Tantalum Coatings Research Articles

Fast three-dimensional rules-based simulation of thermal-sprayed microstructures

Thermal spray processes involve the repeated impact of millions of discrete particles, whose melting, deformation, and coating-formation dynamics occur at microsecond timescales. The accumulated coating that evolves over minutes is comprised of complex, multiphase microstructures, and the timescale difference between the individual particle solidification and the overall coating formation represents a significant challenge for analysts attempting to simulate microstructure evolution. In order to overcome the computational burden, researchers have created rule-based models (similar to cellular automata methods) that do not directly simulate the physics of the process. Instead, the simulation is governed by a set of predefined rules, which do not capture the fine-details of the evolution, but do provide a useful approximation for the simulation of coating microstructures. Here, we introduce a new rules-based process model for microstructure formation during thermal spray processes. The model is 3D, allows for an arbitrary number of material types, and includes multiple porosity-generation mechanisms. Example results of the model for tantalum coatings are presented along with sensitivity analyses of model parameters and validation against 3D experimental data. The model’s computational efficiency allows for investigations into the stochastic variation of coating microstructures, in addition to the typical process-to-structure relationships.

Electrodeposition of Tantalum Coatings on Nitinol Stent and Composition of Intermetallic Compounds Forming During Electrolysis

The electroreduction of tantalum complexes in a chloride-fluoride melt was studied on tungsten, and nitinol electrodes. It was found that on a nitinol electrode in addition to the peak associated with the discharge of fluoride tantalum complexes, several peaks on the voltammogram related to the formation of intermetallic compounds of nickel and tantalum were observed. The electrodeposition of tantalum coatings from the NaCl-KCl-NaF(10 wt.%)-K2TaF7(10 wt.%) melt onto nitinol stent was investigated. The formation during electrolysis of several intermediate layers between the deposited layer and substrate was found and their microstructure and chemical composition were determined. It was determined that the surface layers of the nitinol are depleted in titanium due to corrosion in the melt. During electrodeposition a barrier intermetallic layer TiNi2.4Ta0.6 is formed, which prevents the penetration of tantalum into the substrate, but does not prevent the diffusion of nickel and titanium from the substrate into the deposited layer of tantalum.

Optimization for Solderability of Large-Size Single-Crystal Diamond with Heterogeneity Alloys by Tantalum Coating

Optimization for Solderability of Large-Size Single-Crystal Diamond with Heterogeneity Alloys by Tantalum Coating

Study on Improving Corrosion Resistance of Tantalum Coating by Anodic Oxidation

Study on Improving Corrosion Resistance of Tantalum Coating by Anodic Oxidation

DEPENDENCES OF HELIUM RETENTION IN TUNGSTEN AND TANTALUM COATINGS IRRADIATED WITH He+ IONS ON FLUENCE AND TEMPERATURE

The processes of helium accumulation and thermal desorption for tungsten and tantalum coatings deposited on a stainless-steel substrate with an intermediate titanium layer were studied at various temperatures of the samples when irradiated with He+ ions to various fluences. The dependences of the concentration of captured helium and the form of the spectra of its thermal desorption into vacuum were found both on the fluence of He+ ions and on the temperature of the samples upon irradiation. Possible mechanisms for the accumulation and thermal desorption of helium, as well as the formation of defects in the crystal lattice of the samples, are discussed.

Effect of the Substrate Biasing on the Structure and Properties of Tantalum Coatings Deposited Using HiPIMS in Deep Oscillations Magnetron Sputtering Mode

The influence of energetic ion bombardment on the properties of tantalum coatings was studied. To achieve such energetic ion bombardment during the deposition process of tantalum coatings, a combination of deep oscillation magnetron sputtering (DOMS), an ionized physical vapour deposition technique, with substrate biasing was used. The substrate biasing was varied between 0 and −120 V. In this work, the structure (XRD), microstructure (SEM), surface morphology (AFM) and hardness, and Young’s modulus (nanoindentation) of the coatings were characterized. The results show with the use of such conditions it was possible to deposit a pure α-Ta (the most desired at industrial level) with improved mechanical properties (hardness equal to 22.4 GPa and Young’s modulus equal to 235 GPa). The roughness of the Ta coatings decreases up to values of about 1 nm with an increase of substrate biasing. It was possible to deposit very dense Ta coatings with 2 µm of thickness. Therefore, these results are significantly different than in previous works, offering Ta coatings with a combination of very interesting properties.

