Ta Coatings Research Articles

In vitro investigation of Nb[sbnd]Ta alloy coating deposited on CoCr alloy for biomedical implants

Cobalt-chromium (CoCr) alloys are widely used as implant materials but their corrosion in physiological conditions can trigger severe immunological response leading to inflammatory and allergic reactions. The present study was aimed at the development, characterization and in vitro evaluation of niobium-tantalum (NbTa) alloy coating on CoCr alloy. Alloy coating with three different compositions was prepared by varying weight proportion of Nb and Ta (70:30, 50:50 and 30:70) through the plasma spray technique. Pure Nb and Ta coatings were also deposited for comparative analysis. Nb and Ta were recognized as the primary phases in respective coatings. Microcracks were observed in case of pure coatings, while alloy coatings displayed crack-free morphology. The coatings demonstrated microroughned surfaces and hydrophobic properties. Microhardness of the CoCr alloy was notably enhanced with the deposition of coatings. Corrosion investigation revealed that the coated surfaces had higher protection ability than the uncoated CoCr and alloy coatings imparted better corrosion resistance than pure coatings. The alloy coatings were more conducive to cell proliferation and showed superior hemocompatibility. The findings of this study indicate that the surface modification with NbTa alloy coatings is a promising approach to improve the performance of CoCr alloys for biomedical applications.

Material Application of a Transformer Box: A Study on the Electromagnetic Shielding Characteristics of Al–Ta Coating Film with Plasma-Spray Process

In this study we present the results of two experiments. In the first one, a Ta–Al–SS (stainless steel (SS)) multilayer coating structure was prepared using plasma spraying equipment to investigate the coating structure and interface properties. In the second one, Ta–Al on multilayer glass was prepared using the sputtering process to measure the thickness effect of thin film on electromagnetic wave shielding (EMI) characteristics and on the design of high-power switchboard covers. According to the experimental results, the multilayer structure of Ta–Al on SS improves the mechanical properties of a stainless steel plate by enhancing the explosion-proof property. An appropriate thickness of the plasma-sprayed pure aluminum layer can increase the adhesion to the stainless steel substrate and buffer the stress effect. After heat treatment (annealing), the Ta–Al–SS multilayer structural characteristics are excellent and suitable for shielding effects at different temperatures and humidity, which can be used as a reference for the engineering application of communication rooms and base power stations. According to EMI test of multi-coated glass (Ta–Al–glass), by increasing the thickness of Ta layer, we cannot effectively improve full-frequency EMI shielding with improved shielding at low-mid frequency condition. In addition, the Ta–Al interface formation of an Al–Ta–O compound layer can improve the adiabatic effect to reduce the thermal conductivity.

Microstructure and properties of Ta coatings on the 3Y-TZP ceramic fabricated by plasma alloying technique

Ta coatings on the 3Y-TZP ceramic substrate were successfully fabricated by plasma alloying technique, and its effect on the tetragonal-to-monoclinic phase transformation was investigated. The results indicate that the surface morphology and grain size of Ta coatings were influenced by the deposition temperature. Results of the surface roughness and static contact angle provide further supports. Scratch tests of Ta coatings deposited at 800 °C (S2 specimen) show the good adhesion. The Ta coating has a thickness of ∼590 nm in S2 specimen. Moreover, the friction properties of these Ta coatings in phosphate buffered saline solution exhibit the low friction coefficient. The Ta coating of S2 specimen exhibits an effectively protection for the phase transformation of the 3Y-TZP ceramic tested by hydrothermal aging.

