2. Materials and Methods
Laboratory-size specimens (~60 g) of the Ti30Zr38Nb20Ta8Sn4, Ti40Zr38Nb10Ta8Sn4, and Ti50Zr38Ta8Sn4 alloys (hereafter designated as Ti30Nb20, Ti40Nb10, and Ti50Nb0, respectively) were produced by vacuum arc melting using Ti, Zr, Nb, Ta, and Sn granules (≥99.9 wt.% purity in each case) in a high-purity argon atmosphere. Before the melting procedure, the chamber was degassed and flushed with argon 3 times; the last vacuuming reached 10−5–10−6 millibars. The microstructure of the obtained alloys was analyzed using scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD) analysis. Specimens for EBSD observations were prepared through careful mechanical polishing. EBSD was conducted with a FEI Quanta 600 FEG (Thermo Fisher Scientific, Hillsboro, OR, USA) field-emission-gun scanning electron microscope (FEG-SEM) operated at an accelerating voltage of 20 kV and equipped with a TSL OIM™ system (EDAX, Pleasanton, CA, USA). The maps were obtained using a scan step size of 0.05 µm. The size of each scanned region was 1 × 1 mm2. The grain size was estimated using at least 3 images covering ~150 grains. Kernel average misorientation (KAM) maps were used for a more comprehensive analysis of the microstructures. KAM is the average misorientation angle of a given pixel in an EBSD map with respect to its neighbors. Therefore, it shows the local orientation spread and can be used as a measure of excess dislocation density of the same sign and local lattice distortion/curvature.
Tensile tests were conducted using an Instron 5882 machine (Instron, Canton, USA) at room temperature with an initial strain rate of 10
−3 s
−1. Dog-bone-shaped tensile specimens with a gauge of 6 × 3 × 1.5 mm
3 were used. The digital image correlation (DIC) technique was employed to visualize the distribution of local strains produced during the tensile tests. The in-plane Lagrangian strains were measured using a commercial Vic-3D
TM system (Correlated Solutions, Inc., Irmo, SC, USA). The resonance frequency damping analysis (RFDA) method [
15] using the IMCE measuring system (IMCE NV, Genk, Belgium) was applied for Young’s modulus determination. The size of the measured samples was 55 × 12 × 5 mm
3. Microhardness was measured using an automated Vickers hardness testing machine (Instron, Norwood, MA, USA) with a 300 g load for 50 s.
A direct-contact cytotoxicity assay of the composites was carried out in vitro using rat mesenchymal stem cells (MSCs). A photometry technique using a microplate photometer Multiskan FC and an MTT reagent (cat. M5655, Sigma-Aldrich, St. Louis, MO, USA) [
16] was utilized. MSCs with metal samples were cultivated in a CO
2 incubator (95% humidity, 37 °C temperature, 5% CO
2) for 72 hours in a nutrient medium (DMEM/F12) (cat. 11320033 Thermo Scientific, Waltham, MA, USA) supplemented with 10% fetal bovine serum (Cytiva, HyClone, USA) and antibiotics. A polystyrene surface without a composite disc was used as a control sample. Cell viability was calculated using the formula Cell viability (%) = (A) test/(A) control × 100, where (A) test is the absorption of the test sample, and (A) control is the control sample absorption. The obtained results were statistically processed using the Wilcoxon T-test on the Statistica 6.0 software (StatSoft, Krakow, Poland). A qualitative assessment of cytotoxicity was performed microscopically using an inverted optical microscope Eclipse Ti-S (Nikon, Tokyo, Japan) equipped with a digital camera.
4. Discussion
The obtained results suggest significant differences in the properties and mechanical behavior of the Ti(50-x)Zr38NbxTa8Sn4 alloys depending on the content of Ti and Nb. The most apparent change is related to the decrease in strength and Young’s modulus as the Ti content increases (
Table 1). The mechanical properties of HEAs are known to be dependent on the choice and concentration of the constitutive elements (the so-called “cocktail effect” [
21], which can be noteworthy). For instance, the present study revealed a linear relationship between the Nb content and Young’s modulus in the program alloys (
Figure 7). The vast knowledge obtained from bcc Ti alloys suggests that Nb doping generally decreases the modulus of the materials [
22,
23,
24,
25], yet this effect strongly depends on the Nb concentration. However, at a certain concentration range, the opposite trend (i.e., an increase in the moduli) can be observed [
26]. The same trend seems to hold true for the program alloys.
