Evaluation of the Electrochemical Behavior of the Hot-Rolled Ti–12Mo–30Nb Alloy Applied in Biomedical Implants

Abstract

β-Ti alloys are essential for biomedical applications due to their low elastic modulus, high strength, fatigue resistance, ductility, and corrosion resistance. β-metastable alloys such as Ti-12Mo-30Nb offer safer alternatives to Ti-6Al-4V by eliminating biotoxic elements (Al and V) linked to cell death and neurodegeneration. This study analyzed the microstructural, mechanical, and electrochemical properties of hot-rolled Ti-12Mo-30Nb (90% reduction). Characterization was conducted by XRD, OM, and SEM, while Vickers microhardness and impulse excitation tests were used to assess mechanical performance. The alloy exhibited a single-phase β microstructure, an elastic modulus of 72 Gpa, mitigating the “stress shielding” effect, and a hardness of 228 HV. The hardness-to-modulus ratio (H/E = 3.2) was higher than that of Ti-6Al-4V (2.9) and cp-Ti (2.6), confirming superior mechanical behavior. Electrochemical tests in Ringer’s solution revealed the formation of a stable TiO₂ passive layer, with corrosion and passivation current densities of approximately 10⁻¹ μA.cm-2 and 10 μA.cm-2, respectively. These results indicate excellent corrosion resistance and biocompatibility, demonstrating that Ti-12Mo-30Nb is a promising and safe material for medical devices compared to conventional Ti alloys.

Keywords:
Ti Alloys; Microstructural Characterization; Mechanical Properties; Electrochemical Behavior; Biomaterials

1. Introduction

The use of biomaterials is growing rapidly, driven by the increasing life expectancy in the population. This shift is associated with a higher incidence of degenerative diseases, fractures, and corrective procedures to address their consequences¹,². For a material to be suitable as a metallic implant and serve as a bone substitute, it must strike a balance between high strength and low elastic modulus¹-³. Additionally, it should demonstrate high biocompatibility, excellent corrosion resistance in biological environments, and other crucial mechanical properties, such as good fatigue resistance, low density, wear resistance, and the absence of toxic elements⁴.

Ti alloys are widely chosen for orthopedic and spinal implants due to their outstanding properties, including excellent corrosion resistance, biocompatibility, exceptional fatigue resistance, and a lower elastic modulus compared to other metallic biomaterials such as, nickel-free stainless steel and cobalt-chromium alloys. A key advantage of the titanium alloys under study is the absence of toxic elements. In contrast, stainless steel and Co-Cr alloys contain nickel, chromium, and cobalt, which are associated with potential health risks. For instance, nickel can trigger dermatitis, and cobalt has been linked to carcinogenic effects. Concerns have also arisen regarding the release of aluminum and vanadium ions from specific titanium alloys, as these ions have been associated with conditions such as Alzheimer’s disease, osteomalacia, and neuropathy. Despite these issues, titanium alloys are preferred for biomedical applications due to their superior biocompatibility and lower toxicity risk⁴-¹⁰.

In general, β-metastable Ti alloys are considered the most appropriate for orthopedic and spinal implants¹,¹⁰-¹³. These alloys consist primarily of titanium, combined with biocompatible and β-phase stabilizing elements such as Mo, Nb, Ta, Sn and Zr. Specifically, it is worth noting that Nb enhances corrosion resistance and promotes cell growth without inflammatory reactions and Mo contributes to cytocompatibility. The β phase offers a lower elastic modulus compared with the α and α + β phases, fulfilling most requirements for an ideal metallic implant material¹⁴-¹⁷.

Studies conducted by Wang et al.¹⁸ reported that the compatibility of Ti and its β-type alloys is significantly enhanced by the formation of a stable surface layer rich in TiO₂. This passive layer can be induced by anodic polarization of the Ti substrate, a process that promotes controlled oxidation of the metal and the formation of a protective film on the surface. The presence of this layer not only increases the corrosion resistance of the alloys, protecting the material against degradation in aggressive environments, but also contributes to the reduction of bacterial activity, providing antibacterial properties to the surface. Thus, the evaluation of electrochemical properties through the formation of controlled oxides clarifies the applicability of Ti-Mo-Nb system alloys for biomedical uses.

Although previous studies have investigated phase stability, mechanical performance, and corrosion resistance in Ti–Mo–Nb alloys, limited information is still available regarding the combined influence of hot-rolling processing with high area reduction on the simultaneous evolution of microstructure, mechanical and electrochemical properties. In addition, the relationship between deformation-induced microstructural changes and the stability of passive films in β-type Ti–Mo–Nb alloys is still not fully understood. In this context, hot-rolling processing may represent an effective strategy to tailor the mechanical compatibility and corrosion resistance of β-Ti alloys, enabling a more rational optimization of properties required for load-bearing biomedical applications.

Therefore, the present study aims to characterize the microstructure and evaluate the mechanical and electrochemical properties of the hot-rolled Ti-12Mo-30Nb, highlighting its potential as a promising alternative to cp-Ti and the commercial Ti-6Al-4V alloy for biomedical applications.

2. Materials and Methods

2.1. Sample Production

The Ti–12Mo–30Nb ingot was produced from commercially pure Ti, Mo, and Nb. Alloy preparation was carried out under a high-purity argon atmosphere (>99.9999%), and the material was remelted five times to ensure high purity and chemical homogeneity. Subsequently, the alloy was heat-treated at 950 °C for 1 h, followed by water quenching. The cylindrical ingots were then hot-rolled at 860 °C, with a rolling speed of 66.7 cm·s⁻¹ (40 m·min⁻¹), and water-cooled after each pass in the rolling mill until approximately 90% area reduction was achieved.

2.2. Microstructural characterization

Phase characterization was performed using X-ray diffraction (XRD) with a Shimadzu XRD-6000 diffractometer, operated at 40 kV and 30 mA. The scan range was from 20° to 90°, with a step size of 0.02°. The analysis utilized Ni-filtered Cu Kα radiation (λ = 1.5418 Å). Phase identification was carried out by comparing the obtained diffractograms with simulated patterns generated using the PowderCell program¹⁹, incorporating data on the α, ω, and β-Ti phases, including their space groups, lattice parameters, and atomic positions²⁰.

The microstructure of the alloy was analyzed using scanning electron microscopy (SEM) with a JEOL JSM-6460LV. Sample preparation involved hot mounting in resin followed by standard metallographic polishing techniques. After polishing, the samples were etched with Kroll’s reagent (3 mL HF, 6 mL HNO₃, and 100 mL H₂O).