Correction to: Microstructure and Oxidation Performance of TiAl-(Cr, Nb, Ta) Coatings Fabricated by Warm Spray and High-Velocity Oxy-Fuel Spraying

Correction to: Microstructure and Oxidation Performance of TiAl-(Cr, Nb, Ta) Coatings Fabricated by Warm Spray and High-Velocity Oxy-Fuel Spraying

Microstructure and Oxidation Performance of TiAl-(Cr, Nb, Ta) Coatings Fabricated by Warm Spray and High-Velocity Oxy-Fuel Spraying

To improve the oxidation resistance of near α-titanium alloy IMI834, TiAl-(Cr, Nb, Ta) coatings were deposited by applying high-velocity oxy-fuel (HVOF) and warm spray (WS). Comparison was made in terms of microstructure, surface morphology as well as isothermal and cyclic oxidation behaviors in the air at 750 °C up to 100 h and 100 cycles, respectively. The results show that smoother and less oxidized coatings were deposited by warm spraying. The microstructure of all coatings underwent an appreciable change during the oxidation tests, as in as-sprayed state it occurred in the nonequilibrium state. It was revealed that a small difference in the initial oxidation between the two spraying processes as well as microstructure, the level of porosity and surface roughness significantly influences the oxidation kinetics of the sprayed coatings at high temperature, which should affect the service lifetime as an oxidation-resistant layer for potential applications. After exposure at 750 °C in air, rutile TiO2 was found in addition to α-Al2O3 in the oxide scale formed on the HVOF and warm sprayed coatings. However, isothermal and cyclic oxidation tests of all WS TiAl-(Cr, Nb, Ta) coatings showed improved oxidation resistance of IMI 834 as well as good adherence to the substrate alloy.

Fabrication of Ta2O5 Reinforced Ta-based Coatings on Ta Substrates by Laser Cladding

Tantalum (Ta) is a remarkable biological substance, with excellent corrosion resistance and biocompatibility. However, pure Ta coatings do not possess sufficiently high mechanical properties, especially wear resistance. To improve the wear resistance of Ta, Ta2O5 reinforced Ta-based coatings were fabricated on Ta substrates using laser cladding with a direct pre-placed powder method. The microstructure of the coating was primarily the result of a monotectic reaction and can be interpreted using the Ta-O phase diagram. The results suggested that Ta-Ta2O5 graded coatings can be fabricated on Ta substrates by controlling the amount of melting of the Ta substrate and/or adjusting the oxygen level of the processing chamber during laser cladding. The corrosion and wear resistances of the composite coating were higher than those of the uncoated Ta material when free corrosion potential, corrosion current density and wear track width were considered.

Coating of Sandblasted and Acid-Etched Dental Implants With Tantalum Using Vacuum Plasma Spraying.

The objective was to prepare tantalum (Ta)-coated sandblasted and acid-etched (SLA) dental implants using vacuum plasma spraying (VPS) and to analyze their morphologies. Twelve SLA implants were coated with Ta using VPS. The topographies of the coatings and Ta/SLA surface interfaces were examined using scanning electron microscopy. The thickness at 4 locations for 6 Ta-coated and 6 uncoated SLA implants and pore sizes of the neck, central, and root areas of Ta-coated implants were measured. SPSS v20.0 was used for statistical analysis. The Ta coatings were rough and consisted of pitted structures with various pore sizes; no cracks were observed. The Ta/SLA surface interface was tightly bonded. The 95% confidence interval of the Ta coating thickness was (114.0759, 129.3574). The maximal pore diameter was concentrated at 200 to 400 nm. SLA dental implants were successfully coated with Ta using VPS. The nanoporous structure of these implants may facilitate osseointegration compared with uncoated SLA implants.

Argon Shrouded Plasma Spraying of Tantalum over Titanium for Corrosion Protection in Fluorinated Nitric Acid Media

Argon shrouded plasma spraying (ASPS) was used to deposit a Ta coating on commercially pure Ti (CP-Ti) under inert argon, for dissolver vessel application in the aqueous spent fuels reprocessing plant with high plutonium content. Oxidation during plasma spraying was minimized by shrouding argon system. Porosity and oxide content were controlled by optimizing the spraying parameters, to obtain a uniform and dense Ta coating. The Ta particle temperature and velocity were optimized by judiciously controlling the spray parameters, using a spray diagnostic charge-coupled device camera. The corrosion resistance of the Ta coatings developed by ASPS was investigated by electrochemical studies in 11.5 M HNO3 and 11.5 M HNO3 + 0.05 M NaF. Similarly, the durability of the ASPS Ta coating/substrate was evaluated as per ASTM A262 Practice-C test in boiling nitric acid and fluorinated nitric acid for 240 h. The ASPS Ta coating exhibited higher corrosion resistance than the CP-Ti substrate, as evident from electrochemical studies, and low corrosion rate with excellent coating stability in boiling nitric, and fluorinated nitric acid. The results of the present study revealed that tantalum coating by ASPS is a promising strategy for improving the corrosion resistance in the highly corrosive reprocessing environment.

