5C, Fe–10.5Al–0.9C and Fe–10.5Al–0.8C–0.2Ce (in wt%) has been studied in 0.25 mol/l H 2 SO 4 solution using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry techniques. A 0.05% C steel was used for comparison purposes. EIS studies were conducted after 1 h and 24 h of immersion in the acidic solution. The results obtained indicated improved surface film properties in the case Ce-alloyed Iron Aluminides as compared to the other two Iron Aluminides. This has been attributed to enhancement in surface passivity with Ce addition. Cyclic voltammetry experiments indicated that addition of Ce modified the electrochemical reactions on the surface.
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Effect of cerium addition on the corrosion behaviour of carbon-alloyed Iron Aluminides
Corrosion Science, 2006Co-Authors: S. Sriram, R Balasubramaniam, M. N. Mungole, S. Bharagava, R G BaligidadAbstract:Abstract The effect of Ce addition on the microstructure and corrosion behavior of carbon-alloyed Iron Aluminides Fe–20.0Al–2.0C, Fe–18.5Al–3.6C and Fe–19.2Al–3.3C–0.07Ce (in at.%) has been studied. The potentiodynamic polarization behaviour of the alloys was evaluated in freely aerated 0.25 mol/l H 2 SO 4 . A 0.05% C steel was used for comparison purposes. All the alloys exhibited active–passive behaviour in the acidic solution. The addition of Ce destroyed passivity as indicated by lower breakdown potentials in polarization studies. This has been related to the finer distribution of the carbides in the microstructure. Corrosion rates were evaluated by immersion testing. The Iron aluminide with Ce addition exhibited a lower corrosion rate compared to the Aluminides without Ce addition. This has been attributed to modifications in surface film with Ce addition. Scanning electron microscopy of corroded surfaces indicated that the carbon-alloyed intermetallics were susceptible to localized galvanic corrosion due to the presence of carbides in the microstructure.
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Hot corrosion of carbon-alloyed Fe3Al-based Iron Aluminides
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: R Balasubramaniam, M. N. MungoleAbstract:Abstract The oxidation and hot corrosion behavior of two Fe 3 Al-based Iron Aluminides, Fe–25Al and Fe–27.5Al–3.7C (at.%) have been studied at 1100, 1225 and 1330 K. Hot corrosion studies were conducted by coating the specimen surfaces with 2.5±0.2 mg cm −2 of Na 2 SO 4 prior to exposure in pure oxygen. The oxidation kinetics of the carbon-alloyed Iron aluminide were generally slower than that of the binary alloy. Alumina was identified in the scale after oxidation of both the alloys. The rates of hot corrosion were generally higher than the rates of oxidation for both the alloys. The presence of α-Fe 2 O 3 in addition to alumina was indicated by X-ray diffraction analysis of the scales present on the surface of the samples after hot corrosion. Fourier transform infrared spectra from the spalled scales in hot corrosion divulged the presence of α-Al 2 O 3 , α-Fe 2 O 3 and sulfate. Cross-sectional microscopy revealed that the scale–metal interfaces were pitted under hot corrosion conditions and the pits contained aluminum sulfide. Aluminum sulfide was also identified along the grain boundaries in the binary aluminide matrix below the scale–metal interface. The hot corrosion process has been explained based on sulfide formation and its subsequent oxidation. The lower rate of hot corrosion in the carbon-alloyed Iron aluminide has been related to the blocking effect of carbides, present along the grain boundaries, for the penetrating sulfur.
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hydrogen in Iron Aluminides
Journal of Alloys and Compounds, 2002Co-Authors: R BalasubramaniamAbstract:Abstract Ordered intermetallic alloys based on the stoichiometric Iron aluminide compositions of Fe3Al and FeAl are being actively considered for high-temperature structural applications. They exhibit poor room temperature ductilities due to hydrogen embrittlement. Surface passive films reduce embrittlement by lowering the rate of hydrogen liberation on the surface. This has been explained by the mixed potential theory. The mechanism of hydrogen embrittlement in Iron Aluminides (namely, decohesion) has been addressed. Methods to minimize the degree of embrittlement have been discussed. These include passivity induction, addition of oxygen active elements, recrystallization inhibition and addition of irreversible hydrogen traps. The diffusion of hydrogen in Iron Aluminides has also been reviewed.
