Evaluation of the Electrochemical Behavior of the Biomedical Alloy Ti-10Mo-3Nb

Abstract

This work analyzed the Ti-10Mo-3Nb, a biomedical alloy very promising and deserving of further study in order to contribute to the literature. Microstructural characterization, evaluation of mechanical properties and analysis of electrochemical behavior are part of the methodology. The electrochemical assays were evaluated by: Open Circuit Potential (OCP), Polarization Curves and Chronoamperometry tests. All tests were performed in the following media: M1 = 0.9 wt% NaCl, M2 = 0.9 wt% NaCl pH 1.0, M3 = 0.35 wt% NaCl. The alloy was producted in laboratory and solution-treated at 950ºC under argon atmosphere for 1 hour and then quenched in water. Results showed that the microstructure presented β matrix with distribution of α`` and ω phases, analised by X-ray diffraction and Scanning Electron Microscopy (SEM). The value measured of Elastic Modulus was 105.51 GPa and hardeness 332.08 HV. The OCP response and the polarization curves obtained in media M1 and M2 showed that the Ti-10Mo-3Nb alloy exhibited greater corrosion resistance compared to the Ti-6Al-4V alloy. The evaluation of the Ti-10Mo-3Nb alloy behavior in relation to the composition of corrosive medium showed that the alloy is more susceptible to corrosion in media with higher chloride ion concentration and high acidity (M2).

Keywords:
Ti alloy; Metallic biomaterial; electrochemical tests

1. Introduction

Titanium alloys are used in a variety of applications, such as in the aerospace, nuclear, oil & gas and healthcare industries. The latter is the most important application, as titanium stands out for being a metal with excellent biocompatibility, the highest among metallic biomaterials. In addition to this characteristic, titanium alloys have high mechanical strength, high corrosion resistance and low density (relatively). This set of properties and characteristics make them suitable for use mainly in orthopedic and dental implants¹-⁵.

One of the most widely used titanium alloys as a biomaterial is the Ti–6Al–4V alloy. However, in recent times, it has been observed that the presence of Al and V can lead to the release of toxic ions into human cells, causing degenerative diseases⁴-¹⁰. Research and technological developments on titanium alloys have been expanding increasingly and studies have drawn greater attention to a group of these alloys, in which greater performances are observed when it comes to bioapplication. These alloys contain Ti, Mo and Nb and the concentrations of these elements vary in order to achieve an optimal level of performance¹,²,⁵-¹⁴.

The effects of Mo addition in Ti alloys are well known. The literature shows that the addition of Mo, or Mo equivalent (Mo eq), stabilizes the β-phase¹-³. An alloy with a Ti-β matrix is very advantageous, since this microstructural characteristic exhibits excellent combinations of properties suitable for biomedical use, such as lower elastic modulus. It is known that lower values of elastic modulus are desirable because they resemble that of bone. In addition, the stabilization of the β phase also provides greater mechanical strength and corrosion resistance. The resulting microstructure depends, among other factors, on the Mo/Mo eq concentration. Values above 10% of Mo are capable of maintaining a microstructure of only the β phase. Mo concentrations lower than 10% cause the precipitation of the α’ (hexagonal), α’’ (orthorhombic) and/or ω (hcp structure) phases in the matrix. The presence of these phases, although they increase mechanical resistance, also increase the modulus of elasticity, which should be avoided, as mentioned¹,².

In addition to Mo, Nb is also known to stabilize the β phase and maintain the elasticity limit at low levels, combined with high mechanical strength. The addition of Nb to Ti alloys is very interesting, especially because it is also an element with good biocompatibility. In recent years, research has been conducted and shows results of studies with different percentages of Nb in Ti-Mo alloys⁵-¹⁴. Gabriel et al.⁶ investigated the effect of adding different percentages of Nb in Ti-10Mo-xNb alloys (x = 3, 6 and 9). The authors showed that the addition of Nb decreased the precipitation of the ω and α’ phases and that the Ti-10Mo-3Nb alloy presented the best combination of hardness and modulus of elasticity. In the study by Xu et al.⁷, in which they evaluated Ti–10Mo–nNb alloys (n = 3, 7, 10), it was found that when n = 7 and 10, the microstructure was solely of β -Ti. According to the authors, all the alloys evaluated presented high Vickers hardness values and low elastic modulus values, all of them being indicated for biomedical applications. A more recent study⁸, also varying the Nb contents in the Ti-xNb-5Mo alloys (x = 0, 10, 20, 30), found results similar to those mentioned above and highlighted that higher Nb contents cause the precipitation of the ω phase, which led to an increase in the elastic modulus in the Ti-20Nb-5Mo alloy.