In terms of strength, Nb atoms can generate lattice elastic strains due to differences in atomic size and modulus compared to the atoms of the other constitutive elements. The resulting increase in strength (i.e., solid solution strengthening), in this case, is expected to be proportional to C
1/2Nb according to the classic Fleisher approach [
27]. The comparison between experimental yield strength values and C
1/2Nb (
Figure 7) suggests that solid solution strengthening is the main responsible for strength variations in the program alloys. Other sources, such as grain boundary strengthening [
28,
29], are likely to have a minor effect.
Another interesting aspect found in this study is the difference in mechanical behavior of the studied alloys after yielding. The Ti30Nb20 and Ti40Nb10 alloys showed a gradual decrease in flow stress in the post-yielding region, which was due to strain localization without early necking (
Figure 3). In contrast, the Ti50Nb0 alloy demonstrated more uniform deformation after the yield point, as reported previously for a number of alloys [
30,
31,
32,
33]. The tendency toward apparent premature strain localization can be attributed to a non-uniform spatial distribution of dislocations in the microstructure. For example, the Al-induced B2 ordering of a NbTiZr HEA resulted in the localization of plastic deformation in multiple DBs [
34]. Instead of deteriorating the mechanical properties, this localization increased the ductility of Al-containing alloys compared to the Al-free NbTiZr HEA, in which dislocation distribution was uniform.
In the Ti30Nb20 and Ti40Nb10 alloys, the formation of DBs and the activation of cross-slip were also observed (
Figure 5a,b). In addition to microscopic localization, noticeable heterogeneity in strain distribution at the mesoscale (
Figure 4b,d) resulted in macroscopic plastic flow instability (
Figure 3). Moreover, the formation of KBs (
Figure 4), which caused geometric softening due to stress relaxation and crystal reorientation [
35], seemed to be another factor contributing to a reduction in flow stress. The KAM maps showed a considerable increase in dislocation density around KBs, indicating the KB boundaries could contribute to strengthening, as seen in the upturn trend in the dσ/dε curves of the Ti30Nb20 and Ti40Nb10 alloys (the so-called dynamic Hall–Petch effect) (
Figure 2b and
Figure 4). In contrast, the lamellar-like KB-free microstructure with parallel DBs (without visible cross-slipping;
Figure 5c) prevented early macroscopic localization in the Ti50Nb0 alloy, resulting in relatively larger uniform elongation (
Figure 2a and
Figure 3).
The observed difference can probably be attributed to the stability of the bcc phase in these alloys. In Ti alloys, the stability of the bcc phase is typically evaluated using the molybdenum equivalent, in which the contribution of all bcc-stabilizing elements is calculated using the equation [
36] Mo
eq. = 1.0 Mo + 0.67 V + 0.44 W + 0.28 Nb + 0.22 Ta + 2.9 Fe + 1.6 Cr − 1.0 Al. In our case, the program alloys have Mo
eq. = 7.36, 4.56, and 1.76 for Ti30Nb20, Ti40Nb10, and Ti50Nb0, respectively. This approach, without a doubt, cannot be used for HEAs with a high content of Ti, since, according to the accepted classification, a Mo
eq. < 3 is typical for near α alloys with an hcp lattice, while Ti50Nb0 has the bcc structure.
