Fe-Y Alloys Research Articles

Characterizing the Effect of ECAP on Particle Dispersion and Thermal Stability of Internally Oxidized Fe-Y Alloys

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Influence of Oxygen Supply on Oxide Coarsening During the Internal Oxidation of Two-Phase Fe-Y Alloys

Fe-Y binary alloys underwent thermogravimetric analysis while exposed to low oxidant partial pressures using a mixture of 5 pct H2-95 pct Ar gas at two flow rates. The alloys experienced in situ internal oxidation of Y-rich intermetallic phases. Kinetics and microstructures were both affected by flowrate. Lower flow rates resulted in coarser oxides and decreased oxidation rates. Results show the possible impacts of rate-controlling processes in the gas phase on internal oxidation with dilute oxidants.

P105] Phase relationship and magnetostriction of Tb0.26Dy0.49Ho0.25Fey alloys

We report on the results pertinent to structural, magnetic, magnetostrictive studies of the Tb0.3Dy0.7−xNdxFe1.93 [x = 0, 0.05, 0.1, 0.15 and 0.2] compounds. From the evidenced magnetization and magnetostriction results, the crucial finding that we emphasize is that the realization of minimum anisotropy for the compound with the composition x = 0.1. From the X-ray diffraction on magnetically aligned samples, (4 4 0) peak splitting analysis and Mössbauer studies, we ascertain that the easy magnetization direction (EMD) for x = 0.2 compound it is towards 〈1 1 0〉. Above results also affirmed that indeed there exists transformation of the structural distortion from rhombohedral to orthorhombic from x = 0 to x = 0.2. The Laves phase compound Tb0.3Dy0.6Nd0.1Fe1.93 with a large magnetostriction (λ111 ≈ 1270 × 10−6) and a low anisotropy may be a potential candidate for magnetostriction applications.

Vertical sections of Tb0.15Ho0.85Fey-Tb0.3Dy0.7Fey (y=1.85, 1.9, 2.0) in Tb-Dy-Ho-Fe system

The x(Tb0.15Ho0.85Fey)+(1–x)(Tb0.3Dy0.7Fey) (x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9; y=1.85, 1.9, 2.0) samples were prepared by a vacuum arc furnace, and annealed at 1000 °C for 1 d and at 950 °C for a week. Three vertical sections of Tb0.15Ho0.85Fey-Tb0.3Dy0.7Fey (y=1.85, 1.9, 2.0) in the Tb-Dy-Ho-Fe system were determined using optical microscopy, scanning electron microscopy, energy dispersion X-ray spectroscopy, X-ray diffraction, and differential thermal analysis. These vertical sections consisted of two single-phase regions: L and (Tb,Dy,Ho)Fe2; four two-phase regions: L+(Tb,Dy,Ho)Fe3, L+(Tb,Dy,Ho)Fe2, (Tb,Dy,Ho)Fe2+(Tb,Dy,Ho)Fe3, and (Tb,Dy,Ho)Fe2+(Tb,Dy,Ho). The high Ho content of (Tb,Dy,Ho)Fey alloys led to the elevation of the peritectic temperature of L+(Tb,Dy,Ho)Fe3→(Tb,Dy,Ho)Fe2. The region of (Tb,Dy,Ho)Fe2 phase was shifted towards the side of rich-Ho with the Fe content increasing. It meant that the substitution of Ho for Dy or Tb had a marked effect on the solidification process of (Tb,Dy,Ho)Fe2 compounds.

High Temperature Scaling of Binary Fe-Y Alloys in Pure Oxygen

The scaling of two iron-based alloys containing 15 and 30wt% yttrium as well as of pure yttrium has been studied at 600-800 degrees C in 1 atm of pure O-2. Both alloys formed external scales containing a mixture of iron and yttrium oxides plus double Fe-Y oxides followed by a region of internal oxidation of yttrium, so that the oxidation of iron could not be prevented. Corrosion of the two alloys was generally irregular and occurred at rates not very different from those of oxidation of pure iron. No yttrium depletion was observed in the alloys beneath the region of internal oxidation, in spite of the much larger stability of Y2O3 with respect to iron oxides. The scaling behavior of the two alloys is interpreted by taking into account the limited solubility of yttrium in iron.

