Ta Ti Alloys Research Articles

Performance Enhancement of Ti/IrO2-Ta2O5 Anode through Introduction of Tantalum-Titanium Interlayer via Double-Glow Plasma Surface Alloying Technology.

Ti/IrO2-Ta2O5 electrodes are extensively utilized in the electrochemical industries such as copper foil production, cathodic protection, and wastewater treatment. However, their performance degrades rapidly under high current densities and severe oxygen evolution conditions. To address this issue, we have developed a composite anode of Ti/Ta-Ti/IrO2-Ta2O5 with a Ta-Ti alloy interlayer deposited on a Ti substrate by double-glow plasma surface alloying, and the IrO2-Ta2O5 surface coating prepared by the traditional thermal decomposition method. This investigation indicates that the electrode with Ta-Ti alloy interlayer reduces the agglomerates of precipitated IrO2 nanoparticles and refines the grain size of IrO2, thereby increasing the number of active sites and enhancing the electrocatalytic activity. Accelerated lifetime tests demonstrate that the Ti/Ta-Ti/IrO2-Ta2O5 electrode exhibits a much higher stability than the Ti/IrO2-Ta2O5 electrode. The significant improvement in electrochemical stability is attributed to the Ta-Ti interlayer, which offers high corrosion resistance and effective protection for the titanium substrate.

Compositional Modifications to Alter and Suppress Laves Phases in AlxCrMoTayTi Alloys

Herein, the development of refractory complex concentrated alloys in the Al–Cr–Mo–Ta–Ti alloy system is reported. Alloys with modified Al and Ta concentrations are designed using CALPHAD tools and produced via arc melting and characterized in both as‐cast and annealed forms. Properties of the alloys, nature of the microstructures, and phase transformation behavior are described via X‐ray diffraction, microstructural characterization, microhardness, and differential scanning calorimetry. Two alloys, namely, Al0.25CrMoTa0.8Ti and Al0.75CrMoTa0.8Ti, are represented by a body‐centered‐cubic matrix phase after annealing, along with a secondary Cr–Ta Laves phase of the C15 and C14 polytypes, respectively. In as‐cast and annealed forms, the Al0.75CrMoTa0.45Ti alloy comprises a single‐bcc phase. Microhardness of the Laves phase containing alloys demonstrates susceptibility to cracking, whereas the Al0.75CrMoTa0.45Ti alloy displays high specific hardness, signs of ductility as evidenced by slip traces near indentations, and minimal scatter of hardness values.

Microstructure and mechanical properties of Ta–Ti alloy by plasma-activated sintering

Tantalum-based alloys have developed rapidly in the fields of aerospace, nuclear industry, weapons, and national defense heavy industries due to their high melting point, low ductility-brittle transition temperature, and well ductility. However, pure tantalum exhibits low room-temperature strength and intergranular fracture, which is attributable to its strong adsorption to interstitial oxygen during sintering. In this work, high-strength Ta–Ti alloy is achieved by introducing Ti to consume oxygen by forming TiO2 and inhabiting the solution of oxygen in Ta alloys. The Ta–Ti alloys mainly consist of dense Ta matrix and dispersed TiO2 second phase. With the addition of 2 wt% Ti, the Ta–Ti alloy with high densification of 99.2% not only exhibits high ultimate bending strength of 1345 MPa from dispersion strengthening by TiO2 oxides, but also has good plasticity of 6% with a transgranular fracture and numerous dimple. The present work may facilitate the development and industrial application of Ta-based alloys.

