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► EIS spectra for Ti6Al4V1Zr alloy were fitted with one time constant electric equivalent circuit. ► For covered alloy the equivalent circuit contains two time constants. ► ...Resistances of films increased in time revealing the improvement of the alloy protection capacity. ► Surface roughness significantly increased by apatite formation, being favourably to cell adhesion.
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 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.
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► New Ti–10Zr–5Nb–5Ta alloy was processed by an accumulative roll bonding (ARB) method. ► After three ARB cycles, total deformation degree/layer is 86%; medium layer thickness is about 13 μm. ► ARB processed alloy has a low Young’s modulus (46 GPa), very close to the value of the natural cortical bone (30 GPa). ► Ultimate tensile strength for ARB processed alloy is high, suitable for a bone implant. ► Improvement of corrosion resistance as result of ARB processing positive influence was obtained.
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► The native film on the alloy surface contains TiO2, Nb2O5, ZrO2, Ta2O5 as was demonstrated by XPS. ► After 2000h, XPS revealed the same oxides and calcium, phosphorous ions ...deposited as hydroxyapatite. ► Impedance data exhibited a passive film with two layers: an inner, barrier and an outer, porous. ► In Ringer and Ringer–Brown solutions, the new alloy presented low corrosion rates.
A new quaternary Ti–20Nb–10Zr–5Ta alloy with β-near microstructure was obtained. Its native passive film composition and its modification and corrosion resistance after 2000 immersion hours in simulated biofluids were studied. The native film on the alloy surface contains TiO2, Nb2O5, ZrO2, Ta2O5 protective oxides as was demonstrated by XPS. After 2000h, XPS revealed the presence of same oxides and calcium, phosphorous ions deposited from physiological solutions as hydroxyapatite. In Ringer and Ringer–Brown solutions, the new alloy presented low corrosion rates. Impedance data exhibited a passive film with two layers: an inner, barrier layer and an outer, porous layer.
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.
► New superelastic biomedical Ti alloy synthesised by cold crucible levitation melting. ► Ti-25Ta-25Nb alloy having a very low Young’s modulus at 55 GPa. ► Superelastic recoverable strain evaluated at 0.75%. ► Low corrosion rate for the Ti-25Ta-25Nb alloy in neutral Ringer solution.
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•Native passive film (TiO2, Ta2O5, ZrO2) on Ti–15Ta–5Zr alloy surface has a thickness of 8.5nm.•Duplex oxide film formed by inner, compact and by outer porous layer was modelled by ...EIS.•Passive film thickened over time by new depositions from physiological solutions.•After 1500h in acid Ringer solution the brushite was detected by XPS.•In neutral and alkaline Ringer solutions the hydroxyapatite was identified by XPS and SEM.
The native passive film on the new Ti–15Ta–5Zr alloy surface contains the protective TiO2, Ta2O5 and ZrO2 oxides (XPS analysis). The decrease of the corrosion current densities and the increase of the polarisation resistances values signify the thickening of the passive film in time. The duplex oxide film formed by the inner, compact, layer and by the outer, porous layer was modelled; electrical parameters indicated the thickening over time both of the barrier and porous layers. XPS and SEM analyses demonstrated the in time deposition of new layers consisting by brushite in acid Ringer solution and from hydroxyapatite in neutral and alkaline Ringer solutions.
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•Ti–15Zr–5Nb alloy exhibits a two-phase α+β lamellar microstructure.•Compact, native passive film (TiO2, Ti2O3, ZrO2, and Nb2O5) on alloy surface was determined by XPS.•After 1500h, ...XPS, Raman, SEM and EDX revealed in addition Ca3(PO4)2 compound (precursor of hydroxyapatite).•EIS spectra depicted a bi-layered passive film: inner, barrier layer and outer porous layer.•The alloy shows good passivity in Ringer solution.
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 1500h 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.
Passivating coatings of brushite (CaHPO
4·2H
2O) 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.
► X-ray diffraction confirms formation of primary brushite coating by cathodic electrodeposition. ► After 48
h soaking in Ringer's solution typical reflections of hydroxyapatite were identified. ► Raman spectra of the final coating revealed a single peak assigned to the hydroxyapatite. ► Electrochemical parameters had more favorable values for coated than for uncoated biomaterials. ► Polarization resistances increased with time owing to gradual thickening of the deposited HA coatings.
In this study, the new Hardion+ micro-implanter technology was used to modify surface properties of biomedical pure titanium (CP-Ti) and Ti–6Al–4V ELI alloy by implantation of nitrogen ions. This ...process is based on the use of an electron cyclotron resonance ion source to produce a multienergetic ion beam from multicharged ions. After implantation, surface analysis methods revealed the formation of titanium nitride (TiN) on the substrate surfaces. An increase in superficial hardness and a significant reduction of friction coefficient were observed for both materials when compared to non-implanted samples. Better corrosion resistance and a significant decrease in ion release rates were observed for N-implanted biomaterials due to the formation of the protective TiN layer on their surfaces. In vitro tests performed on human fetal osteoblasts indicated that the cytocompatibility of N-implanted CP-Ti and Ti–6Al–4V alloy was enhanced in comparison to that of the corresponding non treated samples. Consequently, Hardion+ implantation technique can provide titanium alloys with better qualities in terms of corrosion resistance, cell proliferation, adhesion and viability.
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.
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.
