Influence of the rotation frequency of the magnetic field on the dynamics of the domain structure of thin Fe–3% Si crystals

Some specific features of the reconstruction of the domain structure of thin (0.10 mm) Fe–3% Si single crystals have been investigated depending on the frequency of the magnetization reversal in rotating magnetic fields. The studies have been carried out in the range of frequencies of 60–300 Hz and induction amplitudes of 0.5–1.6 T. It has been established that the magnetization reversal of the samples of this thickness occurs via the displacements of 180° domain walls of the stripe domain structure without the participation of the C-domain walls. A qualitative explanation to the revealed features of the behavior of the domain structure has been given, and their possible contribution to the magnetic losses of the investigated samples has been evaluated.     

Influence of Fe substitutions on the deformation behavior and fault energies of Ni3Ge–Fe3Ge L12 intermetallic alloys

Ni₃Ge exhibits a yield strength anomaly, whereas the yield strength of Fe₃Ge shows a normal decline with temperature, and there is a gradual transition from anomalous to normal behavior as Fe content increases. A dramatic strengthening for 77 K deformation has also been noted to occur in these alloys as a result of increasing Fe content. The combined use of transmission electron microscopy (TEM) and image simulations has facilitated identification of the operative deformation mechanisms and allowed for a quantitative measure of superdislocation dissociations. A transition from octahedral glide and Kear–Wilsdorf locking to cube glide of superdislocations has been observed to coincide with an increase in either deformation temperature or Fe content. The low-temperature strengthening has been correlated with enhanced cross-slip, which is aided by a significant lowering of the cube-plane antiphase boundary energy with increasing Fe content. It is proposed that the strengthening and the transition to cube glide are promoted by an increase in the complex stacking fault energy, which enhances both cross-slip and cube-plane mobility.     

Effect of Asymmetric Hot Rolling on the Texture Evolution of Fe–3%Si Steel

In Fe–3%Si steel, the hot rolling process affects not only the hot rolling texture but also the primary recrystallization texture. Here, the effect of asymmetric hot rolling was studied by comparing the difference in the texture evolved between asymmetric and symmetric hot rolling. The effect of asymmetric hot rolling on the texture of primary recrystallized Fe–3%Si steel was also studied. The symmetric hot rolling of Fe–3%Si steel produces a rotated cube texture at the center but Goss and copper textures near the surface. Asymmetric hot rolling tends to produce Goss and copper textures even at the center like the texture near the surface. After primary recrystallization, the dominant texture at the center changes from {001} <210> to {111} <112> and the new texture has a higher fraction of the grains which make the low energy boundary with Goss grains than that of symmetric hot rolling.     

High-Temperature Oxidation of Fe3Al and Fe3Al–Zr Intermetallics

The oxidation behavior of Fe₃Al and Fe₃Al–Zr intermetallic compounds was tested in synthetic air in the temperature range 900–1200 °C. The addition of Zr showed a significant effect on the high-temperature oxidation behavior. The total weight gain after 100 h oxidation of Fe₃Al at 1200 °C was around three times more than that for Fe₃Al–Zr materials. Zr-containing intermetallics exhibited abnormal kinetics between 900 and 1100 °C, due to the presence and transformation of transient alumina into stable α-Al₂O₃. Zr-doped Fe₃Al oxidation behavior under cyclic tests at 1100 °C was improved by delaying the breakaway oxidation to 80 cycles, in comparison to 5 cycles on the undoped Fe₃Al alloys. The oxidation improvements could be related to the segregation of Zr at alumina grain boundaries and to the presence of Zr oxide second-phase particles at the metal–oxide interface and in the external part of the alumina scale. The change of oxidation mechanisms, observed using oxygen–isotope experiments followed by secondary-ion mass spectrometry, was ascribed to Zr segregation at alumina grain boundaries.     

Effect of Ni/Fe ratio of electrolyte salts on the magnetic property of electrodeposited Fe–Ni alloy

Electrodeposition of Fe–Ni thin films has been carried out on a copper substrate from simple as well as complex baths containing sulfate salts with Ni/Fe ratio of 1 : 1 and 12 : 1. Complex baths consistedeither all of ascorbic acid, citric acid and saccharine in addition to the salts viz. NiSO₄ · 7H₂O; FeSO₄ · 7H₂O; H₃BO₃ and Na₂SO₄ in simple bath. The chemical composition of the deposit was determined by an energy dispersive X-ray analyzer. Magnetic properties of the Fe–Ni films were measured by avibrating sample magnetometer (VSM). The X-ray diffraction was done on the electrodeposited thin films to determine Fe–Ni alloy phases. Magnetic properties of films were studied before and after heat treatment of the samples. It is found that the saturation magnetization decreases with increasing Ni content in the films obtained from simple baths with low Ni/Fe ratio (1 : 1) while the saturation magnetization increases with increasing Ni content obtained from complex bath with high Ni/Fe ratio (12 : 1). Among different baths with high Ni/Fe ratio of 12 : 1, the saturation magnetization of deposited film is higher deposited from a bath containing three complexing agents, namely, ascorbic acid, citric acid and saccharine than from a bath containing a single complexing agent–ascorbic acid. The ideal nature of the M _s–H (saturation magnetization vs. applied field) curve was obtained from complex baths with a high Ni/Fe ratio (12 : 1).     