Karakterizacija tantal prevlake deponovane vakuum plazma sprej procesom

Tantalum is a very popular material for the industry as a whole because of very important characteristics such as: high melting point, significant thermal and electrical conductivity, high toughness and resistance to corrosion and good biocompatibility. Since the tantalum metal is sensitive to O, N and H gases, tantalum coating layers are deposited only using the vacuum plasma spray process (VPS), which has, in the past few years been used successfully for preparing coatings which are widely used in the preparation of metal implants. The aim of this paper was to, at a low pressure inert gas eliminate the influence of the surrounding atmosphere on the melted Ta powder particles and produce coatings with mechanical and structural characteristics which will find application in biomedicine. For depositing the coating a commercial tantalum powder AMPERIT® 151065 grain size of 10 - 30 μm was used. The powder was deposited with a plasma F4 gun at a distance of substrates at 300 mm. The Ta coating layers were deposited with a thickness of 60 to 70 μm on steel substrates. As the plasma gas used was a mixture of Ar and He inert gases. The microhardness of the coating was tested using the HV0.3 method and the tensile strength of the coatings bond was tested by the tensile method in accordance with the ASTM C633-1 standard. The microstructure of the coating in deposited state and after etching was studied on an optical microscope (OM) and scanning electron microscope (SEM). Etching the coating was carried out in the reagent which consisted of two parts of nitric acid, two parts hydrofluoric acid, and five parts water (2HNO3: 2HF: 5H2O). The structure of the coating consists solely of a tough αTa phase with a body centered cubic lattice. Tests have shown that layers of VPS - Ta coatings have the microstructure and mechanical properties which completely support the use of the coating in the process of making implants.

Tribo-corrosion performance of filtered-arc-deposited tantalum coatings on Ti-13Nb-13Zr alloy for bio-implants applications

Tantalum coatings were deposited on Ti-13Nb-13Zr alloy by filtered cathodic vacuum arc deposition in order to improve the alloy's wear and corrosion resistance under load-bearing, biomedical applications. The Ta coating exhibits an amorphous structure, which transforms into a mixture of alpha and beta phases as the substrate is heated to 300°C during deposition. Tribo-corrosion tests were performed using a ball-on-disk tribometer under simulated joint fluid at 37°C by sliding the uncoated and Ta-coated surfaces against alumina balls. The Ta coatings showed a significant reduction in the coefficient of friction under these test conditions. The wear rates of the Ta-coated disk surfaces are slightly lower than those of the bare Ti-13Nb-13Zr alloy, while the wear rate of the alumina balls was one order of magnitude higher when it slid against the Ta-coated samples than when it was slid against the Ti-13Nb-13Zr alloy. The wear debris generated from the Ta-coated samples sliding against alumina was comparatively smaller than that generated by the uncoated alloy against alumina. The wear characteristics of the Ta coatings do not favour using such coatings on implant materials. The Ta coatings exhibited a strong capacitive response which is proposed to enhance corrosion protection of the Ti-13Nb-13Zr alloy.

