Ti-29Nb-13Ta-4.6Zr Research Articles

Synthesis and Characterization of Hydroxyapatite/TiO2 Coatings on the β-Type Titanium Alloys with Different Sintering Parameters using Sol-Gel Method

In this study, hydroxyapatite (HA) based composite films were successfully syntheses on the β-type Ti29Nb13Ta4.6Zr (TNTZ). The solutionized TNTZ substrates coated with HA and HA/Titania (TiO2) bioactive composite coatings by sol-gel method under various sintering parameters related to sintering temperatures and heating ramp rates. Microstructural observations of the coatings revealed that apatite was formed on the substrates. The hardness values of the coatings increase with increasing both the sintering temperature and the TiO2 concentration in the coatings layer. However, it was found that the heating ramp rate of the sintering was not affecting the hardness values so much. Also, the hardness values of the HA/TiO2 composite coatings at all sintering temperatures were higher than only HA coated TNTZ samples due to the existence TiO2 phases in the HA matrix. Results indicating that the doping of HA with TiO2, improve the physical consistency between the coating layer and the substrates and provide a better inter-particle bonding due to the existence TiO2 phases in the HA.

Fully Depleted Ti-Nb-Ta-Zr-O Nanotubes: Interfacial Charge Dynamics and Solar Hydrogen Production.

Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO2 photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO2, with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge-transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO2 originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.

Biomedical porous Ti-16Nb-10Zr-(0–15)Ta alloys

Abstract To improve the properties of compact Ti alloys for biomedical applications, porous Ti-16Nb-10Zr-(0–15)Ta (wt.%) alloys were produced by the space-holding method using an ammonium hydrogen carbonate space holder. The pore size distribution, porosity ratio and mechanical properties of the obtained porous alloys were investigated. Also, the effect of Ta addition on the microstructure and mechanical properties was investigated. It has been determined that the sintered porous Ti–Nb–Zr–Ta alloys have suitable mechanical properties (elastic modulus: 36.32–38 GPa, transverse rupture strength: 154–281 MPa) for hard tissue implants.

Effects of shot-peening and atmospheric-pressure plasma on aesthetic improvement of Ti–Nb–Ta–Zr alloy for dental applications

Ti and Ti alloys are widely used for biomedical applications such as artificial joints and dental devices because of their good mechanical properties and biochemical compatibility. However, dental devices made of Ti and Ti alloys do not have the same color as teeth, so they are inferior to ceramics and polymers in terms of aesthetic properties. In a previous study, Ti–29Nb–13Ta–4.6Zr was coated with a white Ti oxide layer by heat treatment to improve its aesthetic properties. Shot-peening is a severe plastic deformation process and can introduce a large shear strain on the peened surface. In this study, the effects of shot-peening and atmospheric-pressure plasma on Ti–29Nb–13Ta–4.6Zr were investigated to form a white layer on the surface for dental applications.

In-situ formation of textured TiN coatings on biomedical titanium alloy by laser irradiation.

The Ti-35Nb-7Zr-5Ta (TNZT) alloy has received much research attention among the biomedical titanium alloys for its low Young's modulus and outstanding biocompatibility. This paper provided an innovative technique for improving the wear and corrosion resistance of the TNZT alloy, by developing in-situ formed TiN coatings on the surface of the TNZT alloy through laser irradiation. The new technique combines the advantages of laser surface texturing and laser gas alloying. The experimental results showed that the phase compositions of the textured TNZT samples were β-Ti, martensitic α'' phase and TiN after laser texturing in N2. The diameter of the surface dimples increased, when the width of laser pulse increased from 0.3ms to 0.7ms, and the depth decreased accordingly. In comparison to the samples without treatment, both the wear rate and the frictional coefficient of the TNZT samples with textured TiN coatings decreased significantly. The surface dimples served as micro-hydrodynamic bearing, which were able to keep liquid inside. As a result, the sample with a width of pulse of 0.3ms treated in N2 exhibited the lowest wear rate of 0.025 × 10-2m3/Nm, while the value of the sample without treatment was 0.351 × 10-2m3/Nm. The TiN contained surface coatings also exhibited higher electrochemical impedance, higher corrosion potential and lower corrosion current density.

Research: Design and Analysis of a Low-Stiffness Porous Hip Stem.