High-Temperature Oxidation Behavior of ODS–Fe3Al

The high-temperature oxidation behavior of an oxide dispersion-strengthened (ODS) Fe₃Al alloy has been studied during isothermal and cyclic exposures in oxygen and air over the temperature range 1000 to 1300°C. Compared to commercially available ODS–FeCrAl alloys, it exhibited very similar short-term rates of oxidation at 1000 and 1100°C, but at higher temperatures the oxidation rate increased because of increased scale spallation. Over the entire temperature range, the oxide scale formed was -Al₂O₃, with the morphological features typical of reactive-element doping and was similar to those formed on the ODS–FeCrAl alloys. Although initially this scale appeared to be extremely adherent to the Fe₃Al substrate, an undulating metal–oxide interface formed with increasing time and temperature, which led to cracking of the scale in the vicinity of surface undulations accompanied by a loss of small fragments of the full-scale thickness. In some instances, the surface undulations appeared to have resulted from gross outward local extrusion of the alloy substrate. Similar features developd on the FeCrAl alloys, but they were typically much smaller after a given oxidation exposure. The ODS–Fe₃Al alloy has a significantly larger coefficient of thermal expansion (CTE) than typical FeCrAl alloys (approximately 1.5 times at 900°C) and this appears to be the major reason for the greater tendency for scale spallation. The stress generated by the CTE mismatch was apparently sufficient to lead to buckling and limited loss of scale at temperatures up to 1100°C, with an increasing amount of substrate deformation at 1200°C and above. This deformation led to increased scale spallation by producing an out-of-plane stress distribution, resulting in cracking or shearing of the oxide.     

Effect of Plastic Deformation on the Structure and Properties of High-Nitrogen Alloys of the Fe – Cr System

The structure, strength, and ductility of alloys of the Fe – Cr – N system bearing from 15 to 24% chromium and from 0.4 to 1.3% nitrogen are studied after rolling at 20, 450, 800, 900, 1000, 1100, and 1200°C. It is shown that the highest hardening due to cold plastic deformation is provided in alloys with metastable -solid solution that undergoes transformation into strain martensite ( ). In hot plastic deformation the alloys are hardened due to the formation of a fragmented structure. The data of electron microscopic studies are used to determine the role of the phase composition in the hardening of the alloys.     

Effect of Microstructure on the Internal Oxidation of Two-Phase Fe–Y Alloys

This work demonstrated the role of microstructure on the internal oxidation rate of two-phase alloys. Fe–Y alloys with Y contents between 1.5 and 15 wt% were employed as a model system. Alloys were prepared by arc-melting and the starting structures were as-solidified mixtures of Fe + Fe₁₇Y₂ intermetallic. An alloy with 1.5 wt% Y was cold-rolled to alter the intermetallic morphology. Oxidation was conducted in an Fe–FeO Rhines pack at 600, 700, and 800 °C up to 72 h. Pre- and post-oxidation microstructures were characterized with electron microscopy. Consistent with other studies, only the Fe₁₇Y₂ phase oxidized. Transmission electron microscopy showed the Fe₁₇Y₂ transformed into nanometer-scale oxides. Oxidation rates were always greater than those predicted by Wagner theory. Parabolic kinetics were obeyed until approximately 10 h. During this time the parabolic rate constants decreased with wt% Y. The effect of alloy microstructure on oxidation kinetics was attributed to connectivity of the Fe₁₇Y₂ phase.     

The effect of oxygen on the open-circuit passivity of Fe18Cr

Electrochemical studies were conducted to determine the critical amount of oxygen necessary to prevent corrosion by maintaining the open-circuit passivity of Fe18Cr samples initially passivated at 0.6 V(NHE) in 1N H₂SO₄ solutions. Samples passivated at 0.6 V(NHE) and then released to open circuit in O₂-saturated (29.4 ppm O₂ dissolved) solution maintained a state of passivity. Samples passivated and released to open circuit in N₂-purged solution decayed to a state of active corrosion in 800–2000 min. A passive state, however, could be maintained if O₂ were added to the N₂ flow so that a minimum of 1.7 ppm O₂ was present in solution. Furthermore, this critical amount of O₂ had to be added before open-circuit decay reached 0.45 V(NHE). Auger electron spectroscopy measurements indicated that following open-circuit stabilization of passivity by O₂ the percentage chromium in the film increased with increasing open-circuit potential. X-ray photo-electron spectroscopy measurements indicated that the film thickness decreased with increasing open-circuit potential.     

Effects of the spinning wheel velocity on the microstructure of Fe–Pd shape memory melt-spun ribbons

Fe–Pd with approximately 30 at.% of Pd shape memory ribbons have been manufactured by the free jet melt-spinning method with various wheel velocities. The microstructure of the as-spun ribbons have been investigated.     

