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The novel Ti-20Zr-5Ta-2Ag alloy was characterised concerning its microstructure, morphology, mechanical properties, its passive film composition and thickness, its long-term electrochemical stability, corrosion resistance, ion release rate in Ringer solution of acid, neutral and alkaline pH values and antibacterial activity. The new alloy has a crystalline α microstructure (by XRD). Long-term XPS and SEM analyses show the thickening of the passive film and the deposition of hydroxyapatite in neutral and alkaline Ringer solution. The values of the electrochemical parameters confirm the over time stability of the new alloy passive film. All corrosion parameters have very favourable values in time which attest a high resistance to corrosion. Impedance spectra evinced a bi-layered passive film formed by the barrier, insulating layer and the porous layer. The monitoring of the open circuit potentials indicated the stability of the protective layers and their thickening in time. The new alloy releases (by ICP-MS measurements) very low quantities of Ti, Zr, Ag ions and no Ta ions. The new alloy exhibits a low antibacterial activity.

A new Ti-20Zr-5Ta-2Ag alloy was elaborated and characterized regarding its microstructure, its native passive film composition and thickness, its surface wettability, its electrochemical behavior in Ringer solution of different pH values, and its ion release. The new alloy has a bi-phase, α + β, acicular, homogeneous microstructure (scanning electron microscopy (SEM)). Its native passive film (12-nm thicknesses) consists of the protective TiO2, ZrO2, and Ta2O5 oxides, Ti and Ta suboxides, and metallic Ag (X-ray photoelectron spectroscopy (XPS) data). The alloy possesses high hydrophilic properties. The main electrochemical parameters of the new alloy are superior to those of Ti as a result of the beneficial influence of Zr, Ta, and Ag alloying elements, which reinforce its native passive film. Electrochemical impedance spectroscopy (EIS) spectra in Ringer solutions for the new alloy displayed better values of impedances and phase angles, proving a more insulate passive film than that on the Ti surface. The main corrosion parameters for the new Ti-20Zr-5Ta-2Ag alloy are more favorable by about 25 to 38 times than those of Ti, confirming extremely resistant passive film. The new Ti-20Zr-5Ta-2Ag alloy releases into Ringer solution low quantities of Ti4+, Zr4+ metallic ions (inductively coupled plasma–mass spectroscopy (ICP-MS)). The Ag+ ions are released in low quantity, conferring to this alloy’s low antibacterial activity. All experimental results show that the new Ti-20Zr-5Ta-2Ag alloy fulfills the requirements for biocompatibility, corrosion resistance, and antibacterial protection.

In this paper, the microstructure, mechanical and anticorrosive properties of the new CoCrNbMoZr alloy were studied in comparison with those of the commercial CoCrMo, Heraenium CE alloy. SEM and XRD techniques were used to evince the microstructure, and the morphology of the two alloys. Electrochemical linear and potentiodynamic polarisation and electrochemical impedance spectroscopy methods showed the electrochemical and corrosion behaviour of the alloys in artificial Carter-Brugirard saliva of different composition (doped with NaF, pH = 8.21 and undoped) and pH values (3.83; 7.84; 9.11) simulating the various functional conditions from the oral cavity. The new CoCrNbMoZr alloy showed self-passivation, more favourable values of the corrosion, passivation and transpassive potentials and tendency to passivation than those of the commercial Heraenium CE alloy and lower values of the passive current density; the values of the corrosion current densities and corrosion rates are lower and polarisation resistances are higher comparing with those of the reference alloy. EIS spectra revealed a passive film, a compact, resistant layer formed especially by the chromium, cobalt, niobium and zirconium oxides. Taking into consideration the microstructural features, electrochemical behaviour, corrosion resistance, and mechanical characteristics, it results that the new CoCrNbMoZr alloy is recommended for the dental applications.

We applied a new nitrogen-implantation technique (trademark Hardion+) using a source of nitrogen ions, electron cyclotron resonance that assures higher energy and deeper implantation than the conventional techniques. The N-implantation surface of the new Ti-25Ta-25Nb alloy was analyzed as follows: for the phase identification by x-ray diffraction (XRD) in a glancing geometry (1°); for the hardness by the nano-indentation method; for the corrosion behaviour in Ringer solutions of different pH values (simulating the real conditions from the human body) by cyclic and linear polarization, electrochemical impedance spectroscopy and the monitoring of the open circuit potentials and corresponding potential gradients. XRD pattern was indexed with face-centred cubic TiN compound partially substituted with TaN and NbN. The hardness increased about 2 times for the N-implantation alloy. The implantation layer had a protection effect, increasing the corrosion and passivation potentials and decreasing the tendency to passivation and passive current density, due to its compactness, reinforcement action. The corrosion current density and rate decreased by about 10 times and the polarization resistance increased by about 2 times, indicative of a more resistant nitride layer. The porosity was much reduced and the protection efficiency had values closed to 90%, namely the implantation treatment led to the formation of a dense, resistant layer. Impedance spectra showed that the capacitive behaviour of the N-implantation alloy was more insulating and protective. An electric equivalent circuit with two times constants was modelled.