2.3. Mechanical properties

The Vickers hardness (HV) of the hot-rolled Ti-12Mo-30Nb alloy was measured using a CETR micro-indenter, applying a 100 gf (0.981 N) load for 20 s. The final hardness value was determined as the average of ten measurements per sample.

Young’s modulus was assessed using Sonelastic equipment, evaluating the alloy under different conditions alongside standard samples (Ti-cp and Ti-6Al-4V). Five measurements were recorded for each alloy.

2.4. Electrochemical tests

The surface preparation of the samples for the electrochemical tests consisted of grinding the surface of the working electrodes with SiC papers up to a final grit size of approximately 6–8 μm (#2400), followed by rinsing with distilled water. After cleaning, the working electrode was immersed in the electrochemical cell containing Ringer’s solution (8.6 g·L⁻¹ NaCl, 0.3 g·L⁻¹ KCl, and 0.33 g·L⁻¹ CaCl₂), at pH 7.0 and 25 °C, under naturally aerated and quiescent conditions.

All electrochemical tests were carried out using an Autolab^® PGSTAT204 e PGSTAT302N potentiostats in a three-electrode configuration, consisting of a reference electrode (SCE), a platinum counter electrode (Pt), and a working electrode (cp-Ti, Ti-6Al-4V, and hot-rolled Ti-12Mo-30Nb).

The stabilization of the working electrode consisted of applying cathodic chronoamperometry at a fixed potential of −1.5 V (vs SCE) for 300 s, aimed at promoting the reduction of residual surface oxides without inducing significant H₂ evolution, while maintaining the current density below −50 μA·cm⁻².

The working electrodes were subjected to open-circuit potential (OCP) measurements for 1 h to monitor the kinetics of passive film formation and ensure system stabilization. After stabilization, potentiodynamic polarization was performed by sweeping the potential from −1.0 to +2.0 V (vs SCE) at a scan rate of 20 mV·s⁻¹.

The electrochemical parameters, including the corrosion potential (E_corr.) and the corrosion current density (j_corr,), were determined using the Tafel extrapolation method applied to the polarization curves, in accordance with ASTM G3–89. The passivation current densities (j_pass.) were obtained from the current density values within the potential range associated with passive film formation in the polarization curves.

Based on the polarization curves, the samples were subjected to anodic chronoamperometry at potentials of +0.5, +1,0 and +1.0 V (vs SCE) for 1800 s in order to evaluate the stabilization and behavior of the passive TiO₂ film.

To evaluate the dynamic electrochemical behavior of the alloy surface, including the redox processes of Ti⁰ and the formation and stability of the passive TiO₂ film through faradaic processes, cyclic voltammetry measurements were performed within a potential range from -1.0 to +2.0 V (vs SCE) at a scan rate of 20 mV·s⁻¹ for 10 cycles, aiming to monitor the evolution of the passive layer without promoting excessive thickening of the TiO₂ film.

The electrochemical impedance measurements were performed at open-circuit potential, with voltage amplitude of 7 mV (rms), in the frequency range from 100 kHz to 3 mHz, and 7 points per decade.

All electrochemical tests were performed in triplicate to ensure result reproducibility.

3. Results and Discussion

Figure 1 shows the X-ray diffractogram of the hot-rolled Ti-12Mo-30Nb alloy, with 90% area reduction. The results revealed the presence of only the β-Ti phase in the alloy microstructure after the rolling process, confirming previous studies that indicate Ti alloys with molybdenum equivalent concentrations greater than 10 wt.% are classified as β²¹-²⁴.

Figure 1
X-ray diffractogram of the hot-rolled Ti-12Mo-30Nb alloy (90% area reduction).

Figure 2 presents the micrographs obtained by optical microscopy (OM), and Figure 3 presents those scanning electron microscopy (SEM) of the Ti-12Mo-30Nb alloy after hot rolling, with an area reduction of ~90%. Corroborating the X-ray diffraction results, a homogeneous single-phase β microstructure is observed throughout the analyzed field. The morphology exhibits an elongated appearance and preferred orientation, attributed to the direction of plastic flow imposed during the rolling process. The poorly defined grain boundaries, together with the presence of deformation bands, suggest a high dislocation density and the formation of subgrains, indicating the occurrence of partial recrystallization associated with the rolling temperature. In addition, the microstructure exhibits crystallographic texture, with no evidence of secondary phase precipitation.

Figure 2
OM of the hot-rolled Ti-12Mo-30Nb alloy (~90% area reduction).

Figure 3
SEM micrograph of the hot-rolled Ti-12Mo-30Nb alloy (~90% area reduction).

Table 1 presents a comparison of the mechanical properties of the hot-rolled Ti-12Mo-30Nb alloy with cp Ti²⁵, the commercial Ti-6Al-4V alloy²⁶, and other Ti alloys reported in the literature²⁷-²⁹.

Table 1
Comparison of mechanical properties of the hot-rolled Ti-12Mo-30Nb alloy and reference Ti-based materials reported in the literature.

Materials	Hardness	Young’s modulus	Reference
	[HV]	[GPa]
CP Ti	268	103	24
Ti-6Al-4V	346	118	25
Ti-20Zr-20Nb-20Ta	240	90	26
Ti-25Zr-15Nb-5Ta	220	78
Ti-30Nb-20Ta	250	80	27
Ti-10Nb-5Fe	260	90	28
Hot-rolled Ti-12Mo-30Nb	229 ± 8	72 ± 0.9	In this work

Among the alloys analyzed in this work, the hot-rolled Ti-12Mo-30Nb alloy with a 90% area reduction exhibited the lowest elastic modulus (72 GPa), corresponding to an approximately 40% reduction relative to the Ti-6Al-4V alloy (118 GPa) and about an 8% reduction compared to the Ti-30Nb-20Ta alloy (78 GPa) studied by Hua et al.²⁷.

The Vickers microhardness values also exhibited a decreasing trend, in agreement with previous studies²⁶,³⁰-³³. The Vickers microhardness of the hot-rolled Ti-12Mo-30Nb alloy (229 HV) was lower than that of other Ti-based materials, such as Ti-6Al-4V (346 HV) and commercially pure Ti (268 HV). Figure 4 illustratesthe comparative behavior of the mechanical properties among the evaluated materials.

Figure 4
Vickers Hardness and Young's Modulus of cp-Ti, commercial Ti-6Al-4V alloy, Ti-12Mo-30Nb alloy, and other Ti-based alloys.

This reduction suggests the potential application of hot-rolled Ti-12Mo-30Nb as a biomaterial due to its greater mechanical compatibility with bone tissue (30-40 GPa). The proximity of these values promotes better stress distribution between the metallic implant and the adjacent bone structures, reducing the risk of stress shielding³⁴,³⁵.