Electrodeposition of Tantalum Coatings on Nitinol Stents

The Ni-Ti shape memory alloys are currently a topic of notable interest in medicine. They provide a unique opportunity to make novel surgical implants and instruments for vascular and orthopedic surgery. However, a high nickel content in these alloys could cause the problem of biocompatibility because of nickel toxic effect. In turn, a tantalum is successfully used in medicine as a wire or sheet. It does not irritate the living tissue and does not harm the functioning of the organism, but it has a high specific weight. Therefore, using of tantalum coatings on various materials is more appropriate than utilization of a bulk metal. Thus, it is necessary to improve a corrosion resistance of nickel-titanium alloys (nitinol) that can be achieved with applying of protective porousless tantalum coating.For obtaining of tantalum coatings the NaCl-KCl-NaF(10 wt%)-K2TaF7(10 wt%) melt was used at a temperature 1023 K. Direct (DC), unsteady state (USC) and pulsed current (PC) were supplied for electrodeposition. A cathodic current density was changed from 5 to 200 mA/cm2 at the galvanostatic mode. The same cathodic current densities and the time of electrolysis (tel = 0.5-5.0 s) with pauses (tp = 1-5 s) were used at unsteady state and pulsed electrolysis. It was found that a pulsed electrolysis allow to produce coatings with lower roughness than galvanostatic electrolysis.Electroreduction of tantalum complexes in chloride-fluoride melt at a nitinol electrode was investigated. A voltammetric curve registered at a nitinol electrode except of the electroreduction peak of tantalum fluoride complexes to tantalum has several peaks corresponding to the formation of intermetallic compounds of nickel and tantalum.In the case of formation intermetallic compounds between a substrate and coating is an important aspect of the coating adhesion to substrate. The adhesion was measured by cross-sections method using a tester of adhesion Elcometer 107. The measurements showed that coatings obtained by DC and USC could be classified as adhesion to international standards ISO (1) and ASTM (4B). At the same time, coatings deposited on nitinol by PC have a maximum class of adhesion ISO (0) and ASTM (5B). These results were obtained for intermetallic compounds with a thickness around 1-2 μm.Additional experiments were carried out for obtaining of thick layers of intermetallics and study their composition by SEM and EDX.The porosity of tantalum coatings was determined by Erhard’s technique based on measuring a current dissolution at a certain potential, in which dissolves a substrate material and coatings remain passive.Corrosion resistance of the composition tantalum coating-nitinol was studied in different corrosion media.

Biomedical evaluation of vacuum plasma sprayed tantalum coatings processed by alkali treatment and alkali-heat treatment with different NaOH concentrations

Alkali-heat treatment (AHT) is an effective surface treatment technology for improving the bioactivity of medical metal biomaterials. However, the effects of AHT on the biocompatibility of the original material are not yet fully clear. Accordingly, in the present study, tantalum (Ta) coatings are deposited on Ti6Al4V substrates using a vacuum plasma spraying (VPS) technique and the coatings are then processed using either alkali treatment (AT) or AHT using 0.5 M and 1.0 M NaOH aqueous solution. In vitro bioactivity tests are performed in simulated body fluid for 3~14 days. It is shown that the surface of the AHT sample treated with 0.5 M NaOH (0.5 M AHT) has excellent bioactivity, irrespective of whether or not ultrasonic cleaning (UC) is performed following the heat treatment process. The surface of the AHT sample processed with 1.0 M NaOH (1.0 M AHT) contains a large number of irregular block-shaped compounds, which hinder the bioactivity of the coating. However, following UC treatment, the block-shaped compounds are removed, and the bioactivity of the AHT-UC sample is similar to that of the 0.5 M AHT sample. In in vitro biocompatibility tests for 1–7 days, the Ta coating and 0.5 M AHT-UC coating exhibited significantly better cellular attachment, growth, spreading, and viability of osteoblast-like osteosarcoma MG-63 cells than the 1.0 M AHT-UC coating. It is speculated that this is due to the presence of excess amorphous sodium tantalate on the surface of the 1.0 M AHT-UC coating. Overall, the present results show that AHT treatment performed with an appropriate NaOH concentration yields a significant improvement in both the bioactivity and the biocompatibility of VPS Ta coatings.

Structure and Properties of Tantalum Coatings Obtained by Electron Beam Technology on Aluminum Substrates

The paper deals with the study of the structure and properties of tantalum coatings formed by electron beam evaporation and deposition of tantalum powder on 300–450 °C aluminum substrate. The research results of surface morphology, phase and elemental composition show that high activity of an aluminum substrate and specific conditions for vapor-phase technology promote formation of tantalum coatings characterized by a high degree of crystalline grains, with high adhesion and hardness despite the surface cracks. It was observed that the optimum deposition temperature of tantalum on aluminum substrates varies from 300 °C to 350 °C. These coatings demonstrate excellent physical and mechanical properties due to formation of intermetallic phases in the reactive zone.