This paper describes the synthesis of a novel Ti-15Ta-5Zr alloy with an α + s stable, homogeneous, biphasic microstructure (by optical microscopy, X-ray diffraction and scanning electron microscopy) and the determination of its mechanical properties, hardness and a Young’s modulus of 42.2 GPa. The alloy passive film composition and thickness were analyzed by X-ray photoelectron spectroscopy; a thick, compact native passive film containing the protective oxides of all constituent elements (TiO2, Ta2O5, ZrO2) was identified. The electrochemical parameters confirmed a nobler behaviour and a more capacitive, resistant passive film on the alloy surface compared to Ti and other existing implant alloys; these facts are due to the alloying elements that, by their oxides stabilize and reinforce the alloy passive film. This passive film thickened in time, which increased its protective capacity. The new alloy had no susceptibility to galvanic or local corrosion. Ti-15Ta-5Zr alloy is recommended as an advanced orthopaedic implant material.

The new Ti-15Ta-5Zr alloy revealed a homogeneous bi-phase α + β microstructure without inclusions or secondary phases. The alloy native passive film contains both Ti2O3, and TiO2 oxides and very resistant Ta2O5 and ZrO2 oxides (X-ray photoelectron spectroscopy). All main electrochemical and corrosion parameters in artificial Carter-Brugirard saliva had more favourable values than those of Ti and other implant alloys, due to the Ta and Zr alloying elements, which contributed with their protective oxides to the native passive film and due to the alloy very homogeneous microstructure. Impedance spectra indicated a passive film formed by two layers: an inner, insulating, barrier layer that provides the high corrosion resistance and an outer, porous, less protective layer that permits the absorption of ions and species from surrounding environment into its pores, favouring both interaction and bioactivity. X-ray photoelectron spectroscopy and scanning electron microscopy detected new depositions (Na3PO4 and K3PO4 protective compounds) of 5 nm thickness on the alloy surface after 1000 h in Carter-Brugirard saliva, which confer to the substrate both corrosion resistance and bioactivity.

There is a recent trend in tissue engineering and regenerative medicine to use nanotechnology and bionanomaterials to obtain materials that mimic the surface properties of a natural tissue. From this perspective, nanolevel tissue engineering can be viewed as a novel anatomy of the future. In this paper, a novel titanium-based alloy is studied following this strategy. The alloy nanostructuration is proposed as an improved alternative for restorative prosthodontics or an implantable biomaterial. Tests in (i) standard solution of simulated body fluid (SBF) and (ii) natural saliva were performed to investigate the alloy’s electrochemical stability. The results show that nanochannel growth on the alloy surface confers a higher stability than that of the untreated one in both natural and simulated environments.

A novel ternary Ti–15Zr–10Nb alloy with innovative microstructural and mechanical properties and very good long-term corrosion resistance in simulated physiological solutions was studied in this paper. Optical and scanning electron microscopy (SEM) observations revealed α + β biphasic Widmanstatten microstructure with characteristic interleaving lamella of α and β phases. Energy dispersive spectroscopy (EDS) measurements gave good compositional homogeneity with wt.% contents of 75 ± 5% for Ti, 15 ± 2% for Nb, and 10 ± 2% for Zr. The XRD pattern was indexed to a biphasic crystalline structure containing the hexagonal α phase with calculated lattice parameters of a = 2.92 A, c = 4.63 A and the cubic β phase with calculated lattice parameter of a = 3.19 A. The alloy has very good mechanical properties: Young’s modulus of 64 GPa, very close to that of the human bone; superior ultimate tensile strength, appropriate 0.2% yield strength and strain to fracture to those of Ti. The alloy native passive film has a thickness of 5.5 ± 0.5 nm and contains protective TiO 2 , ZrO 2 and Nb 2 O 5 oxides (X-ray photoelectron spectroscopy – XPS analysis). The cyclic voltammetry in Ringer’s solutions indicated a nobler electrochemical behaviour of the alloy in comparison with Ti due to the beneficial influence of the alloying elements, which participate with their oxides to the compactness, thickening, reinforcement of the native passive film. The electrochemical impedance spectra were modelled with an electric equivalent circuit comprising two time constants: for inner, compact layer and outer, porous slightly inferior protective layer.

A porous, homogeneous, phosphorous-enriched oxide nanolayer was realized on the new Ti-15Ta-5Zr alloy surface by the anodic galvanostatic electrodeposition in phosphoric acid solution. This nanolayer contains TiO2, ZrO2oxides, tantalum suboxides, andPO43-ions incorporated in the time of the electrodeposition process and has a thickness of 15.5 nm (X-ray photoelectron spectroscopy data). Atomic force microscopy determined a homogeneous roughness. Scanning electron microscopy evinced a porous microstructure that can stimulate the growth of the bone tissue into pores. The presence of thePO43-anions promotes the electrostatic bonds between the nanolayer and different species from the biofluid, namely, osteoinduction. The anodic oxidation nanolayer improved all electrochemical and corrosion parameters conferring superior protection to the substrate by its higher resistance to the ion migration. Impedance spectra showed that the electrodeposited nanolayer is formed by an inner, dense, barrier layer and an outer porous layer. The nanolayer thickened in time, namely, is bioactive. The oxidized nanolayer is able to protect the alloy from ion release, to assure long-term corrosion resistance, to minimize adverse reactions, to increase alloy bioactivity, to stimulate cell growth, and to favor osseointegration.