Another approach for predicting the main deformation mechanism in Ti alloys was proposed by Morinaga and co-authors [
37]. In this approach, the bond order Bo and the metal d-orbital energy level Md were used to predict the β-phase stability in titanium alloys. Later, the Bo–Md map was used to tailor the chemical composition of Ti-rich HEAs [
38]. Although some Ti-rich HEAs can indeed be clustered as per their main deformation mechanism (
Figure 8), the Ms = RT is barely a straight line as it was initially proposed by Lilensten and co-authors [
37]. Indeed, the results obtained in the present work show that the program alloys are located above (Ti30Nb20), on (Ti40Nb10), and below (Ti50Nb0) the Ms = RT line, but none of them exhibits TRIP/TWIP effects, and the two upper alloys (Ti30Nb20 and Ti40Nb10) have similar behavior, which differs considerably from that of the Ti50Nb0 alloy. Furthermore, another well-known HfNbTaTiZr HEA with a microstructure evolution essentially similar to that of Ti30Nb20 and Ti40Nb10 is located well above the proposed Ms = RT line (
Figure 8).
However, it should be noted that the developed alloys (Ti30Nb20 and Ti40Nb10) have properties that make them highly attractive for biomedical application, owing to a combination of very high yield strengths (1090 and 930 MPa, respectively), low Young’s moduli (~78 and ~69, respectively), and reasonable ductility. The results of the cytotoxicity assay also show that the Ti40Nb10 alloy has a somewhat low cytotoxic effect, while Ti50Nb0 can be considered an absolutely biocompatible alloy. However, the Ti30Nb20 alloy has a more pronounced cytotoxic effect (without causing total cell death) that inhibits the proliferation processes and triggers MSC apoptosis.
Author Contributions
Conceptualization, S.Z., N.S. and N.Y.; methodology, M.O., N.Y., V.S. and E.P.; validation, S.Z. and M.O.; formal analysis, S.Z., N.Y. and M.O.; investigation, M.O., N.Y., E.P., E.N., V.S. and S.N.; resources, S.Z.; data curation, S.Z., M.O. and S.N.; writing—original draft preparation, M.O.; writing—review and editing, S.Z., N.S. and N.Y.; visualization, M.O.; supervision, S.Z. and M.O.; project administration, S.Z.; funding acquisition, S.Z. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by the Ministry of Science and Higher Education of the Russian Federation, project No. 20180167 “Development of high-entropy alloys for biomedical applications” within the program “Priority-2030”. A part of this research (TEM specimens’ preparation) was partially funded by the Ministry of Science and Higher Education of the Russian Federation as part of the World-class Research Center program: Advanced Digital Technologies (Contract no. № 075-15-2022-312 dated 20 April 2022).
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
The raw/processed data required to reproduce these findings cannot be shared at this time as the data also form part of an ongoing study.
Acknowledgments
This work was performed under the framework of the Development Program of Belgorod State University for 2021–2030 (“Priority 2030”). Investigations were carried out using the equipment of the Joint Research Center of Belgorod State National Research University «Technology and Materials» with financial support from the Ministry of Science and Higher Education of the Russian Federation within the framework of agreement No. № 075-15-2021-690 (unique identifier for the project RF----2296.61321X0030).