Ductile W0.4MoNbxTaTi refractory high-entropy alloys with excellent elevated temperature strength

In order to obtain refractory alloys with both high strength and good ductility simultaneously, the novel W0.4MoNbxTaTi high entropy alloys were developed, of which the crystal structure, microstructure, and compression properties were investigated as well. The as-cast alloys had a single BCC phase structure with dendritic substructure in coarse polygon crystal grains. The alloys exhibited outstanding mechanical properties at testing temperatures. The optimal yield strength and fracture strain were 1334 MPa and 38.9% in W0.4MoNb1.3TaTi alloy at ambient temperature. Furthermore, its yield strength decreased to 1125, 905, and 425 MPa at 1073, 1273, and 1373 K, respectively. And it showed high specific yield strength at elevated temperature. The compression performances of the W0.4MoNb1.3TaTi alloy were superior in comparison with other refractory high entropy alloys.

Coarsening behavior of γʹ precipitates and compression deformation mechanism of a novel Co–V–Ta–Ti superalloy

The coarsening behavior of γʹ precipitates at different temperatures and the compression deformation mechanism of a novel Co–V–Ta–Ti superalloy are investigated. It is found that the coarsening behavior of the γʹ precipitates follows the classical Lifshitz-Slyozov-Wagner (LSW) model based on measured results of the temporal evolution of the mean radius, volume fraction, and number density of the γʹ precipitates. The coarsening rate constant, K, of the γʹ precipitates is strongly dependent on the aging temperature, and it increases nearly ten times with the aging temperature rising from 800 to 900 °C. Within this temperature range, the activation energy for coarsening of the γʹ precipitates is determined to be 230 kJ/mol. This value is close to the activation energy for the diffusion of V in Co, suggesting that the coarsening rate of γʹ precipitates is limited by the diffusion of V element. A lot of slip bands are observed in the alloy after compression deformation, which shows the crystal slip is the primary deformation mechanism for the Co–V–Ta–Ti alloy. It is found that the dislocations bypass the γʹ precipitates below 700 °C in the alloy, and pairs of dislocations shear the γʹ precipitates with a high density of stacking faults (SFs) above the peak temperature of 700 °C.

Plasma surface tantalum alloying on titanium and its corrosion behavior in sulfuric acid and hydrochloric acid

An anti-corrosion Ti-Ta alloy coating was prepared on pure titanium surface by double glow plasma surface alloying technology. Electrochemical corrosion test was applied to test the anti-corrosion property of Ti-Ta alloy layer. The microstructure and the phase composition of Ti-Ta alloy coating were detected before and after corrosion process by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The results showed that the Ta-Ti alloy layer has a thickness of about 13–15 μm, which is very dense without obvious defects such as pores or cracks. The alloy layer is composed mainly of β-Ta and α-Ti. The Ta alloy layer improves the anti-corrosion property of pure titanium. A denser and more durable TiO2 formed on the surface Ta-Ti alloy layer after immersing in strong corrosive media may account for the excellent corrosion resistant.

Effect of Mo on microstructural characteristics and coarsening kinetics of γ' precipitates in Co–Al–W–Ta–Ti alloys

The solvus temperature, volume fraction, coarsening behavior of γ' precipitates and the partitioning behavior of alloying elements as well as lattice misfit of γ/γ' phases influence the creep behavior of Ni- and Co-base superalloys. However, few investigations about the microstructural characteristics and the coarsening behavior of γ' precipitates were reported in multicomponent novel Co-base superalloys during thermal exposure. Two alloys containing different contents of molybdenum and tungsten have been investigated to explore the effect of molybdenum on γ' solvus temperature, γ+γ' microstructure and γ' coarsening in Co–Al–W–Ta–Ti-base alloys. The results showed that the γ' solvus temperature decreases with the addition of Mo. Mo addition reduces the γ' volume fractions after aging above 1000°C, but results in negligible influence on the γ' volume fractions aging at 900°C. Meanwhile, γ' coarsening is controlled by diffusion in experimental alloys after aging at 900°C and 1000°C, and the kinetics of γ' growth in experimental alloys are consistent with the predictions of LSW theory.

