Ta Implants Research Articles

DynaCT-Guided Anatomical Rotation of the SAPIEN XT Valve during Transapical Aortic Valve Implantation: Proof of Concept

Transcatheter aortic valve implantation (T-AVI) by using the Edwards SAPIEN (Edwards Lifesciences LLC, Irvine, California, United States) prosthesis is currently being performed by the implantation of valved stent into the aortic annulus without respecting the native commissural (rotational) orientation. Anatomical orientation may, however, be beneficial regarding optimal physiological valve performance, optimal coronary flow, and avoidance of the fully covered commissural stent part in front of the coronary ostia. With the recently introduced SAPIEN XT, transcatheter valve identification of the commissures during fluoroscopy is feasible. The aim of this study was to evaluate the concept of Dynamic-CT (DynaCT)-guided anatomical rotation of the SAPIEN XT valve during transapical-AVI (TA-AVI). Intraoperatively, an automatically segmented DynaCT was performed using the Siemens Syngo Aortic ValveGuide (Siemens AG, Forchheim, Germany) software prototype. Commissures of SAPIEN XT could be identified with a high-quality fluoroscopic system. Before standard TA implantation, one radiopaque stent commissure of the crimped SAPIEN XT prosthesis was aligned with the native aortic valve commissure visualized by DynaCT. Resulting rotational orientation of the valve after implantation was assessed by transesophageal echocardiography. Feasibility of anatomical rotation was evaluated in 10 patients scheduled for TA-AVI by an interdisciplinary heart team. Mean logistic EuroSCOREs and Society of Thoracic Surgeons scores were 23.7 ± 4.9% and 8.6 ± 2.1%, mean aortic gradient improved from 46.0 ± 21.9 to 9.6 ± 3.1 mm Hg, and there was no death within 30 days. All valves were implanted successfully with none or trivial paravalvular regurgitation in seven patients, mild (1 + ) in two patients, and moderate (2 + ) in one patient. An optimal anatomical position could be achieved in six patients, minor rotational deviation (< 10 degrees) in three patients, and moderate deviation (10 to 20 degrees) in one patient only. DynaCT-guided anatomical rotation of the SAPIEN XT valve is feasible during TA-AVI, avoiding implantation of the fully covered commissural posts in front of the coronary ostia. This might reduce the risk of coronary obstruction. In addition, the technique provides the potential benefit of physiological valve position and performance.

Hemocompatibility investigation of the NiTi alloy implanted with tantalum

A composite TiO(2)/Ta(2)O(5) nano-film has been formed on the NiTi shape memory alloy by Ta implantation. The wettability, protein adsorption, platelets adhesion and hemolysis tests are conducted to evaluate the hemocompatibility. The contact angle measurements showed that the surface of the NiTi alloy kept hydrophilic before and after Ta implantation, although the water contact angle increased with the increasing of implantation current. Both of the surface energy and the interfacial tension decreased after Ta implantation. The protein adsorption behavior was investigated by (125)I isotope labeling. The fibrinogen adsorption was enhanced by a high surface roughness or a large interfacial tension, while the albumin adsorption was insensitive to the surface modification. Platelet adhesion and activation were weakened and the hemolysis rate was reduced at least 46% after Ta implantation due to the decreased surface energy and improved corrosion resistance ability, respectively.

Effective inhibition of nickel release by tantalum-implanted TiNi alloy and its cyto-compatibility evaluation in vitro

Titanium–nickel (TiNi) shape memory alloy is modified with tantalum (Ta) plasma immersion ion implantation (PIII). Scanning electron microscope (SEM), atomic force microscopy (AFM), inductively coupled plasma mass spectrometry (ICP-MS), methyl-thiazol-tetrazolium (MTT), and cell culture are adopted to evaluate the surface morphology, roughness, Ni release, in vitro cytotoxicity, and cell behavior of TiNi and Ta-implanted TiNi (Ta–TiNi) alloys. Results showed that the surface became rougher and was covered by ordered and uniform grains after Ta implantation. Ni release was averagely inhibited by Ta–TiNi to up to 60% of that in unmodified TiNi alloy within 30 days. MTT assays demonstrated that Ta–TiNi sample allowed greater degree of cell proliferation for both smooth muscle cell and osteoblasts, indicating excellent protection and cyto-compatibility. A negative correlation was observed between Ni release and cell proliferation. Analysis of the cell morphology revealed healthy cells extending on the alloy surface, which indicated that TiNi alloy had good cyto-compatibility despite the initial Ni dissolution, but the implanted Ta would endow traditional TiNi alloy much lower Ni release, improved cyto-compatibility and other potential merits.

