Tantalum Samples Research Articles

The influence of low degree of deformation on the corrosion resistance of pure tantalum in corrosive media

This study investigates the influence of minor deformation on the corrosion resistance of pure tantalum in strongly acidic and alkaline solutions. The electrochemical behavior of samples with varying degrees of deformation was characterized through open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy. The results indicate that in acidic solutions, the corrosion current density and EIS results suggest that low degree deformation reduces the corrosion resistance of tantalum viewed from a kinetic perspective. Conversely, in alkaline solutions, the corrosion potential shifts towards more positive values, but the corrosion current density remains relatively stable, and the electrochemical impedance increases, indicating enhanced corrosion resistance in minor deformed tantalum samples. Analysis reveals that in acidic solutions, the corrosion resistance is primarily affected by the density of geometrically necessary dislocations and the degree of strain, whereas in alkaline solutions, the crystal orientation and grain boundaries are the predominant factors influencing the corrosion resistance.

Express X-ray fluorescent analysis of technical-grade tantalum and niobium: from raw materials to products

Determination of impurities in Ta- and Nb-based materials is a necessary operation in supporting technological processes. The existing approaches involve the transfer of a sample into a solution with subsequent isolation of impurities. This procedure is rather complicated and takes a lot of time. For this reason, it is of interest to study the possibilities of direct analysis of solid-phase samples of materials, e.g., X-ray fluorescence analysis (XRF). The usual scheme of X-ray fluorescence analysis, which involves the experimental construction of calibration characteristics for each element to be determined, requires using a large number of reference samples containing a rather wide range of impurities. We present the results of preliminary characterization of samples of technical-grade tantalum and niobium and products on their base. It is shown that for starting materials, only a significant absence of impurities can be determined using XPA, but even for sintered niobium hydride and Ta powder, XPA can be used as a method for rapid assessment of the composition. A SPECTROSCAN MAX GVM crystal-diffraction spectrometer can be used for analysis and a standard software that implements the fundamental parameter method (FPA) can be used for calibration. In this case, the obtained values of the content of impurities may differ by 1 – 2 orders of magnitude from the reference values. However, such an accuracy is often enough to correct technological processes. The limits of detecting impurities by XRF in Ta- and Nb-based materials are revealed: for elements determined by K-series (from Ti to Co), the detection limits lie in the range from 30 to 60 ppm, whereas for the elements determined by M-series (Ta) the detection limit is approximately 200 ppm and for L-series (Nb) the detection limit is in the range from 100 to 150 ppm.

Study on deformation behavior of tantalum under cryogenic temperature dynamic plastic deformation

Tantalum samples were dynamically deformed at liquid nitrogen (LN) temperature to obtain one pass (LN-DPD-1pass) and three pass LN-dynamic plastic deformation (LN-DPD-3pass) samples, and Ta was also dynamically loaded at room temperature (RT-DPD) for comparison. Results showed that although all the three DPD samples are essentially formed by {100} and {111} grains, the LN-DPD-3pass sample is significantly more severely fragmented. The low-angle grain boundaries are fairly uniformly distributed indicating a high homogeneity of the deformed microstructure. Meanwhile, the proportion of random texture in LN-DPD-3pass sample is higher as compared to the other two samples due to the rotation of dynamic recrystallization grains during DPD. Uniform deformation structure and similar stored energy of the deformed grains lead to the formation of excellent microstructure in the annealed LN-DPD-3pass samples.

Measurement of Photoneutron Yields Using the RPI LINAC and Assessment of Evaluated Photoneutron Data for Tantalum and Beryllium

A new experiment configuration was designed, developed, and implemented to measure photoneutron yields using the Rensselaer Polytechnic Institute (RPI) electron linear accelerator (LINAC) at the RPI Gaerttner LINAC Center. The experiment configuration includes a new target assembly that converts the LINAC electron beam into a high energy bremsstrahlung photon flux incident upon a sample material of interest. The photons excite nuclei in the sample of interest, which can subsequently emit neutrons (photoneutrons). The photoneutrons emitted in the direction of the detector system travel through a series of collimated vacuum pipes before reaching a pair of proton-recoil high-energy neutron detectors. The signals generated by the neutron detectors are processed using a digital data acquisition system and subsequently analyzed to determine the energy-dependent photoneutron yield from the sample of interest. The new experiment configuration was used to perform proof-of-concept experiments to measure the photoneutron yields from samples of tantalum and beryllium. The measured results were then compared against the results from Monte Carlo simulations of the detailed experiment configurations to perform preliminary assessments of evaluated photoneutron data libraries.