The relationship between microstructure, chemical composition, and corrosion resistance of titanium alloys was evaluated by El-Bagoury et al.¹⁵ using electrochemical techniques and X-ray photoelectron spectroscopy (XPS). In that study, the authors compared the electrochemical behavior of Ti-Al-V and Ti-Al-Nb alloys with that of commercially pure titanium in a 0.9% NaCl solution. The results indicated that the Ti-Al-Nb alloy exhibited higher resistance to pitting and uniform corrosion compared to the Ti-Al-V alloy. This superior performance was attributed to the formation of a thicker, denser, and more stable passive film on the surface of the Ti-Al-Nb alloy after exposure to the corrosive environment. Similarly, Sharma et al.¹⁶ evaluated the effect of the corrosive medium on the electrochemical behavior of Ti-6Al-4V alloys produced by additive manufacturing, using the Selective Laser Melting (SLM) technique, and by the conventional casting method. The tests were carried out in four different electrolytes: NaOH, SBF, NaCl, and H₂SO₄. The results showed that the alloy produced by additive manufacturing exhibited lower corrosion resistance compared to the cast alloy. Regarding the test environments, the alloy displayed higher resistance in the alkaline medium, while it showed greater susceptibility to corrosion in the acidic medium (H₂SO₄), followed by the chloride-containing medium (NaCl). In the presence of chloride ions, pitting corrosion was observed, whereas exposure to H₂SO₄ caused cracking and dissolution of the passive layer. Chelariu et al.¹⁷ investigated alloys from the ternary Ti–Mo–Nb system with the aim of understanding the effect of niobium on corrosion resistance. The alloys were prepared by varying the Nb/Mo ratio while keeping the molybdenum equivalent constant at 12 wt%. Electrochemical tests were carried out in a 0.9% NaCl solution, and it was observed that all alloys exhibited spontaneous formation of a passive film upon exposure to the medium. Increasing the Nb content resulted in a shift of the corrosion potential toward more positive values, accompanied by a decrease in both corrosion current density (i_corr) and passivation current density (i_pass). Therefore, the authors concluded that increasing the Nb content, while maintaining Moeq = 12%, leads to an improvement in the corrosion resistance of the Ti–Mo–Nb alloys.

Although research on Ti-Mo alloys is available in the literature, it is still necessary to better understand the alloys of the Ti-Mo-Nb system. Above all, the behavior of this last system in relation to its behavior when subjected to different corrosive environments. In this context, the present work aims to evaluate the effect of the composition of the corrosive media on the corrosion resistance of the Ti-10Mo-3Nb alloy.

2. Materials and Methods

The Ti-10Mo-3Nb alloy was produced from commercially pure Ti (grade 2 according to ASTM F6706), Mo (> 99.9% pure, supplied by Plansee Group, Austria) and Nb (>99.9% pure, supplied by EEL/USP, Brazil) metals. An arc melting process with a tungsten electrode on a water-cooled copper hearth was used to melt the alloys. The Ti-10Mo-3Nb was prepared under high purity argon atmosphere, and the ingots were melted six times to improve their chemical homogeneity. The obtained ingots were solution-treated at 950ºC under argon atmosphere for 1 hour and then quenched in water.

The microstructural characterization of the Ti-10Mo-3Nb alloy was carried out by X-ray diffraction in a XRD Shimadzu, model XRD 6000 diffractometer, operated at 40 kV, 30 mA and CuKα radiation (λ =1.5418 Å). The microstructure was investigated by Scanning Electron Microscope (SEM), LEO-ZEISS 1450 VP SEM. The samples were prepared using conventional metallographic preparation. The etching solution used was Kroll’s reagent (3 mL of HF, 6 mL of HNO₃ and 100 mL of H₂O).

