Titanium-tantalum Alloys Research Articles

SPH-FEM Analysis of Effect of Flow Impingement of Ultrasonic Honing Cavitation Microjet on Titanium-Tantalum Alloy Surface.

To investigate the machining effect of ultrasonic honing microjets on a titanium-tantalum alloy surface, a cavitation microjet flow impingement model was established using the smoothed particle hydrodynamics-finite element method (SPH-FEM) coupling method including the effects of wall elastic-plastic deformation, the ultrasonic field and the honing pressure field. Simulation analysis was conducted on a single impact with different initial speeds and a continuous impact at a constant initial speed. The results showed that the initial speed of the microjet needed to reach at least 580 to 610 m/s in order to obtain an obvious effect of the single impact. The single impact had almost no effect at low speeds. However, when the microjet continuously impacted the same position, obvious pits were produced via a cumulative effect. These pits were similar to that obtained by the single impact, and they had the maximum depth at the edge rather than the center. With the increase in the microjet's initial speed, the total number of shocks required to reach the same depth gradually decreases. When the number of impacts is large, with the increase in the number of impacts, the growth rate of the maximum pit depth gradually slows down, and even shows no growth or negative growth at some times. Using the continuous impacts of the microjet by prolonging the processing time can enhance titanium-tantalum alloy machining with ultrasonic honing for material removal.

Corrosion behavior of anodized Ti-Ta binary surface alloys in various physiological fluids for implant applications

In this study, corrosion-resistant surface-modified biometals were developed by coating titanium-tantalum alloy thin films onto titanium substrates, followed by anodization. These films were systematically investigated for their crystal structure, morphology, and microstructure. Electrochemical studies were carried out in 0.9% NaCl, PBS, and SBF. EIS data was evaluated using equivalent circuit models and a physical model is proposed to describe the corrosion process. The polarization resistance values suggest that the anodized Ti-Ta thin film alloy possesses favorable corrosion resistance properties, thereby indicating its potential for use in orthopedic applications.

Investigation on the Microstructure and Mechanical Properties of the Ti-Ta Alloy with Unmelted Ta Particles by Laser Powder Bed Fusion

Titanium-tantalum (Ti-Ta) alloy has excellent biomechanical properties with high strength and low Young's modulus, showing great application potential in the biomedical industry. In this study, Ti-Ta alloy samples were prepared by laser powder bed fusion (LPBF) technology with mixed pure 75 wt.% Ti and 25 wt.% Ta powders as the feedstock. The maximum relative density of Ti-Ta samples prepared by LPBF reached 99.9%. It is well-accepted that four nonequilibrium phases, namely, α', α″ and metastable β phase exist in Ti-Ta alloys. The structure of α', α″ and β are hexagonal close-packed (HCP), base-centered orthorhombic (BCO) and body-centered cubic (BCC), respectively. X-ray Diffraction (XRD) analysis showed that the α' phase transformed to the α″ phase with the increase of energy density. The lamellar α'/α″ phases and the α″ twins were generated in the prior β phase. The microstructure and mechanical properties of the Ti-Ta alloy were optimized with different LPBF processing parameters. The samples prepared by LPBF energy density of 381 J/mm3 had a favorable ultimate strength (UTS) of 1076 ± 2 MPa and yield strength of 795 ± 16 MPa. The samples prepared by LPBF energy density of 76 had excellent ductility, with an elongation of 31% at fracture.

Directional transport and coalescence behavior on Titanium-Tantalum alloy surface: Insights from experiment and molecular dynamics simulation

Friction and wear of artificial joints are severe problems. By designing a structure for directional transporting lubricant onto the Ti-Ta alloy surface, the friction or wear can be effectively reduced. Herein, molecular dynamics (MD) simulation and experiment were employed to study the directional transport and coalescence behavior of droplets on wedge-shape structure Ti-5Ta (wt%) alloy surface. Results show that water droplets can be continuously transported. Moreover, the experimental results of static and dynamic contact angle measurement show that the experiment agrees well with the MD simulation. Finally, the anti-gravity directional transport was achieved on a tilting Ti-5Ta (wt%) alloy surface. This work provides insights for reducing friction and extending service life of artificial joints in the medical field.

