Fe Solid Solution Research Articles

Controlled synthesis of nanocrystalline CeO 2 and Ce 1−xM xO 2−δ ( M=Zr, Y, Ti, Pr and Fe) solid solutions by the hydrothermal method: Structure and oxygen storage capacity

CeO 2 and Ce 1− xM x O 2− δ ( M=Zr, Ti, Pr, Y and Fe) nanocrystallites of 5–10 nm sizes have been synthesized by hydrothermal method using diethylenetriamine (DETA) and melamine as complexing agents. Compounds have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX) and their structures have been refined by the Rietveld method. All the compounds crystallize in cubic fluorite structure. Even up to 50% Zr and Y, 40% Ti, 25% Pr and 15% Fe is substituted for Ce 4+ in CeO 2 by this method. Sizes of crystallites can be tuned by changing the complexing agent and reaction temperature. Nanocrystalline CeO 2 and Ce 1− x Zr x O 2 prepared here have higher or at least competitive oxygen storage capacity (OSC) than those reported in literature. Ce 1− x Fe x O 2− δ shows higher OSC and higher percentage of CO oxidation at lower temperature than Ce 1− x Zr x O 2.

Electromagnetic properties of FeNi alloy nanoparticles prepared by hydrogen-thermal reduction method

FeNi alloy nanoparticles were prepared by hydrogen-thermal reduction in nickel ferrite nanoparticles at 400 °C for 1 h. FeNi alloy nanoparticles with average particle size of 150 nm in diameter are composed of Fe, Ni, and FeNi solid solution. The effective complex permittivity and complex permeability of FeNi alloy nanoparticles in the frequency range of 2–18 GHz were measured, and the microwave reflection loss of FeNi/wax with different assumed coating thicknesses was calculated according to the transmission line theory. The hydrogen-thermal reduced FeNi alloy nanoparticles were found to possess high permeability and superior microwave absorption performance in the microwave band.

How to Get Ternary Solid Solutions Fe1–xM′xO (M = Co, Ni)? A Thermodynamic Concept

AbstractThe existence ranges of ternary solid solutions Fe1–xM′xO (M = Co, Ni) have been estimated using thermodynamic modelling by CALPHAD methods: a complete series of mixed crystals Fe1–xCoxO is stable only at higher temperatures ≥ 900 °C. Below the solid solution shows a miscibility gap due to the different redox potentials [p(O2) = f(T)] of the binary phases “FeO” and CoO. Hence CoO becomes reduced into metallic cobalt while “FeO” is oxidised into Fe3O4. The pseudo binary system FeO/NiO shows solubility ranges only at the border of the binary oxides, the phases built areα(Fe1–xNixO) (x ≤ 0.13) and α′(FeyNi1–yO) (y ≤ 0.60, ≤ 1400 °C). Due to the broader difference of redox potentials [p(O2) = f(T)] of “FeO” and NiO a complete series of mixed crystals cannot exist. In application of the results of thermodynamic modelling the syntheses of mixed crystals Fe1–xCoxO and their characterisation by X‐ray diffraction and thermal analysis succeeds. The mixed phases crystallise in the halite structure type (space group Fm$\bar {3}$m) with a progress of the lattice constants corresponding to the Vegard rule [a(Fe1–xCoxO) = 430.0(2) pm (x = 0), 427.8(2) pm (x = 0.5), 425.0(2) pm (x = 1)].(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Large-scale synthesis of Al–Cu–Fe submicron quasicrystals

Al–Cu–Fe alloy with a nominal composition of Al62Cu25.5Fe12.5 (at.%) has been fabricated by a combination of pressure-assisted self-propagating high-temperature synthesis and rapid solidification. The as-synthesized Al–Cu–Fe alloy mainly consists of icosahedral quasicrystalline (IQC) ψ-Al65Cu20Fe15 and cubic β-Al (Cu, Fe) solid solution phases, and exhibits finely equiaxed grains with a size ranging from 50 to 200 nm. The mechanism for the formation of the ultrafine-grained IQC phase has been explained.

Mechanically activated synthesis of nanocrystalline ternary carbide Fe 3Mo 3C

In this investigation, Fe 3Mo 3C ternary carbide was synthesized from the elemental powders of 3Mo/3Fe/C by mechanical milling and subsequent heat treatment. Structural and morphological evolutions of powders were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results showed that no phase transformation occurs during milling. A nanostructure Mo (Fe) solid solution obtained after 30 h of milling. With increasing milling time to 70 h no change takes place except grain size reduction to 9 nm and strain enhancement to 0.86%. Milled powders have spheroid shape and very narrow size distribution about 2 μm at the end of milling. Fe 3Mo 3C was synthesized during annealing of 70 h milled sample at 700 °C. Undesired phases of MoOC and Fe 2C form at 1100 °C. No transformation takes place during annealing of 10 h milled sample at 700 °C. Mean grain size and strain get to 69 nm and 0.23% respectively with annealing of 70 h milled sample at 1100 °C.

