Fe Ti System Research Articles

Experimental study and thermodynamic re-assessment of the binary Fe–Ta system

Phase relations and thermodynamic properties in the binary Fe–Ta system were re-assessed taking into account available and new experimental data. Seven alloys with different chemical composition were prepared. Both, as-cast and annealed samples were analyzed by means of DTA, SEM/EDX and XRD techniques in order to experimentally verify the phase relations in the system. The experimental results showed congruent melting of the Laves phase (λ), two eutectic reactions L ↔ (δFe) + λ, L ↔ (Ta) + μ and one peritectic reaction L + λ ↔ μ. Samples with 45.1, 52.3 and 56.2 at. % Ta seem to contain small amounts of the metastable Ta 3Fe 2 phase, the fractions being too small to be identified by conventional X-ray diffraction. The enthalpies of formation of solid Fe–Ta alloys referred to bcc-Fe and bcc-Ta at 298 K were determined by isoperibolic dissolution calorimetry using liquid Ni at 1773 K as solvent. A new thermodynamic description of the binary Fe–Ta system was obtained by CALPHAD modeling of the Gibbs energy of all individual phases, taking into account the above experimental data as well as assessed published data. Calculations of the phase diagram and of thermodynamic properties were performed with the Thermo-Calc software. They are shown to properly reproduce experimental data.

Structural phase transition in the Fe–Ta system studied by ion beam mixing

For the Fe–Ta system characterized by a negative heat of formation (−22 kJ/mol), 200 keV xenon ion beam mixing with nano-sized Fe–Ta multilayered films was conducted to study the non-equilibrium alloy phase formation. The results show that uniform amorphous alloys can be obtained within a composition range of 25–80 at.% Ta, which falls in the maximum possible amorphization range (MPAR) (3–93 at.% Ta) predicted by the empirical model. Besides, two metastable crystalline phases both of fcc structures, yet with different lattice constants were obtained. The possible mechanisms for the formation of both amorphous alloys and metastable crystalline phases are also discussed in terms of the atomic collision theory.

Phase equilibria in the Fe–Rh–Ti system II. CVM calculations

Cluster Variation Method (CVM) calculations of phase equilibria in the bcc Fe–Rh–Ti system were performed in the irregular tetrahedron (IT) approximation including tetrahedron interactions. The energy parameters were obtained from a fit to recent experimental data on phase equilibria at 1000 °C and 800 °C. At these temperatures the ordering between first nearest neighbours dominates leading to large single-phase fields with B2 ordering. At lower temperatures the calculations predict additional ordering between second nearest neighbours of type D0 3. In the Fe–Ti system the second neighbour interactions are of segregation type leading to miscibility gaps between the disordered A2 and the ordered B2 phases extending from the binary Fe–Ti system into the ternary system. Calculated isothermal sections are presented at several temperatures. The complex ordering in the ternary system leads to strong variations of chemical potentials with composition. This is shown by calculated iso-chemical potential contours.

Assessment of the Al–Fe–Ti system

The Al–Fe–Ti system has been assessed and the limiting binary systems are shortly reviewed. Based on a thorough review of the literature, isotherms at 800, 900, and 1000 °C have been re-evaluated and a provisional isotherm at 1200 °C is presented for the first time. The effect of alloying the binary phases with the third component is reviewed with regard to the ternary homogeneity ranges, crystallography, order/disorder transformations, and site occupancies. Of the variously reported ternary compounds only the existence of “Al 2FeTi” (τ 2) and “Al 8FeTi 3” (τ 3) is confirmed. The occurrence of the phases τ 2 ∗, τ′ 2, and of a new stacking variant of TiAl is still under discussion, while the existence of the phases Fe 2AlTi (τ 1) and Fe 25Al 69Ti 6 (X) is ruled out. The presented reaction scheme corroborates the isothermal sections and also a representation of the liquidus surface is given. Magnetic, electrical, thermochemical, atomistic and diffusion data for Al–Fe–Ti alloys are summarised and an overview about studies on modelling of phase equilibria and phase transformations is given.