Evaluation of cell activation promoted by tantalum and tantalum oxide coatings deposited by reactive DC magnetron sputtering

Previous studies have shown both Ta and TaO to be bioactive, rapidly forming a strongly-bonded surface-adherent layer of bone-like hydroxyapatite (HAp) when immersed in simulated body fluid (SBF). Consequently, Ta and TaO coatings are promising for the surface-modification of Ti or stainless steel endodontic endosseous implants, being conducive to a reduction in the risk of developing post-operatory infection and/or peri-implantitis disease. That said, few studies have investigated the effect of Ta or TaO coatings on such phenomena as cell activation, adhesion, and proliferation.To that effect, Ta, and TaO films were deposited onto type 316L stainless steel (SS 316L) substrates by reactive DC magnetron sputtering, after which their biological response was evaluated following co-incubation with the murine macrophage-like cell line RAW 264.7. Cell morphology after adhesion was observed by SEM, whereas cell viability and proliferation were evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay. Lastly, inflammatory response was assessed by quantification of the cytokines interleukin-6 (IL-6) and interleukin-10 (IL-10).In terms of phase composition, Ta showed a mixture of the α-Ta and β-Ta phases, whereas TaO showed a nanocrystalline structure. Moreover, a decrease in average roughness (Ra) from 21nm to 7nm was observed between Ta and TaO, accompanied by a decrease in water contact angle (θW) from 106° to 83°.In vitro studies showed that cells exhibited significantly better adhesion to Ta, in comparison with both TaO and SS 316L. Furthermore, both Ta and TaO were shown to be non-cytotoxic, with Ta outperforming TaO in terms of relative cell viability, both at 24h and 48h. Lastly, both Ta and TaO showed vastly inferior IL-6 and IL-10 levels to those obtained for cells treated with bacterial lipopolysaccharides (LPS)—prompting the conclusion that the coatings do not in any way induce an inflammatory response from macrophage cells.

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.

Adhesion and fatigue resistance of Ta-doped MoS2 composite coatings deposited with pulsed-DC magnetron sputtering

MoS2–Ta composite coatings were deposited using the pulsed-DC magnetron sputtering technique. X-ray diffraction (XRD), scanning electron microscopy, energy dispersive spectroscopy, and atomic force microscopy were used to determine the structural properties of the MoS2–Ta composite coatings. The hardness values and adhesion and fatigue features of the coatings were determined using a microindentation hardness test and a scratch test, respectively. The scratch tests were evaluated using two modes: a standard mode (under a progressive load) and a multimode (sliding-fatigue with a constant sub-critical load within the same scratch track). Failure mechanisms of the scratch tracks were determined by examining the resulting micrographs. The MoS2–Ta coatings have a dense columnar microstructure. XRD patterns of the coatings revealed MoS2 (0 0 2), MoS2 (1 0 0), MoS2 (1 0 3), and α-Ta (1 1 0) reflections. The thickness, roughness, hardness, and elemental ratio values of the coatings were significantly affected by the target currents. The adhesion of the coatings dramatically increased with an increase in the thickness, hardness, and Ta/Mo ratio and with decreases in the roughness. The MoS2–Ta composite coatings with a high load-bearing capacity exhibited excellent fatigue resistance.

Corrosion behaviour and adhesion properties of sputtered tantalum coating on Ti6Al4V substrate

Abstract Tantalum coating on Ti6Al4V substrate was prepared by sputtering and the mechanical and corrosion performance of the tantalum coating was investigated. In addition to the normal structure of a sole tantalum film on the substrate, a buffer layer of titanium was first deposited on the substrate in a hope to improve the film adhesion. XRD examination shows that the Ta coatings exhibit a α/β dual-phase structure. Both the sole Ta coating and the Ta coating with a Ti buffer layer increased the apparent hardness of the surface of the Ti6Al4V substrate significantly. The compressive residual stress of the Ta/Ti of the order of 0.9 GPa is noticeably reduced comparing to 1.2 GPa of the sole Ta coating, resulting in an improved adhesion between the coating-substrate interface. The hydrophobicity of the Ti6Al4V surface after Ta coating also increased, which is believed to help in protein absorption and enhance lubrication. The corrosion current density of the Ta coated Ti6Al4V decreased from 2.0 × 10 − 8 to 3.4 × 10 − 9 A·cm − 2 (at high scan rates) comparing to the uncoated Ti6Al4V substrate. The mechanisms of the improved corrosion current density by the Ta coating and the enhancement of mechanical bonding of the Ta coating by a Ti buffer layer are further discussed.