The Vickers microhardness values of the alloy were measured by using a DHV-1000 Micro Vickers Hardness Tester with a 100 gf load for 30 s. The Vickers microhardness value is the average of ten measurements. The Elastic modulus (E) was determined by ultrasonic method, measuring the density (ρ) as well as the longitudinal VL and transversal VT sound velocities. A piezoelectric transducer (5 MHz), in contact with the sample via a coupling (honey), was used for such measurement. The Elastic modulus value is the average of ten measurements. The results of the mechanical properties of the Ti-6Al-4V alloy, obtained in a previous study⁶, were used as a comparative reference to the results of the Ti-10Mo-3Nb alloy.

The electrochemical tests used to estimate the behavior of the Ti-10Mo-3Nb and Ti-6Al-4V alloys consisted of monitoring the open circuit potential (OCP), anodic polarization curves and cronoamperometry. All the electrochemical tests were performed using a PGSTAT 302N AUTOLAB potentiostat. To evaluate the effect of electrolyte composition on the corrosion resistance of the Ti-10Mo-3Nb alloy, measurements were performed in three different corrosive media: Medium 1 (M1), saline solution, 0.9% NaCl, pH (~5.6), Medium 2 (M2), saline solution, 0.9% NaCl, adjusted pH (~1.0), and Medium 3 (M3), 0.35% NaCl solution, pH (~5.6).

The measurements were conducted in a naturally aerated solution, at room temperature. The electrochemical assays were carried out using a three-electrode cell design. The Ti-10Mo-3Nb and Ti-6Al-4V alloys was as a working electrode, a platinum wire was employed as the counter electrode, and a saturated calomel electrode (SCE) was applied as the reference electrode.

The working electrode sample was prepared by embedding the alloys in epoxy resin and leaving it to cure. Prior to electrochemical measurements, the alloys were prepared by sequential grinding with silicon carbide paper, washed with water and alcohol, and dried with cold air. The open circuit potential was monitored for a period of 3600 s. Polarization curves were performed in a potential range of -0.25 to +2.0 V (SCE) relative to OCP. The curves were performed at a scan rate of 1 mV/s. Chronoamperometry tests were performed only the Ti-10Mo-3Nb alloy, at a potential of E = 0.5 V and E = 1.0V, chosen after analysis of the polarization curve. Current monitoring at this potential was performed for a period of 3600 s.

3. Results and Discussion

3.1. Microstructural characterization

Figure 1presents the XRD analysis of the Ti-10Mo-3Nb alloy treated at 950°C for 1 h and quenched. The highest intense peak in the diffractogram was cut in order to better define the low intense peaks near the background. According to the XRD pattern, a strong peak of β phase is observed. This indicate that the sample mainly contain the β phase in the microstructure, as expected to a metastable β-type Ti alloy. The analysis also revealed reflections of α`` and ω phases. It is reported in the literature in β-Ti alloys these quenched structure β + α`` and β + ω³,⁶,¹⁰. The presence of α`` phase is observed in binary alloys as Ti-Mo and Ti-Nb. However, when Nb contents increases, wich is a β-stabilizer element, α`` and ω phases are supressed.

Figure 1
XRD pattern of the Ti-10Mo-3Nb alloy treated at 950°C/1h and WQ.

The Figure 2 presents the microstructure of Ti-10Mo-3Nb alloy. The micrographs were obttained by MEV, where it can be seen the β matrix and a significant distribution of fine acicular martensitic phase (α``). The presence of martensite is due to the heat-treatment adopted, in which the temperature (950ºC) was not effective to eliminate all the as-cast dendrite structures. The Ti-10Mo-3Nb alloy exhibits [Mo eq = 10.8], and its [Mo eq] is lower than the other alloys studied in previous research, as alloys Ti-10Mo-6Nb [Mo eq = 11.7] and Ti-10Mo-9Nb [Mo eq = 12.5], which presented less martensite structure, comparatively. So, as reported in the literature¹,²,⁶-¹¹, the amount of α’’martensite decreases for higher Nb contents. This is in agreement with the fact that Nb additions increase the [Mo eq] and, therefore, the β phase stability.