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high temperature oxidation of fe3al based Iron Aluminides in oxygen
Corrosion Science, 2001Co-Authors: N Babu, R Balasubramaniam, Avijit GhoshAbstract:The isothermal high-temperature oxidation behavior of Fe3Al-based Iron Aluminides in oxygen has been studied. Fe–25Al was oxidized at 1225, 1330, 1425 and 1530 K, while Fe–28Al, Fe–24Al–5Cr, Fe–24Al–5Ti, Fe–28Al–2Cr and Fe–30Al–4Cr (all compositions in atom percent) were oxidized at 1330 K. The weight gain data were analyzed and rate constants (kp) determined by assuming a parabolic rate law. The variations of instantaneous parabolic rate constant with time reflected the complexity of the oxidation behavior. These have been attributed to the changes taking place in the nature and properties of the scale as a function of time. The values of kp for oxidation of Fe3Al were one to two orders of magnitude lower than those for Ti3Al-based intermetallics. As revealed by X-ray diffraction, the scale formed on Fe–25Al was predominantly α-Al2O3 at higher temperatures, while θ-Al2O3 was observed after oxidation at lower temperatures. The observed kinetics matched with α-Al2O3-formation kinetics at higher temperatures and θ-Al2O3-formation kinetics at lower temperatures. For all the other intermetallics, only α-Al2O3 was identified at 1330 K. The whisker morphology of θ-Al2O3 and the ridged morphology of α-Al2O3 were confirmed by scanning electron microscopy. Alloying with Cr or Ti increased the oxidation rate of Iron Aluminides, especially during the initial stages. Addition of Ti changed the nature, color, and morphology of the scale, leading to improved adherence.
J H Schneibel - One of the best experts on this subject based on the ideXlab platform.
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vacancy strengthening in fe3al Iron Aluminides
Intermetallics, 2014Co-Authors: G Hasemann, J H Schneibel, E P George, Manja KrugerAbstract:Abstract The room temperature strength of FeAl alloys can be increased significantly by freezing in the high thermal vacancy concentrations present at elevated temperatures. In contrast, because of their lower thermal vacancy concentrations, vacancy strengthening in quenched Fe3Al alloys is believed to be much smaller and has not received much attention to date. In the present work, the influence of annealing time and quench temperature on the room temperature strength of extruded and recrystallized Fe3Al alloys is evaluated. For aluminum concentrations between 28 and 32 at% and quench temperatures between 400 and 900 °C both the magnitude and the kinetics of strengthening are found to be consistent with reported values for the thermal vacancy concentrations and vacancy migration rates. To assess the potential contributions of other strengthening mechanisms, appropriate heat treatments will need to be designed in follow-on studies that alter microstructural features relevant to those mechanisms while maintaining a constant vacancy concentration.
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strengthening of Iron Aluminides by vacancies and or nickel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1998Co-Authors: J H SchneibelAbstract:Abstract At room temperature, Iron Aluminides may be strengthened by quenched-in thermal vacancies as well as by solid solution alloying additions. Since the separation of these two effects requires precise vacancy concentration measurements, a novel extrapolation procedure was developed to determine vacancy volume fractions with an accuracy approaching 1 part in 10 000. The rate of removal of quenched-in vacancies during annealing, as well as the hardening by vacancies, were found to be influenced by solid solution additions of Ni to Fe-45 at.% Al. First, yield strength and density measurements showed that nickel slows down the removal of vacancies, making it more difficult to obtain Iron Aluminides with low vacancy concentrations. Second, in the absence of vacancies, additions of nickel result in substantial strengthening. Third, for high vacancy concentrations (e.g. 0.2 vol.%), nickel additions can cause softening. These results are rationalized in terms of the interaction between the vacancies and the nickel atoms.
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tensile ductility slow crack growth and fracture mode of ternary b2 Iron Aluminides at room temperature
Intermetallics, 1997Co-Authors: J H Schneibel, E P George, I M AndersonAbstract:Abstract B2 Iron Aluminides containing 45 at% Al and microalloying additions of 0.2 at% B and 0.1 at% Zr were alloyed with 5 at% of the 3 d transition elements Ti, V, Cr, Mn, Co, Ni, and Cu. The extruded and annealed alloys were essentially single phase except for isolated stringers which appeared to be borides. Their strength, tensile ductility in air and dry oxygen, and slow crack growth behavior in air were determined at room temperature. Consistent with water vapor-induced embrittlement, the tensile ductility depended on the envIronment, and the crack growth resistance on the crack velocity. The binary Iron aluminide Fe-45 at% Al exhibited ductilities of 8 and 19% in air and dry oxygen, respectively. Ternary alloying increased in most cases the yield strength, and always reduced the ductility. Different alloying additions influenced the slow crack growth behavior in different ways. For example, the crack growth resistance of Fe-45Al-5Cr (at%) did not depend significantly on the crack velocity, whereas that of Fe-45Al-5Mn (at%) decreased strongly as the crack velocity decreased. Alloying additions which are to the left of Iron in the periodic system, such as Ti, Cr, and Mn, were associated with intergranular fracture, whereas Co, Ni, and Cu additions, to the right of Iron, were associated with substantial amounts of transgranular fracture. For a given alloy, the fraction of intergranular fracture increased with decreasing crack velocity. The experimental results are rationalized in terms of the envIronmental sensitivity of the grain boundaries, the increase in yield strength upon alloying, and the site occupation of the ternary alloying additions. This does, however, not preclude the influence of additional factors such as differences in the chemical composition and strength of the grain boundaries in the different alloys.