Effect of Ta 2O 5/TiO 2 thin film on mechanical properties, corrosion and cell behavior of the NiTi alloy implanted with tantalum

The NiTi shape memory alloy has been modified by plasma immersion ion implantation (PIII) with Ta at different incident currents to improve the corrosion resistance and other surface and biological properties. The surface topography, chemical components, mechanical properties, corrosion resistance and cytocompatibility are investigated. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) revealed that Ta implantation led to the formation of compact Ta 2O 5/TiO 2 nano-film on the surface of the NiTi alloy. The results of Auger electron spectroscopy (AES) showed that Ni was suppressed in the superficial surface layer of the modified NiTi alloy samples. The results of nano-indentation illustrated a lower level of nano-hardness and Young's modulus after Ta implantation. Potentiodynamic anodic polarization curves showed that the corrosion resistance of NiTi alloys was enhanced by Ta implantation. Cells reached confluency and a double-layered structure had developed after cultured for three days. The NiTi alloy modified by a moderate incident current possesses a uniform and slippery surface morphology and the largest surface roughness, leading to the best corrosion resistance and the highest cell proliferation rate, respectively.

Precursor system for bio-integration ceramics and deposition onto tantala scaffold bone interface surfaces

Modern orthopaedic bone implants and joint replacements employ hydroxyapatite (HA) coatings to stimulate bone growth. Metal Ti and Ta implants are also moving to rough and porous contact surfaces to enhance integration and long term stability. The current methods of applying HA to implants have problems with adhesion, and there is no MOCVD precursor system reported in the literature. We have investigated a methanolic MOCVD precursor solution of calcium-dibenzoylmethane and trimethylphosphate in combination with a unique pulsed-pressure MOCVD (PP-MOCVD) process to apply a thin adherent film of HA onto a tantalum implant scaffold material. This technique will allow use of multiple precursors and is not limited by precursor volatility. Calcium and phosphorous deposits were identified at depths of up to 4 mm on the tantalum scaffold sample by EDS analysis.

Improved Electromigration Lifetime for Copper Interconnects using Tantalum Implant

ABSTRACTIn this study, a novel method is explored for improving the electromigration lifetime of Cu wires, using Ta implantation into Cu. For high implant doses (2E15 cm−2), the electromigration lifetime is improved by over 5X using this method. An increase in lifetime is achieved, even for an average surface concentration of Ta on the order of 0.1 atm%. We propose that the improvement in electromigration lifetime is due to the reduction of defects at the SiN/Cu interface due to the presence of Ta. The line-to-line leakage at high voltages (&gt; 5V) increases with the Ta implant, with higher leakage at higher Ta concentrations, so the Ta dose must be limited to avoid excessive leakage.

Tribological properties changes of H13 steel induced by MEVVA Ta ion implantation

The tribological properties of Ta-implanted H13 steel was studied using a metal vapor vacuum arc (MEVVA) ion source. The doses of Ta and C ions implanted on H13 steel were 5×1017 and 2×1017cm−2, respectively. The extraction voltages were 48kV for Ta implantation and 30kV for C implantation. Rutherford backscattering spectrum (RBS) was used to measure the surface composition of the samples implanted. The observation of phase induced by Ta, C implantation was carried out by grazing-angle X-ray diffraction (GXRD). The wear test of the implanted surface revealed that Ta+C dual implantation reduced the wear of the implanted steel by nearly a factor of 2. This wear mechanism of the Ta-implanted steel was compared with that of Ti implantation.

Osteointegration of biomimetic apatite coating applied onto dense and porous metal implants in femurs of goats.

Biomimetic calcium phosphate (Ca-P) coatings were applied onto dense titanium alloy (Ti6Al4V) and porous tantalum (Ta) cylinders by immersion into simulated body fluid at 37 degrees C and then at 50 degrees C for 24 h. As a result, a homogeneous bone-like carbonated apatitic (BCA) coating, 30 microm thick was deposited on the entire surface of the dense and porous implants. Noncoated and BCA-coated implants were press-fit implanted in the femoral diaphysis of 14 adult female goats. Bone contact was measured after implantation for 6, 12, and 24 weeks, and investigated by histology and backscattered electron microscopy (BSEM). After 6 weeks, bone contact of the BCA-coated Ti6Al4V implants was about 50%. After 12 and 24 weeks, bone contact was lower in comparison with the 6-week implantations at, respectively 24 and 39%. Regarding the BCA-coated porous Ta implants, bone contacts were 17, 30, and 18% after 6, 12, and 24 weeks, respectively. However, bone contact was always found significantly higher for BCA-coated dense Ti6Al4V and porous Ta cylinders than the corresponding noncoated implants. The results of this study show that the BCA coating enhances the bone integration as compared to the noncoated implants.

