Ta-rich Phase Research Articles

The effect of γ′ and δ phases evolution on the mechanical properties of high-entropy CoCu0.5FeNiTa0.1 alloy during heat treatment

To simultaneously improve the mechanical strength and plasticity of the CoCu0.5FeNiTa0.1 high entropy alloy, we adopted the heat treatment and investigated the evolution of different phases containing γ′, δ and γ phases. Two different γ′ phases, the Cu-rich phase and the Ta-rich phase, were detected in the as-cast alloy. During heat treatment, Cu outwards diffused from γ′(Cu-rich) into γ matrix, γ′(Ta-rich) phase and δ phase. The accumulation of Cu and Ta into the δ phase strongly promoted its growth. One significant increase was measured in the compressive yield strength from 1040 MPa to 1370 MPa, ultimate compressive strength from 2020 MPa to 2735 MPa, compressive strain from 34% to 50.2% and hardness from 3.854 GPa to 4.315 GPa. The substantial enhancement in ductility mainly resulted from the distance increase among γ′ particles in γ matrix, the reduction of lattice distortion and the decrease in aspect ratio of δ phases. The yield strengthening mechanisms were mainly from solid strengthening and Orowan strengthening.

Evolution of the Microstructure and Mechanical Properties of a Biomedical Ti-20Zr-40Ta Alloy during Aging Treatment

The research focus in the field of medical titanium alloys has recently shifted towards the development of low-modulus and high-strength titanium alloys. In this study, the influence of aging temperature on the microstructure and mechanical properties of a β-type Ti-20Zr-40Ta alloy (TZT) was investigated. It was found that the recovery and the recrystallization occurred in the as-rolled alloy depended on the aging temperature. The periodically distributed Ta-lean phase (β1) and Ta-rich phase (β2) were produced by the spinodal decomposition in all the samples aged at different temperatures. The spinodal decomposition significantly influenced the mechanical properties and deformation mechanisms of the TZT alloy. Upon aging at 650 °C and 750 °C, the as-rolled alloy exhibited a double-yield phenomenon during tensile testing, indicating a stress-induced martensitic transformation; however, its ductility was limited due to the presence of ω phases. Conversely, aging at 850 °C resulted in an alloy with high strength and good ductility, which was potentially attributed to the enhanced strength resulting from modulated structures introduced with spinodal decomposition.

The Impact of Various Superalloys on the Oxidation Performance of Nanocrystalline Coatings at High Temperatures

Nanocrystalline coatings with the same chemical composition as an N5 superalloy were prepared on K38 and N5 superalloys by magnetron sputtering. The effect of different superalloys on the high temperature oxidation behavior of nanocrystalline coatings was investigated through oxidation kinetics, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and wavelength dispersive spectrometry (WDS). The results indicated that K38-N5 had better oxidation resistance than N5-N5 due to the diffusion of Zr from the K38 superalloy into the oxide scale. In addition, no interdiffusion occurred in the K38 superalloy. The formation of Ta-rich phases in the Al2O3 scale leads to decrease the oxidation resistance of nanocrystalline coatings. However, the presence of Zr inhibits the formation of Ta-rich phases.

Traveling solvent floating zone growth and anisotropic ionic conductivity of Li<i><sub>x</sub></i>La<sub>(1−</sub><i><sub>x</sub></i><sub>)/3</sub>TaO<sub>3</sub> single crystals

In this study, single crystals of double-perovskite-type oxide LixLa(1−x)/3TaO3 (LLTaO) were successfully grown using the traveling solvent floating zone (TSFZ) method. The Ta-rich phase, which was precipitated in the crystals, was grown via the conventional floating zone (FZ) growth process, indicating that LLTaO behaved as an incongruent melt. For the TSFZ growth for solvents with a LiTa3O8 composition of 8 %, which is less than the LLTaO (x = 0.18) stoichiometric composition, the black grown crystals were homogeneous and crack-free, with a typical size of approximately 20 mm in length and 5 mm in diameter. The grown crystals turned colorless and transparent after being left overnight in the air at room temperature (about 25 °C). The Li concentration in the grown crystals was determined to be x = 0.086(1). This value is lower than the nominal composition (x = 0.18) of the feed owing to Li evaporation during the crystal growth. The ionic conductivities of the grown crystals along [110] and [001] were 2.8 × 10−5 and 1.8 × 10−5 S·cm−1, respectively. The anisotropic parameter was determined to be 1.56 indicating that the ionic conductivity along the ab-plane is higher than that along the c-axis. Furthermore, the calculated activation energies along [110] and [001] were 0.29 and 0.34 eV, respectively.