The corrosion resistance of new Ti–15Zr–5Nb alloy was correlated with its microstructure, surface structure and composition of its native passive film and of film formed after immersion for 1500 h in Ringer solutions of different pH values. Nobler passive behaviour of alloy in comparison with Ti and similar ternary alloy was determined due to its more compact passive film (containing TiO2, Ti2O3, ZrO2 and Nb2O5). EIS spectra depicted predominantly capacitive behaviour, passive film formed by two layers. After long-term immersion, XPS, Raman spectroscopy, SEM and EDX revealed the same protective oxides and Ca3(PO4)2 compound (precursor of hydroxyapatite) deposited on alloy surface.

An advanced Ti–20Zr alloy was obtained by double vacuum melting in a semi-levitation furnace with cold crucible. The alloy shows fully lamellar α + β microstructure. Cyclic potentiodynamic polarization curves revealed that the alloy passivated easier, more rapid than Ti, having a more stable passive film in Ringer solutions of different pH values, simulating severe functional conditions of an implant. In neutral and alkaline Ringer solutions, the alloy passive film improved its properties in time (1500 h) by the deposition of protective hydroxyapatite, as was demonstrated by XPS, SEM, EDX, Raman and FT-IR measurements. Alloy presented lower corrosion rates and higher polarization resistances (from linear polarization measurements) than those of Ti (tens of times) proving a more resistant passive film. Alloy open circuit potentials had more electropositive values in comparison with Ti and tended to nobler values in time, which denote better passive state and its enhancement in time, due to the new depositions from the physiological solutions. Nyquist and Bode spectra depicted a more protective passive film on the alloy surface than on Ti surface. The passive film is formed by two layers: an inner barrier layer and an outer porous layer. An electric equivalent circuit with two time constants was modeled.

A new Ti-20Nb-10Zr-5Ta bioalloy with low Young's modulus (59 GPa) was coated with nanocrystalline hydroxyapatite (HA) ceramic layer by chemical method of soaking in a slightly supersaturated calcium and phosphate ions solution. The formation of HA was demonstrated using XRD, Raman microscopy and energy-dispersive X-ray spectroscopy; the coating morphology and microstructure were determined using SEM. The coating protective capacity and its long-term (2000 h) stability in simulated biofluids were revealed by the improvement of the all electrochemical parameters; also, HA ceramic coating reduced the alloy corrosion and ion release rates. After 2000 immersion hours in biofluids no compositional change occurs in the HA ceramic coating, only depositions from solution take place that change the coating morphology. Also, the in time increase of the coating stability and thickness (as a result of the new deposition from physiological solutions) indicates bioactivity.

In the present work, nitrogen ion implantation (original method) to enhance the corrosion performance and cytocompatibility of biomedical pure titanium (CP Ti) and Ti–6Al–4V alloy has been studied. Different characterization methods were used to investigate the corrosion resistance of the nitrided Ti and Ti–6Al– 4V samples such as anodic polarization, electrochemical impedance spectroscopy, monitoring of the open circuit potentials and corresponding gradients, evaluation of corrosion rates. Further, cell viability, initial cell spreading and osteoblast proliferation were tested in order to assess cytocompatibility of modified Ti and Ti–6Al–4V alloy. In severe functional conditions, the main electrochemical parameters for nitrided biomaterials presented better values, revealing nobler behaviour than un-nitrided samples; these more favourable values assure a very good corrosion resistance for long term of the treated biomaterials. The results of biological performance evaluation indicated that nitrided Ti and Ti–6Al–4V represent suitable biomaterials for the adhesion and proliferation of human osteoblastsin vitro. All these findings demonstrate that nitrided biomaterials exhibited a very good improvement of their corrosion resistance and biocompatibility, characteristics which recommend them as potential candidates for bone implants.

For an alloy to be suitable for use as an implant material, it must have a low specific weight and Young’s modulus, good mechanical properties that are similar to those of bone, and very good corrosion resistance and biocompatibility. In this study, we have developed a novel Ti-20Nb-10Zr-5Ta alloy that is composed of nontoxic, nonallergenic, corrosion-resistant elements. This alloy has low specific weight and Young’s modulus and good mechanical properties. It has a fine microstructure with a matrix that is mainly composed of the β phase and some α phase due to recrystallization during cooling. It shows elastoplastic behavior with a fairly linear elastic behavior and low Young’s modulus (59 GPa). In addition, its ultimate tensile strength, 0.2% yield strength, and hardness are higher than those of CP Ti, commercial Ti-6Al-4V, and similar β-type alloys. It exhibited a very stable passive state and its electrochemical parameters and corrosion and ion release rates were better than those of CP Ti in Ringer’s solutions of different pH values that simulate the severe functional conditions of an implant; this is attributable to the beneficial influence of the alloying elements and to the better protective properties of the coated passive film.

In this work, a new ternary Ti–25Ta–5Zr alloy (with nontoxic alloying elements) was obtained and used to develop a thermo-mechanical procedure in order to optimize the balance strength – elastic modulus. Data about structural (by SEM) and mechanical properties are investigated. Also, its electrochemical behaviour in Ringer–Brown and Ringer solutions of different pH values (simulating severe functional conditions of an implant) was studied by cyclic potentiodynamic and linear polarization and electrochemical impedance spectroscopy (EIS). From cyclic potentiodynamic polarization curves it resulted the nobler behaviour of the thermo-mechanical treated alloy than as-cast alloy due to the favourable influence of the applied processing. Impedance spectra were fitted with one time constant equivalent circuit characterizing a very stable, resistant oxide passive film. The values of the open circuit potentials for the treated alloy are nobler than of the as-cast alloy and tended to more positive values in time, proving that the passive film on its surface is more compact and thickened in time.