Figure 2
Micrographs obtained by SEM of the Ti-10Mo-3Nb alloy treated at 950°C/1h and WQ showing matrix β with distribution of α`` phase.

3.2. Mechanical properties

The results for the mechanical properties of the Ti-10Mo-3Nb and Ti-6Al-4V alloys are presented in Table 1. The Ti-10Mo-3Nb alloy presents 105.51 GPa of elastic modulus and hardness of 332.08 HV. Comparing with the alloy Ti-6Al-4V - 123.76 GPa and 337.31 HV, respectively - it is observed that the mechanical properties of the Ti-10Mo-3Nb are slightly smaller than Ti-6Al-4V alloy. Xu et al.⁷, analyzing the alloy Ti-10Mo-3Nb, they found a value of 441 HV. This value, higher than that in this study, is probably related to the microstructure. The authors observed the presence of β and α, while in this study the presence of β, α`` and ω, wich can be explained by difference in the treatment and cooling protocol adopted. In all Ti alloys, the maximization of the ratio of yield strength or hardness to Young’s modulus should be pursued. So, it is possible to observe that the Ti-10Mo-3Nb alloy presented 3.16 of ratio, higher than that obtained by Ti-6Al-4V alloy, which presented 2.74.

Table 1
Mechanical properties of the Ti-10Mo-3Nb and Ti-6Al-4V alloys.

Alloy	Elastic Modulus (GPa)	Hardness (HV)	Ratio (Hardness/ Elastic Modulus)
Ti-10Mo-3Nb	105.51 ± 6.69	332.08 ± 23.76	3.16
Ti-6Al-4V	123.76 ± 4.41	337.31 ±15.81	2.74

3.3. Electrochemical behavior

Figure 3 shows the effect of the medium composition on the evolution of the open circuit potential (OCP) for the Ti-10Mo-3Nb and Ti-6Al-4V (reference) alloys during a 1-hour interval. It can be observed that, regardless of the medium, the OCP behavior for both alloys gradually evolve from more negative regions to more positive potential over the exposure time. This trend shows that spontaneous oxide film formation occurs on the alloy surface, independent of the medium to which it is exposed. The spontaneous formation of oxides on different titanium alloys has been reported in the literature; this behavior has been verified in different corrosive media¹⁶,¹⁸-²¹.

Figure 3
Monitoring of the open circuit potential of the Ti-10Mo-3Nb and Ti-6Al-4V alloys in: M1 = 0.9 wt% NaCl, M2 = 0.9 wt% NaCl, pH 1.0, and M3 = 0.35 wt% NaCl solution.

The OCP for the alloy Ti-10Mo-3Nb, after 1 hour of stabilization in the three evaluated media, it presented the following values: E_M1 = -362 mV, E_M2 = -283 mV e E_M3 = -261 mV. For the Ti-6Al-4V reference alloy, the OCP reached the following values: E_M1 = -407 mV, E_M2 = -324 mV.

These results indicate that the corrosive medium influences the naturally formed oxide film at the equilibrium potential. This behavior suggests that the film forms more easily in an environment with a lower concentration of chloride ions (M3 = 0.35 wt% NaCl). In other words, the passive TiO₂ film is less stable in a medium with a higher chloride content. Furthermore, when comparing the alloys, it is observed that the open circuit potential of the Ti-10Mo-3Nb alloy presents more positive values ​​compared to the reference (Ti-6Al-4V) in both M1 and M2 media. This result suggests that the evaluated alloy spontaneously forms more resistant films in comparation with reference alloy in both media.

The anodic polarization curves, obtained in potentiodynamic mode for the Ti-10Mo-3Nb alloy, obtained immediately after OCP stabilization, in the three different corrosive media (M1, M2 and M3) are shown in Figure 4. The shape of the curves is very similar throughout the polarization range. A similar profile was verified by Assis et al.²²,²³, when evaluating titanium alloys in Hank's solution and 0.9% NaCl.

