Effects of Cu,Re,and Mo ternary additions on the tribological and electrochemical properties of NiTi-based alloys fabricated by mechanical alloying and spark plasma sintering

Abstract

The toxicity of Ni²⁺ ions has been the bane of NiTi shape memory alloy (SMA) in various applications, such as biomedical. However, the formation of TiO₂ film, which doubles as a resistance to corrosion and wear in frictional applications, has been reported as unstable when exposed for a long period, further causing the mobility of Ni²⁺ to the surface. Therefore, this study investigated the enhancement in corrosion and tribological resistance of NiTi-based ternary alloys incorporated with two of the Cu, Re, and Mo for a given sample. The NiTi-based ternary alloys were fabricated via spark plasma sintering (SPS). The microstructure and crystal phases of the sintered sample were investigated using a scanning electron microscope and X-ray diffractometer, respectively. Their electrochemical responses in H₂SO₄ and NaCl solutions and their tribological features were determined, which showed different enhancement levels compared to the NiTi alloy. For the tribological properties, a combination of NiTi-0.5Re-0.8Mo gave the best wear resistance with a wear rate of about 1.219 × 10⁻⁷ mm³/N·m at 15N. The electrochemical test also revealed that the NiTi-Re-Mo ternary alloy group has the lowest corrosion rate, which can be attributed good chemical resistance of the combined Re and Mo that aided in TiO₂ film stability in both acidic and saline environments.

Keywords

NiTi alloy tribological corrosion molybdenum rhenium copper

Introduction

One persisting issue with NiTi-based SMAs is their corrosion response, which hinders their wide applications, especially in the human body due to the risk of toxicity to the body.^1,2 In a near-equiatomic NiTi alloy, Ti has a higher affinity for oxygen than Ni.³ When exposed to oxidizing conditions, whether through thermal treatments (such as autoclaving or controlled heat treatments) or electrochemical processes (like anodization), the surface titanium atoms preferentially react with oxygen, leading to the formation of a thin, continuous, rutile-structured TiO₂ film on the alloy's surface while the nickel becomes enriched in the subsurface.^4–6 In corrosive environments like H₂SO₄ and NaCl solutions, the integrity of the passive oxide layer on NiTi surfaces can be compromised. Chloride ions (Cl⁻) from NaCl are particularly aggressive, penetrating and disrupting the oxide layer, leading to localized corrosion or pitting.⁷ This degradation facilitates the release of nickel ions (Ni²⁺) into the solution, which not only deteriorates the material but also raises compatibility concerns due to the potential toxicity of nickel ions.^8,9 Studies have shown that exposure to Cl⁻ results in nickel ions being released into the solution and a decrease in the local nickel concentration at the pitting sites. Similarly, in acidic environments like H₂SO_4, the oxide layer's stability is challenged. The acidic medium can lead to the dissolution of the protective oxide film, exposing the underlying alloy to further corrosive attack and subsequent nickel ion release.¹⁰

On the other hand, this TiO₂ film also plays a key role in the tribology of the material, where the oxide film acts as a physical shield between the metal substrate and any contacting surface. By preventing direct metal-to-metal (or metal-to-counterface) contact, thereby reducing abrasive wear.¹¹ This is particularly important under cyclic or sliding conditions, where direct contact would otherwise accelerate material loss. Moreover, TiO₂ has a relatively low friction coefficient compared to NiTi, possessing a smooth and chemically resistant surface that minimizes friction during sliding and lowers the overall wear rate. Lower friction also means that less shear stress is transferred to the substrate. Through a strong interfacial adhesion with the substrate, applied loads are more evenly distributed across the surface, reducing localized stress concentrations that can initiate cracks, thereby preventing catastrophic delamination. Singh, Sharma¹² asserted that metal oxides are particularly beneficial in improving the wear resistance of NiTi due to their inherent hardness and ability to form an oxide protective film aided by the presence of hard phases in the alloy. Zhao et al.¹³ alloyed NiTi with hafnium and reported that the resulting alloy formed a combination of TiO₂ and HfO₂ films that yielded a good friction coefficient with increasing film thickness. Also, Farvizi et al.¹⁴ added nano-alumina to NiTi and reported a good wear resistance but at the expense of its psuedoelasticity.