In this work, a multi-elementary Ti–10Zr–5Nb–5Ta alloy, with non-toxic alloying elements, was used to develop an accumulative roll bonding, ARB-type procedure in order to improve its structural and mechanical properties. The alloy was obtained by cold crucible semi-levitation melting technique and then was ARB deformed following a special route. After three ARB cycles, the total deformation degree per layer is about 86%; the calculated medium layer thickness is about 13 μm. The ARB processed alloy has a low Young’s modulus of 46 GPa, a value very close to the value of the natural cortical bone (about 20 GPa). Data concerning ultimate tensile strength obtained for ARB processed alloy is rather high, suitable to be used as a material for bone substitute. Hardness of the ARB processed alloy is higher than that of the as-cast alloy, ensuring a better behaviour as a implant material. The tensile curve for the as-cast alloy shows an elastoplastic behaviour with a quite linear elastic behaviour and the tensile curve for the ARB processed alloy is quite similar with a strain-hardening elastoplastic body. Corrosion behaviour of the studied alloy revealed the improvement of the main electrochemical parameters, as a result of the positive influence of ARB processing. Lower corrosion and ion release rates for the ARB processed alloy than for the as-cast alloy, due to the favourable effect of ARB thermo-mechanical processing were obtained.

Passivating coatings of brushite (CaHPO 4 ·2H 2 O) were obtained on Ti and Ti–6Al–4V ELI alloy substrates by cathodic polarization. After soaking in Ringer's solution for 48 h brushite was transformed to hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ) as confirmed by XRD, FT-IR and Raman spectroscopy. Electrochemical cyclic polarization curves of the coated biomaterials obtained in Ringer's solution at pH values of 7.1 and 8.91 as well as in Hank's Balanced Salt Solution (HBSS) at pH value of 7.4 show a nobler behavior than of the uncoated biomaterials. The coated biomaterials had lower corrosion rates than the uncoated biomaterials suggesting a protective character of the hydroxyapatite coating. Electrochemical impedance spectra (EIS) revealed capacitive behavior, owing to the protective, very resistant layer, the thickness of which increased with soaking time. The coated biomaterials presented higher electropositive open circuit potentials compared to the uncoated biomaterials as result of the protective effect of the coating. The morphology of the coatings changed with soaking time as the coatings became denser, smoother and better adhering. Hence such coatings may provide favorable structure for cell adhesion and proliferation.

A new Ti-6Al-2Nb-1Ta alloy was obtained for to satisfy the mechanical and anticorrosion requirements in neutral corrosive environment. The corrosion behaviour of this new Ti-6Al-2Nb-1Ta alloy in 0.1 M Na2SO4, 3% NaCl solutions and synthetic sea water was studied in this paper, using potentiodynamic and linear polarisation method, electrochemical impedance spectroscopy (EIS) and monitoring of the open circuit potentials. The structure of the alloy represents an α + β uniform structure with un-oriented grains. From the potentiodynamic polarisation curves it resulted that the studied alloy is self-passivated in all three solutions having a very good and very easy tendency to passivation. The most favourable values of the electrochemical parameters were registered in 0.1 M Na2SO4 solution due to its reduced corrosivity. EIS measurements proved the improvement of the passive layer resistance with the immersion time. An electric equivalent circuit with two time constants was fitted. The values of the polarisation resistances showed very good protective capacities which improved in time. The open circuit potentials have the general tendency to ennoble in time, suggesting the thickening of the passive films and the increase of their protective capacities.

A new titanium base Ti–6Al–4V–1Zr alloy covered with hydroxyapatite or bovine serum albumin/hydroxyapatite was characterized in this paper in order to be used as implant material. Following techniques were used: linear polarization, electrochemical impedance spectroscopy, scanning electronic microscopy, Fourier transform infrared spectroscopy and atomic force microscopy. For HA or BSA/HA covered alloy, the electric equivalent circuit contains two time constants (for the passive film and for coatings). The resistance of the protective films increased in time and BSA/HA coating was slightly rougher than HA coating, this situation being favourably to the cell adhesion.

In this study, a new Ti-25Ta-25Nb (mass%) β alloy was synthesised by cold crucible semi-levitation melting. After melting, each ingot was solution treated in the β-phase domain and water quenched in order to obtain a fully recrystallised homogeneous β-phase microstructure. To evaluate the bio-corrosion property of this new alloy, corrosion tests (cyclic potentiodynamic and linear polarisation, EIS) and surface analysis (SEM) were carried out in Ringer solution at different pH values (acid, neutral and basic). The results indicated that the corrosion resistance of the Ti-25Ta-25Nb alloy is quite higher than that of the commercially pure CP Ti alloy. These results show that this new alloy possesses all the characteristics necessary for its long-term use as medical implants.