The hardness-to-modulus (H/E) ratio is a fundamental parameter in the selection of biomaterials for bone implant applications. This parameter directly influences the stress distribution between the implant and the surrounding bone tissue. A high H/E ratio is associated with better wear resistance and a lower risk of the stress shielding effect, reducing bone resorption caused by the significant stiffness difference between the implant material and the bone³⁶.

Preliminary studies have shown that evaluating the H/E ratio enables the initial selection of candidate materials, identifying those with the potential to provide better biomechanical performance before proceeding to more complex tests, such as tensile and compression tests. This screening process ensures that only the most promising materials advance to the subsequent stages of development and testing for validation as bioimplants³⁷.

As illustrated in Figure 5, the Ti-12Mo-30Nb HR alloy exhibited the highest H/E ratio (3.2) among the evaluated alloys, surpassing major Ti alloys used for this application, such as Ti-6Al-4V (2.9). This result reinforces the potential of Ti-12Mo-30Nb HR as a biomaterial for bone implants.

Figure 5
Hardness-to-modulus (H/E) ratio of cp-Ti, commercial Ti-6Al-4V alloy, Ti-12Mo-30Nb alloy, and other Ti-based alloys.

3.3. Electrochemical characterization

The samples were subjected to a cathodic pre-treatment at −1.5 V (vs SCE), as shown in Figure 6, prior to the electrochemical measurements in order to reduce residual surface oxides formed during sample preparation. The chronoamperometric response initially exhibited a high cathodic current density, followed by a rapid decrease and subsequent stabilization over time, which is characteristic of the reduction of electroactive oxide species present on the alloy surface. This cathodic process can be associated with the partial reduction of the titanium oxide passive film according to the following reaction:

Figure 6
Chronoamperometric surface treatment of Ti-based materials at −1.5 V (vs.. SCE) in lactate-free Ringer’s solution for 300 s.

$$Ti{O}_{2(s)}+4H^{+}{}_{(aq.)}+4e^{-}\to T{i}^0{}_{(s)}{+}_{}2O{H}^{-}{}_{(aq.)}+H_{2(g)}$$ (1)

The pronounced current decrease observed during the first seconds of polarization suggests that the reduction process occurred predominantly in the outer and more reactive regions of the passive film. As the reaction progressed, the cathodic current gradually approached a steady-state condition, indicating the depletion of the more readily reducible oxidized species present on the surface.

Figure 7 shows the Open Circuit Potential (OCP) behavior during 1 h of exposure in Ringer’s solution without lactate for cp-Ti and the Ti-6Al-4V and hot-rolled Ti-12Mo-30Nb alloys. The OCP curves indicated that, after 1 h of immersion, the exposure time was sufficient to achieve electrochemical stabilization of the surfaces. This behavior provided preliminary information regarding the reactivity and passivation behavior of the metallic materials after exposure to the corrosive medium³⁸.

Figure 7
Open-Circuit Potential (OCP) of cp-Ti, commercial Ti-6Al-4V alloy, and Ti-12Mo-30Nb alloy in lactate-free Ringer’s solution after 1 h of exposure.

For all evaluated materials, the OCP initially exhibited more cathodic values and progressively shifted toward more noble potentials throughout the exposure time. This behavior is characteristic of the spontaneous formation, thickening, and stabilization of a protective oxide layer on the alloy surfaces³⁹,⁴⁰. The gradual increase in potential indicates that the passive films formed remained stable throughout the test, favoring the maintenance of the surfaces in a passivated state in the physiological solution.

Differences in the stabilized OCP values were observed among the investigated materials. The cp-Ti exhibited the most noble potential vs SCE (−0.36 ± 0.04 V), followed by the hot-rolled Ti-12Mo-30Nb alloy (−0.41 ± 0.07 V) and Ti-6Al-4V (−0.43 ± 0.04 V). Although the hot-rolled Ti-12Mo-30Nb alloy did not present the highest OCP values, a continuous shift toward more positive potentials over time was observed, indicating the progressive stabilization of the passive oxide film. Furthermore, compared with the conventional Ti-6Al-4V alloy, the hot-rolled Ti-12Mo-30Nb alloy exhibited a nobler electrochemical behavior, suggesting higher surface stability and improved passivation capability.

This improved electrochemical response may be associated with the incorporation of Nb and Mo into the alloy, which contributes to the formation of a chemically stable passive layer composed not only of TiO₂ but also enriched with Nb₂O₅ and MoO₃ species⁴¹,⁴². These oxides are known to increase the stability and protective character of the passive film, which may explain the superior electrochemical performance of the Ti-12Mo-30Nb alloy compared with Ti-6Al-4V. In addition, the OCP evolution observed for all materials indicates that the addition of alloying elements did not hinder the spontaneous passivation process, confirming the ability of the investigated alloys to rapidly develop protective oxide layers under conditions simulating body fluids.

The potentiodynamic polarization curves shown in Figure 8 clearly reveal the active-passive regions of the analyzed materials. The active region is observed from the corrosion potential (E_corr.), marking the onset of the metallic dissolution process, highlighted as region 1. In this region, by applying the Tafel extrapolation method to the polarization curves, the corrosion potential (E_corr.) and corrosion current density (i_corr.) were obtained. This approach is widely used by several authors to evaluate the corrosion resistance of titanium alloys⁴³-⁴⁶. The active region extends from E_corr. up to the onset of a second region (region 2), where the current density stabilizes. This region is characterized by the formation of a protective film that shields the sample surface, preventing the continuation of the corrosion process. In the passive region, observed between 0.70 and 2.0 V (vs SCE), the passivation current (i_pass.) was determined at a potential of approximately 1.0 V (vs SCE). The i_pass. values are important as they provide information about the characteristics of the protective oxide formed under anodic conditions⁴⁷,⁴⁸.

Figure 8
Polarization curves of cp-Ti, commercial Ti-6Al-4V alloy, and hot-rolled Ti-12Mo-30Nb alloy in lactate-free Ringer’s solution after 1 h of exposure.

The electrochemical parameters obtained from the OCP monitoring and polarization curves are presented in Table 2.

Table 2
Electrochemical parameters (E_OCP, E_corr., j_corr., and j_pass.) of cp-Ti, Ti-6Al-4V alloy, and hot-rolled Ti-12Mo-30Nb alloy after Open Circuit Potential and potentiodynamic polarization tests in Ringer’s solution without lactate.

