Al Nb Alloys Research Articles

Protective coatings on orthorhombic Ti<SUB>2</SUB>AlNb alloys

Protective coatings on orthorhombic Ti<SUB>2</SUB>AlNb alloys

The Structure of the Ti3Al Phase in Ti—Al and Ti—Al—Nb Alloys.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Use of electropolishing for enhanced metallic specimen preparation for electron backscatter diffraction analysis

The effects of mechanical polishing with Al 2O 3 and colloidal SiO 2 followed by electropolishing were studied for preparation of metal alloy specimens for Electron Backscatter Diffraction (EBSD). The alloys studied were Inconel 718, a commonly used nickel-based superalloy, and a Ti–Al–Nb alloy (nominally Ti-22Al-28Nb(at.%)). Atomic Force Microscopy was used to measure the surface topography to attempt to correlate nano-scale surface roughness with EBSD pattern quality. The results suggest that mechanically polishing with Al 2O 3 followed by electropolishing for a short time can produce EBSD pattern confidence indices and image quality values that are equal to or better than those produced by mechanically polishing with colloidal SiO 2 alone. The data suggests that surface roughness on the scale considered here has much less effect on EBSD pattern quality than had been previously believed. The data suggests that removing the surface damage is more critical than reduction of topography for EBSD.

Passivity and its breakdown in Al-based amorphous alloys

The effect of Cl − ions (0–1 M NaCl) on the anodic behaviour of two series of sputter-deposited Al–Ta (11–46 at.%) and Al–Nb (13–46 at.%) amorphous alloys was investigated in a neutral electrolyte by using electrochemical methods and the results were compared with those for Al–Mo and Al–W alloys. In solutions containing Cl − the alloys broke down at and above the pit nucleation potential E np. They exhibited a stable passivity within a much wider (Δ E > 1 V) potential range than crystalline Al. The anodically formed oxide films in Cl −-free electrolyte were characterized by surface analytical measurements including high-energy resolution AES. Galvanostatic polarization was used to produce thicker anodic films than those formed under natural conditions, to facilitate detailed examination of their depth composition profiles. It was found that the anodic films grown on Al–Ta and Al–Nb alloys had a homogeneous structure in contrast to those on Al–Mo and Al–W. Transition metal Ta or Nb was detected at any depth of the composition profile. A relative enrichment of refractory metal within the inner part of the anodic film was not found, for these alloys. Tentative mechanisms of enhanced stability of the passive state of the Al-based amorphous alloys (AAs) are discussed.

A study of precipitation in DO 3 ordered Fe–Al–Nb alloy

Precipitation and ordering has been examined in Fe 3Al-base alloy with a small addition of Nb. At low temperatures the alloy shows DO 3 order with no precipitation, at least for short annealing times. At intermediate temperatures, 700–750 °C, planar precipitates of a phase with L2 1 structure form, which transform at longer times and high temperatures to blocky precipitates of the stable Laves phase of C14 structure. The L2 1 precipitates form on {001} planes, coherently with the ordered matrix, while the C14 particles form in a { 1 ¯ 010 } C 14 / / { 1 ¯ 01 } matrix relationship with < 1 2 ¯ 1 0 > C 14 approximately parallel to the 〈010〉 matrix and 〈0001〉 C14 approximately parallel to the 〈101〉 matrix. These particles grow relatively quickly in the intermetallic matrix, and hence are unsuitable for matrix strengthening at temperatures above about 750 °C.