Enhancing giant dielectric properties of Ta5+‐doped Na1/2Y1/2Cu3Ti4O12 ceramics by engineering grain and grain boundary

AbstractVarious strategies to improve the dielectric properties of ACu3Ti4O12 (A = Sr, Ca, Ba, Cd, and Na1/2Bi1/2) ceramics have widely been investigated. However, the reduction in the loss tangent (tanδ) is usually accompanied by the decreased dielectric permittivity (ε′), or vice versa. Herein, we report a route to considerably increase ε′ with a simultaneous reduction in tanδ in Ta5+–doped Na1/2Y1/2Cu3Ti4O12 (NYCTO) ceramics. Dense microstructures with segregation of Cu– and Ta–rich phases along the grain boundaries (GBs) and slightly increased mean grain size were observed. The samples prepared via solid‐state reaction displayed an increase in ε′ by more than a factor of 3, whereas tanδ was significantly reduced by an order of magnitude. The GB–conduction activation energy and resistance raised due to the segregation of Cu/Ta–rich phases along the GBs, resulting in a decreased tanδ. Concurrently, the grain–conduction activation energy and grain resistance of the NYCTO ceramics were reduced by Ta5+ doping ions owing to the increased Cu+/Cu2+, Cu3+/Cu2+, and Ti3+/Ti4+ ratios, resulting in enhanced interfacial polarization and ε′. The effects of Ta5+ dopant on the giant dielectric response and electrical properties of the grain and GBs were described based on the Maxwell–Wagner polarization at the insulating GB interface, following the internal barrier layer capacitor model.

Effect of Ta addition on microstructures, mechanical and damping properties of Cu–Al–Mn–Ti alloy

Cu–Al–Mn–Ti–xTa alloys (x = 0, 1, 2, 3, wt.%) prepared by spark plasma sintering were investigated for the effect of Ta content on the microstructure, mechanical and damping properties. The microstructure and phase composition indicate that the alloy is mainly composed of β′1 martensite, γ′1 martensite, Ti-rich and Ta-rich phase. As the Ta content increases, the grain size of the alloy first decreases and then increases. The reverse trend was observed for hardness, tensile and compressive strength. The hardness, tensile strength and compressive strength increased by 18.2%, 44.9% and 28%, respectively, when the Ta content was 1 wt.% compared to the alloy without Ta element. The presence of martensite provides the alloy with promising damping properties. Meanwhile, the formation of the second phase has a two-sided effect on the damping characteristics. That is, the increase in grain boundaries provides more interfaces for energy dissipation, but the increased compressive stress between the interfaces also hinders the movement of the interfaces. Excellent damping performance is demonstrated with the addition of 1 wt.% of Ta element. The peak values of damping capacity at room temperature and at about 580 °C reached 0.026 and 0.19, respectively. The results confirm that the addition of Ta elements is achievable to obtain Cu–Al–Mn–Ti alloys with both high mechanical and damping properties.

Plasma spheroidized MoNbTaTiZr high entropy alloy showing improved plasticity

Refinement of the harder phase in two-phase MoNbTaTiZr high-entropy alloys (HEA) prepared by a powder metallurgy route has enhanced strength and plasticity of the alloy. The MoNbTaTiZr HEA powder used in this study was prepared by hydrogenation–dehydrogenation followed by plasma spheroidization, having an inherent dual-phase structure (bcc1 and bcc2) similar to the arc melted alloy of the same composition but with much finer morphology of the bcc2 phase. The homogenous and fine distribution of the harder Zr-rich phase (bcc2) with ~10% volume fraction embedded inside the Ta-rich phase (bcc1) evaded the strength–ductility trade-off. The shear-band delocalization in the bcc1 matrix phase improved the strength as well as the plasticity of the alloy. The alloy has potential in biomedical implants because it shows excellent corrosion resistance and lower magnetic susceptibility, making it an MRI (magnetic resonance imaging)-friendly alloy.