Two major problems are associated with total hip replacement: 1) stress shielding and 2) the adverse tissue reaction to certain elements of the implant material. In this regard, a porous implant provides lower stiffness and vacancies for bone ingrowth, making it more suitable for the human bone compared with a solid stem. Moreover, second-generation titanium biomedical alloys, such as TNZT (Ti35Nb7Zr5Ta) and TMZF (Ti12Mo6Zr2Fe), have been introduced to prevent the adverse tissue reactions related to aluminum and vanadium elements of the popular Ti6Al4V alloy. In the current work, an analysis was performed based on uniaxial compression testing of cubic Ti6Al4V structures of different porosities to predict the governing equations that relate the relative density of the structure to the mechanical properties of the structure according to the Gibson-Ashby model. A numerical study was conducted to evaluate the change in stress distribution obtained by incorporating the new titanium alloys in porous hip stem implants. Implants modeled with the mechanical properties of TNZT and TMZF showed a minimum safety factor of 1.69 and 3.02, respectively, with respect to the yield strength. The results demonstrated an increase in the equivalent von Mises stresses and maximum principal elastic strain up to 7% and 15%, respectively, compared with the porous Ti6Al4V implant and up to 108% and 156%, respectively, compared with the solid Ti6Al4V implant.

The effects of second phases on superelastic behavior of TNTZ bio alloy

The present work was conducted to investigate the effects of second phases on the stability of β phase and superelastic behavior of a Ti–Nb–Ta–Zr (TNTZ) bio-alloy. For this purpose, the as-hot forged material was subjected to different thermal treatments. These included solution annealing, aging treatments at 500°C for 48h, and annealing at 850°C for 45min followed by quenching in water and ethanol solution, to obtain alpha (α) precipitate and α″ martensite, respectively, as the second phase in the β phase structure. These ended to different microstructures. The superelastic behavior of single β phase structure showed pseudoelastic (S) ratio of 20%. Furthermore, the precipitation of α phase reduced the S ratio to 6%. The α phase decreased the superelasticity by impeding the stress induced martensite (SIM) formation at the loading stage. On the other hand, the athermal α″ martensite, didn't significantly change superelasticity of β phase, (S ratio = 18%). The dissimilarity of α precipitate and α″ martensite in changing the superelastic behavior of the β phase was attributed to the their different mechanical and chemical stabilization potential. The TEM micrographs showed that the α precipitates hindered the growth of SIM needles, while the athermal α″ martensite was easily cut through by SIM. According to the EDS analysis, despite the presence of athermal α″ martensite, the segregation of β stabilizing elements from α precipitate to the β phase was traced; this was introduced as the second factor in spoiling the superelastic behavior of the β phase.

Experimental clarification of the cyclic deformation mechanisms of β-type Ti–Nb–Ta–Zr-alloy single crystals developed for the single-crystalline implant

Quaternary Ti–Nb–Ta–Zr (TNTZ) type β-Ti alloys with a body-centered cubic (bcc) structure have been of great interest as new implant biomaterials for bone replacement. Recently, we have proposed a “single crystalline β-Ti implant” as a novel hard-tissue replacement to suppress the stress shielding to bone after healing. To develop this, the fatigue properties and its controlling mechanisms of the TNTZ single crystals must be clarified. In this study, we focused on three alloys: Ti–25Nb–10Ta–5Zr(25Nb), Ti–29Nb–13Ta–4.6Zr(29Nb), and Ti–35Nb–10Ta–5Zr(35Nb) (mass%), and the cyclic deformation behaviors were examined using their single crystals. The shapes of the hysteresis loops were significantly different for these alloys, which was ascribed to the operation of different deformation modes: stress-induced α”-martensite (α”-SIM), {332}<113> twinning, and {101}<111> slip in the 25Nb, 29Nb, and 35Nb alloys, respectively. The hysteresis loops during cyclic deformation exhibited very irregular shapes for 25Nb and 29Nb, accompanied by a flow-stress asymmetry in tension and compression. This was caused by the polarized feature on the formation of them in tension and compression. In addition, the apparent yield stress in a hysteresis loop greatly decreased after the second cycle, owing to the reversible motion of the interfaces of the SIM and {332} twins by altering the direction of the applied stress. Although the cyclic deformation behavior was controlled by a similar mechanism in them, 29Nb was found to exhibit a much shorter fatigue life than 25Nb. This is because of the difference in the decreasing tendency of the reversibility for the SIM and {332} twins as cyclic deformation proceeded. The obtained results demonstrate that the controls of their asymmetric features and the reversible motion are the important factors to develop these alloys as a practical “single crystalline β-Ti implant”.