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strength thermal defects and solid solution hardening in nickel containing b2 Iron Aluminides
MRS Proceedings, 1996Co-Authors: J H Schneibel, Paul Munroe, L M PikeAbstract:Nickel-containing ternary Iron Aluminides with an aluminum concentration of 45 at.% were investigated with respect to room temperature strength, equilibrium vacancy concentration, and the kinetics of vacancy removal. As compared to binary Iron Aluminides with the same Al concentration, nickel additions reduce the thermal equilibrium vacancy concentration at 1,273 K, whereas they increase this concentration at 973 K. Furthermore, at low temperatures such as 673 K, nickel additions increase dramatically the time needed to reach vacancy equilibrium. During prolonged annealing at 673 K, the density of dislocations in Fe-45Al-3Ni (at.%) increased by an order of magnitude. This suggests that dislocations act as sinks for vacancies. At the same time, the number density of small (20--50 nm) voids decreased, indicating that they were not stable in the absence of substantial vacancy supersaturations. The findings show also that the solid solution strengthening of Iron Aluminides due to Ni is much weaker than previously thought.
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solid solution strengthening in ternary b2 Iron Aluminides containing 3d transition elements
Intermetallics, 1996Co-Authors: J H Schneibel, E D Specht, W A SimpsonAbstract:Abstract The room temperature yield strengths of extruded ternary Iron Aluminides with the composition Fe-45Al-5X-0.2B-0.1Zr (at%), where X stands for Ti, Cr, Mn, Fe, Co, Ni or Cu, were measured. With the exception of the Mn-containing alloy, all alloys showed solid solution strengthening following a 1 week/673 K vacancy removal anneal. Densities, lattice parameters and elastic constants were measured to determine vacancy concentrations as well as atomic size and modulus misfits. Although the strengthening could not be well described by established theories for dilute binary alloys, it could be reasonably well correlated with the magnitude of the atomic size misfit of the ternary alloying additions.
Seetharama C Deevi - One of the best experts on this subject based on the ideXlab platform.
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properties of incommensurate spin density waves in Iron Aluminides invited
Journal of Applied Physics, 2004Co-Authors: D R Noakes, Seetharama C Deevi, A S Arrott, M G Belk, J W Lynn, R D ShullAbstract:Neutron diffraction in Fe(Al) reveals incommensurate spin density waves (SDWs) in alloys known to be spin glasses. The wave vectors for crystals of Fe(34Al), Fe(40Al) and Fe(43Al) show n varying from 11 to 6 for q=2π(h±1/n,k±1/n,l±1/n)/ao, where (h,k,l) and ao characterize the parent bcc lattice of the CsCl structure. The magnetic reflections are present far above the spin-glass freezing temperatures. These SDWs keep the spins on nearest-neighbor Fe atoms close to parallel, in contrast with SDWs in Cr, which keep nearest-neighbor spins close to antiparallel. The competition between near-neighbor Fe–Fe ferromagnetism and 180° superexchange through the Al site has been used to explain the spin-glass behavior, but the appearance of the SDWs calls for a more fundamental source of the periodicity. The phase shift mechanism for SDW interactions with magnetic moments is invoked to explain the breadth of the peaks, which resemble the results for Cu(Mn), Pd(Mn), and Pd(Cr). The data are interpreted using cubic sym...
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incommensurate spin density waves in Iron Aluminides
Physical Review Letters, 2003Co-Authors: D R Noakes, Seetharama C Deevi, A S Arrott, M G Belk, Q Huang, J W Lynn, R D ShullAbstract:Neutron diffraction in Fe(Al) reveals incommensurate spin density waves (SDWs) in alloys known to be spin glasses. The wave vectors for crystals of Fe(34Al), Fe(40Al), and Fe(43Al) show $n$ varying from 11 to 6 for $\stackrel{\ensuremath{\rightarrow}}{q}=2\ensuremath{\pi}(h\ifmmode\pm\else\textpm\fi{}1/n,k\ifmmode\pm\else\textpm\fi{}1/n,l\ifmmode\pm\else\textpm\fi{}1/n)/{a}_{0}$, where $(h,k,l)$ and ${a}_{0}$ characterize the parent bcc lattice of the CsCl structure. The magnetic reflections are present far above the spin-glass freezing temperatures. These SDWs keep the spins on nearest-neighbor Fe atoms close to parallel, in contrast with SDWs in Cr, which keep nearest-neighbor spins close to antiparallel.
