The use of NbTiTa as a high field superconducting alloy

NbTi-based alloys containing 8% and 25% tantalum have been studied for use at fields around 12 tesla and at temperatures between 2 K and 3 K. These materials have significantly higher current densities at reduced temperatures than other NbTi-based alloys. Using the results of these studies, a 10,000 A, nominal 12 tesla conductor has been designed and is presently being fabricated for use in a test coil for the Lawrence Livermore Laboratory HFTF. The alloy selected for that conductor is Nb-43% Ti-25% Ta.     

Microstructure and superconductivity in annealed Cu-Nb-(Ti,Zr, Hf) ternary amorphous alloys obtained by liquid quenching

Melt-quenched Cu-Nb-(Ti, Zr, Hf) ternary alloys have been found to be amorphous possessing high strength and good bend ductility. The niobium content in the amorphous alloys was limited to less than 35 at % and the titanium, zirconium or hafnium contents from 25 to 50 at %. The Cu₄₀Nb₃₀(Ti, Hf)₃₀ alloys showed a superconducting transition above the liquid helium temperature (4.2 K) after annealing at appropriate temperatures. The highest transition temperatures attained were 5.6 K for the Cu₄₀Nb₃₀Ti₃₀ alloy annealed for 1 h at 873 K and 8.4 K for the Cu₄₀Nb₃₀Hf₃₀ alloy annealed for 1 h at 1073 K. In addition, these alloys exhibited upper critical magnetic fields of 1.8 to 2.3×10⁶ Am^–1 at 4.2 K and critical current densities of 2×10³ to 1×10⁴ A cm^–2 at zero applied field and 4.2 K. Since the structure of the superconducting samples consisted of ordered phases based on a b c c lattice with a lattice parameter of 0.31 nm, it was concluded that the superconductivity in the Cu₄₀Nb₃₀Ti₃₀ and Cu₄₀Nb₃₀Hf₃₀ alloys was due to the precipitation of the metastable ordered b c c phases.     

Electrochemical oxide nanotube formation on the Ti-35Ta-xHf alloys for dental materials

In this study, we investigated the electrochemical oxide nanotube formation on the Ti-35Ta-xHf alloys for dental materials. The Ti-35Ta-xHf alloys contained from 3 wt.% to 15 wt.% Hf were manufactured by arc melting furnace. The nanotube oxide layers were formed on Ti-35Ta-xHf alloy by anodic oxidation method in 1 M H3PO4 electrolytes containing 0.5 wt.% NaF and 0.8 wt.% NaF at room temperature. The surface characteristics of Ti-35Ta-xHf alloy and nanotube morphology were determined by FE-SEM, STEM, and XRD. The nano-porous surface of Ti-35Ta-xHf alloys showed in 0.5 wt% NaF solution and nanotubular surface showed in 0.8 wt% NaF solution, respectively. The highly ordered nanotube layer without regular knots was formed on the Ti-35Ta-15Hf alloy in the 0.5 wt% NaF solution compared to on Ti-35Ta-3Hf and Ti-35Ta-7Hf alloys in 0.8 wt% NaF solution. Also, the nanotube length of Ti-35Ta-xHf alloys increased as Hf content increased.     

稀土元素对富Ni的Ti-Ni形状记忆合金马氏体相变的影响

在本文中,向Ti-50.7at.%Ni合金分别加入1at.%的稀土元素Ce、Dy、Gd和Y,并利用X射线和示差扫描热分析研究了稀土掺杂对富Ni的Ti-Ni合金马氏体相变行为的影响.结果表明:向富Ni的Ti-Ni合金中添加稀土元素能使合金的马氏体相变温度显著增加,且添加稀土Ce使合金相变温度的增幅最大.此外,Ti-50.2Ni-1Gd和Ti-50.2Ni-1Y合金中发生两步马氏体相变,而添加Ce和Dy的Ti-Ni合金中仍只发生一步马氏体相变.     