Fabrication of Porous Tantalum and Tungsten Black Coatings for Artificial Earth Satellites

Coatings are fabricated using plasma-ion sputtering and codeposition of ultradispersed Ta and Cd particles and Nb- and Mo-doped W and Cd particles. The fabricated coatings consist of a mixture of crystallized cadmium and the amorphized refractory metals. Subjecting the coatings to thermal annealing in vacuum at 800°C for 1 h results in complete evaporation of cadmium from the coatings and the formation of cellular structures, their light-absorbing capacity depending on doping with Nb and Mo. The Nb-doped tantalum coatings and Nb- and Mo-doped tungsten coatings exhibit the highest light absorption. The electrical resistance of fabricated black coatings is sufficient to drain static charge accumulating due to contact with near-Earth plasma.

Corrosion behavior of tantalum coatings on AISI 316L stainless steel substrate for bipolar plates of PEM fuel cells

Corrosion resistance of tantalum coatings 30 μm thick deposited by chemical vapor deposition on SS316L coupons has been evaluated by electrochemical impedance spectroscopy (EIS). To this end, anodic and cathodic operating conditions of proton exchange membrane fuel cells (PEMFC) have been simulated in a three-electrode heated corrosion cell. Interfacial contact resistance (ICR), contact angle and durability tests have been performed in long-term tests (>100 h) polarizing the electrode to 1.193 V vs. Ag/AgCl. Results obtained by different experimental techniques show a dense coating structure with a high polarization resistance, mainly formed by surface crystals of α-Ta (bcc), Ta2O5 and carbon. An atomic ratio (in %) of oxide to metallic species (Taox/Tamet) of 4.8 was verified from XPS spectra, which is slightly increased to 6.23 after the anodizing treatment. The modified surface composition yielded a coating capacity higher than the amorphous oxide, favoring the in-plane electrical conduction. After the treatment, no noticeable changes were observed neither in surface morphology nor in contact angle (>90°). ICR values in the range of 22.3–32.6 mΩ cm2 were obtained for a clamping pressure of 140 N cm−2. No morphological changes or loss of coating adherence were observed during the long-term tests.

Influence of the Second Coordination Sphere on the Roughness of Niobium and Tantalum Coatings Obtained in Chloride-Fluoride Melts

The influence of the second coordination sphere complexes on the roughness of niobium and tantalum coatings was studied. It was found that the discharge potential of niobium oxofluoride complexes has a more positive potential than fluoride ones in the NaCl-KCl-NaF (10 wt%)-K2NbF7 melt. For the СsCl-CsF (10 wt%)-CsNbF6 molten system the inversion of potentials corresponding to discharge of oxofluoride and fluoride complexes was observed. Due to micropassivation by oxygen impurities as niobium suboxides and oxygen-niobium solid solution the coating roughness in the NaCl-KCl-NaF (10 wt%)-K2NbF7 (8 wt%) melt diminishes in comparison with СsCl-CsF (10 wt%)-CsNbF6 (8 wt%) melt. In molten salts NaCl-KCl-NaF (10 wt%)-K2TaF7 and СsCl-CsF (10 wt%)-CsTaF6 tantalum oxofluoride complexes are discharged at more negative potentials than fluoride ones and changes in the composition of the second coordination sphere from sodium to cesium led to a lower level of roughness. For melts containing in the second coordination sphere cesium cations, the roughness of the tantalum coatings was less than that of niobium due to the greater strength of the fluoride complexes of tantalum. It was found that pulsed current electrolysis for deposition of niobium and tantalum coatings has significant advantages in comparison with direct current electrolysis.

Анализ состава слоев, образующихся на подложках из нержавеющей стали при газофазном осаждении тантала

Interaction of the reagents and the substrate stainless steel was analyzed during the deposition of tantalum coatings by reduction of tantalum bromide with cadmium. It was found that at deposition temperatures above 1000 K, the iron and chromium contents in stainless steel will reduce tantalum pentabromide passing into the gas phase in the form of bromides. As a result, not only tantalum bromide is reduced on the substrate, but also iron bromide which in the initial stages of deposition leads to the formation of iron containing sublayer in the coating. An increase in the contact surface of stainless steel interacting with reagents leads to an increase in the content of iron bromide, in which case a coating is formed from a Ta + Fe2Ta mixture. In addition, chromium bromide is formed on the substrate, which is removed along with the rest of the reaction products. It causes chromium depletion in the surface layers of steel.

Investigation of the thermal stability of titanium nickelide tantalum coating using photometric analysis of structural images

The paper considers the thermal stability of tantalum coatings on TiNi (titanium nickelide or nitinol) used in medicine (especially in endovascular surgery) and having their own characteristics. A method is proposed to control magnetron sputtered tantalum film coatings on titanium nickelide — a method of photometric analysis of structural images (PASI).

Thromboresistant properties of nanostructured tantalum coatings on the stainless steel surfaces

The nanostructured coatings of tantalum and its compounds on the stainless steel surfaces were investigated by atomic force microscopy. Their hydrophilic properties were studied by sessile drop and atomic force spectroscopy methods. The thromboresistant properties of samples were analysed in vitro by incubation of the samples in the rich platelets plasma of patients with acute coronary syndrome. The effect of surface properties on the thromboresistant properties was analysed.