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electrical properties of Iron Aluminides
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1998Co-Authors: A C Lilly, Seetharama C Deevi, Z P GibbsAbstract:Abstract Electrical properties of Iron Aluminides covering a wide range of Al contents have been investigated using a four-probe electrical resistivity method at room temperature. Room temperature electrical resistivities of Iron Aluminides indicate a monotonic increase with Al content up to ∼ 33 at.% Al, followed by a steep decrease with further increase of Al content. Heat treatments in a vacuum at 1100°C for 1 h, and at 700°C for 2 h followed by cooling to room temperature in helium and argon exhibited an identical trend, with resistivity values comparable to the values obtained after a prolonged annealing. A similar trend was observed with the fine grained sheets of FeAl obtained by roll compaction and sintering. Interpretation of literature band calculations with the help of the Mott and Jones model suggests that the electrical resistivity should increase with an increase in Al content until ∼ 33 at.% Al is reached, due to the filling up of holes by the electrons from Al in the narrow d-bands. Further addition of Al above 33 at.% value essentially adds more electrons to a nearly free electron conduction band and the resistivity falls sharply thereafter approaching the resistivity of Al.
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yielding hardening and creep behavior of Iron Aluminides
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1998Co-Authors: Seetharama C Deevi, R W SwindemanAbstract:Abstract Engineering properties of powder processed Iron Aluminides(Fe-24 wt.% Al alloy).obtained by hot extrusion and roll compaction of water atomized powder were investigated to assist in the structural analysis of FeAl components exposed to short-time, thermal-mechanical loadings. The test matrix for high-temperature deformation of FeAl incorporated powder processed sheet and bar product forms. Tensile, cyclic, creep and relaxation tests were carried out from room temperature to 750 ο C on the bar products. Sheets were characterized for their tensile and creep properties. The experimental data were sufficient to provide rules for yielding, hardening and creep in the temperatures range of 23–750 ο C. The room temperature curve adjusted for the temperature dependence of the modulus may be used for the yield and hardening behavior between 23 and 600 ο C. Above 600 ο C, the yield can be obtained from the tensile curve for the temperature of interest. Exposure to 750 ο C causes sufficient recovery and resets the kinematic and isotropic hardening parameters to their initial values. Variation of Young's modulus with increase of temperature is also presented. Limited creep behavior is also discussed. Structural analysis of the FeAl components can be carried out using finite element modeling techniques with the availability of the tensile, cyclic, relaxation and creep behavior of FeAl at elevated temperatures.
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nickel and Iron Aluminides an overview on properties processing and applications
Intermetallics, 1996Co-Authors: Seetharama C Deevi, V K SikkaAbstract:Intermetallics have long been recognized as potential candidates for a variety of high-temperature structural applications to operate well beyond the operating temperatures of conventional materials due to their excellent oxidation and corrosion resistances. In this paper, we compare and contrast the mechanical properties such as yield strength, ultimate tensile strength, and tensile elongations of Ni3Al-based alloys, Fe3Al-based alloys, and FeAl alloys with several of the commercially available superalloys such as Haynes 214 (NiCrAlY), MA-956 (yttriadispersed FeCrAlY), and a FeNiCr alloy (HU steel) used in carburizing applications. Our comparisons clearly show that cast and wrought Ni3Al-based alloys exhibit superior mechanical properties over the commercially available alloys such as the FeNiCr HU steel and Haynes 214. Electrical resistivity of Iron Aluminides increases with the increase of aluminum content, and the electrical resistivities of Fe3Al- and FeAl-based alloys are 50–100% higher than those of commercially available heating-element materials. Processing problems associated with the melting and casting of intermetallics are discussed in light of their large, negative heats of formation; high-aluminum content of intermetallics; and the safe operating temperatures of crucible materials for melting them. A furnace-loading sequence enabled us to properly utilize the heat of reaction of intermetallics resulting in the development of the Exo-Melt™ process for melting and casting of intermetallics for a variety of structural applications. The Exo-Melt™ process allowed us to cast a wide variety of structural intermetallic parts using sand, centrifugal, and investment casting techniques, and a total of 15 000 kg of intermetallic parts were cast by the Exo-Melt™ process during 1995.