Etching of spin-valve capping layers for sensor stabilization applications

Certain magnetic recording head designs require a controlled etching of the tantalum (Ta) capping layer of the giant magnetoresistive (GMR) read sensor, in order to establish electrical and/or magnetic coupling between the active layer of the sensor and a subsequently deposited layer. This is useful in schemes such as, but not limited to, lead-overlay and exchange stabilization of the sensor free layer. This paper discusses ion beam etching and reactive ion etching of the Ta sensor capping layer. Advantages and limitations of each approach are discussed. Limitations of physical etching due to issues such as Ta implantation in the NiFe active layer of the spin valve, shadowing, and poor selectivity are presented. A reactive ion etching approach that exhibits excellent selectivity between Ta and NiFe or CoFe is presented. The properties of exchange tab material deposited after using this etching process is shown.

Microchemical and microstructural changes of Co cemented WC induced by ion implantation

Changes in the microchemistry and microstructure of cobalt cemented tungsten carbide (WC–Co) hard alloy which were implanted with energetic Ta ions, with and without an additional C ion beam, have been investigated. Ion implantation was carried out at room temperature using a metal vapor vacuum arc source ion implanter. The extraction voltage and average current density of the ion beam was 45 kV and 50 μA/cm 2, respectively. The concentration depth profiles and microstructure of implanted the WC–Co alloy were analyzed by Rutherford backscattering spectroscopy, Auger electron spectroscopy, and glancing angle X-ray diffraction, respectively. The results showed that as compared with the control, there were no significant microstructural changes in the tungsten carbide phase of implanted WC–Co alloy substrate; both Ta implantation and Ta+C dual implantation induced a transformation from a metastable cubic form to a stable hcp form of cobalt binder phase.

Some features of the ion-beam mixing during simultaneous ion implantation and metal deposition

Experimental results on the ion implantation of Ta and Cu ions into an Al substrate, accompanied by the deposition of these ions in the form of a surface coating are reported. The coatings composed of the implant elements exhibit a complicated structure and lead to an increase in the microhardness, adhesion properties, and corrosion resistance of the substrate. An analysis of data on the energy distribution of secondary ions shows that the surface layer of ion-implanted substrates contains intermetallic phases.

Macro-particle free metal plasma immersion ion implantation and/or deposition in a multifunctional configuration

For high-dose metal ion implantation, the use of plasma immersion offers the high-rate advantage, but the simultaneous formation of a surface film along with the sub-surface implanted layer is sometimes a detriment. In this work, we describe a metal plasma immersion approach in which pure and macro-particle free implantation (metal and/or gas ions), pure deposition without ion implantation, or dynamic metal ion beam assisted deposition and gaseous plasma immersion ion implantation (DIBAD metal and gas plasma immersion) can be obtained. We have demonstrated the technique by carrying out Ti and Ta implantation at approximately 80 keV (Ti) and 120 keV (Ta) and doses on the order of 1×10 17 ions/cm 2. In our experiments, the Ta and Ti plasma immersion process can be tuned to give rise to implantation solely with no concomitant surface film formation. The atomic fraction of the applied dose that deposits as a film vs. the part that is energetically implanted during the DIBAD of metal and gas plasma immersion can be precisely controlled. This is a valuable method to fabricate advanced materials.

A Surface Charge Model of Corrosion Pit Initiation and of Protection by Surface Alloying

The isoelectric point of the oxide‐covered aluminum surface is an important parameter in the pitting behavior of aluminum and of aluminum binary surface alloys. Contact angle measurements show that ion implantation of Ta into Al modifies the isoelectric point of the resulting oxide film to a value which is intermediate between that of and . The critical pitting potential is shown to be a function of the flatband potential of the oxide‐covered aluminum surface. For a series of alloys where the matrix metal (and host oxide) is held fixed, the flatband potential is a function of the isoelectric point of the oxide film on the alloy surface, which in turn is a function of the isoelectric point of the oxide of the alloying element. Thus, the critical pitting potential of a binary surface alloy is related to the isoelectric point of the oxide of the alloying element in the binary alloy. Surface alloying affects the pitting potential by (i) modifying the isoelectric point of the surface so as to change the surface charge, (ii) affecting the heat of adsorption of the chloride ion, and (iii) changing the concentration of oxygen vacancies in the oxide film. © 1999 The Electrochemical Society. All rights reserved.