Dissimilar material welding of tantalum foil and Q235 steel plate using improved explosive welding technique

Achieving high quality tantalum coatings on common metals is still a challenging task, due to potential technical problems such as high differences in melting points and formation of intermetallic compounds. In this work, an improved explosive welding technique was successfully employed to prepare tantalum coatings on a steel substrate, where a special charging structure and a double-layer buffer structure were used to obtain an ideal welding condition. The microstructure analyses of the achieved joints were conducted using electron backscatter diffraction (EBSD), and scanning electron microscope (SEM) cooperated with energy dispersive X-ray spectroscopy (EDS) system. Tensile, three-point bending, and nanoindentation tests were carried out to investigate the mechanical properties. It was concluded that the improved explosive welding technique was a suitable method to produce Ta coatings on steel substrate. In both microstructure observation and mechanical tests, an excellent bonding quality between Ta foil and Q235 plate was confirmed. In addition, a novel vortex structure, good for preventing crack propagation from the brittle melted area, was observed at the Ta/Fe interface. Finally, the corrosion test indicated that the corrosion resistance of Q235 plate was remarkably improved after being coated by Ta foils using explosive welding.

სპილენძის ფუძეშრეზე ნიობიუმის და ტანტალის დანაფარების მიღების ტექნოლოგია

სპილენძის ფუძეშრეზე ნიობიუმის და ტანტალის დანაფარების მიღების ტექნოლოგია

VACUUM CVD COATINGS TA ON TARGET W PLATE OF NEUTRONS SOURCE

The paper presents data on the creation of a tungsten target, protected from corrosion under irradiation with a power of up to 100 kW. A protective coating of tantalum with a thickness of 250 μm was deposited on the surface of tungsten plates 66x66 mm, thickness 10; 6; 4; 3 mm. The coating has a solid-phase compound over the entire surface of tungsten and is hermetic. This was achieved by CVD (chemical vapor deposition) tantalum deposition in a vacuum of 2.66•10-2 Pa on a plate surface heated to ~ 1700 K using the thermal dissociation reaction of tantalum pentachloride vapor. Such tungsten plates, equipped with tantalum coatings with desired properties, were used in the Neutron Source installation of the NSC KIPT.

Modelling of transition zone formation between thin Si or Ta film deposited on TiNi under low-energy electron beam irradiation

Nickel titanium or nitinol is very often coated by biocompatible and corrosion-resistant silicon and tantalum coatings. One of the methods for the formation of a continuous transition zone between the coating and nitinol is pulsed or continuous electron beam treatment. Surface heating accelerates diffusion processes that facilitate the formation of new phases. However, the interpretation of experimental results is hindered due to the impossibility of directly observing the processes. Here we model the phenomena accompanying the transition zone formation. The mathematical model used takes into account thermal and diffusion phenomena and the stages of the main chemical reactions in the heated area. Numerical studies revealed that the transition zone for the two types of films is formed differently: in the case of silicon the transition zone grows inside nickel titanium, while in the case of tantalum it is formed mainly in the area of the deposited film. The interaction of competing stages determines the absence of regularities in the oxide phase formation under varying treatment conditions.

A COMPARATIVE STUDY ON VACUUM AND ATMOSPHERIC PLASMA SPRAYED TANTALUM COATINGS FOR THE MODIFICATION OF TITANIUM IMPLANTS

In order to improve the mechanical compatibility and cytocompatibility of titanium implants, tantalum coatings were prepared using plasma spraying technology. Tantalum coatings have been deposited via atmospheric plasama spraying (APS) and vacuum plasma spraying (VPS) methods, and then their morphologies, porosities, bonding strengths and elastic modulous were investigated. In vitro cytocompatibility of the two coatings was evaluated via human bone marrow stromal cells (hBMSCs). The results show that oxidation phenomenon was observed for the APS tantalum coatings, while less oxidation was found in the VPS tantalum coatings. Compared with APS tantalum coatings, the VPS tantalum coatings have a more compact microstructure and less impurity content, resulting in a better bonding with the titanium substrate. VPS tantalum coatings were measured to have a lower elastic modulus and a higher hardness than APS Tantalum coatings. Electrochemical corrosion of the coatings were examined and the VPS tantalum coating showed improved chemical stability. Besides, bone marrow stem cells (BMSCs) adhere to and spread well on the surface of both VPS and APS tantalum coatings without significant difference. The proliferation rate of BMSCs is higher on VPS tantalum coating surface than on APS tantalum coatings. Our results suggest that VPS tantalum coatings are more suitable for the application of surface modification of titanium implant due to their lower elastic modulus and better chemical stability for higher mechanical compatibility and cytocompatibility.