EXPERIMENTAL STUDIES ON HIGH-TEMPERATURE CORROSION INTERACTION OF TIN-LITHIUM ALLOY WITH STAINLESS STEEL AND REFRACTORY METALS

This article describes experimental investigations to determine the corrosion compatibility of candidate matrix materials of a capillary-porous structure (CPS) with a liquid tin-lithium alloy at high temperatures. The studies were conducted with the Sn75-Li25 alloy and samples of 12Ch18Ni10Ti grade austenite stainless steel, VEL-3 grade vanadium, and TT grade tantalum. Experiments on the interaction of a liquid tin-lithium alloy with candidate samples of the CPS matrix at high temperatures were carried out on an experimental TiGrA setup based on a TGA/DSC 3+ thermogravimetric analyzer. The paper provides a description of the methodology and conditions for conducting high-temperature corrosion tests. In the course of this work, experiments were carried out to study the compatibility of a tin-lithium alloy in the liquid phase with a stainless steel, vanadium and tantalum samples in the temperature range from 600 ℃ to 1000 ℃. Based on obtained results, the thermal effects of the processes occurring as a result of the interaction of the alloy with a candidate materials of the CPS matrix were determined. As a result of the analysis of the results obtained it has been revealed that at interaction of the studied materials with liquid tin-lithium alloy Sn75-Li25 at high temperatures complex physical and chemical processes take place, such as: selective dissolution of components by liquid alloy (solvent); penetration of component of liquid alloy (tin) into stainless steel depth; mass transfer of dissolved metals from solid metal into liquid.

Constrained model calibration of grain structure dependent spall dynamics in shock-loaded tantalum

We perform a gas gun experiment by shock loading tantalum samples of varying grain structures to assess the suitability of a numerical model for simulating spall behavior. The observed differences in spall strength, as well spallation and re-compression history, are not captured in uncalibrated hydrodynamic simulations. An optimization is performed on the Johnson spall model to determine the best parameters that fit the observed trends. Linear stability analysis is employed to motivate bounds on those parameters. Herein, optimized simulations agree well with the experimental results, reproducing pullback depth and recompression timescales across the different samples tested. Further, the observed pullback time of the single crystal sample was found to imply, via the stability analysis, a percolation threshold in good agreement with the theoretical value for a body centered cubic lattice. Therefore, the combined linear stability and percolation analysis shows promise and may be applied to other materials with diverse microstructures. Collectively, the findings demonstrate that the model is suitable for reproducing spall-induced free surface behavior across various microstructures, but also points to caution in using model coefficients for uncalibrated microstructures.

High precision half-life measurement of the extinct radio-lanthanide Dysprosium-154

Sixty years after the discovery of 154Dy, the half-life of this pure alpha-emitter was re-measured. 154Dy was radiochemically separated from proton-irradiated tantalum samples. Sector field- and multicollector-inductively coupled plasma mass spectrometry were used to determine the amount of 154Dy retrieved. The disintegration rate of the radio-lanthanide was measured by means of α-spectrometry. The half-life value was determined as (1.40 ± 0.08)∙106 y, with an uncertainty reduced by a factor of ~ 10 compared to the currently adopted value of (3.0 ± 1.5)∙106 y. This precise half-life value is useful for the the correct testing and evaluation of p-process nucleosynthetic models using 154Dy as a seed nucleus or as a reaction product, as well as for the safe disposal of irradiated target material from accelerator driven facilities. As a first application of the half-life value determined in this work, the excitation functions for the production of 154Dy in proton-irradiated Ta, Pb, and W targets were re-evaluated, which are now in agreement with theoretical calculations.

Improvement of microstructure and texture homogeneity of tantalum by dynamic plastic deformation and subsequent annealing: Effect of pass number

In the paper, tantalum (Ta) samples were processed with one pass (1-pass), two passes (2-pass) and three passes (3-pass) dynamic plastic deformation (DPD). The deformed and annealed microstructures were studied by using multiple characterization techniques, such as electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Results showed that the yield strength increases from 611.81 MPa at the first DPD to 1055.19 MPa at the third DPD and all samples reached a 70% reduction finally. The deformed samples are mainly composed of {111}(<111>//LD) and {100}(<100>//LD) grains, and the grains are arranged alternately. Meanwhile, numerous micro shear bands (MSBs) appear in {111} grains of the 1-pass sample. In contrast, they are rarely observed in 2-pass and 3-pass samples, and the distribution of low-angle grain boundaries (LAGBs) and kernel average misorientation (KAM) are more uniform than 1-pass samples. Compared with the 1-pass sample, the 3-pass sample exhibits lower geometrically necessary dislocations (GND) density differences between {111} and {100} grains. The relative Schmidt factor (SR) results indicate that the 2-pass and 3-pass sample is more likely to activate multiple slips than the 1-pass sample. The stored energy variance between {111} and {100} grains in deformed samples is significantly weakened after increasing DPD passes, resulting in that microstructure and texture homogeneity after annealing are improved.

