Ta Matrix Research Articles

Strategy for preparing nanocrystalline Ta-N gradient layer with enhanced mechanical and tribological performance via microwave plasma nitriding

Herein, microwave plasma nitriding (MPN) was employed to fabricate a nanocrystalline tantalum nitride (Ta–N) layer with enhanced mechanical and tribological performance. The results revealed that the nitrogen content in the Ta–N layer appeared as a gradient distribution, resulting in a component gradient structure comprising Ta2N, a solid solution of N in Ta and superlattice TaN0.04 from the top surface to the matrix, which was advantageous for relaxing the stress between the top Ta–N layer and the matrix. Nanocrystalline Ta–N layers (D(avg) = 45–55 nm) with dense and smooth surfaces were obtained at ≤950 °C, while grains grew and pores appeared on the surface of the Ta–N layers (D(avg) = 195–205 nm) at >950 °C. Consequently, the nanocrystalline Ta–N layer with gradient structure and desired thickness exhibited robust hardness and modulus of 26.89 and 247.64 GPa, respectively, which were considerably higher than those prepared by traditional gas/ion/liquid nitriding. The friction and wear test results showed that compared with pure Ta, the MPN-treated Ta matrix exhibited a shallower wear track, lower wear volume, and smaller superficial area, indicating that the Ta–N layer offered excellent surface protection for the matrix.

Cold sprayed Ta-Ag composites: Mechanistic insight into enhanced corrosion resistance and antibacterial ability

In this work, cold spray was used to produce Ta-xAg metal matrix composites (MMCs). The addition of Ag prevents Ta matrix from corrosion and simultaneously induces excellent antibacterial ability. Additionally, varied soft Ag volumes in feedstock powder led to a synergistic deposition phenomenon, profoundly affecting Ag dissolution and correlated antibacterial performance via a microstructural mechanism. Taking advantage of it, a robust antibacterial ability can be facilitated by minimal Ag usage.

Strain-rate-dependent plasticity of Ta-Cu nanocomposites for therapeutic implants

Recently, Ta/Cu nanocomposites have been widely used in therapeutic medical devices due to their excellent bioactivity and biocompatibility, antimicrobial property, and outstanding corrosion and wear resistance. Since mechanical yielding and any other deformation in the patient's body during treatment are unacceptable in medicine, the characterization of the mechanical behavior of these nanomaterials is of great importance. We focus on the microstructural evolution of Ta/Cu nanocomposite samples under uniaxial tensile loading conditions at different strain rates using a series of molecular dynamics simulations and compare to the reference case of pure Ta. The results show that the increase in dislocation density at lower strain rates leads to the significant weakening of the mechanical properties. The strain rate-dependent plastic deformation mechanism of the samples can be divided into three main categories: phase transitions at the extreme strain rates, dislocation slip/twinning at lower strain rates for coarse-grained samples, and grain-boundary based activities for the finer-grained samples. Finally, we demonstrate that the load transfer from the Ta matrix to the Cu nanoparticles via the interfacial region can significantly affect the plastic deformation of the matrix in all nanocomposite samples. These results will prove useful for the design of therapeutic implants based on Ta/Cu nanocomposites.

Microstructure and mechanical property of bonding zones between Ta foil and steel plate fabricated by explosive welding

This work aims to produce a thorough comprehension concerning microstructure related properties of the joint interface between Ta foil and steel plate fabricated by explosive welding. For this, a self-developed explosive welding configuration was employed to join Ta foil and steel plate, and different microscopic methods were adopted to investigate its microstructures and mechanical properties. It was found that the Ta/Fe interface was featured by regular wavy structures with a well-defined amplitude and period. The melted zones were mainly observed within the vortex structures, and occasionally at the Ta/Fe interfaces, which were formed by intense mixing of participating metals. The EBSD analyses revealed a diversity of the grain structures near the Ta/Fe interface, such as formation of the curved and elongated grains in Ta matrix, and fine equiaxed and columnar grains in Fe matrix. Especially, several adiabatic shear bands (ASBs) characterized by small equiaxed grains were found in Fe matrix, which were due to stress wave concentration in the narrow paths, and the materials in these zones underwent a recrystallization process. Finally, the nanoindentation results revealed inhomogenous mechanical behaviors in the bonding zones, which could be well related to the changes of microstructure and chemical composition.