Strengthening mechanism of lamellar-structured Ti–Ta alloys prepared by powder metallurgy

Titanium-tantalum alloys with lamellar microstructure were fabricated by cold isostatic pressing under 400 MPa and pressure-free sintering at 1600 °C. By such a low-cost powder metallurgy method, the Ti–Ta alloy exhibited the tensile yield strength of 1124 MPa at room temperature, which was twice that of the cast Ti–Ta alloys. The microstructure and mechanical properties were characterized in detail to elucidate the deformation behavior and the strengthening mechanism of the Ti–Ta alloys prepared by powder metallurgy. With the increasing Ta content, the width of the α laths decreased, and that of the β laths increased, leading to the precipitation of the acicular α in the β laths. Correspondingly, the yield and ultimate strength increased, while the strain to failure decreased. Lamellar structure strengthening was determined to be the dominating mechanism for the high strength of the Ti–Ta alloys prepared by powder metallurgy. After quantitatively evaluating the contributions of laths, solute atoms, prior β grain boundaries, and dislocations, a model was established to illustrate the yield strength of the Ti–Ta alloys. The calculated values agreed well with the measured strength values of the Ti–Ta alloys, indicating that this model is effective in forecasting the strength of the dual-phase Ti alloys with lamellar structure.

Additive manufacturing of biomimetic Titanium-Tantalum lattices for biomedical implant applications

Although additively manufactured titanium-tantalum alloys can offer unique mechanical and biological advantages for implant applications, their use in conjunction with engineered lattice architectures is yet to be explored. In the present study, the promising gyroid, diamond and Schwarz primitive minimal surfaces are used for the design of 3D lattices for biomedical implants. The lattices are fabricated using laser powder-bed fusion and a blend of elemental titanium-tantalum powder. The processability, compressive mechanical properties and in vitro biological properties of the dense and lattice samples are assessed via non-destructive and destructive characterization methods. The topologies from the designed structures are retained through processing and the compressive tests results show that the strength-to-modulus ratios are comparable to the conventional Ti-6Al-4 V alloy. However, the higher ductility and absence of toxic elements make the Ti-25Ta lattices a more favourable option for a new generation of implants. Compared to conventional lattices, the designs presented here also show advantageous mechanical properties for use in bone implants with higher elastic admissible strains. The in vitro cell cultures confirm the high biocompatibility of the material and improved biological response of the interconnected lattices over dense material.

Finite element analysis on titanium-tantalum lattice structures fabricated using selective laser melting

In this study, Finite Element Analysis (FEA) is used to study the mechanical properties of titanium-tantalum (TiTa) alloy lattice structures fabricated using selective laser melting (SLM) in previous literature. Based on the actual measured dimension of the experiment samples, the geometry is reproduced and analyzed in ANSYS using two different approaches (beam model, full-3D model). The mechanical properties, such as elastic modulus and yield strength, are then predicted using the two ANSYS models and compared to the experiment results. It is found that both beam model and full-3D model can predict the elastic modulus of the fabricated TiTa parts with high accuracy. However, for yield strength, the predictions from beam model and full-3D model are around 50 % and 65 % in average lower than the experimental data respectively. Finally, in order to validate the design parameter, e.g. porosity levels, the mechanical properties of the lattice structures with porosity from 50 % to 90 % are studied using full-3D FEA model and the results are found to follow the Gibson-Ashby model.

The Effect of heat treatment on the fatigue properties of titanium-tantalum alloy

The Effect of heat treatment on the fatigue properties of titanium-tantalum alloy

Titanium-Tantalum Alloy Surface Modification by Hydroxyapatite Layer on TiO2 Nanotubes: Effect on Microbial Activity

Abstract One of the major health security challenges of the 21st century is the occurrence of microbial infections and bacterial complications that could affect 10 million people by 2050. On the biomaterial field, implant metallic currently replaces partial or total body parts and can fail to be integrated into the body due to infections. This study performs two combined surface modifications on Ti-30Ta alloy, in order to obtain an infection-resistance and osseointegration surface on metallic implants to be tested within bacterial biofilm. The Group 1 investigated surface modifications by the anodization process in the electrolyte glycerol + NH4F 0.25% at 30V- 9 hours and annealed in 530°C (5°C/min). The Group 2 underwent the same process as Group 1 and, additionally, the samples were immersed in 0.3 M CaCl2 and 0.5 M Na2HPO4 solutions for hydroxyapatite growth. The substrate was characterized using scanning electron microscopy (SEM), X-ray diffractometer (XRD) and dynamic contact angle. S. epidermidis bacterial adhesion and biofilm formation. The results indicated that the Group 1 shows a higher antimicrobial activity, hydrophilic behavior and potential to be used for metallic implant applications. The Group 2 with the hydroxyapatite film coating did not have an improvement in the antimicrobial response.