Effect of heat treatment on the microstructure and property of cold-sprayed nanostructured FeAl/Al 2O 3 intermetallic composite coating

It is difficult to deposit dense intermetallic compound coatings by cold spraying directly using compound feedstock powders due to their intrinsic low temperature brittleness. A method to prepare intermetallic compound coatings in-situ employing cold spraying was developed using a metastable alloy powder assisted with post heat treatment. In this study, a nanostructured Fe(Al)/Al 2O 3 composite alloy coating was prepared by cold spraying of ball-milled powder. The cold-sprayed Fe(Al)/Al 2O 3 composite alloy coating was evolved in-situ to FeAl/Al 2O 3 intermetallic composite coating through a post heat treatment. The effect of heat treatment on the phase formation, microstructure and microhardness of cold-sprayed Fe(Al)/Al 2O 3 composite coating was investigated. The results showed that annealing at a temperature of 600 °C results in the complete transformation of the Fe(Al) solid solution to a FeAl intermetallic compound. Annealing temperature significantly influenced the microstructure and microhardness of the cold-sprayed FeAl/Al 2O 3 coating. On raising the temperature to over 950 °C, diffusion occurred not only in the coating but also at the interface between the coating and substrate. The microhardness of the FeAl/Al 2O 3 coating was maintained at about 600HV 0.1 at an annealing temperature below 500 °C, and gradually decreased to 400HV 0.1 at 1100 °C.

Effect of Annealing Treatment on the Structure and Microhardness of Cold-Sprayed Nanostructured FeAl/WC Composite Coating

Nanostructured FeAl/WC intermetallic composite coatings were prepared by cold spaying of the ball-milled powders. The effect of annealing on the coating structure and microhardness was examined. It was found that the nanocrystalline structure of the milled feedstock was retained in the cold sprayed coatings. The FeAl intermetallic phases were formed from the milled Fe(Al) solid solution during the post-spraying annealing at 550oC. The microhardness of the as-sprayed coating was about 680HV0.1 and it decreased a little with increasing the annealing time at 550oC.

Structure and composition of the transition zone of welded joints of Fe3Al intermetallic and low-carbon steel

The structure and phase composition of the interface of diffusion welded joints of Fe3Al intermetallic and low-carbon steel are studied. The orientation relation between the crystals of the intermetallic and the Fe(Al) solid solution of the transition zone of a welded joint and the distribution of microhardness in the latter are determined.

Structural and magnetic studies of nanocrystalline Fe<sub align=right>80Ni<sub align=right>20 alloy prepared by high-energy ball milling

Mechanical alloying is a powder metallurgy processing technique involving the cold welding, fracturing and rewilding of powder particles in high energy. It has been used to obtain nanocrystalline alloys. Fe-20 wt. % Ni alloys were synthesised using a planetary ball mill (Retsch PM400). X-ray Diffraction (XRD) was used to identify and characterise various phases during the milling process. It is shown that the bcc Fe(Ni) solid solution was formed after 2 h of milling. The steady state grain size is about 12 nm. Many nanostructures' magnetic materials have exhibited excellent soft magnetic properties, which suit so many applications. We used electromagnetic methods (hysteresis) to characterise the variation of the residual magnetisation and the coercive field.

Structural evolution and grain growth kinetics of the mechanically alloyed Fe42.5Al42.5Ti5B10 induced by annealing

The XRD and TEM techniques were used to study the structural evolution in the mechanical alloying and annealing of Fe42.5Al42.5Ti5B10. The mechanical alloying mechanism during ball milling and the grain growth mechanism during annealing of the powder are also discussed. The results show that the diffusion of Al，Ti and B atoms into Fe lattice occurs during milling，leading to the formation of Fe(Al，Ti，B) solid solution. The process is controlled by continuous diffusion mixing mechanism. The alloying reaction is completed after 50h and the final product is a powder composed of nanocrystalline Fe(Al，Ti，B). Besides the relaxation of crystal defaults and lattice stress，the decomposition of Fe(Al，Ti，B) occurs to form FeAl and TiB2 during heat treatment of the 50h milled powder. The activation energy for the nanocrystalline FeAl growth was calculated to be 525.6kJ/mol according to kinetics theory of nanocrystalline growth.