Properties and structural characteristics of Ti–Nb–Al alloys

The use of Al as an α stabilizer in different Ti–Nb alloys has been investigated for its effect on some properties and changes in structural characteristics. Quenched alloys with 10–40% Nb and 2–15% Al were analyzed in terms of their phase transformations, as well as elastic modulus, density and internal friction. It was found that the rhombic distortion introduced in the α′-HCP phase transforms into another martensitic α″ structure. Above 5% Al, metastable β-BCC is formed and eventually predominates. The appearance of another metastable phase, ω, was verified in alloys between 2 and 5% Al with less than 35% Nb. These structure transformations are a consequence of the obstructing effect of Al on the redistribution of Ti and Nb. The elastic modulus increases with Al and decreases with Nb percentage due to different developed structures, especially at lower Al content. Small fluctuations in the generally increasing variation of the density with Nb, for Al percentages, were attributed to the phase transformations. The internal friction was relatively large for the martensitic, α′ or α″, structure but decreases significantly with the appearance of β phase.

Biocompatibility Evaluation of Ti&amp;ndash;15Al&amp;ndash;33Nb(at%) and Ti&amp;ndash;21Al&amp;ndash;29Nb(at%)

In this work the biocompatibility of two vanadium-free Ti–Al–Nb alloys, Ti–15Al–33Nb and Ti–21Al–29Nb, was evaluated and compared to that for commercially pure titanium (CP Ti) and alumina (Al2O3). Fine particles were milled from sheet-processed material and implanted onto mice calvaria using an established animal model. Various stains, including methylene blue/acid fuchsin, TRAcP, and immunohistochemistry, were used on the particle-treated calvaria to measure the extent of bone deterioration of the calvaria, quantify the amount of osteoclasts, and approximate the presence of T-cells. In addition, reaction with particle-stimulated macrophages was observed and the production of the cytokine TNFα was recorded and quantified. The results indicated that the Ti–Al–Nb alloys statistically outperformed both CP Ti and Al2O3 in terms of their overall biocompatibility with respect to the experiments performed.

On the structure of the Ti 3Al phase in Ti–Al and Ti–Al–Nb alloys

The present work describes the calculation of the atomic shift of titanium atoms (6( h) Wyckoff positions) in Ti–20Al, Ti–25Al, Ti–30Al and Ti–45Al–5Nb alloys (all atom%) in the α 2-phase using a Rietveld refinement procedure. The Ti atoms are slightly shifted from their regular cph atomic sites. This is related to the presence of symmetry elements in the α 2-phase with D0 19 structure, which in turn allows local shifts due to different site occupancies resulting in different atomic potentials. The shift in the Ti positions changes the Ti–Ti and Ti–Al first neighbor bond lengths within and out of plane and also the size of tetrahedron.

Surface characterization of the oxide layer grown on TiNbZr and TiNbAl alloys

AbstractThe surface of the oxide layers formed after oxidation in air at 750°C of three titanium alloys has been characterized by several techniques. The investigated alloys were Ti7Nb6Al, Ti13Nb13Zr and Ti15Zr4Nb, with potential applications as biomaterials. XPS experiments showed that, after 24 h exposure, the surface of the Ti7Nb6Al alloy is mainly formed of Al2O3, with a minor presence of TiO2, and absence of Nb oxide. On the other hand, the surface of both TiNbZr alloys is mainly composed of TiO2, with some amount of ZrO2 and Nb2O5. An enrichment of the Nb signal is observed in both samples with respect to the bulk composition. The topography and surface morphology of the oxidized alloys were investigated by atomic force microscopy. A more regular surface topography was observed for the Ti7Nb6Al alloy than for the TiNbZr alloys and, consequently, a higher potentiality in biomedical applications. Finally, in order to get in‐depth information of the oxide scale, Rutherford backscattering spectroscopy experiments were also performed. The results obtained with this technique confirm those obtained by XPS, and can help to understand the mechanism and kinetics of the oxide film formation. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Oxidation of orthorhombic Ti&lt;SUB&gt;2&lt;/SUB&gt;AlNb alloys in the temperature range 550–1000°C in air

Oxidation of orthorhombic Ti&lt;SUB&gt;2&lt;/SUB&gt;AlNb alloys in the temperature range 550–1000°C in air

Pseudo-elastic deformation behavior in a Ti/Mo-based alloy

It is shown that the pseudo-elastic response in a series of Ti–Mo–V–Nb–Al alloys with 8–11 wt.% Mo is highly sensitive to both composition and heat treatment. Recovery of up to 3.0% strain has been observed but it appears that this may not be due to reversible formation of α ″ martensite.

