Compound TiFe Research Articles

Interaction of hydrogen-absorbing intermetallic compound tife with hydrogen IV. Mechanism of oxidation of TiFe

Interaction of hydrogen-absorbing intermetallic compound tife with hydrogen IV. Mechanism of oxidation of TiFe

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.

Structure and magnetic properties of mechanical alloyed Nd–Fe–Ti compounds and their nitrides

The Nd–Fe–Ti intermetallic compounds with a ThMn12 structure have been successfully prepared by mechanical alloying and then annealed. It has been found that the phase of the hexagonal TbCu7 structure is formed in Nd8Fe84Ti8 mechanical alloy powders annealed at temperatures ranging from 650 to 850 °C. With an increase in the annealing temperature Ta, the metastable TbCu7 structure transforms into a ThMn12 structure at Ta=900 °C. Consequently, the Curie temperature increases from 180 °C of TbCu7 structure at Ta=650 to 300 °C of ThMn12 structure at Ta=1050 °C. In the series of NdxFe92−xTi8 annealed at 960 °C for 30 min, it has been observed that the ThMn12 structure exists only over the range of compositions of 5≤x<11, and the structure of the type Th2Zn17 is formed for x≥11. All the compounds are nitrited at 400 °C for 15 h, and the Curie temperatures are raised from 400 to 450 °C. The Nd9Fe83Ti8 powder, annealed at 960 °C for 30 min, and nitrided at 400 °C for 15 h, has a coercivity iHc=2.3 kOe. The low coercivity perhaps mainly results from an excessive growth of α-Fe grains due to the high annealing temperature necessary for forming the hard magnetic phase Nd(Fe,Ti)12Nδ.

Reaction of the hydrogen-absorbing intermetallic compound TiFe with oxygen. III. Phase composition of the scale formed on TiFe

We have studied the phase composition of the overlayer of scale which forms on TiFe at 700°C and 900°C (τ=5 h) by x-ray and metallographic analysis. The upper layers of the scale were shown to consist of TiO2 and Fe2O3 after heat treatment at 700°C, but the lower layers contain mainly TiO2, FeO, and Fe. The underlayer on the boundary with the scale contains Ti4Fe2O (η-phase). The inert marker is covered with rutile at 900°C, and FeTiO3 + TiO2 is below the marker. But the next (relatively thick) internal layer consists of FeTiO3, TiO2, and Fe. Large pores associated with intensive growth of the FeO phase are detected in the scale formed at 700°C. As a result, the scale cracks. At 900°C, the scale is denser because the pores and cracks are covered by rutile. We have shown that FeO (p-type semiconductor) is nonstoichiometric in the upper layers of the scale, and TiO2 (n-type semiconductor) is nonstoichiometric close to the boundary with the alloy. The results obtained correlate with the results for the oxidation kinetics previously studied for FeTi, and support a change in the oxidation mechanism when the temperature increases from 700°C to 900°C. Such a change occurs because of the influence of diffusion of the metal ion on oxygen diffusion through the boundary between the scale and the alloy: diffusion of iron through the vacancies in the FeO lattice at 700°C, and interstitial diffusion of titanium ions in the TiO2 lattice at 900°C.

Reaction of the hydrogen-absorbing intermetallic compound TiFe with oxygen. II. Kinetics of oxidation of TiFe in air

We have studied air oxidation (600–950°C) of TiFe alloy by the gravimetric method. We describe the oxidation process by a parabolic time law as well as an exponential temperature law. The weight increase isotherms have breaks, the two parts of the lines corresponding to a periodic increase in the rate constant at temperatures less than 800°C and a decrease at temperatures higher than 800°C. The activation energy also increases above 800°C, and the difference between the oxidizability of TiFe and its analog TiNi decreases. The change in the oxidation mechanism for TiFe is hypothetically determined by the increase in the role of rutile in high-temperature oxidation, and the possibility of diffusion of titanium through interstitial positions of the rutile (TiO2) lattice, similar to previously studied oxidation.

The static lattice Green's function of gamma -Fe and FeTi

The computational scheme of MacGillivray and Sholl (1983) for the calculation of the lattice Green's function is extended to crystalline compounds with more than one atom in the unit cell. The lattice Green's function is calculated for the high-temperature gamma -phase of Fe and for the intermetallic compound FeTi using force constants obtained from Born-von Karman fits to experimental lattice vibration spectra.