The evolution of microstructure and microhardness in a biomedical Ti–35Nb–7Zr–5Ta alloy

β-Ti alloys are promising candidates for biomedical applications due to their high strength, high corrosion and wear resistance, and low elastic modulus. This study focuses on phase evolution in a low modulus Ti–35Nb–7Zr–5Ta (TNZT) alloy, systematically examined via isochronal and isothermal annealing, and its influence on microhardness. The observations indicate that the highest microhardness value was achieved at an aging temperature of 400 °C. The microstructural evolution at this temperature was investigated via systematic isothermal annealing treatments, and the results indicate a progressive transformation from β + ω + O’ (solution treated and quenched) to β + ω + α (after isothermal annealing at 400 °C/6 h), with the dissolution of the metastable orthorhombic O’ phase and the formation of the stable α phase. The maximum hardness corresponded to a highly refined mixture of co-existing ω and α phases after prolonged annealing for 48 h at 400 °C. The coexistence of both ω and α phases after such prolonged annealing indicates that at 400 °C, ω is in metastable equilibrium, despite the concurrent precipitation of the equilibrium α phase.

Change in Mechanical Strength and Bone Contact Ratio of Beta-Type TNTZ Subjected to Mechanical Surface Modification

Ti-29Nb-13Ta-4.6Zr (TNTZ), which is one of metastable beta-type Ti alloys, has developed as one of representative biomedical and dental Ti alloys in Japan. TNTZ subjected to solution treatment shows Young’s modulus of 60 GPa, which is close to that of cortical bone. In addition, TNTZ has very low cytotoxicity and good bone biocompatibility as well. Heat treatment like solution treatment and aging (STA) is mainly used for improving the mechanical properties of metastable beta-type Ti alloys because of alpha precipitates, while Young’s modulus also rises drastically. This study was investigated the effects of mechanical surface modifications such as fine particle bombarding (FPB) with steel and hydroxyapatite particles or friction stir processing (FSP) on the mechanical strength of TNTZ in order to maintain low Young’s modulus. The relative bone contact ratios between the cancellous bones of Japanese white rabbits and column-shaped TNTZ subjected to FPB of steel particles were also evaluated. Vickers hardness (HV) of TNTZ subjected to FPB with fine particles of steel and hydroxyapatite particles increased by HV30 to 200 at the edge of the specimen surface to around 100 to 300 mm in depth as compared with that of TNTZ subjected to solution treatment. The hydroxyapatite layer was formed on the specimen surface by FPB with fine particles of hydroxyapatite particles, although the trend was not significant by FPB with steel particles. Furthermore, the fatigue strength in high cycle fatigue region of TNTZ subjected to FPB with steel particles was improved and the fatigue limit showed around 400 MPa, although that of TNTZ subjected to FPB with fine particles of hydroxyapatite particles were around 60 MPa higher than that to TNTZ subjected to solution treatment (230 MPa). TNTZ with a rough surface texture (Ra: 0.65 μm) showed a relative bone contact ratio of more than 80% after undergoing FPB with fine particles of steel particles; this value was significantly higher than that of TNTZ with a surface texture (Ra: 0.07 μm). Lastly, the microstructure of TNTZ subjected to FSP showed the recrystallization area by the frictional heating with very fine equiaxed beta phase with an average grain diameter of 3.0 μm. The change in Vickers hardness of TNTZ subjected to FSP was almost identical to that of Young’s modulus and showed the almost same trend of FPB.

Biocompatibility Evaluation of a Newly Developed Ti–Nb–Zr–Ta–Si Alloy Implant

Biocompatibility Evaluation of a Newly Developed Ti–Nb–Zr–Ta–Si Alloy Implant

Osseointegration behavior of novel Ti-Nb-Zr-Ta-Si alloy for dental implants: an in vivo study.