Computational Analysis of the Mechanical Properties of Ta/Cu Nanocomposite Dental Implants: On the Role of Incoherent Interfaces

In recent years, tantalum (Ta)-based nanostructured dental implants have been widely utilized considering their exceptional biocompatibility, bioactivity, and biomechanical properties. Despite their advantages, the mechanical properties of Ta are higher than those of the adjacent jawbone, weakening the bone structure. It has been demonstrated that soft antibacterial additives such as copper (Cu) nanoparticles can tune the mechanical features of Ta-based implants to be similar to those of the adjacent bone. However, a noticeable gap in this research area is the lack of a computational model to explore the interfacial load transfer through the curved interfaces of Ta/Cu nanocomposites. Accordingly, a series of molecular dynamics simulations is employed to survey the microstructural evolution in Ta/Cu nanocomposites subjected to the uniaxial tensile loading condition at the body temperature. Additionally, to provide a complete picture of the contribution of Cu nanoparticles to the results, the mechanisms governing the plastic deformation of nanocomposite models with fine-grained and coarse-grained Ta matrix is systematically examined during the process. In summary, this work provides a comprehensive molecular dynamics simulation of the role of dislocation networks, twin formation, and their mutual interactions on the extent of the plastic zone in various Ta/Cu nanocomposite models.Graphical

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.

Finnis–Sinclair-type potential for atomistic simulation of defects behaviour in V-Ti-Ta ternary system

• Interatomic potential for V-Ti-Ta ternary system based on F-S formalism has been developed. • The Ti potential well reproduce the point-defect properties of vacancy and self-interstitial atoms and the pressure-volume relation. • The typical defect energies of solute atoms Ti and Ta in the V matrix and Ti and V in the Ta matrix predicted by the present potential were in good agreement with DFT results. Vanadium (V)-based alloys are potential candidates for structural materials of fusion reactors because of their excellent properties; recently, the V–Ti–Ta alloy has received considerable attention. The irradiation-resistant performance is significant for the development and application of fusion reactor materials. In this study, combining with our previously developed potentials of V and Ta, we developed the V-Ti-Ta interatomic potential based on the Finnis–Sinclair (FS) formalism, which is an important step towards an atomic-scale investigation of V-based alloys. The potential parameters were determined by fitting to a large database of experimental data and density functional theory (DFT) calculations. The formation energies of vacancy and self-interstitial atoms, as well as the pressure-volume relation obtained from the present Ti potential, were well reproduced. The typical defect energies of solute atoms Ti and Ta in the V matrix and Ti and V in the Ta matrix, such as the formation energies of substitutional solute atoms, binding energies between solute atoms and point defects, agree well with DFT results. Thus, the developed potentials are expected to be suitable for atomistic simulations of point defects evolution in the V-Ti-Ta ternary system.

Study of Radiation Defects in metal Mo and Ta by Mössbauer effect and EXAFS

The implantation of 57Fe atoms into refractory metals Mo and Ta was studied by X-ray diffraction, Mössbauer spectroscopy, and EXAFS. When irradiated with 57Fe ions with energy of 1 MeV and fluence of 5 × 1016 ions/cm2, Fe implantation occurred to a depth of about 600 nm, while creating an extremely strong level of radiation damage with DPA ≥100. Experimental data have confirmed the preservation of the original bcc crystal structure. The localization of 57Fe atoms in the Mo and Ta was studied by Mössbauer spectroscopy and by the EXAFS method in the Fe K-edge region. Both methods give consistent results. In Mo, Fe atoms are predominantly localized in substitutional positions with 1.4 atomic vacancies localized in the first coordinate sphere. Fe atoms in the Ta matrix have a more complex localization. The model spectra for typical atomic configurations of Fe in the Ta were calculated by the density functional theory. Comparison of the experimental spectra with the calculated ones showed that Fe atoms are localized in Ta in several positions, including interstitial and substitutional positions. It is shown that the EXAFS method more accurately determines the configurations of defects caused by irradiation.