Conflicts of Interest
The authors declare no conflict of interest.
References
- Song, Y.; Xu, D.S.; Yang, R.; Li, D.; Wu, W.T.; Guo, Z.X. Theoretical study of the effects of alloying elements on the strength and modulus of β-type bio-titanium alloys. Mater. Sci. Eng. A 1999, 260, 269–274. [Google Scholar] [CrossRef]
- Long, M.; Rack, H. Titanium alloys in total joint replacement—A materials science perspective. Biomaterials 1998, 19, 1621–1639. [Google Scholar] [CrossRef] [PubMed]
- Braic, V.; Balaceanu, M.; Braic, M.; Vladescu, A.; Panseri, S.; Russo, A. Characterization of multi-principal-element (TiZrNbHfTa)N and (TiZrNbHfTa)C coatings for biomedical applications. J. Mech. Behav. Biomed. Mater. 2012, 10, 197–205. [Google Scholar] [CrossRef]
- Oliveira, J.P.; Panton, B.; Zeng, Z.; Andrei, C.M.; Zhou, Y.; Miranda, R.M.; Fernandes, F.M.B. Laser joining of NiTi to Ti6Al4V using a Niobium interlayer. Acta Mater. 2016, 105, 9–15. [Google Scholar] [CrossRef]
- Miracle, D.B.; Senkov, O.N. A critical review of high entropy alloys and related concepts. Acta Mater. 2017, 122, 448–511. [Google Scholar] [CrossRef]
- Geetha, M.; Singh, A.K.; Asokamani, R.; Gogia, A.K. Ti based biomaterials, the ultimate choice for orthopedic implants—A review. Prog. Mater. Sci. 2009, 54, 397–425. [Google Scholar] [CrossRef]
- Castro, D.; Jaeger, P.; Baptista, A.C.; Oliveira, J.P. An Overview of High-Entropy Alloys as Biomaterials. Metals 2021, 11, 648. [Google Scholar] [CrossRef]
- Motallebzadeh, A.; Peighambardoust, N.S.; Sheikh, S.; Murakami, H.; Guo, S.; Canadinc, D. Microstructural, mechanical and electrochemical characterization of TiZrTaHfNb and Ti1.5ZrTa0.5Hf0.5Nb0.5 refractory high-entropy alloys for biomedical applications. Intermetallics 2019, 113, 106572. [Google Scholar] [CrossRef]
- Ishimoto, T.; Ozasa, R.; Nakano, K.; Weinmann, M.; Schnitter, C.; Stenzel, M.; Matsugaki, A.; Nagase, T.; Matsuzaka, T.; Todai, M.; et al. Development of TiNbTaZrMo bio-high entropy alloy (BioHEA) super-solid solution by selective laser melting, and its improved mechanical property and biocompatibility. Scr. Mater. 2021, 194, 113658. [Google Scholar] [CrossRef]
- Popescu, G.; Ghiban, B.; Popescu, C.A.; Rosu, L.; Truscă, R.; Carcea, I.; Soare, V.; Dumitrescu, D.; Constantin, I.; Olaru, M.T.; et al. New TiZrNbTaFe high entropy alloy used for medical applications. IOP Conf. Ser. Mater. Sci. Eng. 2018, 400, 022049. [Google Scholar] [CrossRef] [Green Version]
- Akmal, M.; Hussain, A.; Afzal, M.; Lee, Y.I.; Ryu, H.J. Systematic study of (MoTa)xNbTiZr medium- and high-entropy alloys for biomedical implants- In vivo biocompatibility examination. J. Mater. Sci. Technol. 2021, 78, 183–191. [Google Scholar] [CrossRef]
- Yuan, Y.; Wu, Y.; Yang, Z.; Liang, X.; Lei, Z.; Huang, H.; Wang, H.; Liu, X.; An, K.; Wu, W.; et al. Formation, structure and properties of biocompatible TiZrHfNbTa high-entropy alloys. Mater. Res. Lett. 2019, 7, 225–231. [Google Scholar] [CrossRef]
- Gurel, S.; Yagci, M.B.; Canadinc, D.; Gerstein, G.; Bal, B.; Maier, H.J. Fracture behavior of novel biomedical Ti-based high entropy alloys under impact loading. Mater. Sci. Eng. A 2021, 803, 140456. [Google Scholar] [CrossRef]
- Yang, W.; Liu, Y.; Pang, S.; Liaw, P.K.; Zhang, T. Bio-corrosion behavior and in vitro biocompatibility of equimolar TiZrHfNbTa high-entropy alloy. Intermetallics 2020, 124, 106845. [Google Scholar] [CrossRef]