This study aimed to evaluate the effects of Ti-Nb-Zr-Ta-Si alloy implants on mineral apposition rate and new BIC contact in rabbits. Twelve Ti-Nb-Zr-Ta-Si alloy implants were fabricated and placed into the right femur sites in six rabbits, and commercially pure titanium implants were used as controls in the left femur. Tetracycline and alizarin red were administered 3 weeks and 1 week before euthanization, respectively. At 4 weeks and 8 weeks after implantation, animals were euthanized, respectively. Surface characterization and implant-bone contact surface analysis were performed by using a scanning electron microscope and an energy dispersive X-ray detector. Mineral apposition rate was evaluated using a confocal laser scanning microscope. Toluidine blue staining was performed on undecalcified sections for histology and histomorphology evaluation. Scanning electron microscope and histomorphology observation revealed a direct contact between implants and bone of all groups. After a healing period of 4 weeks, Ti-Nb-Zr-Ta-Si alloy implants showed significantly higher mineral apposition rate compared to commercially pure titanium implants (P < 0.05), whereas there was no significant difference between Ti-Nb-Zr-Ta-Si alloy implants and commercially pure titanium implants (P > 0.05) at 8 weeks. No significant difference of bone-to-implant contact was observed between Ti-Nb-Zr-Ta-Si alloy implants and commercially pure titanium implants implants after a healing period of 4 weeks and 8 weeks. This study showed that Ti-Nb-Zr-Ta-Si alloy implants could establish a close direct contact comparedto commercially pure titanium implants implants, improved mineral matrix apposition rate, and may someday be an alternative as a material for dental implants.

High-strain induced reverse martensitic transformation in an ultrafine-grained Ti-Nb-Ta-Zr alloy

We report on a novel phenomenon, that is a high-strain-induced reverse martensitic transformation in an ultrafine-grained Ti–36Nb–2Ta–3Zr (wt.%) alloy processed by equal channel angular pressing (ECAP) at room temperature. Our results show that a martensitic transformation from body-centred cubic β matrix to orthorhombic α″ martensite occurs under low-strain ECAP conditions and that a large portion (~34%) of martensite transforms into a matrix phase (i.e. reverse martensitic transformation) with increasing ECAP strain to a high value of 4 (i.e. 6 passes) with a corresponding reduction in the α″-lath thickness and a refinement of grain size in the matrix phase.

Room temperature creep behavior of Ti–Nb–Ta–Zr–O alloy

The room temperature creep behavior and deformation mechanisms of a Ti–Nb–Ta–Zr–O alloy, which is also called “gum metal”, were investigated with the nanoindentation creep and conventional creep tests. The microstructure was observed with electron backscattered diffraction analysis (EBSD) and transmission electron microscopy (TEM). The results show that the creep stress exponent of the alloy is sensitive to cold deformation history of the alloy. The alloy which was cold swaged by 85% shows high creep resistance and the stress exponent is approximately equal to 1. Microstructural observation shows that creep process of the alloy without cold deformation is controlled by dislocation mechanism. The stress-induced α" martensitic phase transformation also occurs. The EBSD results show that the grain orientation changes after the creep tests, and thus, the creep of the cold-worked alloy is dominated by the shear deformation of giant faults without direct assistance from dislocations.

Microstructural evolution during hot and cold deformation of Ti–36Nb–2Ta–3Zr–0.35O alloy

The Ti–36Nb–2Ta–3Zr–0.35O (mass fraction, %) (TNTZO) alloy was produced by cold isostatic pressing and sintering from elemental powders, followed by hot and cold deformation. The effects of deformation process on microstructures and mechanical properties were investigated using the SEM, TEM, OM and the universal material testing machine. Results show that the alloy can be easily hot forged and cold swaged due to the fine-grained microstructure. Only after cold swaging by 85%, the alloy shows the typical “marble-like” structure. And the cold deformation is accompanied by stress-induced α” phase transformations. Moreover, both the strength and the ductility of the alloy are significantly improved by hot and cold working.