Microstructures and Tensile Properties of Isothermally-forgedTi-47Al-2Nb-1Cr-1V and Ti-47Al-2V-1Cr Alloys

Microstructures and room-temperature tensile properties of isothermally-forged γ-base (γ + α2)alloys in Ti-Al-Nb-Cr-V system with different heat treatments were investigated. The results show that the microstructures of Ti-47Al-2Nb-1Cr-1V and Ti-47Al-2V-1Cr (at. pct) alloys are mainly determined by heat treating temperature in the (cr + 7) tWo-phase field, and the joint additions of Nb, Cr and V in the Ti-47Al alloy afFect Ta significantIy. The microstructure of Ti-47Al alloy with additions of Nb, Cr and V (1~2 at. pct) can be dupIex or nearly-lamellar by a suitable heat treatment after isothermal forging at 1000℃ for over 50% plastic strains.Therefore its tensile properties can be improved at room temperature.     

Martensitic transformation and shape memory properties of Ti-Ta-Sn high temperature shape memory alloys

The effects of Ta and Sn contents on the martensitic transformation temperature, crystal structure and thermal stability of Ti-Ta-Sn alloys are investigated in order to develop novel high temperature shape memory alloys. The martensitic transformation temperature significantly decreases by aging or thermal cycling due to the formation of ω phase in the Ti-Ta binary alloys. The addition of Sn is effective for suppressing the formation of ω phase and improves stability of shape memory effect during thermal cycling. The amount of Sn content necessary for suppressing aging effect increases with decreasing Ta content. High martensitic transformation temperature with good thermal stability can be achieved by adjustment of the Ta and Sn contents. Furthermore, the addition of Sn as a substitute of Ta with keeping the transformation temperature same increases the transformation strain in the Ti-Ta-Sn alloys. A Ti-20Ta-3.5Sn alloy reveals stable shape memory effect with a martensitic transformation start temperature about 440 K and a larger recovery strain when compared with a Ti-Ta binary alloy showing similar martensitic transformation temperature.     

Processing TiAl-Based Alloy by Elemental Powder Metallurgy

1. IntroductionTiAl based alloy has long been considered as apromising candidate for high temperature applications, because it has a high specific strength and goodhigh temperattire properties[1-31. The main methods for the preparation of TiAl based alloys includecasting and powder metallurgy. In general, thermomechanical treatment (such as forging and extrusion)and subsequellt heat treatment should be conductedfor cajst TiAl-based alloys in order to refine the coarsemicrostructure[4,5], whe…     

Tailoring the microstructure,martensitic transformation and strain recovery characteristics of Ti-Ta shape memory alloys by changing Hf content

In the present work,the microstructure features,martensitic transformation,mechanical properties and strain recovery characteristics of Ti-Ta based shape memory alloys were tailored by changing Hf contents.The single α"martensite phase was dominated in Ti-Ta alloy with 2 at.％H f.Upon Hf content exceeded 2 at.％,β phase started to appear.Moreover,the amount of β phase gradually increased with Hf content increasing.The martensitic transformation temperatures continuously decreased with the increased Hf content,which was attributed to the rising of valence electron concentration.Meanwhile,Hf addition improved the thermal cycling stability of Ti-Ta alloys due to the suppression of ω precipitation.The yield stress of Ti-Ta based alloys firstly decreased and then increased with Hf content increasing.In addition,the completely recoverable strain of 4％can be obtained in Ti-Ta alloy with 6 at.％Hf as a consequence of the higher critical stress for dislocation slip.Besieds,the Ti-Ta based alloy containing 8 at.％Hf had the superior superelasticity behavior with the fully recoverable strain of 2％at room temperature.     

Influence of solution-aging treatment on damping and tensile properties of Ti-36Nb-2Ta-3Zr-0.3O alloy

High-damping alloys have been used in aerospace, automobile manufacturing and other fields due to its capacity to weaken vibration and noise. The damping and tensile properties of the Ti-36Nb-2Ta-3Zr-0.3O (wt-%) alloy were investigated by dynamic mechanical analysis and tensile tests. The results showed that aging treatment significantly improved the tensile strength. The Snoek-type relaxation was observed in the alloy with and without aging treatment, although the aging treatment exerted a negative influence on damping capacity, especially at high temperatures. This phenomenon could be related to the precipitation of the α phase and the segregation of oxygen in the α phase from the β phase during the aging process. As a result, the alloy aged at 713?K simultaneously presents excellent damping and tensile properties.     