Materials	Phases	EOCP vs	Ecorr. vs	jcorr.	jpass.
		SCE [V]	SCE [V]	[μA•cm-2]	[μA•cm-2]
cp-Ti	α matrix	-0.36 ± 0.04	-0.36 → -0.38	~ 0.15 → 0.30	~ 2 → 4
Ti-6Al-4V	α + β matrix	-0.43 ± 0.04	-0.43 → -0.45	~ 0.60 → 1.00	~ 6 → 10
Hot Rolled - Ti-12Mo-30Nb	β matrix	-0.41 ± 0.07	-0.40 → -0.42	~ 0.30 → 0.60	~ 4 → 7

Comparing the polarization curve behavior of cp-Ti, Ti-6Al-4V, and the hot-rolled Ti-12Mo-30Nb alloy exposed to Ringer’s solution without lactate, slight variations in the corrosion potential (E_corr.) were observed among the investigated materials. These differences are associated with the distinct alloying element compositions (Mo, Nb, Al, and V) relative to cp-Ti, which directly influence the electrochemical stability and passivation behavior of the passive oxide layer. The cp-Ti exhibited the most noble E_corr. values, while the hot-rolled Ti-12Mo-30Nb alloy presented intermediate behavior between cp-Ti and Ti-6Al-4V. Nevertheless, compared with the conventional Ti-6Al-4V alloy, the hot-rolled Ti-12Mo-30Nb alloy exhibited a nobler E_corr. and lower i_corr. values, indicating improved corrosion resistance under the investigated experimental conditions. The corrosion current density remained on the order of 10⁻¹ μA▪cm⁻² for all materials, whereas the passive current density measured at potentials near 1.0 V (vs SCE) remained on the order of 10 μA▪cm⁻².

The polarization behavior was correlated with the microstructural characteristics of the analyzed materials. For the hot-rolled Ti–12Mo–30Nb alloy, the single-phase β microstructure observed in the micrographs was characterized by relatively coarse and elongated grains resulting from the thermomechanical deformation process, leading to a reduced grain boundary density. This microstructural condition likely contributed to the relatively low current densities observed in the active region of the polarization curves. In addition, the homogeneous distribution of the β-stabilizing elements Mo and Nb may have minimized the formation of galvanic micro-couples, contributing to the higher electrochemical stability of the alloy compared with Ti-6Al-4V.

In the passive region, the hot-rolled Ti–12Mo–30Nb alloy exhibited passive current densities intermediate between cp-Ti and Ti-6Al-4V, indicating the formation of a stable and protective passive film. The elongated grain morphology did not significantly impair the passivation behavior of the alloy, although the hot-rolling condition may have contributed to slightly higher passive current densities than those observed for cp-Ti due to residual deformation and surface heterogeneity. Furthermore, the incorporation of Nb and Mo favored the formation of a chemically stable passive layer enriched with TiO₂, Nb₂O₅, and MoO₃ species, promoting uniform oxide growth and enhanced electrochemical stability at higher anodic potentials.

Figure 9 presents the chronoamperometric measurements performed at 0.5, 1.0, and 1.5 V (vs SCE) in lactate-free Ringer’s solution after 30 min of exposure. The results revealed a progressive decrease in current density over time for all investigated materials, indicating the formation and stabilization of passive oxide films in lactate-free Ringer’s solution. At all applied potentials, cp-Ti exhibited the lowest current densities, consistent with the high stability of the naturally formed TiO₂ passive film. In contrast, the Ti-6Al-4V alloy showed the highest anodic current densities, while the hot-rolled Ti-12Mo-30Nb alloy displayed intermediate behavior.

Figure 9
Chronoamperometry of Ti-based materials in lactate-free Ringer’s solution after 30 min of exposure: (a) 0.5 V (vs. SCE); (b) 1.0 V (vs. SCE); and (c) 1.5 V (vs. SCE).

As the applied potential increased, higher current densities were observed for all materials due to the intensified anodic polarization. Nevertheless, the continuous current decay throughout the measurements indicates that the passive films remained stable and protective, with no evidence of severe passive film breakdown. Although the hot-rolled Ti-12Mo-30Nb alloy exhibited greater electrochemical activity than cp-Ti, its chronoamperometric response remained stable even at 1.5 V vs. SCE, suggesting effective repassivation capability and preservation of the passive state.

These findings are consistent with the OCP results, in which the progressive shift toward more noble potentials indicated spontaneous passive film formation and increased surface stability in Ringer’s solution. Overall, the results demonstrate that the addition of Nb and Mo modifies the electrochemical kinetics of passive film formation while maintaining the protective character of the oxide layer under anodic conditions.

Figure 10 shows the cyclic voltammetry measurements after 10 cycles, revealing distinct electrochemical behaviors for cp-Ti and the Ti-6Al-4V and hot-rolled Ti-12Mo-30Nb alloys in lactate-free Ringer’s solution. All materials exhibited an initial increase in anodic current associated with the oxidation of Ti⁰, followed by the progressive formation and stabilization of a passive TiO₂ film on the surface. The electrochemical response can be divided into three characteristic regions and their corresponding reactions: (i) active region related to metal dissolution; (ii) transition region associated with oxide growth and passive region characterized by passivation.

Figure 10
Cyclic voltammetry curves of cp-Ti, Ti-6Al alloy and hot-rolled Ti-12Mo-30Nb after 10 cycles in lactate-free Ringer’s solution.

1. $T{i}^0\to T{i}^{2+}+2e^{-}$

2. $T{i}^{2+}+2H_2{O}_{(l)}\to Ti{O}_2+4H^{+}{}_{(aq.)}+2e^{-}$

Among the investigated materials, the hot-rolled Ti-12Mo-30Nb alloy exhibited the highest anodic current densities and the largest hysteresis loop during the cyclic voltammetry measurements. This behavior suggests enhanced electrochemical activity and more pronounced interfacial charge-transfer processes compared with cp-Ti and the Ti-6Al-4V alloy. The intensified electrochemical response may be attributed to the presence of β-stabilizing elements, particularly Nb and Mo, which are known to modify the passive film growth kinetics, as reported by Xu et al.⁴⁹. In addition, the hot-rolling process may contribute to the formation of microstructural heterogeneities that locally influence passive film formation and ion transport through the TiO₂ layer.

Despite the higher anodic current densities observed for the Ti-12Mo-30Nb alloy, no abrupt increase in current associated with severe passive film breakdown was detected, even at high anodic potentials. Instead, the voltammetric response remained stable throughout the entire potential scan range, indicating preservation of the passive state and efficient repassivation capability. These results suggest that the passive film formed on the Ti-12Mo-30Nb alloy is electrochemically more active, yet sufficiently stable to maintain surface protection in lactate-free Ringer’s solution.