Figure 4
Polarization curves of the Ti-10Mo-3Nb and Ti-6Al-4V alloys in: M1 (0.9 wt% NaCl, pH 5.6), M2 = (0.9 wt% NaCl, pH 1.0), and M3 = (0.35 wt% NaCl, pH 5.6) solution.

Two distinct regions are clearly observed; from the corrosion potential, the current increases with the potential (active region). The increase in current in this region may be associated with the dissolution of the film originally formed near the equilibrium potential²²-²⁴. The current density stabilizes upon reaching the potential corresponding to the second region (passive region), which extends over a wide potential range. This region is related to the passive film, formed under anodic polarization conditions. It is possible to verify that the corrosive medium influences the current density in both the active and passive regions. Comparing the effect of the medium for the Ti-10Mo-3Nb alloy, the results clearly show that the current density related to the active dissolution of the oxide film, formed at a lower chloride concentration (M3 solution), is lower compared to those presented in media M1 and M2. The combination of high chloride concentration and low pH (M2) caused a higher current density in the active region. This behavior suggests that both the chloride concentration and the pH of the medium influence the dissolution of the oxide film formed under equilibrium conditions (open circuit potential).

The oxide film formed in the passive region for the Ti-10Mo-3Nb alloy is also influenced by the composition of the corrosive medium. The enlargement of Figure 4 clearly shows that the passive region obtained in acidic medium (M2) is shifted towards higher current densities compared to the curves obtained at the natural pH of the solution (~5.6). The reference alloy (Ti-6Al-4V) was also analyzed in media M1 and M2 (same chloride concentration, varying pH). For this material, the effect of pH was different than expected, and higher current densities in the passive region were observed for the 0.9 wt% NaCl solution at natural pH. However, when comparing the results in both media, it is observed that the reference alloy presents the passivation region in both media, shifted towards higher current values ​​when compared to the Ti-10Mo-3Nb alloy. This behavior shows that the passive film formed by the evaluated alloy exhibits greater corrosion resistance compared to the reference material.

To further investigate the effect of the electrolyte on passive film formation for the Ti-10Mo-3Nb alloy, chronoamperometric tests were carried out at two points within the passive region. The tests were conducted for a period of 1 hour at potentials of E = 0.5 V and E = 1.0 V, corresponding to the i_pass1 and i_pass2 regions of the polarization curve. These tests allow the evaluation of the current response over time under fixed potentials, making it possible to understand the kinetics of passive film formation and breakdown (El-Bagoury et al.¹⁵). Figures 5 and 6 show the evolution of the passive current over the test duration at the indicated potentials. The current densities were measured at the end of the chronoamperometric tests and are presented in the Table 2. The results indicate that i_pass2 values are higher than i_pass1 in all tested media, suggesting that the film formed at E = 1.0 V contains a greater number of defects compared to that formed at E = 0.5 V. This result indicates that films obtained at more anodic potentials exhibit a higher defect density, which explains the increase in passive current.

Figure 5
Chronoamperometry tests recorded for the Ti-10Mo-3Nb alloy at E = 0.5 V versus SCE in: M1 (0.9 wt% NaCl), M2 = (0.9 wt% NaCl, pH 1.0), and M3 = 0.35 wt% NaCl solution.

Figure 6
Chronoamperometry tests recorded for the Ti-10Mo-3Nb alloy at E = 1.0 V versus SCE in: M1 (0.9 wt% NaCl), M2 = (0.9 wt% NaCl, pH 1.0), and M3 = 0.35 wt% NaCl solution.

Table 2
Current density values obtained from chronoamperometric tests for the Ti-10Mo-3Nb alloy under different experimental conditions.