Interface electron structure of Fe3Al/TiC composites

1 Introduction Recently a few studies[1?3] have been carried out to utilize carbides or borides as reinforcements in iron aluminides, thus improving their mechanical properties. Additionally, an intermetallic matrix reinforced with ceramic phase might mak…     

Fe–27 at% Al: a resistometric study of the kinetics of order–order transformation in the DO3f phase

Order–order transformation in ferromagnetic DO₃ phase of Fe–27 at%Al was studied by in situ resistometry. Small step cooling procedure was adopted in order to minimize the possible influence of non-equilibrium vacancies. Isothermal annealing data were found to optimally fit to the Avrami–Mehl–Johnson equation. The underlying process is characterized by activation enthalpy of ≈220 kJ mol (2.3 eV) and interpreted as diffusion controlled growth of ordered domains.     

Microstructure evolution of components of ZAlSi8Cu3Fe alloy in processing of thixo-diecasting

The microstructures of components of ZAlSi8Cu3Fe alloy in the process of thixo-diecasting were investigated. The effects of processing conditions on the microstructure of the alloy in the thixo-diecasting procedures of original casting billets, remelting billets and casting components were researched, and the morphological evolution of α-particles in the alloy was analyzed quantitatively. The results show that, the microstructure of the original billets poured at 582 ℃ consists of rosette-like primary α-particles; in the procedure of remelting, when the temperature rises over solidus, arms in the rosette-like α-particles begin to fuse off from dendritic branches and after further heating, α-particles surrounded by liquid phase are refined by the diffusion of atoms and rounded owing to the least interface stress and interface energy principles; and in the procedure of thixo-diecasting, the morphologic characteristics of α-particles and the distribution of phases in the structure change greatly for the high shear rate under the restricted area of the ingate.     

Effect of the magnetic state of ferrite on transformations in Fe−C alloys

Conclusions Retardation of the austenite transformation in the interval end of the pearlite—austenite transformation to start of the ferrite—austenite transformation in low-carbon steels, which coincides with the magnetic transformation in ferrite, is connected with the fact that the latter inhibits diffusional transport of the interstitial atoms.Alma-Ata Institute of Railroad Transportation Engineers. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 11–12, February, 1990.     

Effect of titanium on the kinetics of the σ-phase formation in a coarse-grained Fe–Cr alloy

The influence of titanium on the kinetics of the σ-phase formation promoted by an isothermal annealing at T=973 K was studied in coarse-grained quasi-equiatomic Fe–Cr alloys by using the ⁵⁷Fe Mössbauer Spectroscopy. It was found that the kinetics could be well-described in terms of the Johnson–Avrami–Mehl equation. The addition of titanium (up to 3 at%) was revealed to effect the transformation kinetics in the following way: for x_Ti⩽1.5 at%, its presence accelerates the process with the highest transformation rate for x_Ti=0.3 at%, for x_Ti⩾1.5 at%, titanium retards the formation of the σ-phase. Quantitatively, the effect of titanium on the kinetics was described in terms of a change of the effective activation energy.     

Creep of polycrystalline SrCo0.8Fe0.2O3−δ

In this study, a series of compressive creep tests on rectangular specimens of SrCo_0.8Fe_0.2O_3−δ of grain sizes in the range of 2.4–6.8 μm was performed in air, covering a temperature range of 850–975°C and a stress range of 2–80 MPa. The stress exponent has been found to be close to unity in the 10–20 MPa stress range. The apparent activation energy assumes two different values, 471 kJ/mole below 925°C and 275 kJ/mole above 925°C. The microstructural observations of crept samples revealed equiaxed grains and negligible grain growth indicating a diffusion-accommodated grain switching mechanism. The logarithmic plot of strain rate vs inverse grain size has been found to be non-linear. A possible explanation for this behavior is discussed through the incorporation of a threshold stress. The possibility of estimating the lattice and grain-boundary diffusion coefficients from the data is discussed.     

The effect of Cl− ions on the passivation of Fe26Cr alloy

Anodic oxide films formed on Fe26Cr in pH 2.0 H₂SO₄ solution in the presence and absence of Cl⁻ ions have been investigated using electrochemical techniques and Auger electron spectroscopy (AES) combined with ion sputtering. It is possible to incorporate Cl⁻ ions into passive oxide films formed over the entire passive potential range only when Cl⁻ is present in the solution from the very beginning of film formation. Cl⁻ ion incorporation does not cause any change in film thickness or Fe/Cr ratio, or any film thinning or film breakdown. A relatively short anodization in Cl⁻-free solution is sufficient to prevent any subsequent Cl⁻ ion incorporation. The susceptibility of the passive film to Cl⁻ attack appears to depend on the presence of small amounts of impurity in the alloy. A 99.97% pure alloy does not pit, whereas a 99.93% pure alloy, with larger concentrations of C, S, Mn, Co and Ni, does suffer intergranular attack in Cl⁻ solution.