The stabilization of Pt 3Al phase with L1 2 structure in Pt–Al–Ir–Nb and Pt–Al–Nb alloys

It has been reported that the Pt 3Al phase has two crystal structures: the high-temperature cubic form of L1 2 and the low-temperature tetragonal form of the distorted L1 2 structure D0’c. In this study, the structure of the Pt 3Al phase in quaternary Pt–Al–Ir–Nb and ternary Pt–Al–Nb alloys was investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM) technologies. The structure form was determined to be cubic L1 2. The stabilization of the L1 2-Pt 3Al structure in room temperature was attributed to the effect of Nb.

Bulk metallic glass formation in Ni–Zr–Nb–Al alloy systems

Ni-based metallic glasses containing no metalloids are developed in Ni–Zr–Nb–Al alloy system. A partial replacement of Zr with Nb in Ni–Zr–Al alloys significantly enhances the glass-forming ability (GFA) and enlarges the undercooled liquid region during continuous heating of glassy ribbons. A quaternary Ni–Zr–Nb–Al metallic glasses exhibit large undercooled liquid region (>50 K), indicating high glass-forming ability of the alloy. The glass transition and crystallization temperatures of a quaternary Ni 61Zr 28Nb 7Al 4 alloy are 848 and 898 K, respectively, exhibiting a wide undercooled liquid region of 50 K. A complete Ni 61Zr 28Nb 7Al 4 glassy rod (φ1 mm) can be prepared by copper mold injection casting.

Effect of Niobium Addition on the Oxidation Behavior of a Ti3Al Alloy

The effect of niobium on the oxidation behavior of a Ti 3 Al alloy was studied in pure oxygen in the temperature range of 1123-1373 K. The experiments were carried out using Thermogravimetric Analysis (TGA) apparatus. The oxidation curves for the alloy followed parabolic law. Effective activation energy of 284 kJ/mol was deduced for the oxidation of Ti 3 Al-Nb alloy. The oxidation products were analyzed using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDX) techniques. The oxidation products were mainly the mixture of TiO 2 (rutile), TiO, and Al 2 O 3 (alumina) with small amount of niobium oxide. Oxidation resistance of Ti 3 Al was found to have been improved by the addition of niobium. Layered structure comprising of a mixture of rutile and alumina was observed on the oxide scale of the Ti 3 Al-Nb alloy at temperatures higher than 1273 K.

Phase identification and effect of W on the microstructure and micro-hardness of Ti 2AlNb-based intermetallic alloys

The O-phase (orthorhombic Ti 2AlNb phase) intermetallic alloy has been considered one of the strongest materials for high temperature application. The primary compositions of the test alloys in this paper are Ti–22Al–27Nb (at.%) and Ti–22Al–20Nb–2W (at.%). By in-situ X-ray diffraction (XRD) tests, each phase is identified and the lattice parameters of each phase are calculated for different temperatures. XRD tests show that a Ti 2AlNb-β phase, partially ordered b.c.c. phase, exists besides O, α 2 and B2 that are usually expected in the Ti–Al–Nb alloy system. In this paper, the effects of tungsten on the microstructure and micro-hardness of a Ti 2AlNb-based (O+b.c.c.) alloy are investigated. The effects of W on Ti 2AlNb-based intermetallic alloys are widely known to cause a refinement of microstructure and improvement of mechanical strength, however, the reason has not yet been reported. In this paper, the role of W in the improvement of mechanical strength is clarified. The main effect of W addition is not the formation of a solid solution or the formation of W-precipitates but the refinement of the Widmanstätten structure.