Laser powder bed fusion of titanium-tantalum alloys: Compositions and designs for biomedical applications

In this study, laser powder bed fusion (L-PBF), also known as selective laser melting (SLM), was used to fabricate samples of titanium-tantalum (TiTa) alloys with 0, 10, 30 and 50 wt% of tantalum using in-situ alloying. As-fabricated samples comprised of randomly-dispersed pure tantalum particles in a titanium-tantalum matrix. Porosity and unmelted tantalum particles of the samples were revealed using an optical microscope (OM). The microstructure of the alloys were determined by combination of field emission scanning electron microscopy (FE-SEM), electron back scatter diffraction (EBSD) and X-ray diffraction (XRD). The mechanical properties of the alloys were investigated with tensile and Vickers hardness tests. To ascertain the suitability of these alloys as biomaterials, Ti50Ta scaffolds with 60% porosity were characterized biologically. This study further shows that porous TiTa scaffolds fabricated using L-PBF are biocompatible with comparable biological results and manufacturability as Ti6Al4V and commercially pure titanium, based on the results obtained from cell culture with human osteosarcoma cell line SAOS-2.

Liquid metal dealloying of titanium-tantalum (Ti-Ta) alloy to fabricate ultrafine Ta ligament structures: A comparative study in molten copper (Cu) and Cu-based alloys

We report dealloying of Ti60Ta40 (wt.%) in molten copper, eutectic Cu28Ag72 alloy and Cu20Ag40Bi40 alloy for the fabrication of ultrafine Ta ligament structures across a 1-mm thick section. When dealloyed in molten Cu and Cu20Ag40Bi40, the melt temperature dictated the length scale of Ta ligaments, which decreased exponentially with decreasing temperature. Conversely, dealloying in molten eutectic Cu28Ag72 alloy led to complex Ta ligament structures due to the enhanced surface diffusivity of Ta by Ag. Ultrafine (<100 nm) Ta ligament structures were produced by dealloying in molten Cu20Ag40Bi40 at 650 °C due to both low melt temperature and low surface diffusivity of Ta.

A Method for the Production of Titanium-Tantalum Binary Alloys Using the Metalysis-FFC Process

Titanium-tantalum alloys have historically been difficult to produce using conventional techniques due to the large difference in melting point and poor interdiffusivity rates of the two elements, leading to large levels of segregation. In this work we have investigated using the Metalysis-FFC process to overcome this problem. The Metalysis-FFC process is an electrochemical process where metal oxides are reduced by acting as a cathode in an electrolytic cell combined typically with a graphite anode and molten calcium chloride electrolyte. Previous work has proven that the process works when applied to mixed oxides to produce alloys. The reduction process is performed in the solid state and so negates the problems associated with traditional melting practices such as segregation and evaporation losses. In this work we have been able to successfully produce a range of Ti-Ta alloy powders from pure titanium to pure tantalum in 10 wt% increments using the Metalysis-FFC process. Moreover, energy dispersive spectroscopy analysis of the powders suggests uniform distribution of titanium and tantalum within all compositional ranges, suggesting the Metalysis-FFC process has the potential to be a transformative manufacturing methodology for producing titanium-tantalum alloys.

Improvement on mechanical properties and corrosion resistance of titanium-tantalum alloys in-situ fabricated via selective laser melting

In this study, the role of tantalum (Ta) on the phase transformation, microstructure evolution, mechanical properties and corrosion resistance of titanium-tantalum (Ti–Ta) alloys in-situ fabricated via selective laser melting (SLM) was investigated. Ti–Ta mixed powders with different Ta ratios ranging from 0 to 25 wt % were prepared by ball milling for the SLM process. With the increase of Ta content, the SLM-processed Ti–Ta alloys exhibits the microstructure evolution from the lath α grain to acicular α' + primary cellular β grains, accompanying with the gradual suppression of martensite transformation. The β-stabilized effect of Ta promotes the formation of β (Ti, Ta) solid solution phase in the alloys. The rise of Ta addition in SLM-processed Ti–Ta alloys contributes to the improvement on the tensile strength from 641 to 1186 MPa and the microhardness from 257 to 353 HV, which results from a combined effect of grain refinement strengthening and the solid solution strengthening. The Young's modulus decreases from 115 to 89 GPa due to the increasing amount of β phase. Additionally, the corrosion resistance of the Ti–Ta alloys is enhanced with few pits on the surfaces due to the increasing amount of Ta2O5 identified through X-ray photoelectron spectroscopy. These findings provide the knowledge and boost the further understanding on the SLM-processed Ti–Ta alloys as promising candidates for biomedical application.