The aims of the study were to investigate the electrochemical response of a new dental Au-20Pd-10Ag-5Ti alloy in artificial Carter-Brugirard saliva and to assess its biocompatibility using gingival fibroblast culture. Electrochemical techniques of potentiodynamic and linear polarization were used. Also, the open circuit potentials and the corresponding open circuit potential gradients were monitored for 5000 exposure hours. The gingival fibroblast response to Au-20Pd-10Ag-5Ti alloy was estimated by LDH-cytotoxicity, MTT cell proliferation assays, the assessment of substrate-dependent changes in extracellular fibronectin network, cell morphology and actin cytoskeleton organization. The cyclic potentiodynamic curves of Au-20Pd-10Ag-5Ti alloy exhibited a passive behaviour with transpassive dissolution of silver, without pitting corrosion. Open circuit potentials were finally stable at noble values. Open circuit potential gradients have low values that could not generate galvanic or local corrosion. The new Au-20Pd-10Ag-5Ti alloy did not promote cell damage and alterations in cell adhesion and morphological features, exhibiting a good biocompatibility.

This paper studies the long term (3000 exposure hours) behaviour of a new titanium base Ti-6Al-4V-1Zr alloy un-covered and covered with hydroxyapatite (HA) or bovine serum albumin/hydroxyapatite (BSA/HA) in Ringer solution of different pH values for to reproduce the complex conditions from the human body. Electrochemical cyclic voltammetry and linear polarization methods were used. Also, open circuit potentials and gradients were monitored for 3000 immersion hours in Ringer solution of different pH values. Bare Ti-6Al-4V-1Zr alloy presented more electropositive corrosion potentials, lower values of the tendency to passivation and passive current densities indicating an easier passivation and a very resistant passive film than of Ti. Covered BSA/HA/Ti-6Al-4V-1Zr alloy exhibited lower values of the tendency to passivation and lower passive current densities than the covered HA/Ti-6Al-4V-1Zr alloy and bare alloy due to the more stable coating. The corrosion rates have lower values for bare Ti-6Al-4V-1Zr alloy than Ti. Comparing with the un-covered alloy, lower corrosion rates were obtained for covered alloy, proving the very good protective properties both of HA and BSA/HA coating.

Ti6Al4V-ELI alloy was plastically deformed at elevated temperatures in the range of β and α + β fields and was subsequently heat treated; so that five different alloys were obtained. The corrosion resistance of these alloys was studied in Ringer solutions of different pH values using the techniques of electrochemical cyclic potentiodynamic polarization, electrochemical impedance spectroscopy and scanning electron microscopy. All alloys exhibited high corrosion resistance in Ringer solutions for 2000 exposure hours. SEM observations indicated the formation of calcium phosphate on the alloy surface. Two electric equivalent circuits with two time or three time constants were fitted.

A new implant Ti–7Al–3V–2Mo–2Fe alloy was elaborated and its behaviour in Ringer–Brown and Ringer solutions (of different pH values) was studied using cyclic potentiodynamic and linear polarisation, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) with its link energy dispersive X-ray system (EDX). Cyclic potentiodynamic polarisation curves revealed that the Ti–7Al–3V–2Mo–2Fe alloy is self-passivated in Ringer solutions. Pitting corrosion appeared in alkaline Ringer solution but at very electropositive values of the breakdown and pitting protection potentials and it isnotpossibletodeveloplocal corrosionon thisalloy,eveninextremefunctional conditions. EIS spectra at open circuit potential exhibited two phase angles characterising a resistant passive film and some charge transfer reactions. SEM–EDX analysis shows the presence of some aggregates containing complex compounds of calcium, magnesium, phosphor, silicon deposited on the alloy surface.

The mechanical properties of Ti6Al7Nb alloy deformed and heat treated at elevated temperatures were correlated with its microstructure and corrosion behaviour in Ringer (of different pH values: 2.49, 6.9 and 8.9) and Ringer–Brown solutions. Microstructural analysis revealed a Widmanstatten structure for the alloys deformed at 1100 °C (β field) and structure with α grains at 930 °C (α + β field). The thermo-mechanical processing improved the electrochemical behaviour of Ti6Al7Nb alloys, especially their passive state. Open circuit potential variations in time reflected more compact, stable, resistant passive films on the surface of the treated alloys. Open circuit potential gradients simulating the non-uniformities of pH along the implant surface have very low values that cannot generate galvanic corrosion. Corrosion rates and ion release are very much reduced. Impedance spectra were fitted with a two time-constants equivalent circuit for some alloys and with three time-constants equivalent circuit for other alloys.

Monitoring of the titanium, Ti-5Al-4V, Ti-6Al-4Fe implant materials--Ringer 1 and Ringer 2 solutions (of different pH values) interface for long term was studied in this work. In Ringer 1 solution (with high chloride ion content) all biomaterials present self-passivation. On Ti-6Al-4Fe alloy, the breakdown of the passive film was registered but at high pitting potential; pitting protection potential is very noble and can not be reached in human fluids. In Ringer 2 solution was obtained more electropositive corrosion potential values than in Ringer 1 solution; pitting corrosion of Ti-6Al-4Fe alloy is characterised by nobler breakdown and pitting protection potential values, therefore a better pitting corrosion resistance and tendency. Ion release increases in time, for the first 400-600 immersion hours and then tend to a constant level with very low values, non-dangerous for human body. All open circuit potentials oscillate around some electropositive values. The potential gradients calculated for extreme pH values have low values during 20,000 exposure hours and can not accelerate the corrosion. Atomic Force Microscopy images obtained after different exposure periods in Ringer 1 solution revealed that the roughness increased in time, suggesting a dynamic process at biomaterial-biofluid interface. X-ray Photoelectron spectra obtained after 2880 immersion hours in Ringer 2 solution show the existence of protective titanium dioxide TiO(2) and TiO and Ti(2)O(3) oxides both for titanium and Ti-5Al-4V alloy. Also, Al(2)O(3) oxide was detected.