Ductility improvement in iron aluminides

Excellent high temperature properties of intermetallic aluminides recommend their use for structural applications in sulphurous atmospheres. Interest was not sustained in them because of their brittleness at ambient temperatures. Fe₃Al based alloys (air induction melted) were taken up to study the effect of deviations from stoichiometry (both sub and super), third and fourth alloy additions, B, Ti (micro as well as macro), on physical and mechanical properties (at ambient temperatures). The columnar grains observed in sub and stoichiometric compositions were found to become equiaxed on additions of alloy. The microstructures became finer on hot forging and rolling. The hot workability of these alloys increased from 65 to 85% at 973 K on B, Ti additions. The ultimate tensile strength (UTS) and per cent, elongation E increased to 80 kg mm^–2, 3.0% and 94 kg mm^–2, 5%, respectively, for sub and stoichiometric alloys on B and Ti additions. The superstoichiometric alloys displayed dendritic structure and could not be hot worked due to cracking during forging, even after additions of alloys. The stoichiometric Fe₃Al alloy with B and Ti additions exhibited the best properties under the experimental conditions.     

Tensile and Isothermal Fatigue Behaviors of Mg-12Gd-3Y-0.5Zr Alloy at High Temperature

Tensile and isothermal fatigue tests were carried out on an as-rolled Mg-12Gd-3Y-0.5Zr alloy and its heat-treated counterpart at different temperatures. The experimental results show that the ultimate tensile strengths of two alloys decrease very slowly with increasing temperature up to 200?C. The ultimate tensile strength of heat-treated Mg-12Gd-3Y-0.5Zr is slight lower than that of as-rolled counterpart; however, the fatigue strength of heat-treated alloy is higher. The mechanism of fatigue failure was in...     

Microstructure and mechanical properties of LA51 and LA51–0.5Y alloys with different accumulated strains and rolling temperatures

Mg–5Li–1Al (LA51) and Mg–5Li–1Al–0.5Y (LA51–0.5Y) alloys were smelted and rolled with different accumulated strains (36% and 68%) and rolling temperatures (373 K and 573 K). The microstructure, mechanical properties, fracture morphology and texture of the specimens were investigated. Results show that, due to the PSN (particle stimulate nucleation) mechanism, the addition of 0.5 wt.% Y improves the deformation resistance and weakens the basal texture of LA51 alloy. The effect of Y on UTS (ultimate tensile strength) of as-rolled alloys is more obvious than that of the as-cast alloy. Accumulated strain and rolling temperature could influence the twinning number, slip systems and DRX (dynamic recrystallization), thus affecting the microstructure and mechanical properties of the alloy. Under the proper combination of the above factors, the as-rolled LA51–0.5Y alloy with an accumulated strain of 68% at 573 K possesses the best comprehensive mechanical properties.     

Influence of minor additions on characteristics of Cu–Al–Ni alloy

Abstract

The aluminium and nickel contents of Cu–Al–Ni alloy are varied to relate the parent phase chemistry to its shape memory behaviour. Rare earth and grain refining elements (titanium, zirconium, boron, etc.) are added in minor quantities to assess their effects on the grain refinement of the alloy and also on its shape recovery behaviour. It is observed that increasing the aluminium and nickel contents decreases the shape recovery temperature whereas minor additions are found to increase it. The alloys have been aged in the parent as well as the martensitic phase to investigate the influence of minor additions on their aging response. It is observed that precipitation of γ₂ phase occurs during the initial stage of aging of the ternary alloy. The aging behaviour is monitored via changes in resistivity and hardness of the alloys during aging. Minor additions are found to retard the precipitation of γ₂ phase during aging. Titanium and rare earths particularly reduce the tendency for grain coarsening in the alloy. It is further observed that two types of martensite, β′₁ and γ′₁, are produced in the alloys under investigation. The transformation temperatures of these martensites are also related to the aluminium content of the alloy.