Marian Kupka - One of the best experts on this subject based on the ideXlab platform.
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studies on hydrogen diffusivity in Iron Aluminides using the devanathan stachurski method
Journal of Physics and Chemistry of Solids, 2014Co-Authors: Marian Kupka, Karol Stepien, Katarzyna NowakAbstract:Abstract An electrolytic method for cathodic hydrogen saturation developed by Devanathan and Stachurski was successfully used to study hydrogen diffusivity in Iron Aluminides. Both an appropriate electrolyte and a saturating current density are required for this method. A proper form of the saturation curve was only obtained with 35% NaCl electrolyte, which removed the oxide film blocking hydrogen penetration without further corrosive destruction of the Iron aluminide. The optimum saturation current density for determining the most reliable diffusivity was 1.91 A/cm2, yielding Deff,H = 4.81 × 10−6 cm2/s for Fe–40 at.% Al.
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effect of hydrogen on room temperature plasticity of b2 Iron Aluminides
Corrosion Science, 2011Co-Authors: Marian Kupka, Karol Stepien, Katarzyna KulakAbstract:Abstract Different sensitivities to hydrogen embrittlement for the disordered and ordered B2 FeAl alloys have been investigated. The plasticity of annealed alloys (before hydrogenating) has been found to decrease with increasing the long-range order parameter. An intrinsic weakness of FeAl phase grain boundaries revealed at a high degree of ordering. The results of bending tests on specimens annealed and cathodically charged with hydrogen have shown that the influence of hydrogen on the plasticity diminishes with the increase in the degree of FeAl phase ordering.
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diffusivity of hydrogen in b2 Iron Aluminides
Scripta Materialia, 2006Co-Authors: Karol Stepien, Marian KupkaAbstract:The effect of the structure formed during a directional and volume solidification on the hydrogen diffusion coefficient in B2 FeAl alloys was investigated. Hydrogen diffusivity falls off with increasing aluminium content and the long-range order parameter. At the given content of aluminium in the B2 FeAl alloy, the hydrogen diffusivity does not depend on the grain size.
R D Shull - One of the best experts on this subject based on the ideXlab platform.
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properties of incommensurate spin density waves in Iron Aluminides invited
Journal of Applied Physics, 2004Co-Authors: D R Noakes, Seetharama C Deevi, A S Arrott, M G Belk, J W Lynn, R D ShullAbstract:Neutron diffraction in Fe(Al) reveals incommensurate spin density waves (SDWs) in alloys known to be spin glasses. The wave vectors for crystals of Fe(34Al), Fe(40Al) and Fe(43Al) show n varying from 11 to 6 for q=2π(h±1/n,k±1/n,l±1/n)/ao, where (h,k,l) and ao characterize the parent bcc lattice of the CsCl structure. The magnetic reflections are present far above the spin-glass freezing temperatures. These SDWs keep the spins on nearest-neighbor Fe atoms close to parallel, in contrast with SDWs in Cr, which keep nearest-neighbor spins close to antiparallel. The competition between near-neighbor Fe–Fe ferromagnetism and 180° superexchange through the Al site has been used to explain the spin-glass behavior, but the appearance of the SDWs calls for a more fundamental source of the periodicity. The phase shift mechanism for SDW interactions with magnetic moments is invoked to explain the breadth of the peaks, which resemble the results for Cu(Mn), Pd(Mn), and Pd(Cr). The data are interpreted using cubic sym...
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incommensurate spin density waves in Iron Aluminides
Physical Review Letters, 2003Co-Authors: D R Noakes, Seetharama C Deevi, A S Arrott, M G Belk, Q Huang, J W Lynn, R D ShullAbstract:Neutron diffraction in Fe(Al) reveals incommensurate spin density waves (SDWs) in alloys known to be spin glasses. The wave vectors for crystals of Fe(34Al), Fe(40Al), and Fe(43Al) show $n$ varying from 11 to 6 for $\stackrel{\ensuremath{\rightarrow}}{q}=2\ensuremath{\pi}(h\ifmmode\pm\else\textpm\fi{}1/n,k\ifmmode\pm\else\textpm\fi{}1/n,l\ifmmode\pm\else\textpm\fi{}1/n)/{a}_{0}$, where $(h,k,l)$ and ${a}_{0}$ characterize the parent bcc lattice of the CsCl structure. The magnetic reflections are present far above the spin-glass freezing temperatures. These SDWs keep the spins on nearest-neighbor Fe atoms close to parallel, in contrast with SDWs in Cr, which keep nearest-neighbor spins close to antiparallel.
