Fe Solid Solution Research Articles

Nanostructured ceramic composite coating prepared by reactive plasma spraying micro-sized Al–Fe2O3 composite powders

Nanostructured ceramic matrix composite coating was prepared in-situ by reactive plasma spraying micro-sized Al-Fe2O3 composite powders. The microstructure, toughness and Vickers hardness of these coatings were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and mechanical tests. The results indicated that the coating exhibited nanostructures which consisted of FeAl2O4, Al2O3, Fe (or Fe solid solution) and a little FeAl. The composite coating showed significantly higher toughness and wear resistance than the conventional Al2O3 coating.

Microstructure and mechanical properties of in-situ Al13Fe4/Al composites prepared by mechanical alloying and spark plasma sintering

Bulk dense composites of Al–Fe alloys containing 2.5–10at% Fe were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). Supersaturated Al(Fe) solid solutions were obtained by MA for 80h. The sintered samples are composed of nano and ultrafine needle-like Al13Fe4 phase and angular-shaped Al13Fe4 phase with a size range of 1–2μm uniformly distributed in the Al matrix. Needle-like Al13Fe4 phase originates from the precipitation of supersaturated Al(Fe) solid solutions, and angular-shaped Al13Fe4 phase originates from the reaction of undissolved Fe particles and the Al melt. The hardness of the alloys varied from 1.44 to 1.97GPa and Al–10%Fe exhibited highest specific yield strength of 391.1kNm/kg. The yield strength varied from 657 to 1130MPa, depending on the Fe content. Excellent plastic strain (>14.5%) were achieved in the alloys containing 2.5–5%Fe, but the Al–10%Fe exhibited elastic behavior only, failing without any macroscopic yielding or plastic strain. The lack of plastic performance of Al–10%Fe is attributed to large amount of undissolved Fe particles reacted with the Al melt to form angular-shaped Al13Fe4, leading to the absence of soft α-Al phase.

Characterization of nanostructured Fe–Co–Si powder alloy

Abstract The main aim of this research is to fabricate the nano-crystalline Fe–Co–Si alloy to be used in producing soft magnetic composites. The alloy powders were prepared by using a planetary ball mill. Morphological, structural and thermal changes during milling were analyzed by scanning electron microscopy (SEM) coupled with EDX microanalysis, X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results confirm the production of the Fe(Co) and Fe(Co, Si) solid solutions after milling. Increasing the milling time has led to smaller crystallite sizes and lattice parameters, but larger amounts of micro-strain in the lattice. Prolonged milling has led to higher lattice parameters due to the segregation of solvent atoms to the grain boundaries.

Dual-scale oxide dispersoids reinforcement of Fe–40 at.%Al intermetallic coating for both high hardness and high fracture toughness

In this study, Fe–40at.% Al/Al2O3 composite powders with an alternant Fe/Al lamellar structure were prepared by mechanical alloying process with 40vol.% of micrometer scale Al2O3 particles. Using the mechanically alloyed composite powders, Fe–40at.% Al alloy/Al2O3 composite coating was deposited by cold spraying. Nanometeric dispersoids were introduced through in situ oxidation during the mechanical alloying and the post-spray annealing. XRD analysis revealed that after the post-spray annealing, Fe (Al) solid solution and lamellar structured Fe/Al alloy transformed into B2 phase Fe40Al intermetallic. SEM observations indicated that the micrometric Al2O3 dispersoids distributed uniformly in Fe–40at.% Al (Fe40Al) intermetallic matrix. TEM examination revealed that the in situ formed nanometric dispersoids were present both at the grain boundaries and inner FeAl crystallites. The in situ formed nanometric dispersoids were identified to be spinel FeAl2O4 and γ-Al2O3 by the electron diffraction combined with the energy dispersive X-ray spectrometry. A Vickers microhardness of 867±66.5HV0.3 and an indentation fracture toughness of 23.8±2.7MPam0.5 were obtained for the Fe–40at.% Al/Al2O3 composite. These results indicated that dual-scale dispersoids can attain simultaneous strengthening and toughening effects for intermetallics-based composite. The ductile manner of the fracture surface suggested that the toughening effect can be generated by thin Fe–40at.% Al ligaments created by the dispersion of oxides.