The Oxidation of Fe-2 and 5 at.% Y Alloys at 600-800°C in Air

The oxidation of Fe-Y alloys containing 2 and 5at.% Y and pure iron has been studied at 600-800°Cin air. The oxidation of pure iron follows the parabolicrate law at all temperatures. The oxidation of Fe-Y alloys at 600°C approximatelyfollows the parabolic rate law, but not at 700 and800°C, where the oxidation goes through severalstages with quite different rates. The oxide scales on Fe-2Y and Fe-5Y at 700 and 800°C arecomposed of external pure Fe oxides containingFe2O3,Fe3O4, and FeO, with FeO being themain oxide and an inner mixture of FeO andYFeO3. The scales on Fe-2Y and Fe-5Y at 600°C consist ofFe2O3,Fe3O4, andY2O3, with a minor amount of FeO.Significant internal oxidation in both Fe-Y alloysoccurred at all temperatures. The Y-containing oxidesfollow the distribution of the original intermetalliccompound phase in the alloys. The effects of Y on theoxidation of pure Fe are discussed.

Spin-resolved photoemission of in situ sputtered iron and iron-yttrium alloys

Spin-resolved photoemission spectra of amorphous Fe-Y alloys have been obtained and compared with both those of pure Fe and with theoretical electronic structure calculations. The thin iron and alloy films were prepared by in situ sputtering, and the spectra were obtained using 110-eV photons from the UK Synchrotron Facility. From secondary electron spin hysteresis loops, ${\mathrm{Fe}}_{60}$${\mathrm{Y}}_{40}$ starts to order ferromagnetically well before the lowest temperature accessible with our equipment (114 K), but ${\mathrm{Fe}}_{41}$${\mathrm{Y}}_{59}$ shows no polarization down to this temperature. Although the spin-integrated photoemission spectrum of the valence band of ${\mathrm{Fe}}_{60}$${\mathrm{Y}}_{40}$ shows little difference from that of pure Fe, the spin-resolved spectra are significantly different. ${\mathrm{Fe}}_{60}$${\mathrm{Y}}_{40}$ also exhibits a reduced valence band polarization (14%) compared with iron, and contrary to predictions, the majority spin states of ${\mathrm{Fe}}_{60}$${\mathrm{Y}}_{40}$ dominate at the Fermi edge. No evidence is found for strong ferromagnetism. Unexpectedly, the 1-eV secondary electron polarization of ${\mathrm{Fe}}_{60}$${\mathrm{Y}}_{40}$ (7%) is found to be low compared with the valence band polarization, an effect that may be due to a negative moment on the yttrium.

Noncollinear magnetism in amorphous Fe-Y alloys

Iron-rich amorphous alloys with nonmagnetic transition metals (TM) or rare-earth (RE) metals show a rich variety of complex spin-structures that have been described as spin-glass-like, spero- or asperomagnetic. Amorphous Fe-Y alloys have attracted particular attention because it has been suggested that, in contrast to other amorphous Fe-TM and Fe-RE alloys showing re-entrant spin-glass behaviour, in Fe-Y alloys the spin-glass transition could occur directly from the paramagnetic phase. It has also been suggested that, unlike most other alloys where the spin-glass-like phase is restricted to high Fe concentrations, amorphous Fe-Y alloys are noncollinear at all compositions. We have recently presented a technique for a selfconsistent calculation of noncollinear spin-structures in crystalline and amorphous alloys based on a tight-binding-Hubbard Hamiltonian generated via a canonical transformation of the local-spin-density (LSD) Hamiltonian. This approach has been used to analyze the magnetic properties of amorphous Fe-Y alloys. We show that, unlike, for example, amorphous Fe-Zr alloys where the net magnetization is well defined in the spin-glass and in the ferromagnetic phases and independent of the initialization of the magnetic structure, for Fe-Y energetically nearly degenerate low- and high-moment phases can be induced by different initializations. This could explain the observed strong dependence of the magnetic state on the preparation of the amorphous phase and its strong variation under applied external fields or pressures.

Metallic magnetism in amorphous TM-Y (TM = Mn, Fe, Co, Ni) alloys

Systematic variations of magnetic properties in amorphous TM-Y (TM = Mn, Fe, Co, Ni) alloys are investigated on the basis of a finite temperature theory of amorphous metallic magnetism which takes into account both thermal spin fluctuations and the fluctuations due to structural and configurations disorder. It is shown that the magnetic phase diagrams calculated in the most random atomic configuration explain qualitatively the spinglass (SG) in Mn-Y, the SG ferromagnetism (F) transition in Fe-Y, and the F-paramagnetism transition in Co-Y and Ni-Y alloys. Magnetization vs concentration curves and susceptibility vs concentration curves as well as the effective Bohr magneton numbers are also shown to be explained qualitatively or semi-quantitatively by the theory. Their miscroscopic mechanisms are elucidated by means of their electronic structures, magnetic couplings, and atomic short range order. It is found that the magnetism in Fe-Y and Mn-Y amorphous alloys is strongly influenced by the atomic short range order. The result explains different magnetic phase diagrams in amorphous Fe-Y alloys and experimental SG transition temperatures in amorphous Mn-Y alloys.