Structural evolution during transient liquid phase sintering of iron-titanium compacts: A. Cias et al (Akademia Gorniczo-Hutnicxa, Krakow, Poland) Metal Proszkow, vol 26 no 1–2, 1993, 10–20. (In polish)

Elemental equiatomic Fe-Ti powder mixture was mechanically alloyed in high energy ball mill. XRD, DTA and Mössbauer spectroscopy (at liquid nitrogen temperature) were utilized to monitor the kinetics as well as the accompanied structural and phase transformations through different stages of milling. Our experiments showed that formation of nanocrystalline FeTi compound proceeds via the formation of the supersaturated solid solutions β-Ti(Fe) and α-Fe(Ti) at the interface. After 36 hours of milling, the main part of powder mixture transformed not only to FeTi but also to Fe2Ti intermetallic compound. The transition of last part of super saturated solid solutions β-Ti(Fe) to those intermetallic phases was observed after annealing of this sample at 600 °C.

Structures and magnetic properties of the nitrides (Nd 1- xDy x)TiFe 11N y

The rare earth-iron intermetallics (Nd 1- x Dy x )TiFe 11 ( x=0.0, 0.1, 0.2, 0.3 and 0.4) have been nitrided and the structures and magnetic properties of these nitrides have been investigated. The nitrogen contents y in (Nd 1- x Dy x )TiFe 11N y are estimated to be 0.6 for x = 0.0 and 1.2 for x = 0.1, 0.2, 0.3 and 0.4. The anisotropies increase with increasing Dy content and the Curie temperatures are all more than 700 K. It is found that the compounds (Nd 1- x Dy x )TiFe 11N y at small Dy concentrations have excellent intrinsic magnetic properties favourable for permanent magnet applications.

Hydriding of powder alloys based on the intermetallic compound TiFe

Hydriding of powder alloys based on the intermetallic compound TiFe

Heat Capacities of Intermetallıc Compounds in the Iron - Titanium System

Heat capacities of the intermetallic compounds FeTi and Fe 2 Ti have been measured through the temperature range 120 to 700 K by differential scanning calorimetry. The Neel temperature of the magnetic transition of Fe 2 Ti is determined by means of heat capacity measurements. The data of the heat capacities are fitted with the method of least squares. The confidence limits of the heat capacities as well as of other thermodynamic functions are given for a probability of 95%. The Debye temperatures of the intermetallic compounds FeTi and Fe 2 Ti have been determined. The thermodynamic functions, the enthalpy, the entropy and the Gibbs free energy, are calculated for the temperature range from 0 to 1800 K

BONDING OF CERAMICS TO METALS WITH ACTIVATED COATING LAYERS MADE BY PLASMA SPRAYING

ABSTRACT Bonding of ceramics to metals was carried out by using thermal sprayed coatings as interlayer materials. This bonding method is referred as the thermal spray bonding. In the present study, Si3N4 and Al2O3 ceramics were bonded to SS41 mild steel using activated Ti-Cu multilayer coatings plasma-sprayed on the steel in a low pressure atmosphere. The bondability was estimated by SEM/EDX analysis and shear tests of the joints. The results were compared to those obtained using Ti-Cu multilayer foils as interlayers. When using Ti-Cu foils as interlayers, brittle Fe-Ti compound layers were formed in the joint area after long time heating at a bonding temperature of 900°C, which deteriorated the joint strength. In contrast with the activated interlayers made by plasma spraying, the Ti-Cu eutectic reaction took place uniformly at the joint immediately after heating to the bonding temperature. This improved the bondabilrty, and the resultant joints exhibited shear strengths of about 180 MPa.

Fatigue lifetime monitoring in power plants: Riccardella, P.C., Deardorff, A.F. and Griesbach, T.J. Proc. Conf. Advances in Fatigue Lifetime Predictive Techniques, San Francisco, California, USA, 24 Apr. 1990 460–473

This study investigates the effects of Ti addition on the weldability, microstructure and mechanical properties of a dissimilar weldment of Alloy 690 and SUS 304L. Shielding metal arc welding (SMAW) is employed to butt-weld two plates with three welding layers, where each layer is deposited in a single pass. To investigate the effects of Ti addition, the flux coatings of the electrodes used in the welding process are modified by varying additions of either a Ti–Fe compound or a Ti powder. The results indicate that the microstructure of the fusion zone (FZ) is primarily dendritic. With increasing Ti content, it is noted that the microstructure changes from a columnar dendritic to an equiaxed dendritic, in which the primary dendrite arm spacing (PDAS) becomes shorter. Furthermore, it is observed that the amount of Al–Ti oxide phase increases in the inter-dendritic region, while the amount of Nb-rich phase decreases. Moreover, the average hardness of the FZ increases slightly. The results indicate that Ti addition prompts a significant increase in the elongation of the weldment (i.e. 36.5%, Ti: 0.41 wt%), although the tensile strength remains relatively unchanged. However, at an increased Ti content of 0.91 wt%, an obvious reduction in the tensile strength is noted, which can be attributed to a general reduction in the weldability of the joint.