Structural transformations induced in Fe/Ti multilayers by Ar- and Kr-ion irradiation

The structural transformations in Fe/Ti multilayers induced by Ar- and Kr-ion irradiation arestudied by conversion electron Mössbauer spectroscopy (CEMS). Samples of Ti-to-Fe thickness ratiosβ = dTi/dFe = 1 (nominalcomposition Fe0.6Ti0.4) andβ = 1.5 (Fe0.5Ti0.5) with modulationwavelengths Λ = 10–60 nm (Λ = dFe+dTi,where dFe and dTi are the elemental thickness of Fe and Ti layers) were used. The total thickness ofthe films was 240 nm. The ion-beam mixing of multilayers was induced by200 keV Ar2+ and350 keV Kr2+ ion irradiation withfluences ranging from 5 × 1013 to 1.3 × 1017 cm−2 (Ar)and 0.5 × 1013 to 5.6 × 1016 cm−2 (Kr). The ranges of Ar and Kr ions were about 105 and 95 nm, respectively. Ion-beammixing process leads at low ion fluence to the formation of the solid state solution bcc-FeTiwhich at higher ion fluences converts to the amorphous FeTi phase. The degree ofamorphization depends on the ion fluence, composition of the FeTi system and modulationwavelength. It was noted that the mixing efficiency is considerably larger for heavier ions(Kr as compared with Ar). The relative fractions of given phases were determined from theCEMS measurements. Deterioration of the amorphous phase and partial restoration of thebcc-FeTi solid solution at highest Ar-ion fluences was observed. The results wereinterpreted based on the enthalpy curves for amorphous FeTi and bcc-FeTi solid solutions.

Fe-Ni-Ti-Zn (Iron-Nickel-Titanium-Zinc)

The Fe-Zn binary system is briefly reviewed under the Fe-Zn on page 544. For the Fe-Ni and Ni-Zn systems, see the update on the Fe-Ni-Zn system in this issue. In the Fe-Ti system, the two intermediate phases Fe2Ti and FeTi have limited homogeneity ranges at 450 °C. The partially known Ti-Zn system [Massalski2] has seven intermediate phases: TiZn15, TiZn10, TiZn5, TiZn3, TiZn2, TiZn, and Ti2Zn. In the Ni-Ti system [Massalski2], the intermediate phases are Ti2Ni, TiNi, and TiNi3.

Formation of intermetallics during brazing of alumina with Fe, Ni and Cr using Ag–30 Cu–10 Sn as filler metal

The formation of intermetallic compounds during brazing of alumina with Fe, Ni and Cr using Ag–30 Cu–10 Sn filler metal and Ti as the active metal has been studied. The brazing was carried out at 800 °C. The Ti metal reacted with alumina, filler metal and metal members and formed intermetallic compounds. A number of intermetallics of the Ti–Cu system, i.e., TiCu, Ti 2Cu and Ti 2Cu 3 have been observed. Two intermetallics of the Ti–Sn system, namely, Ti 5Sn 3 and Ti 3Sn have been observed. Two intermetallics of the Ti–Ni system, namely, Ni 3Ti and NiTi 2 have been observed when alumina was joined with Ni. The intermetallics Fe 2Ti and FeTi of the Fe–Ti system have been observed during brazing of alumina with Fe. Each intermetallic has shown some solubility for the other elements of the Al 2O 3/Ti/Ag–30 Cu–10 Sn/metal systems. The composition of each intermetallic has been analyzed and tabulated.

A Re-Examination of the Liquidus Surface of the Al–Fe–Ti System

Abstract The liquidus surface of the Al–Fe–Ti system has been reexamined. 34 different alloys have been studied by differential thermal analysis, and the temperatures of invariant reactions have been determined. By examining the as-cast samples by optical microscopy, X-ray diffraction and energy-dispersive spectrometry in a scanning electron microscope, the crystal structures and chemical compositions of the primary phases and two-phase aggregates have been established. In some cases, additional investigations were carried out in the transmission electron microscope. From the combined results of these investigations the solidification paths of the alloys were established leading to a revised representation of the liquidus surface of the Al–Fe–Ti system. A reaction scheme has been set up which shows phase equilibria that are consistent with previous solid-state isothermal sections.