Microstructure and magnetostriction of (Dy0.7Tb0.3)1−xPrxFe1.85 and (Dy0.7Tb0.3)0.7Pr0.3Fey alloys

The structure, Curie temperature, and magnetostriction of R1−xPrxFe1.85 and R0.7Pr0.3Fey (R=Dy0.7Tb0.3, x≤0.5, 1.55≤y≤1.85) alloys were investigated. The matrix of R1−xPrxFe1.85 alloys is the MgCu2-type cubic (Dy,Tb,Pr) Fe2 and the second phase was found to be (Dy,Tb,Pr) Fe3 when x≤0.3. When x>0.4, (Dy,Tb,Pr)Fe3 is the main phase with the PuNi3-type structure and (Dy,Tb,Pr) Fe2 becomes the minority phase. In the range of 0.3<x≤0.4, both MgCu2- and PuNi3-type structures coexist. The R0.7Pr0.3Fey alloys contain a small amount of (Dy,Tb,Pr) Fe3 phase when y>1.55, which increases with increasing y. When y=1.55, the alloy is essentially single phase with the MgCu2-type cubic structure. The lattice parameter of (Dy,Tb,Pr)Fe2 compound for R1−xPrxFe1.85 alloys increases slowly with increasing x when x≤0.3, and sharply increases when x>0.3. The Curie temperature of the alloys decreases steadily with increasing Pr content. The magnetostrictions of R1−xPrxFe1.85 and R0.7Pr0.3Fey alloys decrease with increasing Pr content and Fe content, respectively. The largest magnetostriction at room temperature was found in the alloy R0.7Pr0.3Fe1.55 (1480×10−6 at H=796 kA/m).

Asperomagnetism in amorphous Fe-Y alloys

Iron-rich amorphous alloys with non-magnetic transition metals or rare-earth metals show a rich variety of complex spin structures that have been described as spin-glass-like, spero- or asperomagnetic. Standard local-spin-density (LSD) calculations yield only an Ising-like description of the magnetic structure. The present authors recently presented a technique for a self-consistent calculation of non-collinear spin structures in crystalline and amorphous alloys based on a tight-binding Hubbard Hamiltonian generated via a canonical transformation of the LSD Hamiltonian. This approach has been used to analyze the magnetic properties of Fe-rich amorphous Fe-Y alloys. It is shown that in the limit of very high Fe concentrations the orientation of the magnetic moments is almost, but not completely, random. Hence the Fe-rich amorphous Fe-Y alloys are correctly described as asperomagnets.

Structural, electronic, and magnetic properties of Fe-Y alloys.

Results of ab initio calculations of the structural, electronic, and magnetic properties of crystalline and amorphous Fe-Y alloys are presented. The structure of the amorphous phases is generated via a simulated molecular-dynamics quench, based on effective interatomic forces derived from tight-binding-bond theory. The results show that a pronounced chemical short-range order (preferred heterocoordination) exists at all compositions and that at short distances the local topology is similar in the crystalline and glassy phases. In the Y-rich alloys, medium-range concentration fluctuations are superposed to the local order. The investigation of the electronic structure using self-consistent spin-polarized linear muffin-tin orbital calculations confirms that the bonding properties are similar in the crystalline and amorphous phases. The crystalline compounds are ferrimagnetic, the negative Y moment is induced by a strong covalent interaction of the Y d band with the minority-spin Fe d band. Ferrimagnetism is also found in the amorphous alloys. In the Fe-rich range (more than 80 at. % Fe) competing ferro- and antiferromagnetic Fe-Fe exchange interactions lead to coexisting positive and negative Fe moments. The decrease of the magnetic moments of the Fe atoms with increasing Y content is strongly influenced by the strong coupling of the Fe spins to the Y moments---as a consequence a spontaneous Fe moment exists even at very small Fe-Fe coordination numbers. In addition the structural inhomogeneity of the Y-rich amorphous alloys leads to cluster magnetism.

Differential magnetic susceptibility of amorphous Fe-Y alloys

The spin-glass behaviour of amorphous FexY100-x alloys (70<or=x<or=90) has been investigated by means of differential magnetic susceptibility dM/dH. In low magnetic fields, the dM/dH versus T curves show the peaks, indicating that the spin-glass state occurs through two steps. Two freezing temperatures are defined from the two peaks in the curve, i.e. the higher temperature is Tg and the lower temperature is Tf. From the results of the magnetization measurement as a function of temperature, i.e. the M versus T curve, it is indicated that the magnetization starts to decrease at Tg and a thermal irreversibility appears below Tf with decreasing temperature. With increase in the applied magnetic field, a third peak appears at around 150 K in the dM/dH versus T curve for amorphous Fe84Y16 alloy. The position of this peak corresponds to the upper inflection point in the M versus T curve, being defined as the Curie temperature TC. Therefore, re-entrant behaviour appears in this system on application of a magnetic field. The concentration dependences of TC and Tf for a field of 500 Oe are very similar to those obtained in zero field for other amorphous Fe-RE alloys (RE: rare-earth metal) such as Fe-Lu and Fe-Ce systems.