The efficiency of the film is hinged on the formation of a stable and dense oxide film, which has remained elusive or rather, far from reach and has been one of the foci of research in recent times. This passive layer acts as a barrier, preventing corrosive species from reaching the underlying metal. However, increasing the thickness or density of TiO₂ could exacerbate delamination and initiate cracks due to the high brittleness of the oxide,¹⁵ leading to the further release of Ni²⁺ ions, and the study has established that although oxides of metals could improve resistance, adding them directly as an oxide does not do the alloy favors of retaining its shape memory effect. However, introducing metals that are known to improve NiTi alloy while still being able to form oxides during oxidation could be of advantage. Alloying with such materials can help stabilize the oxide film. For instance, the addition of rhenium (Re) enhances corrosion resistance in NiTi alloys, as its chemical inertness can impede oxide film dissolution and reduce the rate of metal dissolution. Increasing Re content raises the electrochemical potential, leading to increased dissolution impedance.¹⁶ While Mo suppresses the release of Ni²⁺ ions and improves the corrosion resistance of NiTi alloy, which makes it more suitable for medical devices and implants.^1,17 Copper, on the other hand, can aid in maintaining the transformation temperature, even though the oxide film generated is thin and cannot remain stable for a longer exposure duration.^18,19 Moreover, Re and Mo have limited solubility in NiTi, unlike Cu, and can form hard precipitates that are hard and can resist wear.^20,21 Therefore, in this study, NiTi-based ternary alloys incorporated with two of Cu, Re, and Mo in each sample are developed using the SPS technique. The effects of these alloying elements on tribological and electrochemical responses were determined. The results obtained show that the NiTi-based ternary alloys can create a synergy to improve corrosion and wear resistance simultaneously.

Materials and methods

Materials

Nickel powder, possessing a 99.7% purity and an average particle size of roughly 150 μm, along with titanium powder of 98% purity with particles ranging from 45 to 90 μm, was sourced from Alfa Aesar; this supplier also provided molybdenum powder at a 99.5% purity level and particle size of 45–90 μm. Copper powder, characterized by particles less than 100 μm and a purity of 99.5%, was acquired from Aldrich Chemicals, while Thermo Scientific supplied rhenium powder with an approximate particle size of 44 μm and a purity of 99.99%.

Methods

This study used a powder metallurgy process, where six NiTi-based ternary samples composed of Cu-Re, Cu-Mo, and Re-Mo in the proportion detailed in Table 1, were mixed in a tubular mixer containing stainless steel balls at a ball-to-powder ratio of 10:1 for 10 h at a speed of 100 rpm. Before that, Ni and Ti powders were first mixed at a ratio of 1:1 by wt% using the tubular mixer for 10 h at a speed of 100 rpm. Following mixing of NiTi with the alloying elements, the powders were compacted using a hydraulic press (SPEX SamplePrep 35-Ton) to form a green compact. After that, each compacted sample was put inside a graphite die and sintered using an SPS machine with the following parameters: 1050°C for the sintering temperature, 45 MPa for the pressure, 50°C/min for the heating rate, and 10 min for the dwelling period. Once the sintering cycle was complete, the sample was allowed to cool to room temperature, and finally, sandblasting was carried out to remove any residual impurities on their surfaces. NiTi without any alloying element was also sintered using the same conditions. The samples were cut to size for various analyses as contained in the study.

Table 1.

Compositions of the NiTi-Cu-Mo/Cu-Re/Mo-Re ternary materials.

Exp. no	Cu (wt.%)	Re (wt.%)	Mo (wt.%)	NiTi (wt.%)	Samples
1	-	-	-	100 (50Ni50Ti)	NiTi
2	5	-	0.8	94.2	NiTi-5Cu-0.8Mo
3	10	-	0.5	89.5	NiTi-10Cu-0.5Mo
4	5	0.8	-	94.2	NiTi-5Cu-0.8Re
5	10	0.5	-	89.5	NiTi-10Cu-0.5Re
6	-	0.8	0.5	98.7	NiTi-0.8Re-0.5Mo
7	-	0.5	0.8	98.7	NiTi-0.5Re-0.8Mo