Structural study of TM 60Ti 40 (TM=Fe, Co, Ni) amorphous alloys produced by mechanical alloying

This paper describes the determination of the local atomic structure of amorphous TM 60Ti 40 (TM=Fe, Co, Ni) alloys produced by mechanical alloying (MA) technique. The interatomic distances and the coordination numbers for the TM–TM, TM–Ti and Ti–Ti first neighbors were obtained by making the deconvolution of the first atomic shells of the radial distribution functions, which were calculated from the measured X-ray scattering patterns for the three alloys. The deconvolution was possible because the local atomic structures of these alloys can be accurately predicted by the additive hard-sphere (AHS) model. Thus, the number of TM–TM and TM–Ti first neighbors given by the AHS were used in the deconvolution to find the number of minority Ti–Ti pairs. Our results show complete amorphization for the Ni 60Ti 40 and Co 60Ti 40 alloys and partial amorphization in the case of the Fe 60Ti 40 alloy. These results are consistent with the free enthalpies of mixing for these alloys. A chemical short-range order, greater than expected, was found in the Fe 60Ti 40 alloy and attributed to partial amorphization of the Fe–Ti system by MA.

Partial Fe-Ti alloy phase diagrams at high pressure

Recently, high pressure treatments such as hot isostatic pressing have become more familiar in industrial processes. The high pressure induces changes of both the phase equilibrium and the kinetics of the phase transformation in alloys. The iron-rich phase diagrams under high pressure have been previously reported in the Fe-Mo, Fe-W, Fe-Cr, Fe-V, and Fe-Si systems, which have the {gamma} loop in the iron-rich side at the ordinary pressure. These systems exhibit the astonishing changes in phase equilibrium under high pressure: the {gamma} loop expands under high pressure, and especially the {gamma} loop type phase diagrams of Fe-Mo and Fe-W systems transform to the {gamma} shrink type phase diagram at higher pressures. So, it is very interesting to investigate the effect of high pressure on phase equilibrium in the {gamma} loop phase diagram of the Fe-Ti system, which is practically important for hydrogen storage alloys, titanium clad steels, and so on. Therefore, the authors have established the iron-rich Fe-Ti phase diagrams at the high pressure up to 2.7 GPa.

Thirty years of levitation melting calorimetry – a balance

Investigations on liquid high melting metals are frequently tainted with side reactions with the crucible material. Levitation techniques enable the containerless investigation of thermophysical properties over a wide temperature range. An overview is given on enthalpy measurements by levitation drop calorimetry on solid and liquid metals using the electromagnetic levitation technique. The resulting melting enthalpies and melting entropies of the IVb-metals (Ti, Zr, Hf), the Vb-metals (V, Nb, Ta), and the VIb-metals (Cr, Mo, W) show a group dependence where the IVb-metals are characterized by melting entropies in the range 6.8–8 J mol −1 K −1, the Vb-metals have a value between 10 and 11 J mol −1 K −1, and the VIb-metals show melting entropies in the range 13–14 J mol −1 K −1. Another overview is given on mixing enthalpy measurements by levitation alloying calorimetry. The liquid Fe–Ti system is presented as an example for a temperature dependent mixing enthaply where modelling according to the regular associate model enables the calculation of the thermodynamic properties of mixing.

Structural change of Fe⧸Ti multilayer during annealing in vacuum and hydrogen atmosphere

The structure of sputter-deposited Fe⧸Ti multilayers with various layer thickness and its change with annealing at elevated temperatures in vacuum and hydrogen atmosphere have been studied using X-ray diffraction and Auger-electron depth profiling techniques. The multilayers exhibit preferred orientations of Fe (110) and Ti (001) lying parallel to the substrates in the as-deposited states. When they are annealed in vacuum at 523–823 K, interlayer mixing takes place to form a supersaturated bcc solid solution and FeTi compound, and the original modulated structure almost disappears. No indication of solid-state amorphization is obtained during annealing. When the multilayers are annealed under 0.2–0.5 MPa H 2 in the same temperature range, the interlayer mixing is strongly suppressed and the original layer structure is almost preserved, although the Ti layers have transformed to those of δ-TiH 2 or β-TiH x depending on the temperature and H 2 pressure. This effect of hydrogenation on stabilizing the structure of Fe⧸Ti multilayers is well accounted for in terms of a calculated free-energy diagram for the Fe-Ti system.

Metastable crystalline phases formed in the Fe–Ta system by solid-state reaction

Abstract Two metastable crystalline phases of face-centered-cubic and tetragonal structures were sequentially formed in both bcc structured Fe–Ta system by solid-state reaction at moderate temperatures. The heats of formation of the newly obtained phases were calculated based on Miedema’s model and Alonso’s method and a free energy diagram of the Fe–Ta system was established, which can give a relevant thermodynamic interpretation to the observed structural phase evolution.