The properties of the anodic oxide films formed on titanium and its implant alloys Ti-5Al-4V and Ti-6Al-4Fe are investigated in this paper. Anodic oxide films were prepared by electrochemical treatment in 3M sulphuric acid solution at 60 V for 1 min, followed by a thermal treatment consisting of heating at 500 °C for 24 h and then cooling in water. Electrochemical impedance spectroscopy (EIS) measurements were carried out at open circuit potential. Nyquist and Bode spectra exhibit a two-time constant system, attesting an oxide with two layers: a barrier inner oxide and a porous outer one. All spectra change in time, indicating a thickening of the films. Open circuit potentials were monitored (long-term, 25,000 exposure hours) in Ringer 2 solution of different pH values (6.98, 4.35, 2.5) for titanium, Ti5Al-4V and Ti-6Al-4Fe alloy but without treatment with the purpose to compare the biomaterial behaviour. It was pointed out some variations of the open circuit potentials around electropositive values, suggesting slow dissolution, re-passivation or adsorption processes.

The influence of the metallurgical treatment (by forging) and of the plastic deformation degree (four different degrees) on the electrochemical behavior of the ternary alloy Ti-1Ni-0.5Mo in sulfuric acid solutions of different concentrations (5% and 30%) and temperatures (25○, 50○, 75○C) in comparison with the base metal is studied in this paper. The alloy corrosion potentials are nobler than that of titanium due to the favorable effect of the alloying elements. The passive potential range of the casting and forging alloy is lower than that of the titanium. This behavior is due to the alloying elements, which are in the transpassive dissolution state in this potential range. The casting alloy has a reduced stability of its surface state, both by the higher values of the anodic dissolution current densities in the passive state and by the transpassive potential, which is lower than the forging alloy. The metallurgical working by forging improves the passive film stability, enlarging the passive po...

The technical and functional characteristics of some biocompatible, thin, double-layer films (of different compositions; the first layer: Ag30–Cr70 or Co30–Cr70 alloy or stainless steel and the second layer: TiN) on rare-earth-based permanent magnet alloy (Nd30–Dy5–Fe–Al0.4–B) proposed to be used as dental materials have been investigated. Data about electrochemical behaviour, wear resistance and adhesion are presented. The electrochemical behaviour of these films was determined in artificial saliva, using the electrochemical potentiostatic polarisation and electrochemical impedance spectroscopy techniques. The wear behaviour in different conditions of contact and load was tested and the adhesion was determined by scratching test. It resulted that the tested films presented passivation tendency and a very good stability, and no form of local corrosion was detected. The electrochemical behaviour of these films is described by an equivalent circuit with two time constants. The wear resistance is very good. The films own a very good adhesion, which is proper for the proposed purpose.

The passivity of titanium, binary Ti-15Mo and ternary Ti-15Mo-5Al alloys in hydrochloric acid solutions was studied by potentiostatic, potentiodynamic, linear polarization and electrochemical impedance spectroscopy (EIS) techniques. The anodic passivity of binary Ti-15Mo and ternary Ti-15Mo-5Al titanium alloys differs from that of the base metal in hydrochloric acid solutions. The corrosion potentials of both alloys are nobler than of the titanium because the beneficial effect of molybdenum. The critical passivation current density for binary Ti-15Mo alloy is higher than of titanium; this fact can be explained by the instability of the constituent phases in hydrochloric acid solutions. Ternary Ti-15Mo-5Al alloy exhibits two critical passivation current densities (icr1 and icr2) with higher values than of the base metal and two critical passivation potentials (Ecr1 and Ecr2); at the first critical passivation potential (Ecr1) the porous titanium trioxide (Ti3O5) is formed and at the second critical passivation potential (Ecr2) this oxide is converted to a still higher valence oxide, the compact and protective titanium dioxide (TiO2). The dissolution current densities in the passive range of alloys are higher than of the base metal due the dissolution of the alloying elements in this potential range. The alloys are more resistant than titanium presenting lower corrosion rates. A three time constants equivalent circuit was fitted: one time constant is for the double layer capacity (Cdl) and for the passive film (Rp); another time constant is for the charge transfer reactions visualised by a constant phase element (CPE) and a resistance (R1); the third time constant is for diffusion processes through the passive film represented by a resistance (R2) and a Warburg element (W). Anodische Passivitat von verschiedenen Titanbasislegierungen in aggressiven Umgebungen Die Passivitat von Titan sowie der binaren Legierung Ti-15Mo und der ternaren Legierung Ti-15Mo-5Al wurde in Salzsaurelosungen mittels potentiostatischer, potentiodynamischer und linearer Polarisation sowie elektrochemischer Impedanzspektroskopie (EIS) untersucht. Die anodische Passivitat der binaren Ti-15Mo und der ternaren Ti-15Mo-5Al Legierungen unterscheidet sich in Salzsaurelosungen von dem reinen Titan. Die Korrosionspotentiale beider Legierungen sind edler als das des Titans aufgrund des positiven Einflusses des Molybdans. Die kritische Passivierungsstromdichte fur die binare Ti-15Mo-Legierung ist hoher als die von Titan, was durch die Instabilitat der Bestandteile in den Salzsaurelosungen erklart werden kann. Die ternare Ti-15Mo-5Al-Legierung weist zwei kritische Passivierungsstromdichten (icr1 und icr2) auf, die hoher liegen als fur das reine Metall, und zwei kritische Passivierungspotentiale (Ecr1 und Ecr2); beim ersten kritischen Passivierungspotential (Ecr1) wird das porose Titantrioxid (Ti3O5) gebildet und beim zweiten kritischen Passivierungspotential (Ecr2) wird dieses Oxid in ein Oxid mit noch hoherer Wertigkeit, das kompakte und schutzende Titandioxid (TiO2), umgewandelt. Die Auflosungsstromdichten im Passivbereich der Legierungen sind hoher als beim reinen Metall aufgrund der Auflosung der Legierungselemente in diesem Potentialbereich. Die Legierungen sind widerstandsfahiger als das Titan, was sich in niedrigeren Korrosionsgeschwindigkeiten bemerkbar macht. Ein elektrischer Aquivalentschaltkreis wurde angepasst: eine Zeitkonstante steht fur die Doppelschichtkapazitat (Cdl) und fur den Passivfilm (Rp); eine weitere Zeitkonstante steht fur die Ladungsubergangsreaktionen, die durch ein Konstantphasenelement (CPE) und einen Widerstand (R1) dargestellt werden; die dritte Zeitkonstante steht fur den Diffusionsprozess durch den Passivfilm, was durch einen Widerstand (R2) und ein Warburgelement (W) reprasentiert wird.