Characterization

The morphology of the sintered alloys was analyzed using a JEOL JSM−7600F scanning electron microscope (SEM) equipped with EDS and operated at an accelerating voltage of 15 kV. The diffraction pattern was examined with an X'pert PRO PANalytical machine. To assess the electrochemical corrosion behavior of the samples, a linear polarization test was conducted using an Autolab Potentiostat (PGSTAT 101) controlled by NOVA software. The samples were tested in two corrosive environments—0.5 M H₂SO₄ and 3.5% NaCl solutions—with Ag/AgCl in saturated KCl solution serving as the reference electrode, platinum as the counter electrode, and the sample as the working electrode. In the 0.5 M H₂SO₄ environment, the potential was scanned at a rate of 0.001 V/s, whereas in the NaCl solution, a scan rate of 0.01 V/s was used. Subsequently, corrosion parameters such as corrosion rate and polarization resistance were calculated through TAFEL extrapolation. Tribological tests of the sample were performed using a ball-on-disc tribometer (Anton Paar, TRB3) connected to software that generated the coefficient of friction (COF) under dry sliding mode at room temperature. A stainless steel ball of about 6 mm in diameter was employed as the counter surface at applied loads of 15 N and 20 N. The sliding velocity was set at 3 cm/s, with each test lasting 60 min

Results and discussion

Microstructural analysis

SEM/EDS micrographs of NiTi-Mo-Cu alloys are presented in Figure 1. The light and dark gray regions in the micrograph correspond to the NiTi phase and Ti-enriched with NiTi₂ phase, respectively.^22,23 There were no noticeable Mo and Cu elements in the micrograph, which can be credited to the appreciable dissolution of the elements in the NiTi system. This could have resulted from the well-distribution of Cu and Mo powders in the NiTi system during mechanical alloying, followed by the SPS process. The accompanying EDS analysis corroborates the presence of these powders. The enhanced wear and corrosion resistance observed in this study, as discussed in the subsequent section, are due to the presence of good dissolution of the elements, while Cu is linked to increasing plasticity and bonding of the fabricated alloys.²⁴ The incorporation of the alloying elements is associated with enhanced properties compared to the NiTi alloy.

Figure 1.

SEM/EDS micrographs of the NiTi-Mo-Cu, NiTi-Re-Cu, and NiTi-Re-Mo.

Also, the SEM/EDS of the NiTi-Re-Cu alloys is illustrated in Figure 1. The spherical shape of all the powders aided their homogeneous mixing in combined form, which also, in conjunction with elevated sintering temperature, aided in the minimal voids in the microstructure.²⁵ However, comparing the micrographs of the NiTi-Mo-Cu and NiTi-Re-Cu, it is noted that there are precipitations of Re in white-like form in the micrographs of NiTi-Re-Cu. This could have a significant contribution to the improvement of the wear and corrosion resistance. The EDS shows the presence of Ni, Ti, Cu, and Re elements for NiTi-Re-Cu alloy. In the micrograph of the NiTi-Re-Mo alloys, the white-like precipitates of the Re element are also observed in addition to the light gray region (NiTi phase) and dark gray region (Ti-enriched with NiTi₂ phase). However, the phase of NiTi₂ was minimal for the NiTi-Re-Cu compared to the NiTi-Re-Mo, which suggests that the Cu aided in the suppression of the intermetallic NiTi₂ phase in the NiTi-Re-Cu alloy. There could be other phase formations, such as Ni₄Ti₃, and Ni₃Ti₂ in the form of nano-scale precipitates. Although proper dissolution of Re in the alloy is essential for better strength,^25,26 the precipitates of the Re could enhance hardness and plastic deformation resistance, leading to improved tribological properties.

X-Ray diffraction pattern

Figure 2 displays the XRD patterns of the NiTi, NiTi-Cu-Mo, NiTi-Cu-Re, and NiTi-Mo-Re alloys. The diffraction patterns are juxtaposed with those of their respective compositions and the NiTi alloy. Prominent peaks for NiTi alloy manifest at 2θ = 35°, 44°, 53°, and 63°. Notably, the identified phases are monoclinic NiTi, NiTi_2, and hexagonal Ni₃Ti.²⁷ The observed deviations in diffraction peaks across 2θ for various fabricated samples, in comparison to the base of NiTi alloy, can be ascribed to the inclusion of the alloying elements, Cu, Mo, and Re, into the NiTi system. The XRD spectrum for the NiTi-Cu-Mo alloy, illustrated in Figure 2(a), reveals major peaks at 2θ = 38°, 40°, 44°, 52°, and 76°. These peaks correspond to the presence of NiMo₂, NiTiMo₂, NiCuMo₂, NiTi, and NiTi₂ phases. Similarly, in the case of NiTi-Cu-Re alloy, depicted in Figure 2(b), peaks emerge at 2θ = 40°, 44°, 51°, and 76°, signifying the formation of phases including CuTi, Ni, NiTi₃, and Re, respectively. The addition of the copper element has been noted to prevent the formation of the metastable Ni₄Ti₃ phase^28,29 and stabilize the present B2 phase by altering the transformation phase/temperature in the ternary systems under consideration. Furthermore, Figure 2(c) highlights the emergence of distinct phases, namely Mo-NiTi₃, NiTi₂, Ni, and NiTiMoRe, demonstrating the intricate structural transformations induced by the sintering process. The corresponding crystal planes of the diffraction peaks at different 2θ for all the samples are represented in Figure 2.