Hydrogen storage alloys based on titanium

1. A general method of improving the composition of the HSA by complex alloying has been proposed. 2. Systems of alloying the HSA on the basis of intermetallic compounds TiFe, TiCo, TiCr2, TiMn2 have been described and characterized. 3. It is shown that not all possibilities of complex alloying have been exhausted to improve the properties of the HSA based on titanium.

Amorphization in Intermetallic Compounds FeTi and CoTi Under 1-MeV Electron Irradiation

Electron irradiation induced amorphization of FeTi and CoTi was studied by high voltage electron microscopy (HVEM) from 10 to 160°K. The complete amorphization was observed in both compounds, with the critical dose at 10°K and the critical temperature being about 1.7 dpa and 110°K for FeTi, and about 1.3 dpa and 90°K for CoTi. The onset of amorphization occurred in both compounds after substantial chemical disordering when irradiated below Tc, while the point defect clusters formed above Tc. In addition, the pseudo ten fold symmetry (PTEFS) diffraction spots were observed in selected area diffraction (SAD) pattern of both compounds prior to complete chemical disordering and thus complete amorphization.

Localized modes of hydrogen and deuterium in NiTiH x and NiTiD x

The localized vibrations of hydrogen and deuterium in the shape-memory alloy NiTi were investigated by neutron spectroscopy. Measurements were carried out on two hydrogenated samples (NiTiH 0.02 and NiTiH 1.3) and one deuterated sample (NiTiD 0.02). The results are discussed particularly with respect to those reported from previous experiments on the isostructural hydrogen storage compound FeTi.

Special Features of Optical Properties of Ternary Alloys Ti(FexCo1−x)

AbstractMeasurements are made of the optical characteristics: n, k, σ(ω), ϵ1 (ω), ϵ2 (ω) of the ternary pseudo‐binary alloys Ti(FexCo1‐x), 0.2 ≦ x ≦ 0.8 in the spectral range 0.07 to 4.96 eV. The results obtained are compared with the optical properties of the compounds TiFe and TiCo. It is shown that the change in the main absorption band (0.6 ≦ ħω ≦ 3 eV) over the series of alloys can be explained by the shift of EF relative to the special features (minima, peaks) of the density of states curves N(E). An additional low‐energy quantum absorption within 0.2 ≤ ħω ≤ 0.6 eV discovered in ternary alloys is explained by interband transitions between virtual bound states which are due to antistructural Fe atoms and are responsible for ferromagnetism in Ti(FexCo1−x).

Hydriding kinetics of TiFe 0.5Co 0.5 compounds

A thermodynamic reinvestigation of the stability of the compound TiFe 0.5CO 0.5H 1.2 was carried out. It confirmed the easy activation and the change in isothermal stability compared with the classical FeTi alloy. The hydride formation-decomposition kinetics are rate controlled by nucleation and growth during formation and by progress of the interface in spherical symmetry during decomposition.

Localized modes of hydrogen and deuterium in NiTiHx and NiTiDx

The localized vibrations of hydrogen and deuterium in the shape-memory alloy NiTi were investigated by neutron spectroscopy. Measurements were carried out on two hydrogenated samples (NiTiH 0.02 and NiTiH 1.3 ) and one deuterated sample (NiTiD 0.02 ). The results are discussed particularly with respect to those reported from previous experiments on the isostructural hydrogen storage compound FeTi.

Microstructural study of Ti-Rich alloys formed by ion beam mixing of the Fe-Ti system

Abstract An ion beam mixing experiment of the Fe-Ti system has been performed at 320 K. The Fe x Ti100-x phases formed as a function of composition have been studied by transmission electron microscopy within the range 0≤x≤45. The formation of β-Ti(Fe) and FeTi phases is shown for x≥20, β-Ti(Fe), crystalline FeTi and glass for 20<x<35. In every case the amount of the equilibrium FeTi compound is small. For x≥35 a single amorphous state is obtained.

圧延チタンクラッド鋼の接合強度特性と界面性状

In order to produce a titanium clad steel plate by hot rolling process, the effect of insert metal, rolling conditions and oxidation of clad surface on the bonding strength and the microstructure of bonded zone were investigated. The following results were obtained.(1) The titanium clad steel inserted with ultra-low carbon steel, exhibits satisfactory bonding strengths, ductilities and weldabilities.(2) The bonding strength is dominated by the thickness of Fe-Ti intermetallic compound produced at bonding interface and the degree of interdiffusion between Fe and Ti. High bonding strengths with very small scatter band can be obtained in the thickness range of Fe-Ti compound of 0.2 to 0.3μm.(3) A lower bonding strength due to the oxidation on the surface to be bonded is not caused by the oxidized layer but mainly by the remarkable growth of intermetallic compound and, secondarily, by the formation of voids between Ti and steel.