Comparative study of helium bubbles in a Ti-Ta alloy and a Ti/Ta nanocomposite

ABSTRACT The size, density, and distribution of helium (He) bubbles in a Ti-Ta single-phase alloy and a Ti/Ta dual-phase nanocomposite have been investigated using transmission electron microscopy. The Ti/Ta nanocomposite was fabricated via phase separation during high-temperature annealing of the single-phase Ti-Ta alloy. He ion implantation in the Ti-Ta single-phase alloy leads to the formation of nanoscale He bubbles (∼1.7 nm in size, ∼2.6 × 105/μm3 in volumetric density). He bubbles were found to segregate to grain boundaries. Under identical implantation conditions, numerous He bubbles also formed in the Ti/Ta nanocomposite. Closer inspection revealed that the He bubbles in the Ti-rich phase are smaller and of higher volumetric density (∼1.2 nm, ∼8.4 × 105/μm3) than those in the Ta-rich phase (∼3 nm, ∼1.8 × 105/μm3) and the single-phase alloy. He bubbles were also observed to decorate phase boundaries but they were generally smaller than those on grain boundaries. These results suggest that Ti/Ta phase boundaries are less conducive to the growth of large He bubbles than grain boundaries in the Ti-Ta single-phase alloy.

A Biomedical Ti-35Nb-5Ta-7Zr Alloy Fabricated by Powder Metallurgy

Ti-35Nb-5Ta-7Zr alloy for biomedical applications with a reduced Young’s modulus of less than 10 GPa, being comparable to that of human bones, was successfully fabricated by powder metallurgy method. The microstructure, compressive and tensile behavior were studied. Results indicate that Ti-rich and Ta-rich phases co-exist in β-matrix. Ti-35Nb-5Ta-7Zr alloys yield at about 10% in compression, with increasing in the content of process control agent, the resultant compressive yield strength and Young’s modulus increase from 650 ± 46 to 1055 ± 90 MPa and from 6.3 ± 0.03 to 8.24 ± 0.04 GPa, respectively. The tensile fractography of alloy with 9.7 GPa tensile Young’s modulus, 433 MPa UTS at the 5.5% elongation consists of cleavage fracture and ductile fracture with dimples. The failure mechanism has been discussed taking the intrinsic microstructural features into consideration.

Optimizing giant dielectric properties via interface composition: A study of rutile-based ceramics

Abstract In this study, the interface compositions, polarization behaviors, and dielectric properties of Ti1-x(Cu0.333Ta0.667)xO2 (x = 5%, 20%, and 45%) ceramics prepared at various sintering conditions are systematically investigated. An analysis of the crystal structure, cation valence state, and element distribution indicates that increasing the sintering temperature and prolonging the sintering time hardly change the lattice symmetry of the bulk phase of the ceramics, but it does alter their interface chemical composition to produce phase separations of Cu and Ta ions and mixed valence states of Ti and Cu cations. Measurement of their dielectric properties further demonstrates that the altered interface composition changes the polarization mechanism of the ceramic samples. For Ti1-x(Cu0.333Ta0.667)xO2 ceramics, increasing the doping level (x) produces larger lattice parameters and more oxygen vacancies and Cu+ ions. Meanwhile, Cu-rich or Ta-rich phases appear at the grain boundary of the highly doped samples. The Ti0.8(Cu0.333Ta0.667)0.2O2 ceramic has giant permittivity (e’ = 65314) due to the competitive coexistence of the internal barrier layer capacitor and surface barrier layer capacitor effects. This study can provide new possibilities for the design of ceramics with desired performance characteristics by purposefully changing the interface features with different preparation conditions.