Figure 2.

X-Ray diffractograph of the (a) NiTi-Mo-Cu (b) NiTi-Re-Cu and (c) NiTi-Re-Mo alloys.

Tribological properties

Illustrated in Figure 3 is the coefficient of friction (COF) of the alloys subjected to 15N and 20N loadings. As the COF diminishes, the material tends to demonstrate enhanced resistance to wear in practical applications.^30,31 The graphical representations showcase consistent profiles, indicating analogous trends in the samples’ frictional behaviours. However, with the incorporation of Cu, Mo, and Re elements into the NiTi-alloy system, a discernible reduction in the COF values is evident. This suggests that the NiTi-based ternary systems exhibit superior resistance to frictional forces compared to the NiTi alloy. From the COF, it is noteworthy that the sample comprising NiTi-0.8Re-0.5Mo yielded the lowest COF values at both applied loads over the frictional test duration. This observation is attributed to the addition of Re^32,33 and Mo,^34–36 which have good mechanical properties such as hardness, in turn resulting in enhanced friction resistance. Prior studies have indicated that Mo and Re possess notable resistance to friction, consequently contributing to the observed decrease in COF values in this study. Improvement in the tribology properties of NiTi-based ternary alloys can also be credited to the formation of secondary structures on wear surfaces during friction as previously reported.³⁰ There is a slight decrease in the COF as the applied force increases from 15 N to 20 N, which can be accounted for better conformity between the sliding surface and the materials under the frictional test. In addition, as the load increases and the frictional test proceeds, there is internally generated heat within the samples that can react with the atmosphere to form protective oxide layers (in the form of TiO₂ and/or MoO₂), which can further reduce friction. However, due to the possible destruction of such protective layers as the friction continuous and plastic deformation, the samples experience abrasive wear (which is more severe at high applied load), hence, resulting in the larger wear rate of the sample as the applied load increases.

Figure 3.

(a) Coefficient of friction of the NiTi-Cu-Mo, NiTi-Cu-Re and NiTi-Mo-Re alloys at (a) 15N and (b) 20N.

The graphical representation in Figure 4 illuminates the wear rates exhibited by the NiTi-based ternary alloys at 15N and 20N applied loads. Wear rates serve as a crucial measure of resistance to material's removal, providing insights into its propensity to undergo wear-induced failure. In essence, a material with commendable wear resistance is anticipated to yield lower wear rate values. Analyzing the data from Figure 4, it can be seen that the NiTi alloy records the highest wear rate values under both 15N and 20N applied loads. However, the introduction of two of the Cu, Mo, and Re elements into the NiTi alloy system results in a noticeable reduction in wear rates for the ensuing NiTi-based ternary systems. This can be credited to the possible different intermetallic hard phases formed in the NiTi-based ternary alloys as identified by the XRD analysis. The intermetallic phases, in conjunction with the dissolution of the alloying elements and formation of solid solution in the NiTi matrix, contributed to the enhanced wear resistance of the alloys. For instance, NiTi exhibited higher wear rates of 4.768 × 10⁻⁶ mm³/N·m at 15 N and 6.932 × 10⁻⁵ mm³/N·m at 20 N, while NiTi-0.5Re-0.8Mo, on the other hand, exhibited lower wear rates of 1.219 × 10⁻⁷ mm³/N·m and 1.453 × 10⁻⁷ mm³/N·m at 15 N and 20 N applied loads, respectively. Other NiTi-based ternary alloys also revealed different degrees of reduced wear rates compared to the NiTi alloy, as shown in Figure 4. Primarily, NiTi-Re-Mo-based alloy revealed lower wear rates at both applied loads compared to other samples. This can be attributed to the precipitation of the Re in the matrix (as revealed by the SEM micrographs in Figure 1), which aided in the impediment of dislocation propagation and plastic deformation during the wear test. On the other hand, the alloy containing Cu showed lower wear resistance among all the fabricated NiTi-based ternary alloys, especially at a high content of Cu (10 wt%). This can be traced to the softer nature of Cu compared to Mo and Re, with higher hardness and wear resistance properties. In addition, favorable homogenous morphology is achieved through the spherical shapes of NiTi, Mo, and Re powders,³⁷ coupled with the utilization of the SPS technique to fabricate samples with minimal porosity,³⁸ has been linked to improved wear resistance. In general, all the NiTi-based ternary alloys showed better anti-wear features compared to the NiTi alloy.