Compared with the other materials, the Ti-6Al-4V alloy exhibited intermediate behavior, with lower anodic current densities and a smaller hysteresis loop, indicating a relatively more stable and less electrochemically active passive layer. In contrast, cp-Ti exhibited the lowest overall electrochemical activity, consistent with the high stability of the naturally formed TiO₂ passive film.

In all electrochemical tests performed, the passivation region remained approximately within the range of 0.70 to 2.0 V (vs SCE), indicating the ability of all investigated materials to form stable passive films in lactate-free Ringer’s solution. The OCP measurements corroborated this behavior, since the progressive shift toward more noble potentials evidenced the spontaneous formation of the passive film and the increase in surface stability over time.

The potentiodynamic polarization and cyclic voltammetry results demonstrated distinct electrochemical responses among cp-Ti, Ti-6Al-4V alloy, and hot-rolled Ti-12Mo-30Nb alloy. The Ti-6Al-4V alloy exhibited a slight shift of the polarization curve toward lower current densities compared to the other materials, suggesting greater corrosion resistance associated with the formation of a more compact and stable passive layer. This behavior may be related to the formation of mixed oxides, such as Al₂O₃ and V₂O₅, which are capable of locally enhancing the protective character of the passive film.

In contrast, the hot-rolled Ti-12Mo-30Nb alloy exhibited higher anodic current densities and a larger hysteresis loop during cyclic voltammetry measurements, indicating higher electrochemical activity and more pronounced interfacial charge transfer processes. Nevertheless, despite the higher current densities, no abrupt current increase associated with severe passive film breakdown was observed, even at high anodic potentials, indicating preservation of the protective layer stability.

Chronoamperometric measurements performed at 0.5, 1.0, and 1.5 V (vs SCE) further reinforced these results, showing the progressive decay of current over time for all materials, which is characteristic of passive film growth and stabilization. Although the hot-rolled Ti-12Mo-30Nb alloy exhibited higher electrochemical activity compared to cp-Ti, its chronoamperometric response remained stable throughout the entire test, indicating an efficient repassivation capability and preservation of the passive state under anodic conditions.

Taken together, the OCP, potentiodynamic polarization, cyclic voltammetry, and chronoamperometry results suggest that the addition of Nb and Mo modifies the electrochemical kinetics of passive film formation, increasing the electrochemical activity of the surface without compromising the protective character of the oxide layer.

According to Xu et al.⁴⁹, Nnamchi et al.⁵⁰, and Li et al.⁵¹, different chemical compositions favor the formation of mixed oxides, especially in Ti–Mo–Nb and Ti–Al–V systems. These reactions may occur simultaneously, involving the alloying elements and contributing to improved corrosion resistance, although the passive layer formed is predominantly composed of TiO₂ due to the high titanium content present in the analyzed alloys.

The effect of Nb on oxide film formation in titanium alloys was evaluated by Arkman et al.⁵², who investigated the chemical composition of the passive film formed on Ti–45Nb alloy after anodic polarization in PBS solution. The presence of TiO₂ and Nb₂O₅ oxides was confirmed by XPS analyses in both anodically formed and naturally formed oxides. Similarly, Monteiro et al.⁵³ observed the predominance of TiO₂, Nb₂O₅, and ZrO₂ oxides in Ti–Nb and Ti–Nb–Zr alloys polarized in 0.9% NaCl solution. The ternary alloy exhibited a higher oxygen content in the passive film, suggesting a thicker oxide layer compared to the Ti–Nb alloy, resulting in lower passive current density and higher corrosion resistance.

For the Ti–6Al–4V alloy, Wang et al.¹⁸ investigated the composition of passive films formed at different anodic potentials in a solution containing 3.5% chloride. The authors observed that the applied potential strongly influences the oxide composition, with the most stable passive film being formed in the range between 0.3 and 1.0 V (vs SCE), where the oxide layer was predominantly composed of TiO₂.

Considering the electrochemical results as a whole, the differences in current density observed in the passivation region among cp-Ti, Ti-6Al-4V alloy, and hot-rolled Ti-12Mo-30Nb alloy are mainly associated with differences in passive film thickness, defect density, oxide growth kinetics, and the participation of alloying elements in passive layer stabilization. Although the Ti-12Mo-30Nb alloy exhibited a more electrochemically active response, the stable behavior observed in cyclic voltammetry, chronoamperometry, and OCP measurements demonstrates that the passive film remained protective under all evaluated conditions.

The results of the impedance assays are presented in Figure 11 using Bode plots. The phase angle behavior in the medium-to-low frequency range (10^-1 – 10² Hz) reveals the presence of a single capacitive response, characterized by a broad plateau with phase angles close to 80°, suggesting highly capacitive behavior typical of passive metals. This behavior, frequently observed in titanium alloys and often related to the coupling of different time constants, is generally associated with the formation of a protective oxide layer²¹,⁴⁴,⁵⁴-⁵⁸.

Figure 11
Bode diagrams: (a) phase angle and (b) impedance modulus for cp-Ti, Ti-6Al-4V alloy and hot-rolled Ti-12Mo-30Nb in lactate-free Ringer’s solution.

The phase angle at intermediate frequencies reaches the following values for the three studied alloys: cp-Ti (76.2°), Ti-12Mo-30Nb (77.4°), and hot-rolled Ti-6Al-4V (77.4°). No significant differences are observed among the investigated alloys, as all exhibit phase angles close to 80°, consistent with passive materials. This behavior corroborates the open-circuit potential results, which showed a progressive shift toward more noble potential values over time, indicating the spontaneous formation of passive films.

However, in the low-frequency region (f < 10^-2 Hz), the phase angle follows the sequence cp-Ti > hot-rolled Ti-12Mo-30Nb > Ti-6Al-4V. This behavior may suggest that the oxide films formed on cp-Ti and hot-rolled Ti-12Mo-30Nb exhibit more capacitive characteristics, which may be associated with a lower defect density within the passive layers⁵⁷.

The Bode plots also show that the impedance modulus response (log|Z| × log f) is similar for all studied alloys. At high frequencies (10³–10⁵ Hz), the |Z| values remain practically constant while phase angles approach 0°, suggesting that the electrolyte resistance dominates the high-frequency impedance response⁵⁶,⁵⁷,⁵⁹. In the medium-frequency (10⁰ – 10² Hz) and low-frequency (10^-2 – 10⁰ Hz) regions, the impedance modulus exhibits a linear slope behavior, which is frequently associated with the response of passive films formed on the electrode surface²¹,⁵⁷,⁵⁸,⁶⁰.