Preparation of Ti–Nb–Ta–Zr alloys for load-bearing biomedical applications

Ti–Nb–Ta–Zr alloys for biomedical applications were successfully fabricated by arc melting (AM) and diffusion bonding. The microstructure, mechanical properties and electrochemistry behavior in a simulated body fluid (SBF) were studied. It shows that melted Ti–Nb–Ta–Zr alloy mainly contains β phase although there are a few Ti-rich phases and micropores, the number of which is lower than that in sintered sample with a few Ti-rich and Ta-rich phases. The melted alloys present higher strength (1224 MPa), Young’s modulus (15.3 GPa) and corrosion potential (− 0.34 V) in SBF, while total recovery strain ratio (67.5%) and pseudoelastic strain ratio (8.4%) of sintered Ti–Nb–Ta–Zr alloy keep higher value than 35.7% and 5.0% for melted Ti–Nb–Ta–Zr. The reasons were discussed based on the microstructure of the Ti–Nb–Ta–Zr alloys.

Processing and Characterization of Refractory Quaternary and Quinary High-Entropy Carbide Composite.

Quaternary high-entropy ceramic (HEC) composite was synthesized from HfC, Mo2C, TaC, and TiC in pulsed current processing. A high-entropy solid solution that contained all principal elements along with a minor amount of a Ta-rich phase was observed in the microstructure. The high entropy phase and Ta-rich phase displayed a face-centered cubic (FCC) crystal structure with similar lattice parameters, suggesting that TaC acted as a solvent carbide during phase evolution. The addition of B4C to the quaternary carbide system induced the formation of two high-entropy solid solutions with different elemental compositions. With the increase in the number of principal elements, on the addition of B4C, the crystal structure of the HEC phase transformed from FCC to a hexagonal structure. The study on the effect of starting particle sizes on the phase composition and properties of the HEC composites showed that reducing the size of solute carbide components HfC, Mo2C, and TiC could effectively promote the interdiffusion process, resulting in a higher fraction of a hexagonal structured HEC phase in the material. On the other hand, tuning the particle size of solvent carbide, TaC, showed a negligible effect on the composition of the final product. However, reducing the TaC size from −325 mesh down to <1 µm resulted in an improvement of the nanohardness of the HEC composite from 21 GPa to 23 GPa. These findings suggested the possibility of forming a high-entropy ceramic phase despite the vast difference in the precursor crystal structures, provided a clearer understanding of the phase transformation process which could be applied for the designing of HEC materials.

Rejuvenation of Zr-based bulk metallic glass matrix composite upon deep cryogenic cycling

The rejuvenation behavior of Ta-rich particle reinforced Zr-based bulk metallic glass matrix composites upon deep cryogenic cycling treatment has been studied. The composite can be rejuvenated resulting in a higher enthalpy of relaxation and lower density. The internal stress generated from both the intrinsic heterogeneity in amorphous matrix and the interfaces between the matrix and Ta-rich phase should contribute to the rejuvenation behavior. The composite structure can generate a 4 times higher internal stress than that from the intrinsic heterogeneity, which causes the more rejuvenated state of the composites compared with the monolithic counterpart. With a higher volume fraction of Ta-rich phase, both the increment in enthalpy of relaxation and free volume between as-cast and thermal treated state increases almost linearly. The rejuvenated samples show better plasticity compared with as-cast counterparts because of more induced free volume.

Finite temperature thermal expansion and elastic properties of (Hf1-xTax)C ultrahigh temperature ceramics

HfC, TaC, and their solid solution ceramics have been identified as the best materials for ultrahigh-temperature ceramics. However, their temperature-dependent properties, such as their thermal expansion and elastic properties, are mostly unknown. Here, we investigated the thermal expansion and temperature-dependent elastic properties of (Hf1-xTax)C solid solutions over the entire composition range by first principles calculations. Ta-rich solid solutions showed higher elastic properties and metallicity, and these two opposing properties yielded unique thermal expansion behavior with increasing Ta content. The dynamic instability of TaC above its critical volume (23.84 Å3/mol) made it difficult to determine its temperature-dependent elastic properties at ultrahigh temperatures (>1800 K) using the harmonic phonon calculation under the quasi-harmonic approximation. In terms of elastic properties, TaC and Ta-rich solid solutions are the best choice for high-temperature applications; however, the optimal compositions should be determined considering the poor oxidation resistance of the Ta-rich phases. Our results present the important intrinsic properties of (Hf1-xTax)C solid solutions as well as those of HfC and TaC.