Microstructural Characterization of Cold-Sprayed Nanostructured FeAl Intermetallic Compound Coating and its Ball-Milled Feedstock Powders

It is difficult to deposit dense intermetallic compound coatings by cold spraying directly using the compound feedstock powders due to their intrinsic low-temperature brittleness. A method to prepare intermetallic compound coatings in-situ employing cold spraying was developed using a metastable alloy powder assisted with post-heat treatment. In this study, a nanostructured Fe/Al alloy powder was prepared by ball-milling process. The cold-sprayed Fe/Al alloy coating was evolved in-situ to intermetallic compound coating through a post-heat treatment. The microstructural evolution of the Fe-40Al powder during mechanical alloying and the effect of the post-heat treatment on the microstructure of the cold-sprayed Fe(Al) coating were characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy (TEM), and x-ray diffraction analysis. The results showed that the milled Fe-40Al powder exhibits lamellar microstructure. The microstructure of the as-sprayed Fe(Al) coating depends significantly on that of the as-milled powder. The heat-treatment temperature significantly influences the in-situ evolution of the intermetallic compound. The heat treatment at a temperature of 500 °C results in the complete transformation of Fe(Al) solid solution to FeAl intermetallic compound.

Indentation size effect in Ni–Fe solid solutions

The indentation size effect observed during indentation testing is studied in pure Ni, Fe and two different Ni–Fe alloys as well as in a Ni–Fe diffusion couple. The hardness as a function of depth in these solid solutions is modeled in terms of geometrically necessary dislocations (GND). It is found that, for indentation depths varying from 50 to 5000 nm, the depth dependence of hardness could be modeled with a parameter f. Parameter f allows scaling of the storage volume of GND with indentation depth, thus yielding the effective contribution of GND to the hardness in a specific alloy. For the alloy studied, parameter f decreases with solid solution strengthening. Frictional stresses or changes in stacking fault energy might reduce the storage volume for GND. Using these observations, it is shown that diffusion couples and nanoindentation allow macroscopic solid solution hardening to be determined in a combinatorial manner.

Thermodynamics of Fe-Rich Intermetallics along the Rare Earth Series

A set of thermodynamic properties of the Fe-rich part of the Fe/rare earth (RE) systems is presented for almost all the elements in the rare earth series. This set of data comes entirely from electromotive force (emf) vs T experimental measurements obtained by galvanic cells with a CaF 2 single crystal as the electrolyte. The standard enthalpy and entropy of formation of RE 2 Fe 17 intermetallics have been obtained and compared with previous results found for the RE 2 Ni 17 intermetallics. The enthalpy of formation of RE 2 Fe 17 intermetallics is decidedly less exothermic than the enthalpy of formation of RE 2 Ni 17 with the exception of the value of Pr 2 Fe 17 , which is endothermic. The RE 2 Fe 17 entropy of formation is always positive contrary to the values of RE 2 Ni 17 . For comparison purposes, the thermodynamic data of Y 2 Fe 17 and Dy 2 Co 17 have also been determined. The RE solubility in Fe has been evaluated by the shift of the bcc Fe(110) plane spacing with respect to pure Fe as shown by corresponding X-ray diffraction (XRD) data. Along the RE series, the atomic fraction of RE in the Fe solid solution changes from (1.2 ± 0.1)-10-4 for Er to (9.2 ± 0.2)-10-4 for Ho. The values of the thermodynamic activity of RE coexisting between the RE 2 Fe 17 -rich phase and the Fe solid solution are reported along the series, and the related partial excess free energy is given as electronic and dilatation contributions. The electronic partial excess free energy of RE 2 Fe 17 intermetallics is practically independent of the dilatation term contrary to the RE 2 Ni 17 intermetallics.

Synthesis of single-phase Al–Cu–Fe quasicrystals using high-energy ball-milling

Due to their unique combination of physical, thermal and mechanical properties, aluminium-based quasicrystals are of great interest for many applications such as low friction hard coatings. Nevertheless, as quasicrystalline phases are usually stable only within narrow composition domains, their production on an industrial scale meets some difficulties.Alloys with nominal composition Al67Cu23Fe10 were prepared by high-energy ball-milling of elemental powders. The as-milled powder specimens consist of a nanocrystalline Al(Cu,Fe) solid solution. The structural phase transitions of the ball-milled Al–Cu–Fe nanopowders during constant rate heating were investigated by in situ X-ray diffraction at the B2 beamline at desy-hasylab (Hamburg, Germany). High-quality single-phase quasicrystalline (QC) powders were obtained from nanocrystalline precursors by slow heating to temperatures above 750°C. The QC phase is preserved upon quenching and is stable during subsequent heating runs up to 800°C.