Ａｌの溶融塩電析による金属Ｎｂの表面改質とその耐高温酸化性

The surface improvement of Nb to improve the high temperature oxidation resistance was carried out by Al electrodeposition using the molten salt as an electrolyte. Electrolysis of Al was conducted using potentiostatic polarization method at constant potentials in an equimolar NaCl-KCl melt containing 1∼5 mol%AlF3 at 1023K. The mass of electrodeposited Al increased with a decrease in polarization potential. Deposits formed at -1.3∼-1.6V (vs. Ag/Ag+ (0.1)) consisted of hemispherical Al phase and lamellar Nb-Al alloy phase. The alloy phase consisted of NbAl3. Niobium covered by the Nb aluminide was more resistant than bare niobium to high temperature oxidation at 1273K for 10.8ks in air.

Growth of Anodic Oxides on Sputtered Al-Nb Alloys

Growth of Anodic Oxides on Sputtered Al-Nb Alloys

Phase separation tendency in the as-solidified Zr3Al-Nb alloys studied by microstructural observations and thermodynamic analysis

The as-solidified microstructures of Zr 3 Al-Nb alloys with varying Nb concentration, viz., Zr 3 Al, Zr 3 Al-3Nb, and Zr 3 Al-10Nb, have been investigated and the phases occurring in these alloys have been identified in terms of their crystal symmetry and their chemical compositions. The formation of various phases is influenced by solute partitioning. With increasing Nb concentration, the extent of solute partitioning increases, resulting in formation of new metastable phases. The phases that solidify first are rich in Al and lean in Nb, whereas the phases that solidify last are rich in Nb and lean in Al. The formation of these phases has been explained in terms of the driving force for nucleation. For this purpose, the free energy for nucleation has been computed for all pertinent binary intermetallics phases by using thermodynamic data available in the literature. Using solution thermodynamics, it has also been shown that the liquid phase in the Zr-Al-Nb system should exhibit a miscibility gap, and the boundaries of the miscibility gap have been estimated by invoking the regular solution model.

Transient creep of Ti–Al–Nb alloys

The creep tests of seven Ti–Al–Nb alloys, all of which had a microstructure of B2+α2, B2+α2+O, or B2+O, were carried out at 650∼750°C/310 MPa. The activation energy for transient creep was calculated to be 333–439 kJ mol−1, which was approximate to that for the steady-state creep (327–416 kJ mol−1). The values of activation energy indicate that the transient creep, as well as the steady-state creep, was controlled by high-temperature dislocation climb. The relation between transient creep time (ttr) and steady-state creep rate (ε̇s) obeyed the equation ttr=C/ε̇s, with C=5.00×10−3. The transient creep strain increased with increasing volume fraction of B2 phase, and also increased with decreasing creep temperature; these findings are considered to be due to both the low work-hardening rate of B2 phase, and a stress-accelerated phase transformation from B2 to O or α2.

A15型Nb&lt;SUB&gt;3&lt;/SUB&gt;Alにおける超伝導臨界温度と組成分布

Nb3Al is expected for practical application as a superconductive wire material. In this study, the compositional dependence of Tc for Nb-Al alloys, which were annealed at 1373 K, was investigated in the Nb-rich compositional range (from 18 to 23 at%Al). The value of Tc was evaluated by the specific heat measurement. The compositional distributions were analyzed by EPMA, and the phases were refined by powder X-ray diffraction.The 21.9 at%Al specimen, in which only Nb3Al existed, showed comparatively as high Tc (about 18 K) as that of the stoichiometry. On the other hand, in the 23.1 at%Al specimen, Nb3Al and Nb2Al coexisted. The 23.1 at%Al specimen had the same Tc as the 21.9 at%Al specimen. However, from the viewpoint of the superconductive property, the 23.1 at%Al specimen was better than the 21.9 at%Al specimen as a material because Nb3Al homogenized at the edge of the solute region (about 22 at%Al) by the precipitation of Nb2Al. It was indicated that Nb3Al alloy showed the good superconductive property which was almost the same at the stoichiometry despite of a relatively low annealing temperature of 1373 K.