Influence of oxidation temperature on the microstructure evolution of NiCoCrAlYTa powders

In this paper, the microstructure evolution in NiCoCrAlYTa alloy powders at two different oxidation temperatures (900 and 1100 °C) was investigated. The results showed that higher oxidation temperature gave higher oxidation rate. Increasing temperature accelerated the diffusion of alloying elements outwards to the powder surface and oxide growth rate. Alumina was the main oxide when the Al content in the powder was high enough. With Al depletion, β phase was depleted by phase transformation of β-γ′-γ at 900 °C and β-γ at 1100 °C. When the Al content in the powder was not enough to maintain the growth of alumina layer, spinel phases were highly formed above the alumina layer and internal alumina begun to largely form. Y-rich and Ta-rich phases were detected beneath the oxide layers at long oxidation time. The diffusion behavior of alloying elements in the different oxidation stages was discussed.

Three-D Mineralogical Mapping of the Kovdor Phoscorite-Carbonatite Complex, NW Russia: III. Pyrochlore Supergroup Minerals

The pyrochlore supergroup minerals (PSM) are typical secondary phases that replace (with zirconolite–laachite) earlier Sc-Nb-rich baddeleyite under the influence of F-bearing hydrothermal solutions, and form individual well-shaped crystals in surrounding carbonatites. Like primary Sc-Nb-rich baddeleyite, the PSM are concentrated in the axial carbonate-rich zone of the phoscorite-carbonatite complex, so their content, grain size and chemical diversity increase from the pipe margins to axis. There are 12 members of the PSM in the phoscorite-carbonatite complex. Fluorine- and oxygen-dominant phases are spread in host silicate rocks and marginal carbonate-poor phoscorite, while hydroxide-dominant PSM occur mainly in the axial carbonate-rich zone of the ore-pipe. Ti-rich PSM (up to oxycalciobetafite) occur in host silicate rocks and calcite carbonatite veins, and Ta-rich phases (up to microlites) are spread in intermediate and axial magnetite-rich phoscorite. In marginal (apatite)-forsterite phoscorite, there are only Ca-dominant PSM, and the rest of the rocks include Ca-, Na- and vacancy-dominant phases. The crystal structures of oxycalciopyrochlore and hydroxynatropyrochlore were refined in the Fd3¯m space group with R1 values of 0.032 and 0.054 respectively. The total difference in scattering parameters of B sites are in agreement with substitution scheme BTi4+ + YOH‒ = BNb5+ + YO2‒. The perspective process flow diagram for rare-metal “anomalous ore” processing includes sulfur-acidic cleaning of baddeleyite concentrate from PSM and zirconolite–laachite impurities followed by deep metal recovery from baddeleyite concentrate and Nb-Ta-Zr-U-Th-rich sulfatic product from its cleaning.

The osteogenic, inflammatory and osteo-immunomodulatory performances of biomedical Ti-Ta metal-metal composite with Ca- and Si-containing bioceramic coatings.

It is known that good mechanical properties, low modulus to reduce stress-shielding effect, favorable osteogenic activity and limited inflammatory response are critical factors for orthopedic implants to induce excellent osteointegration. In this study, Ti-20% Ta metal-metal composite (referred as Ti-Ta) which consisted of Ti- and Ta-rich phases was fabricated via the strategy of powder metallurgy. Micro-arc oxidation (MAO) was employed to modify the surface of Ti-Ta composite. The surfaces of Ti-Ta composite after MAO treatment at an applied voltage of 250 (referred as MAO-250 V) or 300 V (referred as MAO-300 V) exhibited three distinct zones with significantly different morphological features and surface chemistry. Osteoblast-like SaOS-2 cells were found to be preferential to attach on the Ta-rich phase and its surrounding areas, exhibiting an area-dependent adhesion tendency. However, the attachment of Raw 264.7 macrophages was found to be insensitive to the surface characteristics. The proliferation and differentiation of SaOS-2 cells cultured on various surfaces basically followed the trend: MAO-modified surfaces > Ti-Ta surface > Ti surface. The Ti-Ta and MAO-modified surfaces were found to inhibit the inflammatory response and polarize macrophages to anti-inflammatory M2 phenotype compared to Ti surface. Moreover, the microenvironments created by Ti-Ta, MAO-250 V and MAO-300 V/macrophage interactions promoted the proliferation and differentiation of SaOS-2 cells compared to that created by Ti/macrophage interactions. MAO-300 V surface exhibited further enhanced positive osteo-immunomodulatory effects compared to Ti-Ta surface. Together, the Ti-20% Ta metal-metal composite modified by MAO at an applied voltage of 300 V is considered as a promising implant material for orthopedic applications.