A Special Vortex Formation at the Ta/Fe Interface During Explosive Welding

The vortex at the Ta/Fe explosively welded interface is featured by intermediate zone being fully bounded by Ta matrix, which differs from the vortex structures observed in the most bimetallic interfaces. In this work, advanced characterizations and numerical simulations were integrated to establish a detailed evolution model of the special vortex, and the associated governing mechanisms were identified. It was also inferred that the mesoscale cavity and micro cracks within the vortex resulted from geometric hole and extrusion movement that generated during the vortex evolution, respectively. Furthermore, a diversity of metallurgical structure was revealed at the Ta/Fe interface, which did support the deformation path of the interface material observed in the simulations. The insights gathered here benefit to an in-depth comprehension of impact welding.

Mössbauer Study of the Implantation of Fe-57 Ions into Metallic Ta and Mo and Stainless Steel

The effect of the implantation of 57Fe ions with an energy of 1 MeV and fluence of 5 × 1016 ion/cm2 on the properties of structural materials used in the nuclear industry (metallic Ta and Mo and 12Cr18N10T stainless steel) is studied using 57Fe Mossbauer spectroscopy and X-ray diffraction. The concentration of implanted Fe atoms is calculated using the SRIM program. The formation of two phases is found in Ta and Mo. The main phase in molybdenum (84%) is a solid solution of Fe substitution in Mo. The main phase in tantalum (78%) corresponds to Fe-cluster formation in a Ta matrix. Apparently, additional surface phases are related to the formation of Fe + Ta/Mo + vacancy clusters in the areas of grain boundaries, or are associated with areas of partial amorphization of the material.

A Hybrid Structure Solution of Quaternion Lyapunov Equation and Its Optimal Approximation

Recently, the establishment of a multi-structure control system has demonstrated vital significance in practice. Its stability analysis are mostly determined by Lyapunov matrix equation. Tridiagonal-arrow matrix (TA matrix for short) is a special matrix with hybrid structure. In this paper, the problem of TA constraint solution to continuous Lyapunov equation A*X+XA=C over quaternion field is discussed. By using the representation of vectors of a TA matrix and Kronecker product of matrices, a constrained problem will be transformed into an unconstrained equation. Then the necessary and sufficient conditions for the equation with TA and self-conjugate TA solutions as well as the expression of general solution are obtained. Meanwhile, when the solution set is nonempty, by using invariance of Frobenius norm of orthogonal matrix product, the optimal approximation solution with minimal Frobenius norm for a given TA matrix is derived. Finally, two numerical examples are provided to verify the algorithm.

Difference of Irreversible Strain Limit in Technical RHQT Nb3Al Superconductors

Strain limit for critical current degradation in various technical rapid-heating, quenching, and transformation-processed Nb3Al strands has been studied with respect to the matrix material and filament diameter. This property is one important factor as well as the strain sensitivity to $J_{{\rm{c}}}$ characteristics, especially when we consider to apply the so-called react and wind technique to large magnets such as DEMO reactors. We compared five strands, including a standard Nb matrix, standard Ta matrix, Nb/Ag/Nb three-layered barrier structure, and other two fine filament diameter strands prepared by the restacking method. In normal Nb and Ta matrix strands with a filament diameter of more than 30 μ m, the irreversible strain limit is about 0.3%. Refinement of the filament diameter enables us to significantly improve the irreversible strain limit up to more than 0.7%. The Nb/Ag/Nb three-layered barrier structure appears more attractive from a practical point of view. The irreversible strain limit was improved up to nearly 0.6%, even if the filament diameter is more than 20 μ m. The Ag layer between the Nb3Al filaments seems to act as a cushion to mitigate the stress concentration in the wire. The Ag barrier also seems to be effective for current bypass in existence of cracks, resulting in suppressing $I_{{\rm{c}}}$ degradation in a higher strain range.