Selective laser melting of titanium alloy with 50 wt% tantalum: Effect of laser process parameters on part quality

Selective laser melting (SLM) is a powder bed fusion additive manufacturing (AM) technique that produces three-dimensional (3D) parts by fusing metallic powders with a high-energy laser. SLM involves numerous process parameters that may influence the properties of the final parts. Hence, establishing the effect of the SLM processing parameters is important for producing parts of high quality. In this study, titanium-tantalum alloy was fabricated by SLM using a customized powder blend to achieve in situ alloying. The influence of processing parameters on the microstructure and properties such as relative density, microhardness and surface roughness was investigated. The results show that fully dense titanium-tantalum parts can be obtained from SLM. With laser power of 360 W, scan speed of 400 mm/s, powder layer thickness of 0.05 mm and hatch spacing of 0.125 mm, the titanium-tantalum alloy produced by SLM has relative density of 99.85 ± 0.18%. Despite the variation in process parameters, titanium-tantalum shows laminar β grains in random directions in both xy and yz-plane from optical microscope (OM) analysis in all the parts produced. This observation is further confirmed using x-ray diffraction (XRD).

Novel adaptive finite element algorithms to predict bone ingrowth in additive manufactured porous implants

Bone loss caused by stress shielding of metallic implants is a concern, as it can potentially lead to long-term implant failure. Surface coating and reducing structural stiffness of implants are two ways to improve bone ingrowth and osteointegration. Additive manufacturing, through selective laser sintering (SLS) or electron beam melting (EBM) of metallic alloys, can produce porous implants with bone ingrowth regions that enhance osteointegration and improve clinical outcomes. Histology of porous Ti6Al4V plugs of two pore sizes with and without electrochemically deposited hydroxyapatite coating, implanted in ovine condyles, showed that bone formation did not penetrate deep into the porous structure, whilst significantly increased bone growth along coated pore surfaces (osteointegration) was observed. Finite Element simulations, combining new algorithms to model bone ingrowth and the effect of surface modification on osteoconduction, were verified with the histology results. The results showed stress shielding of porous implants made from conventional titanium alloy due to material stiffness and implant geometry, limiting ingrowth and osteointegration. Simulations for reduced implant material stiffness predicted increased bone ingrowth. For low modulus Titanium-tantalum alloy (Ti-70%Ta), reduced stress shielding and enhanced bone ingrowth into the porous implant was found, leading to improved mechanical interlock. Algorithms predicted osteoconductive coating to promote both osteointegration and bone ingrowth into the inner pores when they were coated. These new Finite Element algorithms show that using implant materials with lower elastic modulus, osteoconductive coatings or improved implant design could lead to increased bone remodelling that optimises tissue regeneration, fulfilling the potential of enhanced porosity and complex implant designs made possible by additive layer manufacturing techniques.

The influence of laser parameters, scanning strategies and material on the fatigue strength of a stochastic porous structure

Additive manufactured (AM) porous materials behave quantitatively and qualitatively differently in fatigue than bulk materials, and the relationships normally used for the fatigue design of continuous bulk materials are not applicable to AM porous materials particularly for low stiffness applications.This study investigated how the manufacturing methods and the material used during powder bed fusion affects the compressive strength and high cycle fatigue strength of a stochastic porous material for a given stiffness. Specimens were manufactured using varying laser parameters, 3 scan strategies (Contour, Points, Pulsing) and 4 materials. The materials investigated were two titanium alloys: commercially pure grade 2 (CP-Ti) and Ti6Al4V ELI, commercially pure tantalum (Ta) and a titanium-tantalum alloy (Ti-30Ta).The trends observed during fatigue testing for monolithic metals and statically for solid and porous AM materials were not always indicative of the high cycle fatigue behaviour of porous AM materials. Unlike their solid counterparts, porous tantalum and the titanium-tantalum alloy had the greatest fatigue strength for a given stiffness, 8% greater than CP-Ti and 19% greater than Ti6Al4V ELI. Optimisation of the laser parameters and scan strategies was found to also increase the fatigue strength for a given stiffness of porous AM materials by 7–8%.