Ion mixing to synthesize amorphous and metastable crystalline alloys inthe Fe-Ta system

Formations of metastable phase in the Fe-Ta system upon ion irradiation are sensitive to the entire composition of the initial multilayered films and ion irradiation dose. Amorphization was achieved at high irradiation dose in the Fe35Ta65 multilayered films, which was in the vicinity of the deep eutectic point. A metastable face centred cubic (fcc) phase was, however, observed at low irradiation dose in the same sample. Detailed examination showed that the fcc phase had a composition of about Fe20Ta80.

Comparison of Fe-Ti assessments

Five assessments of the Fe-Ti system are compared with experimental information, and a new assessment is carried out with particular attention to the properties of dilute solutions of Ti in liquid Fe. All assessments have their shortcomings, but it is concluded that a more ambitious assessment should not be attempted before more experimental information is available.

Assessment of the Fe-Ti system

The literature on the Fe-Ti system is reviewed and the thermodynamic description of the system is reassessed checking the ternary extrapolations in the Fe-Ti-C and Fe-Ti-N systems. The reproduction of the thermochemical and phase diagram information is presented through a series of figures and tables.

The Crystalline-to-Amorphous Transformations in the Ti-Fe and Ti(H<sub>2</sub>)-Fe Systems during Ball Milling

Elemental equiatomic Ti-Fe as well as similar Ti(H 2 )-Fe powder mixtures were mechanically alloyed in ball mill. The structural changes as a function of milling time were investigated by X-ray diffractometry and low temperature Mossbauer spectroscopy. During milling the supersaturated solid solutions β-Ti(Fe) and α-Fe(Ti) in wide range of composition, two intermetallic phases FeTi and Fe 2 Ti, formation and transformation up to quasi-amorphous state were observed. Furthermore in Fe-Ti(H2) system the MA process proceeds much slower and the formation of FeTi and FeTiH x phases and α-Fe(Ti) solid solutions were observed.

Mossbauer and positron life-time studies of FeTi and Fe 46Ti 50Mn 4 hydride systems

The intermetallic compounds FeTi and Fe 46Ti 50Mn 4 and their hydrides are investigated with Mossbauer spectroscopy. The isomer shift of the intermetallic compound FeTi was found to be negative at room temperature relative to the centre of the α-iron and isomer shift change from negative to positive with hydrogen absorption pressure. The quadrupole splitting is observed at 12 atm hydrogen pressure in FeTi system. The isomer shift was also found to be negative in the Fe 46Ti 50Mn 4 compound relative to the centre of iron and found to be decreasing in negative value with hydrogen absorption pressure towards the centroid. It is suggested that changes in the isomer shift is due to charge transfer from alloy to hydrogen with pressure because Fe is combined with the less electronegative partner element. According to the concept of electronegativity the large difference in electronegativity is needed to facilitate the charge transfer to hydrogen. The positron life-time measurements were also carried out to confirm the hydrogen interaction process with alloys. The positron life-time increases in hydrides in comparison to the parent intermetallic alloy because hydrogen takes electron from the conduction band of FeTi and Fe 46Ti 50Mn 4 during the absorption process. It was suggested that hydrogen interacts with the FeTi alloy obeying the anionic model.

Phase relations in the AgFeTi system at 1123 K

Phase equilibria in the AgFeTi system at 1123 K were determined by using polyphase diffusion couples and equilibrated alloys. The experimental observations are in agreement with a thermodynamic evaluation performed on this system. No ternary phases are present on the AgFeTi isotherm at 1123 K. The solubility of iron in the binary intermetallic compounds Ti 2Ag and TiAg as well as the solubility of silver in Fe 2Ti are negligible. The maximum silver content in FeTi was estimated as ≈0.5 at.%, while nearly 6 at.% of silver can be dissolved in the β-Ti(Fe) based solid solution at this temperature.

Formation of metastable phases by ball milling in the FE-TA system

We report here about studies of phase formation during mechanical alloying in the Fe-Ta system. In the concentration range from 20 to 80 at% Fe, amorphous phases are observed. Between 60 and 90 at% Fe, the coexistence of amorphous and nanocrystalline phases is observed. Quantitative phase analysis using Moessbauer spectroscopy and magnetization measurements shows that the fractions of the two phases are not consistent with a true metastable equilibrium. The milling conditions and the vial temperature influence the amounts of amorphous and crystalline phases formed. At elevated temperature, the system seems to be even further away from metastable equilibrium.