Ion implantation technique as research tool for improving oxidation behaviour of tial based intermetallic alloys

The effect of various elements added by ion implantation on the isothermal (up to 150 h) and cyclic (up to 1500 h) oxidation behaviour of γ-TiAl based intermetal lic alloys at 800 and 900°C in air has been studied. At 800°C ion implantation of Si, Nb, Ta, W, and Al showed a large beneficial effect on the oxidation behaviour of Ti–48Al–2Cr. A minor effect was found for Ti, Mo, Y, Mn, Pt, Rh, and Cr. More important was the oxidation of specimens implanted with Si or Nb, which revealed similar results to those for the intermetallic materials alloyed with these elements, i.e. Ti–47Al–2Cr–0·2Si and Ti–48Al–2Cr–2Nb. From this point of view it was concluded that the ion implantation technique can be employed as a ‘screening’ test for evaluating the effect of possible alloying additions. As a followup this technique was used as a research tool to study the effect of Nb, Pt, Rh, Si, Ta, and W on the oxidation behaviour of two types of Nb bearing TiAl based intermetallic alloys, i.e. Ti–48Al–2Cr–2Nb and Ti–48Al–2Mn–2Nb, at 900°C in air. In this case, no significant effect of the implanted elements on the isothermal and cyclic oxidation behaviour was found.

Modification of isothermal and cyclic oxidation behaviour of Ti–48Al–2Cr by ion implantation

The effect of various elements added by ion implantation on the isothermal (up to 150 h) and cyclic (up to 1500 h) oxidation behaviour of γ-TlAl based intermetallics at 800°C in air is discussed. Ion implantation of Si, Nb, Ta, vv: and Al showed a large beneficial effect on the isothermal oxidation behaviour of Ti–48AI–2Cr. Similar results for these implanted elements were found during the initial period of cyclic oxidation experiments. For longer exposure times under cyclic oxidation conditions the corrosion scale formed on the Al and Si implanted specimens was especially prone to spallation. A minor positive effect was found for Ti, Mo, 1: Mn, and Cr. Oxidation of the specimens implanted with Si or Nb revealed similar results to those for the intermetallics alloyed with these elements. Furthermore, it is concluded that care should be taken when studying the cyclic corrosion damage of implanted specimens by gravimetric methods alone. Additional techniques are strongly recommended and often necessary to obtain a full understanding of the exact degradation mechanism.

Corrosion and mechanical behavior of ion implanted bearing steels for improved fretting behavior

Ion implantation of AISI 52100 and 1070 steels was conducted in order to improve the corrosion, wear and ultimately the fretting behavior of the steels. Implantations consisted of 1 × 10 17 Ta + cm -2 , 3 × 10 17 Ti + cm -2 + 1.5 × 10 17 C + cm -2 , and 3.1 × 10 17 Ti + cm -2 + 1.55 × 10 17 N + 2 cm -2 . All implantations were successful in improving the corrosion resistance. On average, the peak anodic current was reduced by over 300 mV, the passivation potential was reduced, and the pitting potential was increased by over 1000 mV in 0.01 M NaCl. Ti + C and Ti + N implantations increased the load-carrying capacity in lubricated scuffing tests by 60% and 40% respectively. Ta produced no improvement in scuffing resistance. Ti + N implantation increased the hardness by 25% over the unimplanted steel and both Ti + C and Ta implantation reduced the surface hardness. Fretting wear was reduced only slightly in the Ta implanted sample and increased in both the Ti + C and Ti + N implanted samples with the latter showing 4–5 times the weight loss as the unimplanted sample. The correlation between fretting and hardness supports a mechanism in which the hard surface layer breaks into fine particles which act as an abrasive under the intense load of the balls.