- Węglewski, W.; Bochenek, K.; Basista, M.; Schubert, T.; Jehring, U.; Litniewski, J.; Mackiewicz, S. Comparative assessment of Young’s modulus measurements of metal–ceramic composites using mechanical and non-destructive tests and micro-CT based computational modeling. Comput. Mater. Sci. 2013, 77, 19–30. [Google Scholar] [CrossRef]
- Edmondson, J.M.; Armstrong, L.S.; Martinez, A.O. A rapid and simple MTT-based spectrophotometric assay for determining drug sensitivity in monolayer cultures. J. Tissue Cult. Methods 1988, 11, 15–17. [Google Scholar] [CrossRef]
- Jiang, Y.; Wang, X.; Jiang, Z.; Chen, M.; Sun, M.; Zhang, X. Phase transition and mechanical performance evolution in TiVZr-Nbx alloys. J. Alloys Compd. 2023, 937, 168458. [Google Scholar] [CrossRef]
- Gutierrez-Urrutia, I.; Raabe, D. Dislocation and twin substructure evolution during strain hardening of an Fe–22wt.% Mn–0.6wt.% C TWIP steel observed by electron channeling contrast imaging. Acta Mater. 2011, 59, 6449–6462. [Google Scholar] [CrossRef]
- Welsch, E.; Ponge, D.; Hafez Haghighat, S.M.; Sandlöbes, S.; Choi, P.; Herbig, M.; Zaefferer, S.; Raabe, D. Strain hardening by dynamic slip band refinement in a high-Mn lightweight steel. Acta Mater. 2016, 116, 188–199. [Google Scholar] [CrossRef]
- Rho, J.Y.; Tsui, T.Y.; Pharr, G.M. Elastic properties of human cortical and trabecular lamellar bone measured by nanoindentation. Biomaterials 1997, 18, 1325–1330. [Google Scholar] [CrossRef]
- Yeh, J.-W. Alloy Design Strategies and Future Trends in High-Entropy Alloys. JOM. 2013, 65, 1759–1771. [Google Scholar] [CrossRef]
- Hu, Q.-M.; Li, S.-J.; Hao, Y.-L.; Yang, R.; Johansson, B.; Vitos, L. Phase stability and elastic modulus of Ti alloys containing Nb, Zr, and/or Sn from first-principles calculations. Appl. Phys. Lett. 2008, 93, 121902. [Google Scholar] [CrossRef]
- Miura, K.; Yamada, N.; Hanada, S.; Jung, T.-K.; Itoi, E. The bone tissue compatibility of a new Ti–Nb–Sn alloy with a low Young’s modulus. Acta Biomater. 2011, 7, 2320–2326. [Google Scholar] [CrossRef] [PubMed]
- Hanada, S.; Masahashi, N.; Jung, T.K. Effect of stress-induced α″ martensite on Young’s modulus of β Ti–33.6Nb–4Sn alloy. Mater. Sci. Eng. A 2013, 588, 403–410. [Google Scholar] [CrossRef]
- Li, P.; Ma, X.; Wang, D.; Zhang, H. Microstructural and Mechanical Properties of β-Type Ti–Nb–Sn Biomedical Alloys with Low Elastic Modulus. Metals 2019, 9, 712. [Google Scholar] [CrossRef]
- Ozaki, T.; Matsumoto, H.; Watanabe, S.; Hanada, S. Beta Ti Alloys with Low Young’s Modulus. Mater. Trans. 2004, 45, 2776–2779. [Google Scholar] [CrossRef]
- Fleischer, R.L. Substitutional solution hardening. Acta Metall. 1963, 11, 203–209. [Google Scholar] [CrossRef]
- Juan, C.-C.; Tsai, M.-H.; Tsai, C.-W.; Hsu, W.-L.; Lin, C.-M.; Chen, S.-K.; Lin, S.-J.; Yeh, J.-W. Simultaneously increasing the strength and ductility of a refractory high-entropy alloy via grain refining. Mater. Lett. 2016, 184, 200–203. [Google Scholar] [CrossRef]
- Eleti, R.R.; Stepanov, N.; Zherebtsov, S. Mechanical behavior and thermal activation analysis of HfNbTaTiZr body-centered cubic high-entropy alloy during tensile deformation at 77 K. Scr. Mater. 2020, 188, 118–123. [Google Scholar] [CrossRef]
- Cao, S.; Zhou, X.; Lim, C.V.S.; Boyer, R.R.; Williams, J.C.; Wu, X. A strong and ductile Ti-3Al-8V-6Cr-4Mo-4Zr (Beta-C) alloy achieved by introducing trace carbon addition and cold work. Scr. Mater. 2020, 178, 124–128. [Google Scholar] [CrossRef]