A new Ti-15Zr-5Nb alloy with suitable microstructure and mechanical properties was processed by galvanostatic anodization in 0.3 M H3PO4solution and a continuous nanostructured layer of protective TiO2oxide was electrodeposited. The obtained anatase oxide layer has a nanotubes-like porosity (SEM observations) and contains significant amount of phosphorus in phosphotitanate compound embedded in the oxide lattice (Raman, FT-IR, SEM, and EDX analysis). This layer composition can stimulate the formation of the bone and its porosity can offer a good scaffold for bone cell adhesion. The electrochemical behaviour, corrosion stability, and variations of the open circuit potentials,Eoc, and corresponding open circuit potential gradients,ΔEoc, for 1500 soaking hours in Ringer solutions of 3.21, 7.58, and 8.91 pH values were studied. The anodized layer was more resistant, stable (from EIS spectra), and was formed from an inner barrier insulating layer that assures the very good alloy corrosion resistance and an outer porous layer that provides the good conditions for cell development. The nanostructured alloy has higher corrosion stability, namely, a more reduced quantity of ions released and a lower toxicity than that of the bare one. The monitoring ofEocandΔEocshowed the enhancement and stabilizing of the long-term passive state of the anodized alloy and, respectively, no possibility at galvanic corrosion.

The corrosion resistance of the new Ti-6Al-4V-1Zr alloy in comparison with ternary Ti-6Al-4V alloy in Ringer-Brown solution and artificial Carter-Brugirard saliva of different pH values was studied. In Ringer-Brown solution, the new alloy presented an improvement of all electrochemical parameters due to the alloying with Zr; also, impedance spectra revealed better protective properties of its passive layer. In Carter-Brugirard artificial saliva, an increase of the passive film thickness was proved. Fluoride ions had a slight negative influence on the corrosion and ion release rates, without to affect the very good stability of the new Ti-6Al-4V-1Zr alloy.

In this study, a new Ti–25Ta–25Nb (mass%) beta alloy was synthesised by cold crucible semi-levitation melting. This technique made it possible to obtain homogeneous ingots although the elements used have very different melting points. After melting, a thermo-mechanical treatment was applied in order to obtain a perfectly recrystallised beta microstructure. For this alloy composition, the tensile tests showed a very low Young’s modulus associated with an important super-elastic behaviour, which contributes to decrease the elastic modulus under stress and to increase the recoverable strain. On the other hand, the corrosion tests, which were carried out in a neutral Ringer solution, indicated a corrosion resistance higher than that of the commercially pure CP Ti alloy. These results show that this new alloy possesses all the characteristics necessary for its long-term use in medical implants.

One objective of this work was to study the corrosion resistance of the new implant Ti–10Zr–5Ta–5Nb alloy in physiological fluids of different pH values, simulating the extreme functional conditions. Another objective was in vitro biocompatibility evaluation of the new alloy using human fetal osteoblast cell line hFOB 1.19. Cytocompatibility was assessed by determination of possible material cytotoxic effects, cell morphology and cell adhesion. The thermo-mechanical processing of the new implant alloy consisted in plastic deformation (almost 90%) performed by hot rolling accompanied by an initial and final heat treatment. The new Ti–10Zr–5Ta–5Nb alloy presented self-passivation, with a large passive potential range and low passive current densities, namely, a very good anticorrosive resistance in Ringer solution of acid, neutral and alkaline pH values. Cell viability was not affected by the alloy substrate presence and a very good compatibility was noticed.