Titanium-Tantalum Alloy Powder Produced by the Plasma Rotating Electrode Process (PREP)

Microstructure of Ti-28Ta powders produced by plasma rotating electrode process (PREP) was investigated by using scanning electron microscopy (SEM), optical microscopy (OM), and transmission electronic microscopy (TEM). Phase constituent of the PREP Ti-28Ta powders was analyzed by X-ray diffraction (XRD). It was found that microstructure of the PREP Ti-28Ta powders was dependent on the powder particle sizes. Predominant martensitic α”, some metastable β and trace athermal ω phases were observed in the powders with the small diameter. While, phase constituent of the PREP Ti-28Ta powders with the large particle size was predominant metastable β, some martensitic α” and trace athermal ω. With the reduction of the powder particle size, the amount of martensitic α” increased and the metastable β decreased. The martensitic α” was formed preferentially on the metastable β grain boundaries of the PREP Ti-28Ta powders. The increase of α” phase and decrease of β with reduction of the powder particle size is attributed to the increase of the volume of the grain boundaries due to the grain refinement.

Microstructural, mechanical and biological characterizations of the promising titanium-tantalum alloy for biomedical applications

In this study, the microstructural, mechanical and biological characterizations of the Ti-25Ta (wt.%) alloy were investigated by means of optical microscope, X-ray diffraction, electron microscope, microhardness test, contact angle goniometer and in vitro cytotoxicity assay. As the alloy underwent heat-treatment at temperatures between 700 °C and 1000 °C for 30 min, its microstructure was a mixture of β phase and needle-like α′′ martensite phase. The analytical results indicated that the volume fraction of the needle-like α′′ martensite phase decreased with increasing heat-treatment temperature. The β transus temperature of the investigated Ti-25Ta alloy was below 700 °C. Moreover, the alloy heat-treated at 900 °C exhibited the maximum hardness Hv 743 ± 12.93. For wettability evaluation, all investigated samples possessed surface hydrophilicity. The cytotoxicity assay results also demonstrated that the heat-treated Ti-25Ta samples have well cell proliferation and adhesion behaviors. Therefore, these results and features could be used to further understand the relationship between the high temperature microstructure, mechanical behavior and in vivo biocompatibility of the Ti-25Ta alloy, and develop as a potential biomedical alloy.

Selective laser melting of lattice structures: A statistical approach to manufacturability and mechanical behavior

Abstract This paper investigates the effect of processing parameters on the dimensional accuracy and mechanical properties of cellular lattice structures fabricated by additive manufacturing, also known as 3D printing. The samples are fabricated by selective laser melting (SLM) using novel titanium-tantalum alloy. The titanium-tantalum alloy has the potential to replace commercially pure titanium and Ti6Al4V as biomedical material. In this study, the unit cell used is specially designed to carry out the analysis using regression method and analysis of variance (ANOVA). Due to the effect of the SLM process parameters, the elastic constant of the cellular lattice structures ranged from 1.36 ± 0.11 to 6.82 ± 0.15 GPa using the same unit cell design. The elastic constant range, while showing the versatility of titanium-tantalum as biomedical material, is rather wide despite using the same lattice structure designed. This shows that there is a need to carefully control the processing parameters during the lattice structures fabrication so as to obtain the desired mechanical properties. Based on the statistical analysis, it is found that the dimensional accuracy and mechanical properties such as elastic constant and yield strength of the cellular lattice structures are most sensitive to laser power as compared to other parameters such as laser scanning speed and powder layer thickness.

Effects of bioceramic particles in dielectric of powder-mixed electrical discharge machining on machining and surface characteristics of titanium alloys

In powder-mixed electrical discharge machining (PMEDM), a suspension of powder particles is added to the dielectric to achieve a high surface quality and to improve the material removal rate (MRR). However, for biomedical applications, the machined surface must be nontoxic and also contain bioactive species; these constraints limit the choice of powder material. This study focuses on machining orthopedic-implant materials based on titanium and titanium–tantalum alloys using bioactive hydroxyapatite (HA)-powder suspension as the dielectric. The influence of the powder particles and the work-piece composition on the machining performance was investigated. Employing a suspension dielectric with 5g/L HA caused a smoother surface (Ra 2.1μm) with a thinner recast layer (∼9μm) as compared to using water to machine titanium which has surface roughness of Ra 2.4μm with a recast layer close to 10μm. In addition, the MRR of titanium machined in the HA-powder-suspension dielectric (6.4×10−4gmin−1) was greatly lower than that in water (28.6×10−4gmin−1). However, increasing the HA concentration led to a gradual increase in the MRR, electrode wear rate (EWR), surface roughness, and recast-layer thickness. The MRR, EWR, and the surface roughness of titanium and titanium–tantalum alloys under PMEDM exhibited an inverse relation with respect to the melting temperature and thermal conductivity of the alloy. Furthermore, calcium and phosphorus were incorporated into the recast layer, and their amounts decreased when the discharge current was increased.