Surface properties of Ti-35Nb-7Zr-5Ta: Effects of long-term immersion in artificial saliva and fluoride solution

Statement of problemThe mechanical properties of new titanium alloys with an elastic modulus closest to cortical bone have been studied. However, potentially damaging conditions experienced in the oral cavity, such as fluoride ions, can initiate a localized or crevice process of corrosive degradation in the alloy surfaces. PurposeThe purpose of this in vitro study was to evaluate the effects of long-term immersion in artificial saliva or in fluoride solution on mean roughness (Ra), Vickers hardness, and topography of the new titanium alloy Ti-35Nb-7Zr-5Ta (TNZT) compared with those of cp Ti and Ti-6Al-4V (TAV). Material and methodsDisks (N=210) were divided into cp Ti, TAV, and TNZT and subdivided according to the following treatments: no immersion (N−, control), immersion in artificial saliva (S), and immersion in fluoride (F) during periods equivalent to 5, 10, 15, and 20 years. The Ra and Vickers hardness were measured with a profilometer and a hardness tester. The topography was analyzed by scanning electronic microscopy. Data were compared using the Kruskal-Wallis and Dunn tests (α=.05). ResultsValues of Ra and hardness were significantly different among the metals (Ra: TAV<TNZT<cp Ti; P<.05); and hardness (cp Ti<TNZT<TAV; P<.05); with a tendency for Ra to increase for TAV after 20 years of fluoride immersion and changes in hardness values of TAV and TNZT after immersion. TAV surfaces showed a heterogeneous appearance. ConclusionsLong-term immersion in NaF did not change the roughness of Ti-35Nb-7Zr-5Ta. However, the hardness of the alloys increased with immersion.

Enhancement of wear and corrosion resistance of beta titanium alloy by laser gas alloying with nitrogen

The relatively high elastic modulus coupled with the presence of toxic vanadium (V) in Ti6Al4V alloy has long been a concern in orthopaedic applications. To solve the problem, a variety of non-toxic and low modulus beta-titanium (beta-Ti) alloys have been developed. Among the beta-Ti alloy family, the quaternary Ti–Nb–Zr–Ta (TNZT) alloys have received the highest attention as a promising replacement for Ti6Al4V due to their lower elastic modulus and outstanding long term stability against corrosion in biological environments. However, the inferior wear resistance of TNZT is still a problem that must be resolved before commercialising in the orthopaedic market. In this work, a newly developed laser surface treatment technique was employed to improve the surface properties of Ti–35.3Nb–7.3Zr–5.7Ta alloy. The surface structure and composition of the laser-treated TNZT surface were examined by grazing incidence X-ray diffraction (GI-XRD) and X-ray photoelectron spectroscopy (XPS). The wear and corrosion resistance were evaluated by pin-on-plate sliding test and anodic polarisation test in Hanks’ solution. The experimental results were compared with the untreated (or base) TNZT material. The research findings showed that the laser surface treatment technique reported in this work can effectively improve the wear and corrosion resistance of TNZT.

Microscopic study of gum-metal alloys: A role of trace oxygen for dislocation-free deformation

A class of Ti–Nb–Ta–Zr–O alloys called gum metal are known to display high strength, low Young's modulus and high elastic deformability up to 2.5%, simultaneously, and considered to deform by a dislocation-free deformation mechanism. A trace of oxygen (∼1%) in gum metal is indispensable to realize such significant properties; however, the detailed mechanism and the role of the oxygen has not been understood. To investigate an effect of trace oxygen included in gum metal, first-principles calculations for gum-metal approximants including zirconium and oxygen are performed. Calculated results clearly indicate that oxygen site with less neighboring Nb atom is energetically favorable, and that Zr–O bonding has an important role to stabilize the bcc structure of gum metal. The three-dimensional atom-probe tomography (3-D APT) measurements for gum metal were also performed to identify compositional inhomogeneity attributed to the trace elements. From the 3-D APT measurements, Zr ions bonding with oxygen ions are observed, which indicates existence of Zr–O nano-clusters in gum metal. Consequently, it is found that (a) coexistence of Zr atom and oxygen atom improves elastical stability of gum metal, (b) inhomogeneous distribution of the compositions induced by the trace elements causes anisotropical change of shear moduli, and (c) Zr–O nano-clusters existing in gum metal are expected to be obstacles to suppress movemen of dislocations.