Corrosive media	E (V)	ipass (μA·cm−2)
M1	0.05	0.014
M2		0.105
M3		0.016
M1	0.1	0.655
M2		0.653
M3		0.261

The current profile obtained for the Ti-10Mo-3Nb alloy is the same regardless of the corrosive medium tested, occurring at both E = 0.5 V and E = 1.0 V, as showed in Figures 5 and 6. A typical two-stage profile is observed on the cronoamperometry tests: in the first stage, there is a sharp drop in current density, followed by a second region where the current reaches values ​​that remain constant over time (steady state). The first stage is related to the formation and growth of the oxide layer (passive film), which justifies the significant drop in current. In the second stage, the passive current values ​​remain stable because the formation and dissolution rates of the film are equal¹⁵,²⁵,²⁶.

Figures 5and 6 show that the effect of the corrosive medium on the kinetics of passive film formation in the Ti-10Mo-3Nb alloy is more pronounced at higher anodic potentials (E = 1.0 V). In tests obtained at a fixed potential of E = 0.5 V, no significant difference was observed in the kinetics of the films obtained in media M1, M2, or M3.

In region I, the decay is faster for M2 (0.9 wt% NaCl pH 1.0), suggesting that the film forms more quickly under these conditions. However, observing the i_pass1 values ​​obtained in the stationary region, it is found that they are approximately ten times greater for the films obtained in M2 compared to the other media. This indicates that although they form more quickly, the films generated in M2 have a greater number of defects. On the other hand, as mentioned earlier, as the potential increases, the difference between the passive films obtained in the different media becomes more significant. At potential E = 1.0 V, the curves show the same profile; however, here the film forms more quickly in the presence of the solution with the lower amount of chloride ions (M3), as can be seen in the enlargement of Figure 6. The effect of the medium on the kinetics and characteristics of the passive film becomes even more evident in the stationary region. In this region, the i_pass2 obtained in solutions with higher chloride ion concentrations (M1 and M2) shows current values ​​approximately 3 times higher compared to the passive current observed at lower chloride concentrations. These results suggest that at more anodic potentials, the chloride ion concentration and the pH of the medium exert a more significant effect on the formation of the passive film.

In this potential range, fluctuations (current peaks) are also observed along the stationary region. These peaks are related to the formation of metastable pits on the sample surface²⁵,²⁶. The current remains stable in this case because, although pit nucleation occurs, the repassivation process also occurs, preventing the growth of metastable pits. It is also observed that in acidic media and higher chloride concentrations, the current peaks associated with the formation of metastable pits are more pronounced, showing that higher concentrations of chloride ions, combined with a high concentration of H⁺ ions (pH 1.0), promote the weakening of the passive film.

4. Conclusions

The Ti-10Mo-3Nb alloy was produced and characterized in terms of microstructure, mechanical properties and electrochemical behavior. The alloy was solution-treated at 950ºC under argon atmosphere for 1 hour and then quenched in water and the microstructural analysis indicated the presence of β matrix and distribution of α`` and ω phases. The value of elastic modulus was 105.51 GPa and hardness 332.08 HV.

The open circuit potential response for the Ti-10Mo-3Nb and Ti-6Al-4V alloys in the M1 and M2 media showed that, regardless of the medium, both alloys spontaneously form a passive film. However, the Ti-10Mo-3Nb alloy shows a shift of the OCP to more positive potentials in both media tested. The polarization results showed that both materials form a significant passive region, however, the lowest currents in this region were observed for the Ti-10Mo-3Nb alloy. These results show that this alloy has greater corrosion resistance compared to the reference alloy.

The results of potentiodynamic polarization and the current response over time, obtained through chronoamperometry, showed that the increase in chloride ion concentration and the acidification of the medium promote a reduction in the corrosion resistance of the Ti-10Mo-3Nb alloy. The resistance of the alloy in relation to the medium studied can be classified as M2<M1<M3.

5. Acknowledgements

This work was supported by CNPq, FAPERJ, CAPES.

6. Data Availability

The experimental data, microscopy images, and analyses generated during this study are available from the corresponding author upon reasonable request.

7. References

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Edited by

• Associate Editor:
  Hugo Sandim.

• Editor-in-Chief:
  Luiz Antonio Pessan.

Publication Dates

• Publication in this collection
  22 June 2026
• Date of issue
  2026

History

• Received
  11 Nov 2025
• Reviewed
  24 Feb 2026
• Accepted
  08 Apr 2026