Study of liquid tin-lithium alloy interaction with structural materials of fusion reactor at high temperatures

The paper presents the experimental studies to determine the corrosion compatibility of various base materials of the capillary-porous structures (CPS) with a liquid tin-lithium alloy under high temperatures. The experiments were carried out with Li-Sn alloy and the samples of vanadium, tungsten, molybdenum, tantalum, and stainless steel. These materials were selected as the candidate ones for the matrix of Li-Sn CPS prototypes. Manufacture of Li-Sn alloy and experiments were carried out at test bench VIKA. The ranges of the temperatures was: 600 °C–800 °C for stainless steel, and 850 °C–1000 °C for other metals; exposure time for every temperature step was up to 100 h.The implemented activities included manufacture of Sn-Li alloys with various lithium contents (25 at.% and 27 at.%), characterization of the samples, experiments to study compatibility of liquid tin-lithium with vanadium, tungsten, molybdenum, tantalum at temperatures of 850 °C–1000 °C, and stainless steel at temperatures of 600–800 °C. As a result of the performed activities, molybdenum and tungsten were selected as the most corrosion resistant materials in respect to Li-Sn alloys.

Limited and unlimited spike growth from grooved free surface of shocked solid

Richtmyer–Meshkov instability developed at a solid–vacuum interface after reflection of a shock wave is studied using the smoothed particle hydrodynamics (SPH) method. SPH simulations are performed for aluminum, copper, and tantalum samples with free surfaces having machined grooves of sinusoidal shape. The obtained simulation results agree well with the experimental data for different loading regimes. Our simulations demonstrate three regimes of material response to shock loading, where conditions depend on the yield strength for a given strain rate. First, at weak elastic shocks, the grooved surface experiences shear oscillations only. Then, a more intense shock loading produces plastic strain resulting in a plastic spike with the limited run from the surface. It is found that after the arrest of the plastic motion, the formed spike oscillates with the same period as in the elastic regime. Finally, the heavy load produces the unlimited growth of plastic or liquid jet, which leads to its fragmentation at later times. The transition from limited to unlimited jet growth depends on the geometry of the corrugated surface. We estimate the critical amplitude of corrugations required for unlimited spike growth. The used simulation techniques can provide the more accurate mechanical properties of materials to achieve a better agreement.

Microstructure and strengthening mechanisms of tantalum prepared using laser melting deposition

Laser melting deposition (LMD) additive manufacturing process has been attractive to the fabrications of pure tantalum due to the advantage of fast near net shaping of complex shaped components. In the present study, the LMD process has been applied to the fabrication of tantalum using two kinds of powders with different interstitial contents. The microstructure, chemistry, and mechanical properties of the LMD samples have been investigated to understand the strengthening mechanisms. The results show that the tantalum samples have near full dense, and large columnar grains with the growth direction slightly deviated from the deposition direction. The LMD tantalum can have high hardness of up to 300 HV, mainly due to the solid solution strengthening of nitrogen and oxygen interstitials. With relative low interstitial contents of about 400 ppm, the LMD tantalum can have ductile properties, showing ultimate tensile strength above 400 MPa, and elongations of about 14–16%, which are comparable to the properties of cold-worked tantalum. The present work suggests the LMD tantalum could have potential usages in the industry fields.

Ta2C precipitation after low pressure carburizing of tantalum

Low pressure carburizing cycles were carried out on tantalum samples. A Ta2C precipitates layer is present under the TaC and Ta2C surface layers. As the TaC and Ta2C layers, the Ta2C precipitates layer (TPL) grows by carbon diffusion in tantalum matrix. Specific zones with low precipitates content were observed at the bulk surface and in the tantalum grain boundaries. Other zones with lower precipitates content are also present in carburized and annealed samples. All the zones with low precipitates content are induced by the Ta2C precipitation mechanism described by Dahmen et al. [1,2]. Indeed, Ta2C needs vacancies to precipitate. If vacancy sinks are present at the bulk surface, at a grain boundary or in a dislocation, then Ta2C precipitation is highly reduced. Another effect of the annealing treatment is an increase of the Ta2C precipitates layers growth rate.