Thermodynamic analysis of (Ni, Fe)3Al formation by mechanical alloying

(Ni, Fe)3Al intermetallic compound was synthesized by mechanical alloying (MA) of Ni, Fe and Al elemental powder mixtures of composition Ni50Fe25Al25. Phase transformation and microstructure characteristics of the alloy powders were investigated by X-ray diffraction (XRD). The results show that mechanical alloying resulted in a Ni (Al, Fe) solid solution. By continued milling, this structure transformed to the disordered (Ni, Fe)3Al intermetallic compound. A thermodynamic model developed on the basis of extended theory of Miedema is used to calculate the Gibbs free-energy changes. Final product of MA is a phase having minimal Gibbs free energy compared with other competing phases in Ni–Fe–Al system. However in Ni–Fe–Al system, the most stable phase at all compositions is intermetallic compound (not amorphous phase or solid solution). The results of MA were compared with thermodynamic analysis and revealed the leading role of thermodynamic on the formation of MA product prediction.

Intermetallic solid solution Fe1−xCoxGa3: Synthesis, structure, NQR study and electronic band structure calculations

Unlimited solid solution Fe1−xCoxGa3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P42/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and 69,71Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe–Fe and Co–Co dumbbells are preferred to the Fe–Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin–lattice relaxation shows that the rate of the relaxation, 1/T1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N2(EF).

Atomic short-range order in Fe1−xCrx alloys studied by 57Fe Mössbauer spectroscopy

The room temperature Mössbauer spectra of 57Fe were measured for iron-based solid solutions Fe1−xCrx with x in the range of 0.01≤x≤0.10. Analysis of the obtained spectra gave clear evidence that the distribution of impurity atoms in the first coordination spheres of 57Fe nuclei is not homogeneous and it cannot be described in terms of binomial distribution. Quantitatively, the effects were described in terms of the short-range order parameters.

X-ray line profile analysis of the ball-milled Fe–30Co alloy

This work deals with the microstructural properties of the Fe–30Co alloy prepared by ball milling of elemental iron and cobalt powders. The obtained mixed powder has been characterized by means of scanning electron microscope, X-ray microanalysis, laser diffraction, X-ray diffraction and microhardness measurements. X-ray line profile analysis based on the Rietveld method and adopting two different models has been used for the microstructural study. The refinement of the X-ray patterns shows that after 3h of high energy milling the Fe(Co) is formed. The obtained Fe(Co) solid solution is characterized by body centered cubic structure with a lattice parameter a=0.28564±0.00004nm and an ellipsoidal crystallite and microstrain field. The dissolution of cobalt in iron matrix is accompanied by the compression of the crystalline lattice by 0.37%. The progress of milling process produces an increase of the Debye–Waller factor and the dislocation density leading to the hardening of the powder. The variation of microhardness with milling time shows a change in hardening mechanisms.

First-principles study of the effect of iron on the crystal structure, stability and chemical bonding in the β-based AlCu ordered η2-phase and the pretransition state of a solid solution

First-principles calculations showed that the thermodynamic stability of β-based ordered η2-AlCu phase doped with Fe is due to iron substitution in the copper sublattice (FeCu), which corresponds to the maximum number of Fe–Al bonds in the first cubic coordination polyhedron. This iron localisation leads to stable ω-like atomic displacements and pentagonal Al-nets in the (010) plane of η2-AlCu(Fe). This phase with iron substituting copper (e/a = 1.925) is an energetically preferred η-based non-canonical approximant of the icosahedral phase (e/a = 1.86). The energy gain for the FeCu position is determined by strong covalent Fe3d–Al3p bonding, while there is a weak Fe3d–Cu4s3d hybridisation for the FeAl substitution. Using a composite cluster model, we demonstrate that short-range order in the pretransition state of the β-Al–Cu–Fe solid solution observed prior to the precipitation of η-phase is stabilised due to formation of Fe–Al bonds in the first cubic coordination polyhedron of the composite cluster.

Mechanochemical reactions in nanocrystalline Cu–Fe system induced by mechanical alloying in air atmosphere

Metastable nanocrystalline FCC and BCC Fe–Cu solid solutions were synthesized from elemental powders using a high-energy ball mill in air atmosphere. The structural and morphological changes during mechanical milling were investigated by X-ray diffraction and scanning electron microscopy. The patterns so obtained were analyzed using the X'Pert High Score Plus program. The final product of the mechanical alloying process was nanocrystalline double-phase FCC Cu(Fe) and BCC Fe(Cu) solid solutions with a mean crystallite size in the range of a few nanometers. Moreover, the mechanical alloying of Fe–Cu, in air atmosphere, resulted in partial oxidation to Cu2O and CuO. Prolonged milling supported the formation of CuO oxide and the interdiffusion between FCC–Cu(Fe), BCC–Fe(Cu) and cupric oxide (CuO). Scanning electron microscopy results showed that flattened Fe–Cu powders were laid and welded on each other and tended to form a matrix of randomly welded thin layers of highly deformed particles.