The impedance results corroborate findings obtained from the other electrochemical tests, confirming that all investigated alloys spontaneously form passive films after exposure to Ringer’s solution. According to Qi et al.⁶¹, the impedance modulus measured at low frequencies is directly related to the corrosion resistance of metals. The low-frequency impedance modulus (f ≈ 0.003 Hz) follows the order: |Z|_cp-Ti = 3.09 × 10⁵ Ω·cm² > |Z|_Ti-6Al-4V = 2.77 × 10⁵ Ω·cm² > |Z|_{hot-rolled Ti-12Mo-30Nb} = 2.16 × 10⁵ Ω·cm².

According to Metikos-Hukovic et al.²¹, low-frequency impedance values greater than 10⁴ Ω·cm² indicate the formation of oxide films with good insulating and protective properties. Zhang et al.⁵⁷ further associated high low-frequency |Z| values with the presence of more insulating passive films, which may contribute to improved corrosion resistance. All evaluated alloys exhibited high impedance modulus values at low frequencies (|Z| > 10⁵ Ω·cm²), suggesting that the oxide films formed under OCP conditions possess excellent barrier properties.

The combination of the OCP evolution toward more noble potentials, low icorr and ipass values (10^-6 A·cm^-2), and high low-frequency impedance strongly suggests that all investigated alloys form passive films with protective characteristics and high corrosion resistance. Based on the obtained results, the corrosion resistance of the studied alloys can be ranked as follows: cp-Ti > hot-rolled Ti-12Mo-30Nb > Ti-6Al-4V.

From a biomedical perspective, the combination of mechanical properties and electrochemical stability observed for the hot-rolled Ti-12Mo-30Nb alloy indicates high potential for applications in implants subjected to mechanical loading. In particular, the high H/E ratio, associated with stable passivation, efficient repassivation capability and high impedance modulus at low frequencies suggests greater resistance to wear, surface damage, and contact fatigue when compared to conventional titanium-based biomaterials. However, additional investigations involving in vitro cytotoxicity, biocompatibility, and tribocorrosion behavior under simulated physiological conditions are still necessary to fully validate the long-term biomedical applicability of this alloy.

4. Conclusion

The hot-rolled Ti–12Mo–30Nb alloy with a 90% thickness reduction investigated in the present study exhibited a single-phase β microstructure, a hardness of 229 HV, a Young’s modulus of 72 GPa, and an H/E ratio of 3.2. Compared with commercial Ti alloys and several β-type Ti alloys reported in the literature, the hot-rolled Ti–12Mo–30Nb alloy demonstrated an attractive combination of properties for biomedical applications, particularly due to its high H/E ratio associated with relatively low hardness and Young’s modulus.

Electrochemical tests demonstrated that all evaluated materials exhibited stable passive behavior, with passivation potentials ranging from 0.30 to 2.0 V (vs.. SCE) and corrosion current densities on the order of 10⁻¹ μA·cm⁻², values indicative of high corrosion resistance. The predominant formation of TiO₂, together with the presence of mixed oxides involving alloying elements such as MoO₃, Nb₂O₅, Al₂O₃, and V₂O₅, contributed to the stability and protective character of the passive films. Among the investigated materials, the Ti–6Al–4V alloy exhibited a slight shift of the polarization curve toward more noble potentials, indicating marginally superior electrochemical performance, although all alloys displayed satisfactory corrosion behavior.

Further validation through complementary biological and mechanical durability assessments is required to support long-term biomedical use.

5. Acknowledgements

The authors acknowledge the financial support provided by the Brazilian funding agencies CNPq, CAPES, and FAPERJ.