Magnetostriction of Amorphous Fe-Y and (Fe-Co)0.8Y0.2 Alloys

The magnetostriction of Fe 1-x Y x (0.2?x?0.6) and of (Fe 1-x Co x ) 0.8 Y 0.2 (0?x?0.6) alloys has been measured in the temperature range from 20 to 300 K. In Fe-Y alloys, the magnetostriction ? is 2.8×10?6 at 20 K when x=0.2, and decreases monotonically with increasing x and temperature. This magnetostriction in FeY alloys is the smallest among all Fe-based amorphous binary alloys investigated so far. In (Fe 1-x Co x ) 0.8 Y 0.2 alloys ? at room temperature shows a minimum of 1.0×10?6 at x-0.3, at which the magnetization and coercive force are 125 emu/g and 0.05 Oe respectively.

Mossbauer and magnetovolume effects in amorphous Fe-Y and (Fe-Co) alloys

The Mossbauer effect and thermal expansion of rapidly quenched amorphous FexY1-x (0.4<or=x<or=0.8) and (FexCo1-x)0.8Y0.2 (0.4<or=x<or=1.0) alloys were studied to clarify the local environmental effect on the Fe magnetic moments and its contribution to the magnetovolume effect. The Fe atom in the rapidly quenched amorphous Fe-Y alloys has a magnetic moment when it has more than six Fe neighbours. The Fe magnetic moment increases with increasing average number of Fe neighbours n and has a maximum of about 1.9 mu B at n approximately=10-11.

非晶質Ｆｅ‐Ｙ及び（Ｆｅ‐Ｃｏ）０．８Ｙ０．２合金の磁歪

The magnetostriction of Fe1-xYx (0.2≤x≤0.6) and (Fe1-x-Cox)0.8Y0.2(0≤x≤0.6) alloys has been measured in the temperature range from 20 to 300 K. In FeY alloys, the magnetostriction λ is 2.8×10-6 at 20K for x=0.2 and shows a monotonic decrease with increasing x and temperature; this magnetostriction of the Fey alloys is the smallest in the Fe-based amorphous binary alloys investigated so far. In (Fe1-x-Cox)0.8Y0.2 alloys, λ at room temperature shows a minimum of 1.0×10-6 at x≈0.3, where the magnetization and coercive force are 125 emu/g and 0.05 Oe, respectively.

Magnetic and mechanical properties of amorphous Fe-Y alloys

The magnetic and mechanical properties of amorphous Fe 100− x Y x alloys (20 ≤ x ≤ 60) fabricated by rapid quenching have been measured. The dependence of the density, Young's modulus and magnetic moment per Fe atom on x shows a break point between x = 30 and 40, accompanied by a drastic change in the X-ray diffraction pattern. The spontaneous volume magnetostriction as well as the forced volume magnetostriction are a maximum at x = 20 and decrease rapidly with increasing x. The variation of the magnetic and mechanical properties with x is explained by a change of the local atomic arrangement in the amorphous state, reflecting the structure of corresponding crystalline compounds.

（Ｆｅ，Ｍｎ，Ｃｏ）‐Ｙ系非晶質合金の磁性

Magnetic moment m, Curie temperature Tc, density ρ and Young's modulus ES of amorphous Mn-Y, Fe-Y, Co-Y, (Fe-Mn)80Y20 and (Fe-Co)80Y20 alloys fabricated by rapid quenching have been measured to make clear microstructures of amorphous alloys. Detailed comparison of m, Tc, ρ and ES between amorphous alloys and corresponding crystalline compounds, and a structural analysis by X-ray diffraction reveal a close correlation of an atomic short range order of both states, which is especially found in alloys with Y content less than 30at%. A structural variation between 30 and 40 at%Y in the Fe-Y amorphous alloys is also indicated by the composition dependence of m, Tc, ρ, ES and by X-ray analysis.

The surface tension of Fe-Y and Fe-C-Y alloys at 1550°C

The surface tensions of liquid Fe-Y and Fe-C-Y alloys containing 0 to 2 wt pct C and up to 0.8 wt pct Y were measured at 1550°C with a sessile drop technique. Yttrium was found to be surface active in both Fe-Y and Fe-C-Y alloys in the composition ranges studied. The addition of carbon reduces the surface tension of Fe-Y alloys.