Deformation-induced phase transformations in the Al–Fe system under intensive plasticdeformation

Mössbauer spectroscopy showed that mechanical activation by compressionshear in Bridgman anvils led to deformation-induced dissolution ofAl6Fe and Al13Fe4 aluminides and iron in the aluminum matrix, which was followed by formation of an Al–Fe solid solution,Al9Fe2 and Al5Fe2 aluminides, and their defective modifications. TheAl6Fe and Al13Fe4 aluminides dissolved with an extraction-type stoichiometry, which was explained by aneasier release of aluminum (as compared to iron) to the aluminum matrix and theaccompanying precipitation of aluminides owing to saturation of the structure withdeformation vacancies. A unified set of metastable phases, which appeared during quickquenching and intensive plastic deformation of the Al–Fe system, pointed to a commondiffusion mechanism of the phase transformations.

Mechanistic inferences on the synthesis of Co 50Fe 50 solid solution by mechanical alloying

An equiatomic Co–Fe solid solution was synthesized by mechanical processing. A dissolution process of Co in Fe was observed. Its kinetic characterization permitted a reliable estimate of the number of Co atoms dissolved in collision events. This number was then compared with the corresponding quantity observed in Co–Fe diffusion couples under thermal activation conditions. The data support a mechanistic hypothesis for mechanochemical transformations alternative to the ones based on thermal diffusion.

Phase separation and rapid solidification of liquid Cu60Fe30Co10 ternary peritectic alloy

The metastable liquid phase separation and rapid solidification of Cu60Fe30Co10 ternary peritectic alloy were investigated by using the drop tube technique and the differential scanning calorimetry method. It was found that the critical temperature of metastable liquid phase separation in this alloy is 1623.5 K, and the two separated liquid phases solidify as Cu(Fe,Co) and Fe(Cu,Co) solid solutions, respectively. The undercooling and cooling rate of droplets processed in the drop tube increase with the decrease of their diameters. During the drop tube processing, the structural morphologies of undercooled droplets are strongly dependent on the cooling rate. With the increase of the cooling rate, Fe(Cu,Co) spheres are refined greatly and become uniformly dispersed in the Cu-rich matrix. The calculations of Marangoni migration velocity (V M) and Stokes motion velocity (V S) of Fe(Cu,Co) droplets indicated that Marangoni migration contributes more to the coarsening and congregation of the minor phase during free fall. At the same undercooling, the V M/V S ratio increases drastically as Fe(Cu,Co) droplet size decreases. On the other hand, a larger undercooling tends to increase the V M/V S value for Fe(Cu,Co) droplets with the same size.

Calorimetric search for the discontinuity in Fe0.96S-Ni0.96S solid solutions

Heat capacity of unstable quenched solid solutions (Fe1−xNix)0.96S was measured by DSC (enthalpy method and scanning heating). According to optic microscopy and X-ray powder diffraction, the samples are homogeneous phase of NiAs type with unit cell parameters changing regularly with composition.

Nanocrystalline FeAl matrix composites reinforced with TiC obtained by hot-pressing consolidation of mechanically alloyed powders

Bulk FeAl matrix nanocomposites reinforced with 50%, 30% and 10% of TiC were produced by hot-pressing consolidation of mechanically alloyed nanocrystalline Fe(Al)–TiC composite powders containing different amounts of reinforcement. The powders were compacted at 1000 °C under a pressure of 7.7 GPa. Structural investigations of the consolidated materials revealed that transformation of the Fe(Al) solid solution into FeAl intermetallic had occurred during sintering and that both the matrix and the reinforcement remained nanocrystalline, with the mean crystallite size of about 20 nm. We infer that applying of a high pressure hinders grain growth at elevated temperature. The microhardness of the produced materials is relatively high, ranging between 1363 and 1608 HV0.2, depending on the amount of TiC. The density of the obtained bulk materials is very close to 100% of the “ideal” value and the open porosity is zero. These results as well as structural investigations show that the quality of compaction with preserving of the nanometric grain size of the composite constituents is satisfactory.

High-temperature oxidation of Fe-Cr alloys in air

The scales formed on the Fe-Cr (19, 29.5, and 46.8 at % Cr) and Fe70Cr15B15 alloys in the initial stages of oxidation in air at 1470 K have been analyzed using depth profiling. The results demonstrate that the Cr/(Fe + Cr) ratio in the scales on the Fe-Cr alloys is close to 30 at %, independent of the bulk chromium concentration. The top scale layers on the Fe-Cr alloys consist predominantly of M2O3 (M = Cr, Fe) solid solutions and CrO2, the intermediate layers are composed of (Fe, Cr)3O4 and FeO, and the internal oxidation and nitridation layers consist of chromium oxides and nitrides. The top scale layers on the oxidized Fe70Cr15B15 alloy contain, in addition, boron oxides, and the internal nitridation product is BN instead of chromium nitrides.