6. Data Availability

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

7. References

• ¹ Hsu HC, Wong KK, Wu SC, Chen YX, Ho WF. Metastable dual-phase Ti–Nb–Sn–Zr and Ti–Nb–Sn–Fe alloys with high strength-to-modulus ratio. Mater Today Commun. 2022;30:103168.
• ² Niinomi M, Nakai M, Hieda J. Development of new metallic alloys for biomedical applications. Acta Biomater. 2012;8(11):3888-903.
• ³ Hao YL, Li SJ, Sun SY, Zheng CY, Yang R. Elastic deformation behaviour of Ti–24Nb–4Zr–7.9 Sn for biomedical applications. Acta Biomater. 2007;3(2):277-86.
• ⁴ Srinivas Kumar GLGSB, Chinara S, Das S, Tiwari C, Prakash GVS, Rao N. Studies on Ti-29Nb-13Ta-4.6Zr alloy for use as a prospective biomaterial. Mater Today Proc. 2019;1:11-20.
• ⁵ Dewangan S, Kulkarni AR., Varshney R, Reddy PPK. Mechanical properties and microstructure of Ti–6Al–4V alloy upon exposure to high heat and chemical quenching. J. Inst. Eng. India. 2024;Series D:1-9.
• ⁶ Polozov I, Nefyodova V, Zolotarev A, Sokolova V, Gracheva A, Popovich A. Development of low-modulus Ti-Ta alloys by in-situ synthesis during selective laser melting for implant applications. J Alloys Compd. 2025;1021:179682.
• ⁷ Kuroda PAB, Quadros FDF, Araújo ROD, Afonso CRM, Grandini CR. Effect of thermomechanical treatments on the phases, microstructure, microhardness and young’s modulus of Ti-25Ta-Zr alloys. Materials (Basel). 2019;12(19):3210.
• ⁸ Vishnu J, Manivasagam G, Rao N, Rack HJ. Fatigue and corrosion resistance of low modulus Ti-35Nb-7Zr-5Ta-0.35 O beta Ti alloy for orthopedic implant applications. Mater Today Commun. 2022;31:103366.
• ⁹ Nag S, Banerjee R, Fraser HL. A novel combinatorial approach for understanding microstructural evolution and its relationship to mechanical properties in metallic biomaterials. Acta Biomater. 2007;3(3):369-76.
• ¹⁰ Majumdar P, Singh SB, Chakraborty M. Elastic modulus of biomedical titanium alloys by nano-indentation and ultrasonic techniques: A comparative study. Mater Sci Eng A. 2008;489(1-2):419-25.
• ¹¹ Niinomi M, Akahori T, Takeuchi T, Katsura S, Fukui H, Toda H. Mechanical properties and cyto-toxicity of new beta type titanium alloy with low melting points for dental applications. Mater Sci Eng C. 2005;25(3):417-25.
• ¹² Raabe D, Sander B, Friák M, Ma D, Neugebauer J. Theory-guided bottom-up design of β-titanium alloys as biomaterials based on first principles calculations: theory and experiments. Acta Mater. 2007;55(13):4475-87.
• ¹³ Hussein MA, Mohammed AS, Al-Aqeeli N. Wear characteristics of metallic biomaterials: a review. Materials (Basel). 2015;8(5):2749-68.
• ¹⁴ Gepreel MAH, Niinomi M. Biocompatibility of Ti-alloys for long-term implantation. J Mech Behav Biomed Mater. 2013;20:407-15.
• ¹⁵ Li SJ, Yang R, Li S, Hao YL, Cui YY, Niinomi M, et al. Wear characteristics of Ti–Nb–Ta–Zr and Ti–6Al–4V alloys for biomedical applications. Wear. 2004;257(9-10):869-76.
• ¹⁶ Long M, Rack HJ. Titanium alloys in total joint replacement: a materials science perspective. Biomaterials. 1998;19(18):1621-39.
• ¹⁷ Konushkina SV, Kaplana MA, Sergienkoa KV, Gorbenkoa AD, Morozovaa YA, Ivannikova AY, Sudarchikovaa, MA, Sevostyanovac TM, Nasakinaa EO, Mikhlika SA, Kolmakova AG, Sevostyanova MA. Effect of heat treatment on the structure and mechanical properties of Ti–10Nb–(1–3)Mo Alloys. Inorg Mater Appl Res. 2023;15(2):395-401.
• ¹⁸ Wang O, Huang F, Chang H, Wu J, Zhang H, Wang W, et al. In situ passivation monitoring of Ti-6Al-4V in 3.5 wt% NaCl solution using ECAFM. Corros Sci. 2025;255:113102.
• ¹⁹ Kraus W, Nolze GJ. Powdercell – a program for the representation and manipulation of crystal structure and calculation of the resulting X-ray powder patterns. J Appl Cryst. 1996;29:301-3.
• ²⁰ Villars P, Calvert LD. Pearson’s handbook of crystallographic data for intermetallic phases 2. ed. Metals Park, Ohio: American Society for Metals; 1991.
• ²¹ Metikos-Hukovic M, Kwokal A, Piljac J. The influence of niobium and vanadium on passivity of titanium-based implants in physiological solution. Biomaterials. 2003;24:3765-75.
• ²² Gabriel SB, Nunes CA, Soares GA. Production, microstructural characterization and mechanical properties of Ti-10Mo-xNb alloys. Artif Organs. 2008;32(4):299-304.
• ²³ Gabriel SB, Dille J, Nunes CA, Soares GA. The effect of niobium content on the hardness and elastic modulus of heat-treated Ti-10Mo-xNb alloys. Mater Res. 2010;13(3):1-5.
• ²⁴ Ferrandini PL, Cardoso FF, Souza SA, Afonso CR, Caram R. Aging response of the Ti–35Nb–7Zr–5Ta and Ti–35Nb–7Ta alloys. J Alloys Compd. 2007;433:207-10.
• ²⁵ Veiga C, Davim JP, Loureiro AJR. Properties and applications of titanium alloys: a brief review. Advanced Study Center. 2012;32:132-48.
• ²⁶ Borborema S, Ferrer VDH, Rocha ADC, Cossú CMFA, Nunes ARV, Nunes C, et al. Influence of Nb Addition on α- and ω Phase Stability and on Mechanical Properties in the Ti-12Mo-xNb Stoichiometric System. Metals (Basel). 2022;12:1508.
• ²⁷ Hua N, Wang W, Wang Q, Ye Y, Lin S, Zhang L, et al. Mechanical, corrosion, and wear properties of biomedical Ti–Zr–Nb–Ta–Mo high entropy alloys. J Alloys Compd. 2021;861:157997.
• ²⁸ Ozerov M, Yurchenko N, Sokolovsky V, Nozdracheva E, Panina E, Nadezhdin S, et al. Microstructure and mechanical properties of biomedical Ti-Zr-Nb-Ta-Sn high-entropy alloys. Metals (Basel). 2023;13(2):353.
• ²⁹ Chen LY, Cui YW, Zhang LC. Recent development in beta titanium alloys for biomedical applications. Metals (Basel). 2020;10(9):1139.
• ³⁰ Gabriel SB, De Almeida LH, Nunes CA, Dille J, Soares GA. Maximisation of the ratio of microhardness to the Young’s modulus of Ti-12Mo-13Nb alloy through microstructure changes. Mater Sci Eng C. 2013;33:3319-24.
• ³¹ Nunes ARV, Borborema S, Araújo LS, Malet L, Dille J, de Almeida LH. Influence of thermo-mechanical processing on structure and mechanical properties of a new metastable β Ti–29Nb–2Mo–6Zr alloy with low young’s modulus. J Alloys Compd. 2020;820:153078.
• ³² Gabriel SB, Panaino JVP, Santos ID, Araujo LS, Mei PR, de Almeida LH, et al. Characterization of a new beta titanium alloy, Ti–12Mo–3Nb, for biomedical applications. J Alloys Compd. 2012;536:208-10.
• ³³ Yamako G, Janssen D, Hanada S, Anijs T, Ochiai K, Totoribe K, et al. Improving stress shielding following total hip arthroplasty by using a femoral stem made of β type Ti-33.6Nb-4Sn with a Young’s modulus gradation. J Biomech. 2017;63:135-43.