Stoichiometry and tribological behavior of thick Ta(N) coatings produced by direct current magnetron sputtering (DCMS)

Abstract Thick Ta(N) coating of 51 μm has been successfully obtained by DCMS technology. Ta(N) is a kind of distorted Ta matrix, which is inter-soluble with N-defect lattice structure, forming the disabled bcc structure. From the XRD and XPS investigations, the composition of Ta(N) coating is consisted of bcc-Ta and bcc-TaN0.06, while that of Ta coating mainly contains β-Ta phase. It can be concluded from wear test, nanoindentation test and SEM observations, wear resistance of Ta(N) coating is much better than that of Ta coating, due to its high hardness, H/E, H3/E2 value and low COF value. The wear mechanism of Ta coating is the compound fatigue and abrasive wear, while that of Ta(N) coating is transformed into adhesive wear mechanism. The secondary adhesion of the plastic deformation for the Ta(N) coating can reinforce the coated surface, to improve the load-bearing and anti-wear capacities, and thus improve the wear resistance.

Temperature-dependent Ta hydride formation for recycling of Ta scraps: Experimental and thermodynamic investigations

We report on the theoretical and experimental investigations about the Ta-hydride formation depending on the temperature for recycling of Ta scraps. The structural investigations based on scanning electron microscope and X-ray diffraction (XRD) showed that the amount of hydrogen incorporated into the Ta matrix varied with hydridation temperature. The XRD measurement showed that the H/Ta mole ratio in Ta-hydride increased with increasing the hydridation temperature up to 700°C and then decreased with increasing the temperature furthermore. Depending on the hydridation temperature, various phase of Ta-hydride, such as TaH0.93 and Ta2H were formed and this hydride process was verified by thermodynamic analysis.

Size-induced moment formation on isolated Fe atoms embedded in a nanocrystalline Ta matrix: Experiment and theory

The plethora of proven and potential applications ofnanocrystalline materials makes it imperative to achieve asound conceptual understanding of the size dependence ofa variety of physicochemical properties. While the influencesof quantum size effects [1,2] and surface effects on variousphysical properties of nanoparticles are relatively well under-stood, the often crucial effect of size-dependent changes inthe lattice symmetry and lattice parameters [3] have not beeninvestigated in detail. Size-dependent structural modificationshavebeenknowntoplayakeyrole,forexample,incontrollingtheferroelectricpropertiesofperovskitematerials[4].Thoughthe magnetic properties of nanoparticles have been studied indetail [5], finite size effects in the formation and stability oflocal magnetic moments, especially for isolated impurities,have received very little attention. Interestingly, the formationoflocalmomentsonisolateddopantatomsina

MgO-Doped Tantalum Coating on Ti: Microstructural Study and Biocompatibility Evaluation

Pure and MgO incorporated Ta coatings were prepared on Cp-Ti substrate using laser engineered net shaping (LENS), which resulted in diffuse coating-substrate interface. MgO was found along the Ta grain boundaries in the Ta matrix that increased the coating hardness from 185 ± 2.7 HV to 794 ± 93 HV. In vitro biocompatibility study showed excellent early cellular attachment and later stage proliferation in MgO incorporated coatings. The results indicated that although Ta coatings had higher biocompatibility than Ti, it could further be improved by incorporating MgO in the coating, while simultaneously improving the mechanical properties.