Study of magnetic phases in mechanically alloyed Fe50Zn50 powder

The mechanosynthesis of Fe50Zn50 alloy resulted in the formation of the bcc Fe(Zn) solid solution after 20h of milling. Structural transformations induced by mechanical alloying and heating, and magnetic properties of the powders were studied by Mössbauer spectroscopy, X-ray diffraction, Faraday balance and vibrating sample magnetometry techniques. All alloys studied exhibit strong magnetic ordering with Curie temperatures close to 900K. Room temperature Mössbauer measurements revealed distinguished magnetic environments in the samples. The decrease of coercivity with prolonged milling time was attributed to the reduction or averaging of local magnetic anisotropies.

Mössbauer effect study of fine atomic structure of Fe50Al40Ni10 powders

In the present paper, we discuss the local atomic environment of Fe atoms in the mechanically alloyed Fe50Al40Ni10 powders on the basis of hyperfine data estimated from 57Fe Mössbauer spectra. Bhf decreases with increasing milling time due to the diffusion of Al and/or Ni into Fe grains. Nickel atoms did not diffuse inside the first coordination sphere of Fe and if the diffusion takes place the number is not more than one atom. Analyses of P(Bhf), indicate that the high hyperfine field values ranging from 30 to 33T have to be partially attributed to Fe crystalline nanograins and the presence of the defects in them, the hyperfine field values ranging from 15 to 30T can be associated to the nanocrystalline bcc Fe(Al, Ni) solid solution while the low hyperfine field values (<15T) result from Fe atoms located in the disordered grain boundaries.

A fabrication method for vertical oxide nano-rod array by internal oxidation of alloys at high-temperatures

A simple metallurgical process for fabricating vertical oxide nano-rod array structures with internal oxidation of alloys is described. Oxidation at high-temperatures and under low oxygen partial pressures can develop internally rod-like oxide precipitates in some dilute alloys such as Ni(Al) solid solutions. The vertical oxide nano-rod arrays can be developed on the metal substrates or components by removing the metallic matrix of the internal oxidation zone. Al2O3 or NiAl2O4 spinel nano-rod arrays were prepared by using M(Al) solid solutions. Pack cementation process to develop Ni(Al) solid solution zone on a metal surface was used for the fabrication of vertical nano-rod arrays on Ni substrates with desired shape. Near-net shape Ni substrates with vertical oxide nano-rod array structures on their surfaces can be prepared by using pack cementation and internal oxidation. Fabrication of vertical nano-rod arrays with Co(Al) and Fe(Al) solid solutions were also described briefly.

An enthalpy of solution of chromium in iron studied with 57Fe Mössbauer spectroscopy

The room temperature Mössbauer spectra of 57Fe were measured for iron-based solid solutions Fe1−xCrx with x in the range 0.01≤x≤0.05. The obtained data were analysed in terms of the binding energy Eb between two chromium atoms in the studied materials using the extended Hrynkiewicz–Królas idea. It was found that the energy is positive or Cr atoms interact repulsively. The extrapolated value of Eb for x=0 was used for computation of an enthalpy of solution of Cr in Fe. The result was compared with corresponding data derived from calorimetric measurements and resulting from the cellular atomic model of alloys by Miedema as well as with the proper values given in the literature which were calculated on the basis of density functional theory (DFT). The comparison shows that our findings are in good agreement with the recent DFT computations for ferromagnetic Fe–Cr alloys.

New solid solution Fe1−xCrxVSbO6 with rutile-type structure

A new solid solution with formula Fe1−xCrxVSbO6 has been prepared by the conventional solid-state reaction technique using the starting mixtures containing V2O5, α-Sb2O4, Cr2O3 and Fe2O3 as well as FeVSbO6 and CrVSbO6. Continuous substitutional solid solution of a tetragonal structure of rutile-type in the FeVSbO6–CrVSbO6 system is formed in the whole concentration range 0.0<x<1.0. The solid solution was characterised by XRD, DTA-TG, IR and SEM/EDX methods. With increasing degree of Cr3+ ion incorporation into the FeVSbO6 structure, the contraction of Fe1−xCrxVSbO6 solid solution crystal lattice increased. The temperature of its thermal stability in the solid state was established and gradual shifting of the corresponding IR absorption bands towards higher wave numbers was observed.