Tribological properties of ion-implanted high-chromium steel

Abstract Changes in the hardness, friction coefficient, and behavior of the element and phase compositions of ion-implanted high-Cr stamp steel X12M have been investigated. The optimization of the implanted ion (Ti, Ta, W, C or Nb) and irradiation dose (10 16 -10 17 ion cm -2 has been conducted. The irradiation by Ti, C and Nb ions gave good results in changing the surface mechanical properties during the implantation of Ti, Ta W, C and Nb ions ( E = 18 keV, D = 7 × 10 15 ion cm -2 ). The friction coefficient decreased by 1.6, 4 and 2 times respectively. The implantation by Nb ions ( E = 18 keV, D = 10 16 -10 17 ion cm -2 ) led to an increase in microhardness by 1.6 times and to a decrease in friction coefficient by 5 times at an irradiation dose of 7 × 10 16 ion cm -2 . A change in the Cr 7 C 3 phase volume fraction was the main cause of the changes in the microhardness and friction coefficient.

Tantalum Ion Implantation into Cu-12Nb for Electromagnetic Railgun Technology

ABSTRACTAnalysis of fired rails from electromagnetic railgun indicates gross surface melting near the breach end of the rails. This effect is most likely caused by joule heating and arc erosion. To improve the mechanical behavior of the rail material, alloys of copper, such as Cu-0.6 Nb, has been used in the past with moderate success. More recently another alloy of copper, Cu-18 Nb, has become available. Preliminary metallurgical research in the thermomechanical properties of this latter alloy indicates it could be a candidate for application in EM gun systems. In this effort we have attempted to study the influence of ion implantation on the thermomechanical properties of Cu-12Nb alloy. In a series of experiments, Ta ions have been implanted at an energy range of 100–180 KeV and a dose of 5 × 1016 cm-2. Several analytical techniques such as Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), arc erosion, and microhardness measurements have been done. It has been shown that although there is an improvement in the microhardness of the implanted materials, the ion implantation saturation dose cannot exceed 5 × 1016 cm-2. Furthermore, the RBS data indicate that the implanted Ta resides mostly at a depth of about 200–300 Å from the surface. Results from the SEM analysis of unimplanted Cu-12Nb indicate the Nb has an acicular morphology and is randomly distributed. Results from microhardness measurements of the implanted materials indicate that implantation enhances the microhardness. In another experiment, such as implantation of Ta in an already TiN coated surface, we observed a similar increase in the microhardness value. We speculate that the microhardness improvement of Cu-18Nb or the Ta implanted TiN surface is due to induce compressional stresses near the lenticular (filament) Nb fibers in the Cu-18Nb composite.

Surface Modification of Electromagnetic Railgun Components

ABSTRACTCopper and aluminum used for rail and armature materials in electromagnetic railgun systems undergo severe degradation during the EM gun operation. The extent of this degradation is especially severe in guns operated at high energy levels or designed for repeated firings. In an effort to improve surface properties of the copper rail, armature, and sabot materials, the technique of metal ion implantation using a vacuum arc ion source has been employed. Preliminary tests have been conducted to identify the best implant species to improve spark erosion resistance, scratch resistance and hardness. The implanted species included Al, Ti, Cr, Ni, Ta, Ag, and W. The implantation energy range and dose varied between 100–180 KeV and 0.4 to 2 × 1017 cm-2, respectively . Several analytical techniques were also used to assess the effect of implanted species. These included Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Microhardness Measurements, Spark Erosion and Scratch Testing. It has been tentatively concluded that Ta and Ni implantation of the copper rail substantially improve wear and inhibit arc erosion. There is also sufficient evidence to indicate that implantation of the aluminum armature with Cr and Ta, involving two stages of implantation, will also improve its mechanical and wear properties.

Lattice location and hardness of Ta-implanted Ni3Al

Implantation of Ta into single crystal Ni3Al was conducted to determine the degree of surface hardening in monolithic alloys in relation to its lattice location. Ta was implanted at 400 keV to doses of 0.07, 0.36, and 2.52 × 1016 cm−2 along the [100] axis of a [100] crystal of Ni3Al at room temperature. Composition versus depth profiles were determined by RBS, and lattice location of Ta was determined by channeling angular yield scans about the [100] axis. The hardness of the surface was measured by ultra-low load indentation. Results show that implantation softens the surface and that the Ta is randomly distributed between Ni and Al sites. Annealing at 1000 °C/1 h significantly reduces the damage and causes preferential occupation of Al sites by Ta, resulting in a slight increase in surface hardness. Further annealing at 1200 °C/0.25 h increases the surface hardness substantially and increases occupation of Al lattice sites to roughly 84%. Results are consistent with a model in which the as-implanted surface is softened by disordering, and subsequent diffusion of Ta to Al sites during thermal treatment causes hardening of the surface.