Genomic selection for QTL-MAS data using a trait-specific relationship matrix

BackgroundThe genomic estimated breeding values (GEBV) of the young individuals in the XIV QTL-MAS workshop dataset were predicted by three methods: best linear unbiased prediction with a trait-specific marker-derived relationship matrix (TABLUP), ridge regression best linear unbiased prediction (RRBLUP), and BayesB.MethodsThe TABLUP method is identical to the conventional BLUP except that the numeric relationship matrix is replaced with a trait-specific marker-derived relationship matrix (TA). The TA matrix was constructed based on both marker genotypes and their estimated effects on the trait of interest. The marker effects were estimated in a reference population consisting of 2 326 individuals using RRBLUP and BayesB. The GEBV of individuals in the reference population as well as 900 young individuals were estimated using the three methods. Subsets of markers were selected to perform low-density marker genomic selection for TABLUP method.ResultsThe correlations between GEBVs from different methods are over 0.95 in most scenarios. The correlations between BayesB using all markers and TABLUP using 200 or more selected markers to construct the TA matrix are higher than 0.98 in the candidate population. The accuracy of TABLUP is higher than 0.67 with 100 or more selected markers, which is nearly equal to the accuracy of BayesB with all markers.ConclusionsTABLUP method performed nearly equally to BayesB method with the common dataset. It also provides an alternative method to predict GEBV with low-density markers. TABLUP is therefore a promising method for genomic selection deserving further exploration.

Effect of thermal annealing on microstructure and mechanical properties of a gradient structured tantalum prepared by plasma activated sintering

Fully dense bulk tantalum compacts of two different nitrogen contents with gradient structure within an individual particle were successfully synthesized by means of plasma activated sintering (PAS). Annealing of the compacts induces disappearing of the gradient structure due to the promoted diffusion of nitrogen in Ta matrix accompanied by enhancement of the strength. For the compact with low nitrogen content of 0.09 wt.%, a drop in ductility was observed. While for the compact with nitrogen content of 0.215 wt.%, improved strength was obtained without sacrificing its ductility.

Magnetization, Low Field Instability and Quench of RHQT ${\rm Nb}_{3}{\rm Al}$ Strands

Since 2005, we made and tested three RHQT Nb3Al strands, one with Nb matrix and two with Ta matrix, which are fully stabilized with Cu electroplating. We observed anomalously large magnetization curves extending beyond 1 to 1.5 Tesla with the F1 Nb matrix strand at 4.2 K, when we measured its magnetization with a balanced coil magnetometer. This problem was eliminated with the Ta matrix strands operating at 4.2 K. But with these strands a similar but smaller anomalous magnetization was observed at 1.9 K. We studied these phenomena with FEM. With the F1 Nb matrix strand, it is explained that at low external field, inter-filamentary coupling currents in the outer layers of sub-elements create a shielding effect. It reduces the inside field, keeps the inside Nb matrix superconductive, and stands against a higher outside field beyond the Hc of Nb. At an even higher external field, the superconductivity of the whole Nb matrix collapses and releases a large amount of energy, which may cause a big quench. Depending on the size of the energy in the strand or the cable, a magnet could quench, causing the low field instability. Some attempt to analyze the anomaly with FEM is presented.

Effective Properties of Multi-layered Multi-functional Composites

A matrix method for evaluating effective electro-magneto-thermo-elastic properties of a generally anisotropic multilayered composite is presented. Physical variables are categorized into two groups: one that satisfies the continuity across the interface between layers and another that satisfies an average interlayer compatibility (which is also exact). The coupled electro-magneto-thermo-elastic constitutive equation is accordingly reassembled into submatrices, which leads to the derivation of concise and exact matrix expressions for effective properties of a multilayered composite having the coupled physical effects. Comparing the results for a purely elastic multiplayer with those from other theoretical approaches validates the developed method. Examples are given for a PZT-graphite/epoxy composite and a BaTiO3–CoFe2O4 multilayer which exhibit piezo-thermoelastic and magnetoelectric properties, respectively. The result shows how a strong magnetoelectric effect can be achieved by combining piezoelectric and piezomagnetic materials in a multilayered structure. The magnetoelectric coefficient of the BaTiO3–CoFe2O4 multilayer is compared with those for fibrous and particulate composites fabricated with the same constituents.