Structural characterization of mechanically alloyed nanocrystalline Cu-Fe: Strain broadening due to dislocations

Nanocrystalline Cu(Fe) solid solution was successfully synthesized by using high-energy mechanical milling. The structural and morphological changes during mechanical milling were investigated by X-ray diffraction and scanning electron microscopy. The patterns so obtained were analyzed using the X'Pert High Score Plus program. The final product of the mechanical alloying process was nanocrystalline FCC Cu(Fe) solid solution with a mean crystallite size in the range of few nanometers. The final microstructure, especially the high levels of lattice strains was explained by the presence of dislocations, with a dislocation density of about 7.4×10 16 m �2 . The identified steady-state saturation values of these parameters can be related to accumulate strain hardening of the powder material during longer milling times.

An enthalpy of solution of platinum in iron studied by 57Fe Mössbauer spectroscopy

The room temperature Mossbauer spectra of 57Fe were measured for iron-based solid solutions Fe1 − xPtx with x in the range 0.01 ≤ x ≤ 0.05. The obtained data were analysed in terms of the binding energy Eb between two platinum atoms in the studied materials using the extended Hrynkiewicz–Krolas idea. It was found that for x < 0.05 the energy is positive or Pt atoms interact repulsively. The extrapolated value of Eb for x = 0 was used for computation of the enthalpy HFe − Pt of solution of platinum in iron. The result HFe − Pt = −0.62(16) eV/atom was compared with the corresponding values resulting from the semi-empirical Miedema’s model of alloys and the proper data obtained with Calphad’s calculations as well as theoretical computations on the basis of the modified embedded-atom model. The comparison shows that all mentioned values of HFe − Pt are in a qualitative agreement i.e. they are negative, and moreover our findings agree also quantitatively with the Miedema’s model predictions.

Mössbauer and X-ray diffraction studies of nanostructured Fe70Al30 powders elaborated by mechanical alloying

We have studied the effect of milling time on the structural and hyperfine properties of Fe70Al30 compound elaborated by mechanical alloying. The elaboration was performed with a vario-planetary ball mill P4 at different milling times. The milled powders were characterized by X-ray diffraction (XRD) and Mössbauer spectroscopy. From XRD diffraction spectra, we show that the bcc Fe(Al) solid solution was completely formed after 27h of milling time. When the milling time increases, the lattice parameter increases, whereas the grain size decreases and the mean level of microstrains increases. The analysis of Mössbauer spectra shows that from 4h of milling, a disordered ferromagnetic Fe70Al30 starts to form and dominates after 36h.

Atomic short-range order in iron based Fe-Mo alloys studied by 57Fe Mössbauer spectroscopy

The room temperature Mossbauer spectra of 57Fe were measured for iron-based solid solutions Fe1 − xMox with x in the range 0.01 ≤ x ≤ 0.05. The obtained spectra gave clear evidence that after annealing process the distribution of impurity atoms in the first and the second coordination spheres of 57Fe nuclei is not random and it cannot be described by the binomial distribution. Quantitatively, the findings are presented with the short-range order parameters.

Microstructure of Ni / WC surface composite layer on gray iron substrate

The surface infiltrated composite (Ni/WC) layers on gray iron substrate were fabricated through a vacuum infiltration casting technique (VICT) using Ni-based composite powder with different WC particles content as raw materials. The microstructures of surface infiltrated composite layer, the interface structures between surface composite layer and the substrate, the changes of macro-hardness with the increasing of WC content and the micro-hardness distribution are investigated. The infiltrated composite layer includes a surface composite layer and a transition layer, and the thickness of the transition layer decreases with the increasing content of WC. The thickness of transition layer with 20%WC content in the surface infiltrated composite layer was 170 μm which was the thickest for all transition layers with different WC content. The surface composite layer was mainly composed of WC, W2C, FeB and NiB, along with Ni-Cr-Fe, Ni (Cr) solid solution, Ni (Si) solid solution and Ni (Fe) solid solution. The transition layer was composed of Ni (Cr) solid solution, Ni (Fe) solid solution, Ni (Si) solid solution, Fe (Ni) solid solution and eutectic. The surface macro-hardness and micro-hardness of the infiltrated layer had been evaluated. The macro-hardness of the surface composite layer decreases with the WC content increasing, and the average macro-hardness is HRC60. The distribution of micro-hardness presents gradient change. The average micro-hardness of the infiltrated layer is about HV1000.