Paula Drob

Synthesis and characterisation of a new superelastic Ti–25Ta–25Nb biomedical 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 Youngs 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.

Mechanical and corrosion resistance of a new nanostructured Ti–Zr–Ta–Nb alloy

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 Youngs 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.

Microstructure, mechanical, and anticorrosive properties of a new Ti-20Nb-10Zr-5Ta alloy based on nontoxic and nonallergenic elements

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.

Corrosion resistance improvement of titanium base alloys

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.

Characterisation of anodic oxide films formed on titanium and two ternary titanium alloys in hydrochloric acid solutions

The purpose of this paper is to characterise the anodic oxide films formed on titanium and two ternary titanium alloys, Ti-15Mo-5Al and Ti-10Mo-10Al in 1%, 10% and 20% hydrochloric acid solutions at 25, 50, and 75°C. The anodic film on titanium in hydrochloric acid is stable between + 0.6 V (SCE) and + 2.0 V (SCE). For our new ternary titanium alloys, the passive film is formed at about + 0.6 V (SCE) and is stable to + 2.0 V (SCE). The anodic polarization curves for alloys differ from the base metal curve, presenting two peaks for the critical passivation current density in the active-passive potential range. At the first current peak (the first critical passivation potential E cr1 ) a porous titanium pentaoxide (Ti 3 O 5 ) is formed. When the potential reaches the second current peak (the second critical passivation potential E cr2 ) the compact and protective titanium dioxide (TiO 2 ) is formed. The impedance spectra exhibit the typical behaviour for a passive film i.e. a near capacitive response illustrated by a phase angle close to - 90 over a wide frequency range. The oxide film on titanium and its alloys in hydrochloric acid solutions exhibits a high resistance and a low capacitance (with the increase of the potential) attributed to the surface roughness decrease as the oxide layer thickens.

Anodic passivity of some titanium base alloys in aggressive environments

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.

CORROSION BEHAVIOR OF SOME TITANIUM BASE ALLOYS IN ACID SOLUTIONS

Abstract Corrosion and passivation behavior of new, ternary titanium alloys Ti-10Mo-10Al and Ti-15Mo-5Al in nitric acid solutions of different concentrations (20% and 60%) and temperatures (25○, 50○, and 75○C) is presented in this paper. Electrochemical impedance spectroscopy (EIS) data were obtained at different potentials as Bode plots. The spectra show some deviations from the ideal behavior, which demonstrate the necessity to consider a complex equivalent circuit with two time constants. This equivalent circuit is composed of the uncompensated ohmic resistance of the solution (R Ω ), the double layer capacity (C dl ) in parallel with the polarization resistance (R p ) for a passive film, and a Warburg element (W) associated with a resistance (R 1 ) for the diffusion processes. The anodic polarization curves present the self-passivation of these alloys. Both titanium and its ternary alloys directly pass into a passive state, due to the fact that, in strong oxidizing nitric acid solutions, the titanium directly oxidizes to Ti 4+ ions and spontaneously forms titanium dioxide TiO 2 . The passivation of the titanium alloys is due to the compact and protective film containing titanium dioxide, TiO 2 , and some insoluble molybdenum oxide, MoO 3 .

Enhancement of the electrochemical behaviour and biological performance of Ti–25Ta–5Zr alloy by thermo-mechanical processing

A new Ti-25Ta-5Zr alloy based only on non-toxic and non-allergic elements was elaborated in as-cast and thermo-mechanical processed, recrystallized states (XRD and SEM) in order to be used as candidate material for implant applications. Its long-term interactions with Ringer-Brown and Ringer solutions of different pH values and its cytocompatibility were determined. The thermo-mechanically processed alloy has nobler electrochemical behaviour than as-cast alloy due to finer microstructure obtained after the applied treatment. Corrosion and ion release rates presented the lowest values for the treated alloy. Nyquist and Bode plots displayed higher impedance values and phase angles for the processed alloy, denoting a more protective passive film. SEM micrographs revealed depositions from solutions that contain calcium, phosphorous and oxygen ions (EDX analysis), namely calcium phosphate. An electric equivalent circuit with two time constants was modelled. Cell culture experiments with MC3T3-E1 pre-osteoblasts demonstrated that thermo-mechanically processed Ti-25Ta-5Zr alloy supports a better cell adhesion and spreading, and enhanced cell proliferation. Altogether, these data indicate that thermo-mechanical treatment endows the alloy with improved anticorrosion and biological performances.

Influence of deposition technique on the protective properties of epoxy films

The electrochemical impedance spectra, the anodic polarization curves and the time dependence of paint capacitance and paint resistance have been used in this paper to evaluate the protective properties of epoxy films on carbon steel substrate. The coatings were formed using four deposition techniques (brushing, immersion, cathodic and anodic electrodeposition) with the aim to determine the effect of deposition type on the anticorrosive performances of epoxy paint. Interpretation of Nyquist and Bode impedance spectra with the immitance analysis Equivcrt. programme has established an electrical equivalent circuit with two time constants fitted to describe the electrodeposited epoxy/carbon steel system in the 3 % sodium chloride solution and an electrical equivalent circuit with four time constants fitted in case of epoxy films applied by brush or immersion. The anodic polarisation measurements show nobler corrosion potentials and smaller dissolution current densities for the carbon steel in the presence of the electrodeposited films in comparison with epoxy coatings applied by brush or with the immersion technique. The values of the porosity, water uptake, and ionic transport through the film emphasize the higher performances of the electrodeposited films, characterized by uniformity, porosity absence, low water permeability and few conductive pathways.

Biomimetic Hybrid Inorganic/Organic Coatings in the Increasing of the Integration Capacity of TiAlVZr Bioalloy

This paper will address key issues related to the synthesis, characterization and utilization of inorganic/organic hybrid coatings on TiAlVZr bioalloy to control adsorption at interface and the integration capacity of the implant. To enhance the integration capacity function of the biomaterial is necessary to control the composition and structure via the use of hybrid materials consisting of organic and inorganic biomimetic phases [1,2]. Such composite coatings mimic the structure of natural materials of tissues, in our case hydroxyapatite (HA) by association of bovine serum albumin (BSA) with calcium phosphates matrices. Calcium phosphate coating have been deposited on metal substrates by electrochemical method.