MST/1744     

Effect of the surface oxide layer on transformation behavior and shape memory characteristics of Ti-Ni and Ti-Ni-Mo alloys

Oxidation behaviors of Ti-49Ni and Ti-48.3Ni-0.7Mo (at.%) alloys in dry air from 723 K to 1273 K have been investigated by means of scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, and then effects of oxidation on transformation behavior and shape memory characteristics of the alloys were studied by means of differential scanning calorimetry and thermal cycling tests under constant load. Three-layered surface scale was formed in both alloys oxidized at temperatures higher than 1023 K, consisting of an outer TiO₂ layer, an intermediate layer of mixture of TiO₂ and Ni and an inner TiNi₃ layer. Thickness of the surface oxide layer increased from 1 m to 50 m with raising oxidation temperature from 923 K to 1273 K. The surface oxide layer raised transformation temperatures associated with the B2-B19 and the R-B19 transformation, while it did not almost change transformation temperatures associated with the B2-R transformation. Recoverable elongation was not changed in the alloys oxidized at temperatures below 823 K with raising oxidation temperature, whereas it decreased in the alloys oxidized at temperatures above 923 K. Transformation hysteresis was not almost changed by oxidation in a Ti-49Ni alloy, but it decreased largely in a Ti-48.3Ni-0.7Mo alloy.     

Effect of aging treatment on microstructure and creep behaviour of Sn–Ag and Sn–Ag–Bi solder alloys

Abstract

The present study was undertaken to investigate the influence of aging temperature on the creep behaviour of Sn–Ag and Sn–Ag–Bi solder alloys at testing temperatures ranging from 333 to 363 K under constant stress of 7·80 MPa. The steady state creep rate was found to increase continuously with increasing aging temperature at all testing temperatures. Results show that addition of Bi to the binary Sn–Ag solder alloy led to a significant increase in the strength and improvement in the creep resistance. The activation energy for the creep process of Sn–Ag and Sn–Ag–Bi solder alloys was found to have an average value of 36 and 45 kJ mol^?1 respectively. This might be characterised by diffusion of Ag in Sn. The microstructure of the aged samples for both alloys examined by X-ray diffraction measurements supported the improvement in the creep resistance for Sn–Ag alloy by adding a small trace of Bi.     

High-field superconducting properties of multifilamentary nbtihf superconductors

A Nb-61.7at%Ti-3at%Hf alloy was fabricated into multifilamentary wires and studied in terms of high field superconducting properties. The effects of precipitation heat treatment and cold working after the heat treatment on the superconducting properties were examined. To obtain high J_c in high fields, a process emerges where the heat treatment producing a maximum upper critical field, B_c2, is followed by severe cold working. The superconducting properties at 1.8 K were then investigated which indicated that the temperature scaling law may hold for this NbTiHf superconductor.     

Phenomena of nanotube nucleation and growth on new ternary titanium alloys

Ti-30Nb-xZr and Ti-30Ta-xNb alloys have been investigated using various methods of surface nanotube formation. Ternary Ti-30Nb-xZr (x = 3 and 15 wt%) and Ti-30Ta-xNb (x = 3 and 15 wt%) alloys were prepared by using high-purity sponge Ti (Grade 4, G&S Titanium, USA), Ta, Zr and Nb spheres. The two groups of ternary Ti alloys were prepared using a vacuum arc melting furnace. Nanotube formation was carried out with a conventional three-electrode configuration with the Ti alloy specimen, a platinum counterelectrode, and a saturated calomel (SCE) reference electrode. Experiments were performed in 1 M H3PO4 with small additions of NaF (0.1-0.8 wt%), using a potentiostat. Nanotubes formed on the surfaces of the two ternary Ti alloys were examined by field emission scanning electron microscopy, EDS and XRD. The Ti-30Ta-xZr alloys had microstructure with entirely needle-like constituents; the thickness of the needle-like alpha-phase increased as the Zr content increased. The Ti-30Nb-xZr alloys had equiaxed microstructures of the beta-phase, and increasing amounts of the needle-like alpha phase appeared at the grain boundaries of the beta-phase as the Zr content increased. The nanotubes were nucleated and grew mainly on the beta phase for the Ti-30Ta-3Zr and Ti-30Nb-3Zr alloys, which had nanotubes with uniform shape, but the nanotubes were nucleated at the alpha phase for the Ti-30Ta-15Zr and Ti-30Nb-15Zr alloys, which had nanotubes with irregular shape and diameters of two sizes. The diameter and depth of the nanotubes could be controlled, depending upon the alloy composition and composition of the surface oxide films (TiO2, Nb2O5, Ta2O5, and ZrO2). It is concluded that this research that selection of the appropriate alloying element can allow significant control of the nanotopography of these Ti alloy surfaces and that it is possible to control the surface nanotube size to promote long-term osseointegration for clinical dental or orthopedic use.     