Mechanical alloying and thermal analysis of Ta–Ti alloys

Tantalum–titanium alloys have widespread potential in biomedical applications due to their superior biocompatibility, favorable mechanical properties, high corrosion resistance, and ability to exhibit shape memory behavior. However, this system is plagued by processing difficulties due to significant differences in melting temperatures, specific weights, and vapor pressures of Ta and Ti. In the present study, mechanical alloying (MA) using high‐energy ball milling of Ti–xTa (where x = 50, 60, 70, and 85 wt%) was investigated. The alloyed powders were characterized by X-ray diffraction, electron microscopy (SEM and TEM), and differential scanning calorimetry. It was established that α-Ti (hcp) gradually dissolves into α-Ta (bcc), with the alloyed particles becoming chemically homogeneous as a bcc structure. This structure corresponds to a meta-stable phase and should decompose to yield two solid solutions, Ti-rich hcp and Ta-rich bcc. To overcome this thermodynamic preference, MA-generated Ta–Ti bcc solid solution powders possess relatively high internal strain energy.

Highly Reliable and Low Resistive Cu/Low-k Dual Damascene Interconnects by Using TaTi Barrier Metal

Novel barrier metal of TaTi alloy has been developed for highly reliable Cu/low-k DD interconnects. TaTi barrier metal with higher Ti concentration improved EM performance, however, it showed both step coverage degradation and line resistance increase. Then, control of Ti diffusion amount from the barrier metal into Cu, determined by Ti concentration in the PVD target, was found to be a key to keep both low line resistance and high reliability. Limited Ti content in the TaTi of Ta-2wt%Ti showed good step coverage, adequate barrier property and better wettability to Cu than Ta. Furthermore, Ta-2wt%Ti achieved 10 times longer EM lifetime than Ta without penalty of line resistance. Thus, Ta-2wt%Ti is one of the promising candidates of barrier metal for highly reliable Cu/low-k interconnects without resistance increase in the future generations.

A combinatorial passivation study of Ta–Ti alloys

A combinatorial study of the kinetics of anodic oxide formation was performed on a co-deposited Ta–Ti composition spread sample (from 2 to 76 at.% Ti). The samples were characterized by High Resolution Scanning Electron Microscopy (HRSEM) and Grazing Angle X-Ray Diffraction (GIXRD). High-throughput-screening was performed with an automated scanning-droplet-cell to anodise incrementally by cyclic voltammetry and perform electrochemical impedance spectroscopy. A comprehensive set of oxide parameters, including film formation factor, dielectric constant, specific oxide resistance, flat band potential and donor density was obtained. The observed changes could be directly correlated to the microstructure of the parent metal.

Dielectric and mechanical properties of anodic films in the Ta–Ti system

AbstractAnodic oxidation at high efficiency of sputtering‐deposited Ta–Ti alloys containing 0.6–40 at.% Ti is shown to result in amorphous films comprising a relatively thin outer layer of TiO2‐based material and an inner layer consisting of units of TiO2 and Ta2O5. The two layers develop due to the faster migration of Ti4+ ions in the inner layer relative to that of Ta5+ ions. The formation ratios for the various films are in the approximate range 1.6–1.9 nm V−1. The dielectric constants of the films are ∼28, which is a similar value to that of anodic tantala. Nanoindentation revealed that the elastic modulus and hardness of the films are essentially independent of film composition, with average values of 134 and 5.3 GPa, respectively. Copyright © 2003 John Wiley & Sons, Ltd.

Interdiffusion in the body cubic centered β-phase of Ta–Ti alloys

Interdiffusion in the β-phase of Ta–Ti alloys is studied in the temperature range 1000–1900°C. Interdiffusion coefficients are calculated with Den Broeder’s method from concentration profiles determined by EPMA. These coefficients depend strongly on the composition: the interdiffusion coefficient for the lower tantalum concentrations is approximately 1000 times greater than the one for the higher concentrations. The activation energy (150–240 kJ/mol) is characteristic of a monovacancy diffusion mechanism. Except for the impurity diffusion of tantalum in titanium, determined by the Vignes and Birchenall method, anomalous behaviour of the diffusion in the β-phase of titanium is not observed. The diffusion in these alloys is characterized by an important Kirkendall effect, materialized by a marker’s shift towards the titanium rich part of the sample. The intrinsic diffusion coefficients have been calculated between 1000°C and 1600°C, at the composition of the Kirkendall plane, by Heumann’s method: the intrinsic diffusion coefficient of titanium is approximately five times greater than that of tantalum.