Crystallographic Structure Analysis of a Ti-Ta Thin Film Materials Library Fabricated by Combinatorial Magnetron Sputtering.

Ti-Ta thin films exhibit properties that are of interest for applications as microactuators and as biomedical implants. A Ti-Ta thin film materials library was deposited at T = 25 °C by magnetron sputtering employing the combinatorial approach, which led to a compositional range of Ti87Ta13 to Ti14Ta86. Subsequent high-throughput characterization methods permitted a quick and comprehensive study of the crystallographic, microstructural, and morphological properties, which strongly depend on the chemical composition. SEM investigation revealed a columnar morphology having pyramidal, sharp tips with coarser columns in the Ti-rich and finer columns in the Ta-rich region. By grazing incidence X-ray diffraction four phases were identified, from Ta-lean to Ta-rich: ω phase, α″ martensite, β phase, and a tetragonal Ta-rich phase (Ta(tetr)). The crystal structure and microstructure were analyzed by Rietveld refinement and clear trends could be determined as a function of Ta-content. The lattice correspondences between β as the parent phase and α″ and ω as derivative phases were expressed in matrix form. The β ⇌ α″ phase transition shows a discontinuity at the composition where the martensitic transformation temperatures fall below room temperature (between 34 and 38 at. % Ta) rendering it first order and confirming its martensitic nature. A short study of the α″ martensite employing the Landau theory is included for a mathematical quantification of the spontaneous lattice strain at room temperature (ϵ̂max = 22.4(6) % for pure Ti). Martensitic properties of Ti-Ta are beneficial for the development of high-temperature actuators with actuation response at transformation temperatures higher than 100 °C.

Triple-yieldable multiphase reinforced bulk metallic glass matrix composites under tension

Multiphase (Ta-rich phase, B2 and B19′-CuZr) reinforced bulk metallic glass matrix composites (BMGMCs) were successfully developed. The Ta-rich phase appeared not only to hinder the propagation of shear bands, but also to act as a nucleant for the B2 and B19′ phases to homogenize their distribution. The composites showed superior tensile plasticity, work-hardening, and a unique triple yielding behavior. The martensitic transformation of B2-CuZr, the deformation of the Ta-rich phase, and the twinning and detwinning of B19′-CuZr all contributed to these mechanical properties. The present novel BMGMC is expected to lead to a breakthrough in designing work-hardenable and ductile BMGMCs.

Microstructure and phase transformation behavior of a new high temperature NiTiHf-Ta shape memory alloy with excellent formability

Microstructure, mechanical properties as well as phase transformation behavior of newly developed Ni49Ti36Hf15-xTa(x=0, 3, 6, 9, 12) high temperature shape memory alloys has been investigated. Ni49Ti36Hf15 alloy consists of (Ti,Hf)2Ni phase which is brittle and incoherent with the martensite matrix. However, addition of Ta in place of Hf suppresses the brittle (Ti,Hf)2Ni phase formation with white Ta rich phase. More than 70% reduction in area has been observed in Ta added Ni49Ti36Hf15 high temperature shape memory alloys. The austenitic transformation temperature is well above 200 °C (473 K) for lower Ta concentrations with up to 6 at. %; however; at higher Ta concentrations (i.e. above 9 at. %) decreases significantly. Overall, the addition of Ta greatly influences the hot deformation behavior and high temperature shape memory properties of Ni49Ti36Hf15 alloy. The present paper discusses the detailed investigation on Ni49Ti36Hf15-xTa(x=0, 3, 6, 9, 12) high temperature shape memory alloys.