In vitro osteoblasts/Ti-6Al-7Nb bioalloy interactions were characterized in this paper. Also, the electrochemical properties of the passive films on titanium and its Ti-6Al-7Nb bioalloy in Ringer 2 and 3 solutions were determined as an aspect of their biocompatibility. Human osteoblast proliferation and viability are very good. "Cell effort" to adhere on metallic support is visualized by some morphologic changes of the osteoblasts. Cytotoxicity effects of Ti-6Al-7Nb alloy appeared after 48 culture hours and decreased in time, demonstrating a very good biocompatibility. In Ringer 2 solution of different pH values (2.5; 5; 6.7 and 9), titanium and Ti-6Al-7Nb alloy presented self-passivation, very large passive potential range, very low passive current densities, confirming a compact, protective, stable layer. The very low corrosion rates and ion release values prove a near imperceptible toxicity. In Ringer 3 solution, open circuit potentials of titanium and its Ti-6Al-7Nb alloy tend to electropositive values, attesting a process of passivity increase by thickening.

Studies concerning the long-term electrochemical behavior in artificial saliva and interactions with fibroblasts of Ti-45.5Ni bioalloy are performed in this paper. Titanium and its Ti-45.5Ni alloy revealed a typical passive metal behavior in Tani&Zucchi (of pH = 2.5 and 7) and Fusayama (pH = 5.5) artificial saliva. Breakdown (pitting) potential has electropositive values that can not be reached in oral cavity. Corrosion potentials for Ti-45.5Ni alloy in Carter-Brugirard saliva presented more electronegative values than titanium, but no form of local corrosion was registered during 4000 exposure hours. Corrosion potential gradients simulated for saliva composition non-uniformity have low values, showing very good corrosion resistance. Human embryonic fibroblasts rapidly adhered (72% cells in 48 hours) on Ti-45.5Ni alloy surface. Cell proliferation is considerable in the first 48 hours of culture. Slight cytotoxic effects specially developed after 72 incubation hours.

This paper studies the long-term (20,000 exposure hours) behavior of titanium and Ti-5Al-4V alloy-Carter-Brugirard saliva interface and the short-term (500 exposure hours) resistance of titanium and Ti-5Al-4V alloy-TaniZucchi saliva interface. Potentiodynamic polarization method was applied for the determination of the main electrochemical parameters. Linear polarization measurements for to obtain the corrosion rates were used. Monitoring of the open circuit potentials (E(oc)) for long-term have permitted to calculate the potential gradients due to the pH, DeltaE(oc)(pH) and to the saliva composition DeltaE(oc)(c) changes which can appear "in vivo" conditions and can generate local corrosion. Atomic force microscopy (AFM) has analyzed the surface roughness. Ion release was studied by atomic absorption spectroscopy (AAS). In Carter-Brugirard saliva both titanium and Ti-5Al-4V alloy present very stable passive films, long-term stability, "very good" resistance, low values of the open circuit potential gradients, which cannot generate local corrosion. In TaniZucchi artificial saliva, pitting corrosion and noble pitting protection potentials (which cannot be reached in oral cavity) were registered; titanium ion release is very low; surface roughness increase in time and in the presence of the fluoride ions, denoting some increase in the anodic activity.

Correlation between the susceptibility to breakdown and surface properties of thin films on implant titanium alloys Ti-5Al-4V and Ti-6Al-4Fe in Ringer 1 and Ringer 2 solutions of different pH values (6.98, 4.35, 2.5) which simulate the conditions that can appear at the longterm (13,000 hours) contact between implant and tissues were studied in this paper. The passive films are very stable up to +1.8 V; Ti-6Al-4Fe alloy presents pitting attack at a pitting initiation potential of +3.5 V in Ringer 1 solution and at +3.9 V in Ringer 2 solution. The pitting protection potential is about +1.75 V in both solutions; this is a very noble potential. Impedance spectra were modeled with one time constant equivalent electrical circuit, typically for a compact oxide film, for all materials, in all tested solutions. The fitting parameters indicate a long-term stability.

The item of the paper is focussed on some bio-compatible coatings for rare earth based permanent magnets, which are used as dental materials for prosthetic devices as retention units. The studied alloy belongs to Nd-Fe-B system with some Dy and Al content. The double-layer coatings had different chemical compositions; first layer: Ag30-Cr70, Co30-Cr70, Stainless Steel and the second layer: titanium nitride (TiN). Data about corrosion behavior, wear resistance and adhesion are presented. The corrosion resistance of these coatings was tested in artificial saliva, using electrochemical potentiostatic and potentiodynamic polarization techniques. The stability in the corrosion media, the localized corrosion susceptibility and the corrosion rates were determined. It resulted that the Nd30-Dy5-Fe-Al0.4-B alloy with Ag30-Cr70 + TiN film is very stable in artificial saliva. The wear behavior of the coatings in different conditions of contact and load was tested, also. The adhesion was determined by scratching test.

In vitro osteoblast culture on Ti-6Al-7Nb bioalloy was characterized in this paper. Also, the corrosion resistance of titanium and its Ti-6Al-7Nb bioalloy in Ringer solutions were determined as an aspect of their biocompatibility. Human osteoblast proliferation and viability are very good. Cell effort to adhere on metallic support is visualized by some morphologic changes of the osteoblasts. Cytotoxicity effects of Ti-6Al-7Nb alloy appeared after 48 culture hours and decreased in time, demonstrating a very good biocompatibility. In Ringer solution of different pH values (2.5; 6.9 and 8.9), titanium and Ti-6Al-7Nb alloy presented self-passivation, very large passive potential range, very low passive current densities, confirming a compact, protective, stable layer. The very low corrosion rates and ion release values prove a near imperceptible toxicity. In Ringer solution, open circuit potentials of titanium and its Ti-6Al-7Nb alloy tend to electropositive values, attesting a process of passivity increase by thickening.