Mechanical Properties of DS NiAl/Cr(Mo) Alloys with Low Addition of Hf for High-temperature Applications

1.IntroductionAs a new type of structural materials based on the B2intermetallics,NiAl offers superior characteristics,suchas low density,high melting point and excellent oxida-tion resistance at high temperature[1].However,the poorfracture toughness at ambient temperature and low creepstrength at elevated temperature limit their applicationcurrently.Although the creep strength has been sig-nificantly improved by precipitation strengthening[2]orforming a particulate composite[3],and ductility…     

Tensile properties and transformation temperatures of Pd added Ti-Ni alloy dental castings

The effect of palladium (Pd) addition to Ti-Ni alloy as the third element was investigated to improve the super-elasticity of the alloy castings at body temperature for dental application. Ti-50.8Ni (at %) alloy, which exhibited super-elasticity at 310 K in castings, was used for comparison. 5.0, 7.5, 10.0 and 15.0 at % Pd was added to Ti-50.0Ni alloy by the substitution for Ni. The change in the proportion of Ti and Ni was also examined at the fixed Pd addition of 7.5 at %. The properties of the alloys were investigated in tensile test and differential scanning calorimetry (DSC). Ti-42.5Ni-7.5Pd alloy castings showed good super-elasticity among the examined alloys from the viewpoint of residual strain and elongation. Moreover, apparent proof stress could be changeable by the proportion of Ti and Ni with residual strain being kept low. Ti-42.5Ni-7.5Pd alloy castings exhibited better super-elastic flexibility than Ti-50.8Ni alloy, which is proven by lower apparent proof stress and larger elongation. This flexibility appears to be caused by its relatively high martensitic transformation starting temperature point. It is suggested that this flexibility with super-elasticity could widen the clinical application of the alloy casting in dentistry. © 2000 Kluwer Academic Publishers     

Phase transformation behavior and wire drawing properties of Ti-Ni-Mo shape memory alloys

Transformation behavior and wire drawing properties of Ti-Ni-Mo shape memory alloys have been investigated by means of differential scanning calorimetry (DSC) measurements, X-ray diffraction, electron microscopy, tensile tests and wire drawing tests. Mo addition to a Ti-Ni binary alloy induced the R phase transformation, and consequently Ti-Ni-Mo alloys showed two stage transformation, i.e., from the B2(cubic) parent phase to the R(rhombohedral) phase, and then from the R phase to B19(monoclinic) phase. In the thermo-mechanically treated 51Ti-48.3Ni-0.7Mo alloy, reverse transformation temperature, Af, kept constant, irrespective of thermo-mechanical treatment conditions, while it changed in the thermo-mechanically treated 51Ti-49Ni and 51Ti-48.5Ni-0.5Mo alloys. Mo addition to Ti-Ni binary alloy decreased wire drawing stress. Wire drawing stress decreased with raising intermediate annealing temperature monotonously when the annealing treatment was made in vacuum. When the annealing treatment was made in air, however, it decreased with raising annealing temperature up to 923 K, and then increased. Optimum intermediate annealing temperature of Ti-Ni-Mo alloys for wire drawing was 823 K, above which a thick oxide film which reduced the drawability of the alloys was formed on the surface of alloy wires.