Mechanically stable tantalum coating on a nano-roughened NiTi stent for enhanced radiopacity and biocompatibility

Mechanically stable tantalum (Ta) coatings were deposited onto nano-roughened and Ta-incorporated nickel-titanium (NiTi) alloy substrates to enhance their radiopacity and biocompatibility. A target-ion induced plasma sputtering process was used to induce highly uniform nanoscale roughness on the NiTi alloys, with Ta implantation. Characterization by field-emission scanning electron microscopy, X-ray diffraction, and transmission electron microscopy revealed that a dense alpha-phase Ta coating layer was tightly anchored to the NiTi substrate via the nano-roughened interface structures. The mechanical stability and stretchability of the Ta coating was examined using scratch and tensile tests, respectively. The adhesion strength and mechanical stability of the Ta coating on the nano-roughened NiTi surface showed remarkable improvement compared with the Ta coating on a flat NiTi surface. X-ray microscopic images showed that the radiopacity of a NiTi stent was enhanced by the Ta coating layer because of its high X-ray absorption coefficient and large thickness. In vitro cell adhesion and MTS assay revealed that the Ta coating was beneficial for endothelial cell attachment and proliferation. These results demonstrate that the Ta coating deposited onto nano-roughened NiTi substantially improved the mechanical stability, radiopacity, and biocompatibility of the NiTi stent.

Corrosion evaluation of alloys and MCrAlX coatings in molten carbonates for thermal solar applications

Stainless steels (SS) 310, 321, 347, Incoloy 800H (In800H), alumina-forming austenitic (AFA-OC6), Ni superalloy Inconel 625 (IN625), and MCrAlX (M: Ni, and/or Co; X: Y, Hf, Si, and/or Ta) coatings were corroded in molten carbonates in N2 and bone-dry CO2 atmospheres. Electrochemical tests in molten eutectics K2CO3–Na2CO3 and Na2CO3–K2CO3–Li2CO3 at temperatures higher than 600°C were evaluated using an open-circuit potential followed by a potentiodynamic polarization sweep to determine the corrosion rates. Because the best-performing alloys at 750°C were In800H followed by SS310, these two alloys were selected as the substrate material for the MCrAlX coatings. The coatings were able to mitigate corrosion in molten carbonates environments. The corrosion of substrates SS310 and In800H was reduced from ~2500µm/year to 34µm/year when coated with high-velocity oxyfuel (HVOF) NiCoCrAlHfSiY and pre-oxidized (air, 900°C, 24h, 0.5°C/min) before molten carbonate exposure at 700°C in bone-dry CO2 atmosphere. Metallographic characterization of the corroded surfaces showed that the formation of a uniform alumina scale during the pre-oxidation seems to protect the alloy from the molten carbonate attack.

Sputtered Tantalum Photonic Crystal Coatings for High-Temperature Energy Conversion Applications

Recent advances in photonic crystals have enabled high-efficiency thermophotovoltaic (TPV) energy conversion by allowing near-perfect spectral control. In this paper, photonic crystals fabricated in thick tantalum (Ta) coatings, sputtered onto a metallic substrate, were investigated as a potential replacement for photonic crystals fabricated in bulk refractory metal substrates in TPV applications. A 2-D photonic crystal was fabricated in a 30-μm thick Ta sputtered coating using standard semiconductor processes as a proof-of-concept for a selective emitter/solar absorber. The reflectance of the fabricated photonic crystal coating was characterized before and after 1 h anneals at 700, 900, and 1100 °C, and after a 24 h anneal at 900 °C. To protect its surface during the anneals, a thin conformal hafnia (HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) layer was deposited by atomic layer deposition on the photonic crystal. The photonic crystal showed high spectral selectivity in good agreement with numerical simulations and sustained the anneals with minimal structural degradation or change in its optical properties. This study presents a promising alternative to bulk substrates as a relatively low-cost and easily integrated platform for nanostructured devices in high-temperature energy conversion systems.