Application of the technology of induction chemical-thermal treatment to improve the physical and mechanical properties of tantalum

The results of the chemical thermal treatment (CTT) of tantalum in a solid carbon- containing medium in the temperature range from 1000 to 1300 °C were presented. CTT consisted in heating a workpiece with a working medium in a container made of a refractory material. The induction heating method was used for heating. After strengthening treatment, tantalum samples were characterized by increased hardness, which grew from 140 to 1100 HV0.02.

Time-resolved prompt-gamma activation analysis at spallation neutron sources and applications to cultural heritage, security, and radiation protection

The present and future developments of time-resolved prompt-gamma activation analysis (T-PGAA) at pulsed neutron sources is discussed in the framework of the successful history of neutron-activation techniques. A brief description of the state of the art and the most important user facilities using standard prompt-gamma activation analysis (PGAA) is provided. Then, we discuss the challenges and the opportunities for T-PGAA at pulsed neutron sources, and the potential impact for applications to cultural heritage, radiation protection, and security. We notice some inversions of trend needed for the further development of T-PGAA with epithermal and fast neutrons, such as the possibility to use fast and high-efficiency γ-ray scintillators with lower energy resolution (compared to usual high-purity germanium detectors) when the signal from neutron capture resonance is selected. We also suggest how detection systems often used in other fields, such as medical physics, can be of interest and inspiration also in the case of neutron-based investigations. Finally, we present new data of T-PGAA measurements on VESUVIO using neutron energies up to the keV using the scintillators available on the instrument, for samples of gold (of interest in cultural heritage), cadmium (for environmental safety), and tantalum (a material used in biomedical implants).

Effects of reuse on the properties of tantalum powders and tantalum parts additively manufactured by electron beam powder bed fusion

The cost of additively manufactured tantalum parts can be effectively lowered by reusing or recycling tantalum powder. To evaluate the effects of reuse of the tantalum powder on the properties of tantalum parts and scaffolds, this study investigated the characteristics of tantalum powder during cycling, including oxygen content, particle morphology, apparent density, tap density, and flowability. Besides, the influence of reuse time on the mechanical properties of electron beam powder bed fusion (EB-PBF) fabricated tantalum parts and scaffolds was studied with tantalum powder reused more than 30 cycles. The results indicated that particle size distribution of the tantalum powder was nearly unchanged with the increase of cycle number, accordingly apparent density, tap density, and fluidity. While the powder became less spherical with increasing reuse times and some particles showed noticeable distortion and rough surface after being reused 25 times. Moreover, the oxygen content of the tantalum powder increased progressively with increasing reuse times, leading to the decrease of plasticity of the dense tantalum after 15 reuse cycles, and some potential micro-defects appeared in the tantalum samples fabricated from EB-PBF process. However, the tensile strength of dense tantalum parts was not sensitive to the number of uses within the research range.

Dynamic properties of additively manufactured tantalum

In this study a series of gas gun plate impact experiments have been conducted on samples of wire arc AM tantalum to investigate the high strain rate behaviour of the material, including tensile failure (spall) mechanisms. Conventionally processed tantalum was fielded alongside the AM material to provide a direct comparison under identical loading conditions. In-situ velocimetry data was supported by pre-shock characterisation of the samples to supply information on the initial material microstructure, and to link these features to the observed differences in dynamic behaviour. Additional post-shock analysis of the damaged region in the samples provided further insight into the failure process.

Employing molecular dynamics to shed light on the microstructural origins of the Taylor-Quinney coefficient

The Taylor-Quinney coefficient (TQC) or the cold-work conversion factor is the fraction of external work that is converted into heat during the plastic deformation of a material. Since it was first proposed almost a century ago, its value was measured experimentally and was found to span over a wide range of values between 0.1 and 1, and it is argued to depend on strain and strain rate. Despite, only little is known on how the microstructure corresponds to the value of TQC, and in particular how dislocations and grain boundaries correspond to energy storage during plastic deformation. We employ molecular dynamics simulations to study the work-to-heat conversion during plastic deformation in single crystal and nanograined samples of aluminum, copper, iron, and tantalum at extremely high strain rates. We found that if dislocation glide in the drag-controlled regime is the only deformation mechanism of plastic deformation, all external work is converted into heat as in the case of single crystals with dislocation dipoles. On the other hand, in nanograined samples we found that some energy is stored in- or released from the crystal as a result of an evolution in the morphology and distribution of grain boundaries. We also emphasize the important distinction between the integral and differential measurements of TQC, showing that the differential measure can become even greater than 1 if the strain increment results in annealing of the defects from the microstructure. Based on the atomistic observations, we propose that grain boundary evolution mechanisms can be responsible for energy storage in polycrystalline material at experimental strain rates.