• ³⁴ Zhou YL, Niinomi M. Microstructures and mechanical properties of Ti–50 mass% Ta alloy for biomedical applications. J Alloys Compd. 2008;466(1-2):535-42.
• ³⁵ Cossú CMFA, Vincente ED, Cardoso IGR, Schettini YS, Precioso JAG, Nunes CA, et al. Mechanical and microstructural characterization of as-cast Ti-12Mo-xNb alloys for orthopedic application. Mater Res. 2019;22(1):e20190178.
• ³⁶ Hynowska A, Pellicer E, Fornell J, González S, Steenberge NV, Surinach S, et al. Nanostructured β-phase Ti-31.0Fe-9.0Sn and sub-μm structured Ti-39.3Nb-13.3Zr-10.7Ta alloys for biomedical applications: microstructure benefits on the mechanical and corrosion performances. Mater Sci Eng C. 2012;32:2418-25.
• ³⁷ Xu Y, Liu H, Zhang S, Xiong H. Effect of duplex aging on microstructural and mechanical behavior of a new β-Ti alloy for biomedical applications. J Mater Res Technol. 2022;18:2870-84.
• ³⁸ Soares FMS, Barbosa DM, Corado HPR, Santana AIC, Elias CN. Surface morphology, roughness, and corrosion resistance of dental implants produced by additive manufacturing. J Mater Res Technol. 2022;21:3844-55.
• ³⁹ Moraes PEL, Contieri RJ, Lopes ESN, Robin A, Caram R. Effects of Sn addition on the microstructure, mechanical properties and corrosion behavior of Ti–Nb–Sn alloys. J Alloys Compd. 2024;933:167569.
• ⁴⁰ Monteiro ES, Soares FMS, Nunes LF, Santana AIC, De Biasi RS, Elias CN. Comparison of the wettability and corrosion resistance of two biomedical Ti alloys free of toxic elements with those of the commercial ASTM F136 (Ti–6Al–4V) alloy. J Alloys Compd. 2020;822:153658.
• ⁴¹ Xu Y, Xiao Y, Yi D, Liu H, Wu L, Wen J. Corrosion behavior of Ti−Nb−Ta−Zr−Fe alloy for biomedical applications in Ringer’s solution. Trans Nonferrous Met Soc China. 2022;25:2556-63.
• ⁴² Kovacı H, Şenel K, Acar MT, Bozkurt YB, Çelik A. Comparative investigation of structural, morphological, mechanical, tribological and electrochemical properties of TiO₂films formed on Cp-Ti, Ti6Al4V and Ti45Nb alloys. Surf Coat Tech. 2024;487:131024.
• ⁴³ Chui P, Jing R, Zhang F, Li J, Feng T. Mechanical properties and corrosion behavior of b-type Ti-Zr-Nb-Mo alloys for biomedical application. J Alloys Compd. 2020;842:155693.
• ⁴⁴ Assis SL, Wolynec S, Costa I. Corrosion characterization of titanium alloys by electrochemical techniques. Electrochim Acta. 2006;51:1815-9.
• ⁴⁵ Cremasco A, Osório WR, Freire CMA, Garcia A, Caram R. Electrochemical corrosion behavior of Ti-35Nb alloy for medical prostheses. Electrochim Acta. 2008;53:4867-74.
• ⁴⁶ Moraes PEL, Contieri RJ, Lopes ESN, Robin A, Caram R. Effects of Sn addition on the microstructure, mechanical properties and corrosion behavior of Ti–Nb–Sn alloys. Mater Charact. 2014;96:273-81.
• ⁴⁷ Bai YJ, Wang YB, Cheng Y, Deng F, Zheng FY, Wei SC. Comparative study on the corrosion behavior of Ti-Nb and TMA alloys for dental application in various artificial solutions. Mater Sci Eng C. 2011;31:702-11.
• ⁴⁸ Rosalbino F, Maccio D, Scavino G, Saccone A. In vitro corrosion behaviour of Ti–Nb–Sn shape memory alloysin Ringer’s physiological solution. J Mater Sci Mater Med. 2012;23:865-71.
• ⁴⁹ Xu Y, Xiao Y, Yi D, Liu H, Wu L, Wen J. Corrosion behavior of Ti−Nb−Ta−Zr−Fe alloy for biomedical applications in Ringer’s solution. Trans Nonferrous Met Soc China. 2022;25:2556-63.
• ⁵⁰ Nnamchi PS, Obayi CS, Todd I, Rainforth MW. Mechanical and electrochemical characterization of new Ti–Mo–Nb–Zr alloys for biomedical applications. J Mech Behav Biomed Mater. 2016;60:68-77.
• ⁵¹ Li M, Pede D, Poleske T, Mozaffari-Jovein H. Influence of heat treatment and surface finishing on the corrosion behavior of additive manufactured Ti-6Al-4V. Advances in Metallurgical and Material Engineering. 2020;3(1):81-94.
• ⁵² Akman A, Alberta LA, Giraldo-Osorno PM, Turner AB, Hantusch M, Palmiquist A, Trobos M, Calin M, Gebert A. Effect of minor gallium addition on corrosion, passivity, and antibacterial behaviour of novel β-type Ti–Nb alloys. Corros Sci. 2023;215:110934.
• ⁵³ Monteiro ES, Soares FMS, Nunes LF, Santana AIC, De Biasi RS, Elias CN. Comparison of the wettability and corrosion resistance of two biomedical Ti alloys free of toxic elements with those of the commercial ASTM F136 (Ti–6Al–4V) alloy. J Alloys Compd. 2020;822:153658.
• ⁵⁴ Bajat JB, Milošev I, Jovanović Ž, Jančić-Heinemann RM, Dimitrijević M, Mišković-Stanković VB. Corrosion protection of aluminium pretreated by vinyltriethoxysilane in sodium chloride solution. Corros Sci. 2010;52:1060-9.
• ⁵⁵ Qin P, Liu Y, Sercombe TB, Li Y, Zhang C, Cao C, et al. Improved corrosion resistance on selective laser melting produced Ti–5Cu alloy after heat treatment. ACS Biomater Sci Eng. 2018;4:2633-42.
• ⁵⁶ Wang Z, Yan Y, Wu Y, Huang X, Zhang Y, Su Y, et al. Corrosion and tribocorrosion behavior of equiatomic refractory medium entropy TiZr(Hf, Ta, Nb) alloys in chloride solutions. Corros Sci. 2022;199:110166.
• ⁵⁷ Zhang Y, Wang Z, Huang S, Liu H, Yan Y. Electrochemical behavior and passivation film characterization of TiZrHfNb multi-principal element alloys in NaCl-containing solution. Corros Sci. 2024;235:112185.
• ⁵⁸ Bakkar A, El-Sayed Seleman MM, Ataya S, Reyad HA, Ibrahim KM, Aly HA. Effect of Si additions on the mechanical and electrochemical behavior of the as-cast Ti–15Mo alloy in simulated body fluid for biomedical applications. RSC Adv. 2026;16:23848-61.
• ⁵⁹ Cvijović-Alagić I, Cvijović Z, Bajat J, Rakin M. Composition and processing effects on the electrochemical characteristics of biomedical titanium alloys. Corros Sci. 2014;83:245-54.
• ⁶⁰ Han J, Zeng X, Yu Y, Wang H, Yang S, Sun S, et al. Corrosion behavior of Y₂O₃ reinforced Ti/TiC/TiB composite in simulated seawater and its dry friction performance. J Mater Res Technol. 2022;20:3875-90.
• ⁶¹ Qi G, Qin X, Xie J, Han P, He B. Electrochemical corrosion behaviour of four low-carbon steels in saline soil. RSC Adv. 2022;12:20929-45.

Edited by

• Associate Editor:
  Prof. Aloisio Klein.

• Editor-in-Chief:
  Luiz Antonio Pessan.

Publication Dates

• Publication in this collection
  25 Sept 2026
• Date of issue
  2026

History

• Received
  27 Oct 2025
• Reviewed
  01 June 2026
• Accepted
  13 Aug 2026