Thick sputtered tantalum coatings for high-temperature energy conversion applications

Thick sputtered tantalum (Ta) coatings on polished Inconel were investigated as a potential replacement for bulk refractory metal substrates used for high-temperature emitters and absorbers in thermophotovoltaic energy conversion applications. In these applications, high-temperature stability and high reflectance of the surface in the infrared wavelength range are critical in order to sustain operational temperatures and reduce losses due to waste heat. The reflectance of the coatings (8 and 30 μm) was characterized with a conformal protective hafnia layer as-deposited and after one hour anneals at 700, 900, and 1100 °C. To further understand the high-temperature performance of the coatings, the microstructural evolution was investigated as a function of annealing temperature. X-ray diffraction was used to analyze the texture and residual stress in the coatings at four reflections (220, 310, 222, and 321), as-deposited and after anneal. No significant changes in roughness, reflectance, or stress were observed. No delamination or cracking occurred, even after annealing the coatings at 1100 °C. Overall, the results of this study suggest that the thick Ta coatings are a promising alternative to bulk substrates and pave the way for a relatively low-cost and easily integrated platform for nanostructured devices in high-temperature energy conversion applications.

Plasma-Coating of Ti and Ta on Graphite Composite As Corrosion-Improved Bipolar Plate in PEM Electrolysis

In Proton Exchange Membrane (PEM) Electrolysis bipolar plates have to be more corrosion resistant than bipolar plates in PEM Fuel Cells. Several materials have been evaluated as cost-efficient material in PEM Electrolyzers. Since the electrochemical conditions in PEM Electrolyzers are quite harsh, cost-efficient materials like stainless steel or graphite composites are not stable. Coating the material with corrosion resistant material by magnetron sputtering is one possibility to enhance the stability. Gago et al.[1] have been coating stainless steel for example with Ti by vacuum plasma spraying. However, Ti is only useable if the oxidation potential is not too high, otherwise it will form an insulating TiO2 layer. Tantal has good corrosion protective characteristics and is not forming an insulating layer.[2] We developed a plasma process to deposit protective coatings on graphite composite bipolar plates. Therefore we used unbalanced magnetron sputtering of Ti and Ta. A new magnetron sputtering process was applied to keep the temperature of the graphite composites constant. Furthermore a combined plasma-process was used to enhance the stability of the deposited layer by activating the graphite composite. The Ti and Ta coatings were tested in a heated (T = 353 K) electrochemical cell amperometric at 2 V vs. RHE and by cyclic voltammetry in oxygen saturated 0.5 M H2SO4. We figured out the layer quality with the 4-Point Probe before and after each experiment. Furthermore we evaluated the film characteristics by microscope (SEM, light microscope), XRD and XPS. We could demonstrate that the coating is protecting the graphite composite as bipolar plate material in harsh electrochemical environment which was choosen close to real conditions in PEM Electrolyzers. Thereby it should be possible to lower the cost of bipolar plates in PEM electrolyzers substantial. [1] A. Gago, A. Ansar, N. Wagner, J. Arnold, K.A. Friedrich, Titanium coatings thermal spraying bipolar plates PEM electrolyzer, in: 64th Annu. Meet. Int. Soc. Electrochem., 2013. [2] O.E. Kongstein, N. Guillet, A. Ødegård, Rapport technique DEHT-DR-10/051, 2010.

Oxidation behavior and mechanical properties of laminated Hf–Ta coatings

This study explores the internal oxidation of laminated Hf–Ta coatings with a cyclically gradient chemical concentration distribution along the growth direction. The oxidation behavior was examined by annealing the coatings at 400–600°C in a 15ppm O2–N2 atmosphere for 30min. The variations in crystalline structure, nanohardness, chemical states, and chemical composition profiles in depth after various annealing conditions were investigated. The results indicate that all the Hf–Ta coatings maintain a laminated structure after annealing at 400–600°C. Internal oxidation conducts during 500 and 600°C annealing, but part of the outmost layers exhibits complex oxides after annealing at 600°C. The nanohardness of annealed Hf–Ta coatings related to the formation of HfO2, Hf6Ta2O17, and amorphous Ta-oxide were studied.