Corrosion behaviour of a new Ti‐6Al‐2Nb‐1Ta alloy in various solutions

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.     

Electrochemical corrosion behavior of biomedical Ti–22Nb and Ti–22Nb–6Zr alloys in saline medium

The aims of this study were to investigate the effects of Zr addition and potentiodynamic polarization on the microstructure and corrosion resistance of Ti–22Nb and Ti–22Nb–6Zr alloy samples. The corrosion tests were carried out in 0.9% NaCl at 37 °C and neutral pH value, utilizing the OCP, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The results of XRD and optical microscopy indicated that the addition of Zr stabilized the β phase, which plays a crucial role in the corrosion resistance improvement of the Ti–22Nb–6Zr alloy. From the polarization curves, it can be seen that the alloys exhibited a wide passive region without the breakdown of the passive films and also low corrosion current densities. In addition, the values of the corrosion current densities and passive current densities decreased with the addition of 6 at% Zr into the Ti–22Nb alloy. The EIS results of these two alloy samples after 1‐h immersion in 0.9% NaCl solution, and being fitted by R_S(Q_PR_P) model, suggested that the corrosion resistance of the passive films improved with the addition of Zr and only a single passive film formed on the surfaces. However, two time constants were observed for the Ti–22Nb and Ti–22Nb–6Zr alloy samples after potentiodynamic polarization, the spectra of which can be fitted using the R_s(Q_o(R_o(Q_bR_b))) model. In addition, the corrosion resistance of the two alloy samples was reinforced significantly because of polarization when compared to the immersed samples. All these observations suggested a nobler electrochemical behavior of the titanium alloys with the addition of Zr element and after polarization.     

Effects of the Zr and Mo contents on the electrochemical corrosion behavior of Ti–22Nb alloy

Ti–22Nb–xZr and Ti–22Nb–xMo (x = 0, 2, 4, 6, in atom percent) were prepared by an arc melting method. The alloys were solution‐treated at 1073 K for 1.8 ks followed by quenching them into ice water, and the electrochemical corrosion behavior in a 0.9% NaCl solution at 25 °C and neutral pH range of the solution‐treated alloys was evaluated by using electrochemical impedance spectroscopy, polarization curves and an equivalent circuit analysis. It was found that the microstructure of the solution‐treated Ti–22Nb alloy mainly contains β phase with small amount of α″ phase, and the addition of Zr or Mo to a Ti–22Nb alloy is efficient to stabilize the β phase. The resulting impedance parameters and passive current densities indicated that the corrosion resistance of the Ti–22Nb alloy was promoted significantly with the addition of Zr and Mo.     

Corrosion behavior of Ti‐xNb‐13Zr alloys in Ringer's solution

Ti‐6Al‐4V alloy has been widely used in restorative surgery due to its high corrosion resistance and biocompatibility. Nevertheless, some studies showed that V and Al release in the organism might induce cytotoxic effects and neurological disorders, which led to the development of V‐free alloys and both V‐ and Al‐free alloys containing Nb, Zr, Ta, or Mo. Among these alloys, Ti‐13Nb‐13Zr alloy is promising due to its better biomechanical compatibility than Ti‐6Al‐4V. In this work, the corrosion behavior of Ti, Ti‐6Al‐4V, and Ti‐xNb‐13Zr alloys (x = 5, 13, and 20) was evaluated in Ringer's solution (pH 7.5) at 37 °C through open‐circuit potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy. Spontaneous passivity was observed for all materials in this medium. Low corrosion current densities (in the order of 10^?7 A/cm²) and high impedance values (in the order of 10⁵ Ωcm² at low frequencies) indicated their high corrosion resistance. EIS results showed that the passivating films were constituted of an outer porous layer (very low resistance) and an inner compact layer (high resistance), the latter providing the corrosion resistance of the materials. There was evidence that the Ti‐xNb‐13Zr alloys were more corrosion resistant than both Ti and Ti‐6Al‐4V in Ringer's solution.     

Ti13Nb13Zr 合金离子氮化层的摩擦磨损性能研究

目的提高医用钛合金的耐磨损性能。方法应用等离子渗氮技术在Ti13Nb13Zr基材上制备改性层,并对改性层组织、成分及硬度进行测试。利用往复磨损试验机研究改性层在干摩擦条件下的摩擦磨损性能,并与未处理的基材进行对比。结果 Ti13Nb13Zr合金表面经渗氮后形成致密均匀的改性层,硬度高达1110HV0.025,改性层的磨损体积约为基材的1/23。结论等离子渗氮技术有效地改善了Ti13Nb13Zr合金的摩擦磨损性能。     

Effect of nitriding on the electrochemical behaviour of Ti‐Al‐Mn alloy

The effect of technological conditions of nitriding such as process time duration and chemical composition of saturating medium, on the corrosion behaviour of nitrided coatings in 14 M solution of sulphuric acid was analyzed. The investigations were done on the alloy Ti‐5,0 Al‐2,0 Mn. The nitriding was carried out in nitrogen both at atmospheric pressure and rarefied nitrogen pressure (1 Pa) at the temperature 850°C and time processing in the range from 5 to 20 h in nitrogen‐containing gas only, and in powder electrode graphite and nitrogen‐containing gas. It was shown that technological conditions of nitriding determine the protective properties of nitrided coatings. It was indicated that the optimal structure of the nitride layer for best corrosion protection is the thin nitride TiN_x with high surface quality and a gas‐saturated layer. Nitriding in graphite powder effects positively the protective properties of nitride coatings due to reducing the nitride‐forming process.     