The study of mechanical and statistical properties of nitrogen ion-implanted Tantalum bulk

In the present study, structural and mechanical properties of Tantalum samples which affected by nitrogen ion implantation have been investigated. The monofractal analysis of the samples has been carried out. These samples have been implanted with ions at different doses of 5 × 1017 and 7 × 1017 at energy 30 keV. For characterizing the samples, atomic force microscopy (AFM), EDX images analysis, and corrosion measurements, have been used. By varying the ion energy, the statistical characteristics will vary. In order to analyse the morphology of produced rough samples, the correlation function of samples have been studied and their correlation length is evaluated. Based on the statistical concept the power spectral density the height distribution, and the higher-order moments (skewness and kurtosis) of the surface height have been measured. These charactristics are the important criterions for the the monofractal evaluation. Our numerical calculations based on experimental data show the deviation from gaussian distribution. Also, the fractal dimension of the films has been calculated based on rougness exponent results. Indeed, irradiating the surfaces with energetic ions results in producing the self-affine fractal surfaces. This process via an erosion process affects the statistical characteristics which have been calculated for different samples. Because of variation in the morphology of rough samples, the corrosion of samples shows a non-uniform behavior.

Microstructure, Hardness, Wear, and Magnetic Properties of (Tantalum, Niobium) Carbide-Nickel–Sintered Composites Fabricated from Blended and Coated Particles

Abstract (Tantalum, niobium) carbide-nickel composites were prepared by the powder metallurgy technique. Microsize (tantalum, niobium) carbide particles were reinforced in the nickel matrix. Different nickel contents were added to (tantalum, niobium) carbide powders by two different methods, namely, blending and electroless coating. The results of the microstructure show a good distribution of the (tantalum, niobium) carbide particles in the nickel matrix. The produced (tantalum, niobium) carbide-nickel composite powders were cold compacted at 400 MPa and sintered under vacuum at 1,450°C for 90 min. The density of the (tantalum, niobium) carbide-nickel–sintered materials was measured by the Archimedes method. The mechanical properties of the obtained sintered materials were evaluated by measuring the Vickers hardness and the wear rate using a pin-on-ring wear test machine. The microstructure of the sintered (tantalum, niobium) carbide-nickel as well as the microstructure of worn samples were investigated by a scanning electron microscope. The results revealed that the (tantalum, niobium) carbide-nickel–sintered materials, which were prepared by the electroless nickel coating of (tantalum, niobium) carbide particles, have a homogeneous microstructure and exhibit higher relative density, hardness, and low specific wear rate than the samples of the (tantalum, niobium) carbide/nickel–sintered materials prepared by blending of nickel with the (tantalum, niobium) carbide powders. The magnetic properties of the obtained blended and coated (tantalum, niobium) carbide particles as well as the sintered one have been studied. It was observed that the saturation magnetization is increased by increasing the nickel content.

Nanosecond laser induced surface micro-structuring of Tantalum targets for improved field emission

In this paper we report our results on nanosecond laser based surface micro (μ)-structuring of Tantalum (Ta) samples and their field emission behavior. Surface micro-structuring has been carried out using a typical laser fluence of 0.9 J cm−2 and varying number of incident laser pulses in the range of 3000 to 9000. Laser treated samples have been characterized in terms of surface morphology, chemical phase and field emission behavior. Nanosecond laser irradiation resulted in formation of self assembled surface μ-protrusions in the laser treated region. Peak height of the generated μ-protrusions and average roughness of the laser treated region increased with increasing number of irradiating laser pulses. Laser treated specimens have shown enhanced field emission in comparison to pristine Ta specimen. Specimens μ-structured using 3000, 6000 and 9000 laser pulses per spot have shown field emission with turn on field (Eon) of 6.6 V−1 μm−1, 4.8 V −1μm−1 and 3.7 V −1μm−1, respectively. Also, maximum emission current density delivered by these laser modified specimens was found to increase with increasing number of laser pulses. Although, Ta specimen μ-structured with 9000 laser pulses has shown highest emission current density, emission current stability of this sample was poorer in comparison to specimens modified using 3000 and 6000 laser pulses.