The abnormal structure of nanocrystalline titanium films prepared by d.c. sputtering

Nanocrystalline titanium films were prepared by d.c. magnetron sputtering and evaporation on copper foil substrates cooled down to liquid N 2 temperature. The results of X-ray diffraction as well as transmission electron microscopy show that the titanium films consist of nanocrystalline particles with 5–15 nm grain size. However, the films deposited by the two different methods are of different crystalline structures. The evaporated films have the normal h.c.p. structure, while the sputtered titanium films have an abnormal b.c.c. structure with the same lattice parameter as the β phase of titanium at high temperature (more than 882 °C). The lattice parameter of the sputtered film was determined as 0.331 78 nm, which is close to that of the β phase measured using Ta-Ti alloy. The mechanism of the film formation process is discussed.

Surface modification of platinum by titanium dioxide overlayers: A case of simple site blocking

The suppression of CO and H 2 chemisorption on Pt surfaces when supported on TiO 2 carriers is well established. Recently, it has been suggested that migration of the support material onto the Pt surface is responsible for this effect. To test this hypothesis, the suppression of CO chemisorption on TiO 2 modified Pt foil has been studied. A combination of X-ray photoelectron spectroscopy (XPS), low energy inelastic ion scattering (LEISS) and temperature programmed desorption were used to fully characterize the composition, electronic structure and chemisorption properties of the modified surface. Surface TiO 2 was prepared by in situ evaporation of Ti from TaTi alloy in a background of 1 × 10 −6 mbar O 2. Subsequent annealing (770 K) of this surface produced a stoichiometric TiO 2. When oxygen vacancies (Ti 3+ centers) were introduced by chemical treatment, an ohmic contact was formed between the reduced TiO 2 and the Pt surface. However, no new major chemisorption states were observed in CO TPD on this modified Pt surface. Rather, a simple suppression of the total amount of chemisorption was observed. Combining LEISS with TPD established a clear linear relationship between the extent of chemisorption suppression and the number of sites physically blocked by the TiO 2.

Effect of alloying materials on thermal stability and TCR-value of resistor films with Ta-basis

The stability of pure tantalum is not high enough for high precision resistors. The stability of alloyed tantalum (TaAl) or Ta compound (TaN) films are suitable, but their temperature coefficients are relatively high. Experiments were made to prepare TaTi alloys for improving the TCR value and at the same time keeping the excellent stability. The determination of characteristic data of thermal stability from in situ measurements were carried out with computer control. A calculation method was developed to determine the parabolic rate coefficient of oxidation, the activation energy and the probable formal kinetic relationship fromt, T andR □ data.

Composition and Structure of Co-Sputtered Ta-Ti Alloy Thin Films

Composition and Structure of Co-Sputtered Ta-Ti Alloy Thin Films

Superconducting Transition Temperature of Solid-Solution Ta–Ti Alloys

The composition dependence of the superconducting transition temperature Tc has been measured for the solid-solution range of the system Ta–Ti. Tc values, determined resistively for heavily cold-worked wire specimens, varied smoothly with composition, exhibiting a maximum of 8.8°K corresponding to a valence-electron-to-atom ratio of 4.5. Little sharpening of transitions was found for annealed samples, and lower values of Tc were obtained. The change in Tc of a nominally equiatomic alloy with heat treatments in the range 300° to 1200°C is discussed in terms of the microstructural changes.