Figure 4.

(a) Wear rate of the NiTi-Cu-Mo, NiTi-Cu-Re and NiTi-Mo-Re alloys.

Electrochemical properties

Potentiodynamic polarization (PDP) and open circuit potential (OCP)

Illustrated in Figures 5 and 6 are the PDP and OCP plots of the NiTi-based ternary alloys when exposed to acid and basic environments. Table 2 provides a detailed overview of the TAFEL extrapolation parameters extracted from the PDP plots. Corrosion resistance in materials is often associated with lower corrosion current, reduced corrosion rate value, higher corrosion potential, and increased polarization resistance.^39–41 The curves depicted for the NiTi-based ternary alloys exhibit consistent trends, indicating a uniform corrosion resistance property. This consistency is attributed to the predominant presence of the NiTi alloy system in higher compositions for all the fabricated samples. The PDP plot in Figure 5 reveals that the NiTi-0.5Re-0.8Mo alloy exhibits the lowest corrosion current and corrosion rate compared to other fabricated alloys in an acid environment. On the other hand, NiTi-0.8Re-0.5Mo alloy showed low corrosion current and corrosion rate compared to other alloys in the salt medium. This observation suggests that a ternary alloy with materials that make up NiTi-Re-Mo is poised to offer superior resistance compared to NiTi-Mo-Cu and NiTi-Re-Cu ternary alloys. The formation of the NiTi-based ternary alloy could have simultaneously formed a stable mixed oxide (TiO₂ and MoO₂), and this is more pronounced in Mo-rich alloys in combination with Re or Cu in smaller quantities in an acidic medium. While the corrosion resistance is not favorable for the NiTi-based ternary alloy with Re in rich quantity and less Cu in an acid medium and all the NiTi-based ternary alloy containing Re and Cu in salt medium, which could be ascribed to Re-based intermetallics formed during sintering and their large differences in electrode potential leading to high localized corrosion attacks. Such Re-rich intermetallics could disrupt and break the already formed protective oxide or passive layers, leading to more corrosion attacks on the samples. The TAFEL extrapolation in Table 2 reinforces this observation, establishing a hierarchy of increased corrosion resistance in the acid medium (which has approximately a similar trend in the salt medium) as follows: NiTi < NiTi-0.8Re-5Cu < NiTi-0.8Re-5Mo < NiTi-0.5Re-10Cu < NiTi-0.5Mo-10Cu < NiTi-0.8Mo-5Cu < NiTi-0.5Re-0.8Mo. The lower corrosion resistance of the NiTi-Re-Cu alloy group could be a result of the Re precipitates in the matrix of the NiTi alloy, as revealed by the SEM micrograph, where the precipitates could act as corrosion concentration sites. However, such corrosion concentration sites could have been suppressed by the presence of Mo in the NiTi-Re-Mo alloy group, resulting in their optimal corrosion resistance. Additionally, both the PDP plots and TAFEL extrapolation indicate that the fabricated alloys generally exhibit enhanced resistance to corrosion in the acid medium compared to the salt medium. This discrepancy may be attributed to the different concentrations of the media and different chemical attack capabilities of Cl⁻ and SO₄²⁻ from NaCl and H₂SO_4, respectively.

Figure 5.

Pontentiodynamic polarization curves of the NiTi-Cu-Mo, NiTi-Cu-Re and NiTi-Mo-Re Alloys in (a) H₂SO₄ and (b) NaCl.

Figure 6.

Open circuit potential curves of the NiTi-Cu-Mo, NiTi-Cu-Re and NiTi-Mo-Re Alloys in (a) H₂SO₄ and (b) NaCl.

Table 2.

TAFEL parameters derived from potentiodynamic polarization curves.