Corrosion behavior of new beta type Ti-29Nb-13Ta-4.6Zr alloy in simulated body fluid solution

Event Abstract Back to Event Corrosion behavior of new beta type Ti-29Nb-13Ta-4.6Zr alloy in simulated body fluid solution Gunawarman Gunawarman1, Andrew Refieska1*, Ilhamdi Ilhamdi1*, Jon Affi1*, Ken Cho2, Maasaki Nakai3*, Hendra Hermawan4* and Mitsuo Niinomi3* 1 Andalas University, Kampus Unand Limau Manis, Mechanical Engineering Dept, Indonesia 2 Graduate School of Engineering, Osaka University, Division of Materials and Manufacturing Science, Japan 3 Tohoku University, Institute for Materials Research, Japan 4 Laval University, Dept. Mining, Metallurgical and Materials Engineering & CHU de Québec Research Center, Canada Introduction: A new β type Ti alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), with low Young's modulus (~58 GPa) has been recently developed for anti-bone absorption implant having low stress shielding impact [1]. Its mechanical properties can be further modulated by performing heat or thermo-mechanical treatments [1],[2]. This study aims to preliminarily assess the yet unknown corrosion behavior of this novel alloy in simulated body fluid as one of the important parameters in view of its application for medical implants. Materials and Methods: TNTZ alloy (31.5Nb, 11.6Ta, 4.7Zr, 0.03Fe, <0.02Al and bal, all in wt.%) was prepared by levitation melting. Samples of the alloy and Ti6Al4V (control) were polished (up to grit #1200) and subjected to corrosion test (surface area 10 x 10 mm2) in simulated body fluid as suggested by Kokubo [3] at pH 7.4 and 37oC. Corrosion tests were conducted by using a Versastat-3 potentiostat with three electrodes system where Ag/AgCl, graphite and the specimens served as the reference, counter and working electrodes, respectively. The specimens were stabilized at open circuit potential (OCP) for 30 min and continued with polarization at a scan rate of 2 mV/s from -1 V to 1.5 V. The corrosion potential (Ecorr), corrosion current (icorr), and corrosion rate were determined by Tafel fit according to the ASTM G102 standard. The surface and cross section of the specimens after the tests was examined by using optical microscope and SEM, EDX and XPS. Results and Discussion: Fig. 1 shows typical potentiodynamic polarization curves for TNTZ specimens. Based on Tafel fitting, the average Ecorr, icorr and corrosion rate of TNTZ and Ti6Al4V, respectively are: -0.4 V, 0.2 V; 2x10-7 A/cm2, 3x10-8 A/cm2; and 1.2x10-9 mm/year, 3x10-10 mm/year. It indicates a slight decrease of corrosion resistance of TNTZ compared to Ti6Al4V alloy. However, its corrosion rate is still far lower than that of 316L type stainless steel (2.1x10-3 mm/year in Ringer’s solution and 1.5x10-4 mm/year in Hanks’ solution) [4], and that of Ti-Ni alloy (4.6 x 10-4 mm/year in Hanks’ solution) [5]. Fig. 1: Typical potentiodynamic polarization curves for TNTZ specimens. Fig. 2 shows evidence of pitting corrosion in TNTZ specimen after subjected to the corrosion test. Further optical microscope examination on the cross sectional area confirm the pitting in the forms of elliptical and undercutting. Chemical compositional examination by EDX near the pitting area revealed higher oxygen content in both alloys with wider distribution on TNTZ without the trace of Zr. It is suspected that Zr was released/leached into the solution provoking pitting. Further analysis by XPS revealed higher binding energy and intensity for O and Ti than for Nb, Zr and Ta indicating the formation of predominantly TiO2 layer on the surface of TNTZ. We suspect micro segregation as the cause for pitting corrosion as the alloy was not homogenized adequately after casting. Fig. 2: Surface morphology of: (a) TNTZ, and (b) Ti6Al4V specimens after corrosion test. Conclusion: This preliminary corrosion study reveals the high corrosion resistance of TNTZ alloy but with a tendency of pitting corrosion. The alloy should be subjected to further treatment such as homogenization to improve its corrosion behavior. The authors acknowledge Andalas University for student travel grant, Universiti Teknologi Malaysia for corrosion test facility and Institute for Materials Research for TNTZ samples.

Biocompatible mechanical surface modification processing and mechanical properties of beta-type titanium alloys

Biocompatible mechanical surface modification processing and mechanical properties of beta-type titanium alloys