Influence of microstructural changes on corrosion behaviour of thermally aged Ti‐6Al‐7Nb alloy

Solution treatment and ageing (STA) is an effective strengthening method for α + β titanium alloys. This paper reports the effect of solution treatment and aging on the corrosion behaviour of Ti‐6Al‐7Nb alloy in a simulated body fluid (Ringer's solution). Ti‐6Al‐7Nb alloy is hot rolled in the α + β field and subjected to solution treatment above and below its beta transus temperature (1283 K). The solution treated specimens are water quenched (WQ), air‐cooled (AC), and furnace cooled (FC) at three different rates, and subsequently aged at 823 K for 4 h. Microstructural changes were examined using optical microscopy and phases developed were analyzed using XRD. The influence of microstructure on the corrosion performance of the alloys are discussed in detail based on the Open Circuit Potential (OCP), passive current density and area of repassivation loop values obtained from the cyclic polarization study in Ringer's solution. The passive current density was low (0.5 μA/cm²) for the specimen with duplex microstructure obtained for specimen solution treated at 1223 K, air‐cooled, and aged, in comparison with that for as‐rolled specimen (1.5 μA/cm²). The corrosion aspects resulting from various heat treatments are discussed in detail.     

激光喷丸强化对Ti13Nb13Zr生物合金摩擦性能的影响

对Ti13Nb13Zr合金进行激光喷丸强化处理,处理前后试样分别在3.5%的Na Cl溶液和Hank’s溶液中进行往复滑动摩擦试验,研究激光喷丸对Ti13Nb13Zr合金生物摩擦磨损性能的影响。通过磨损量和摩擦系数对材料的摩擦磨损性能进行了评价,利用光学显微镜、扫描电子显微镜对磨痕形貌和磨损机理进行了分析。结果表明:与未喷丸试样相比,喷丸处理后试样的磨损量显著降低,无论在3.5%的Na Cl溶液还是Hank’s溶液的润滑下,激光喷丸试样的摩擦系数普遍降低,且随着激光能量的增大而减小;未喷丸试样呈现典型的接触疲劳磨损和擦伤磨损机制,而喷丸处理后试样则主要呈现磨粒磨损和粘着磨损机制。     

Electrochemical evaluation of Ti‐13Nb‐13Zr,Ti‐6Al‐4V and Ti‐6Al‐7Nb alloys for biomedical application by long‐term immersion tests

In this investigation the electrochemical behaviour of the Ti‐13Nb‐13Zr, Ti‐6Al‐4V and Ti‐6Al‐7Nb alloys, for application as implant materials was evaluated in Hanks' solution by electrochemical techniques. The alloys were immersed in this solution for 410 days and periodically they were tested by electrochemical impedance spectroscopy. At the end of this period, polarization curves of the three titanium alloys were obtained. The electrochemical impedance experimental results were interpreted using an equivalent electrical circuit that simulates a duplex structure oxide composed of an inner compact layer, here called barrier layer, and an outer and porous layer. The results indicated that all the alloys present a very high corrosion resistance in the electrolyte used, typical of passive alloys, and that the corrosion resistance is mainly due to the barrier layer. The passive like behaviour was maintained during the whole period of test.     

Effect of Sn addition on the corrosion behavior of Ti‐Ta alloy

In the present paper, the effect of Sn addition on phase constitution and corrosion behavior of Ti₆₅Ta_(35?x)Sn_x (x = 0, 1, 3, 5 at%) alloys has been investigated using X‐ray diffraction and electrochemical measurements. The results show that the β phase is stabilized when quenching after the addition of Sn into Ti₆₅Ta₃₅ alloy, with Ti₆₅Ta₃₀Sn₅ alloy consisting of single β phase at room temperature. The corrosion resistance is enhanced with increase in the Sn content. When the Sn content increases up to 5%, the addition of Sn results in a decrease of corrosion current density from 0.690 µA/cm² of the Ti₆₅Ta₃₅ alloy to 0.098 µA/cm², and corresponding passive current density decreased from 37.7 µA/cm² of the Ti₆₅Ta₃₅ alloy to 9.30 µA/cm².     

Mechanical and corrosion behaviour of a Ti‐Al‐Nb alloy after deformation at elevated temperatures

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.     

Corrosion resistance of the new Ti‐25Ta‐25Nb alloy in severe functional conditions

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.     

Corrosion inhibition of Ti‐6Al‐4V alloy in sulfuric and hydrochloric acid solutions using inorganic passivators

The effect of iodate (IO₃^?), metavanadata (VO₃^?) and molybdate (MoO₄^2?) anions on the passivation of Ti‐6Al‐4V alloy in sulfuric and hydrochloric acid solutions was studied using open‐circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS). The alloy surface was examined by scanning electron microscopy (SEM). It was found that an optimum concentration of the passivator is essential for the corrosion inhibition process. Above this concentration the rate of alloy corrosion decreases as the concentration of the passivating ion increases. Scanning electron micrographs have shown that the flawed regions present in the alloy surface were repaired in the presence of the passivator anion. The optimum concentration of each anion and its corrosion inhibition efficiency for titanium and Ti‐6Al‐4V alloy have been determined. It turned out that the corrosion inhibition efficiencies of IO₃^?, VO₃^? and MoO₄^2? anions for the corrosion of Ti and Ti‐6Al‐4V in both hydrochloric and sulphuric acid solutions exceed 98%.     

In vitro corrosion behaviour of Ti‐5Al‐2Nb‐1Ta alloy in Hanks solution

Electrochemical polarization and impedance spectroscopic (EIS) techniques were used to investigate the corrosion behavior of Ti‐5Al‐2Nb‐1Ta alloy in Hanks solution at different immersion periods (0 h, 120 h, 240 h and 360 h). The impedance spectra are fitted using a non‐linear least square (NLLS) fitting procedure. The EIS spectra exhibited a two time constant system, suggesting the formation of two layers on the metal surface. The surface morphology of the alloy has been characterized by SEM and EDAX measurements.