Corrosion media	Ecorr (V)	Icorr (A)	Corrosion rate (mm/yr)	Polarization resistance (Ω)
H₂SO₄
NiTi	−0.20948	1.17E-4	1.3629	1072
NiTi-0.5Mo-10Cu	−0.1712	1.44E-05	0.16747	2782.8
NiTi-0.8Mo-5Cu	−0.20526	1.15E-05	0.13369	2837.7
NiTi-0.5Re-0.8Mo	−0.20557	9.76E-06	0.11337	4745.8
NiTi-0.8Re-0.5Mo	−0.15755	3.27E-05	0.38022	2165.4
NiTi-0.8Re-5Cu	−0.20901	4.52E-05	0.52543	1105.6
NiTi-0.5Re-10Cu	−0.2160	1.5E-05	0.17438	2789.7
NaCl
NiTi	−0.52114	2.08E-4	2.4149	860.14
NiTi-0.5Mo-10Cu	−0.48613	3.78E-5	0.4398	3673.4
NiTi-0.8Mo-5Cu	−0.43835	9.35E-5	1.086	4369.4
NiTi-0.5Re-0.8Mo	−0.36164	2.06E-5	0.23982	6184.6
NiTi-0.8Re-0.5Mo	−0.47939	1.91E-5	0.22166	4773.8
NiTi-0.8Re-5Cu	−0.55596	8.75E-5	1.017	5542.3
NiTi-0.5Re-10Cu	−0.5221	7.87E-5	0.91487	1115.5

Figure 6 presents the OCP plot of the NiTi-based ternary alloys when exposed to acid and base environments. The OCP graph illustrates the impact of potential variations over time on the corrosion resistance properties of the samples. It is widely acknowledged that a material's ability to resist corrosion is positively correlated with higher potential values; in other words, the higher the potential, the greater the material's resistance to corrosion.^42–44 From the potential changes of the samples over time, a notable pattern emerges— under H₂SO₄, the alloys initially reach their maximum potential at the onset of exposure and subsequently experience a rapid decline with prolonged exposure; however, a steady and slow decline was noted for NaCl medium. This trend suggests that the samples are more influenced by electrochemical degradation in sulfuric acid than in NaCl medium. However, the corrosion rate is higher in NaCl medium due to the low potentials of the alloy samples compared to when exposed to H₂SO₄ medium. Among the samples, the alloy comprising NiTi-0.5Re-0.8Mo exhibits the most robust resistance to corrosion in the exposed mediums, while the NiTi alloy displays the least resistance to corrosion.

Conclusion

Tribological and corrosion resistance of NiTi-based ternary alloys consisting of Cu, Re, and Mo elements were investigated in this study. The NiTi-based ternary alloys were fabricated via spark plasma sintering with parameters of 1050°C temperature, 45 MPa pressure, 10 min duration, and 50°C/min heating rate. On the tribological investigation of the alloys, this study noted that NiTi alloy wears fastest under frictional tests at 15N and 20N applied loads. However, alloying the NiTi matrix with any of the two; Cu, Mo, and Re elements, reduces the wear rate, demonstrating that these materials greatly improve wear resistance, whereas the NiTi-Re-Mo alloy group has more pronounced wear resistance compared to other fabricated samples. For instance, with a wear rate of around 1.219 × 10⁻⁷ mm³/N·m at 15N, a combination of NiTi-0.5Re-0.8Mo provided the best wear resistance for the tribological parameters. Notably, the NiTi-Re-Mo alloy group has smoother surfaces and smaller wear grooves, demonstrating their better anti-wear response and ability to sustain wear force and minimize surface irregularities. On the other hand, this study also examined the electrochemical response of the fabricated NiTi-based ternary alloys. The PDP plot showed that the NiTi-Re-Mo alloy group has the lowest corrosion current and corrosion rate in acid and basic environments. In general, PDP plots and TAFEL extrapolation showed that NiTi-based ternary alloys resist corrosion better than NiTi alloy. The fabricated NiTi-based ternary alloy samples could find potential applications in severe corrosive and frictional environments, especially NiTi-Re-Mo alloys, aiming at advanced engineering use.

Footnotes

Acknowledgment

The authors would love to appreciate Tshwane University of Technology for their support towards this study.

ORCID iDs

Boingotlo I Setlhabi

Uwa O Uyor

Author contribution(s)

Boingotlo I. Setlhabi: Conceptualization; Writing – original draft.

Uwa O. Uyor: Methodology; Supervision.

Abimbola P. Popoola: Formal analysis; Validation.

Olawale M. Popoola: Project administration; Validation.

Chika O. Ujah: Writing – review & editing.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data availability statement

All data sets associated with this study are presented in this article.

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