- Yurchenko, N.; Panina, E.; Tojibaev, A.; Novikov, V.; Salishchev, G.; Zherebtsov, S.; Stepanov, N. Effect of B2 ordering on the tensile mechanical properties of refractory AlxNb40Ti40V20−x medium-entropy alloys. J. Alloys Compd. 2023, 937, 168465. [Google Scholar] [CrossRef]
- Wang, S.-P.; Ma, E.; Xu, J. New ternary equi-atomic refractory medium-entropy alloys with tensile ductility: Hafnium versus titanium into NbTa-based solution. Intermetallics 2019, 107, 15–23. [Google Scholar] [CrossRef]
- Kumnorkaew, T.; Lian, J.; Uthaisangsuk, V.; Zhang, J.; Bleck, W. Low carbon bainitic steel processed by ausforming: Heterogeneous microstructure and mechanical properties. Mater. Charact. 2022, 194, 112466. [Google Scholar] [CrossRef]
- Yurchenko, N.; Panina, E.; Tojibaev; Zherebtsov, S.; Stepanov, N. Overcoming the strength-ductility trade-off in refractory medium-entropy alloys via controlled B2 ordering. Mater. Res. Lett. 2022, 10, 813–823. [Google Scholar] [CrossRef]
- Nizolek, T.; Mara, N.A.; Beyerlein, I.J.; Avallone, J.T.; Pollock, T.M. Enhanced Plasticity via Kinking in Cubic Metallic Nanolaminates. Adv. Eng. Mater. 2015, 17, 781–785. [Google Scholar] [CrossRef]
- Weiss, I.; Semiatin, S.L. Thermomechanical processing of beta titanium alloys—An overview. Mater. Sci. Eng. A 1998, 243, 46–65. [Google Scholar] [CrossRef]
- Abdel-Hady, M.; Hinoshita, K.; Morinaga, M. General approach to phase stability and elastic properties of b-type Ti-alloys using electronic parameters. Scr. Mater. 2006, 55, 477–480. [Google Scholar] [CrossRef]
- Lilensten, L.; Couzinie, J.-P.; Bourgon, J.; Perriere, L.; Dirras, G.; Prima, F.; Guillot, I. Design and tensile properties of a bcc Ti-rich high-entropy alloy with transformation-induced plasticity. Mater. Res. Lett. 2017, 5, 110–116. [Google Scholar]
- Zherebtsov, S.; Yurchenko, N.; Panina, E.; Tojibaev, A.; Tikhonovsky, M.; Salishchev, G.; Stepanov, N. Microband-induced plasticity in a Ti-rich high-entropy alloy. J. Alloys Compd. 2020, 842, 155868. [Google Scholar] [CrossRef]
Figure 1.
IPF maps of the initial microstructure of Ti30Nb20 (a), Ti40Nb10 (b), and Ti50Nb0 (c) alloys.
Figure 2.
Engineering stress-strain curves of the program alloys obtained during tension at 20 °C with a nominal strain rate of 10−3 s−1 (a) and corresponding strain-hardening rate behavior as a function of true strain (b).
Figure 3.
DIC images of tensile specimens of Ti30Nb20 (a,d,g), Ti40Nb10 (b,e,h), and Ti50Nb0 (c,f,i) alloys showing the strain distribution along the gauge.
Figure 4.
EBSD maps of deformed microstructures near the fracture surfaces of specimens after tensile tests; (a,b)—Ti30Nb20, (c,d)—Ti40Nb10, (e,f)—Ti50Nb0; (a,c,e)—IPF maps, (b,d,f)—kernel average misorientation maps. Tension direction is horizontal in all cases; the fracture surfaces are located near the left side of the images.
Figure 5.
TEM images of deformed microstructures near the fracture surfaces of specimens after tensile tests: (a)—Ti30Nb20, (b)—Ti40Nb10, (c)—Ti50Nb0.
Figure 6.
Morphology of MSCs in the control sample (without metallic specimen) (a) and Ti30Nb20 (b), Ti40Nb10 (c), and Ti50Nb0 (d) alloys. Magnification was ×100.
Figure 7.
Dependence of the Young’s modulus of the program alloys on Nb percentage (CNb) and yield strength on C1/2Nb.
Figure 8.
Positions of the program alloys on the Bo–Md map. The references used for plotting this map can be found elsewhere [
39].
Table 1.
Mechanical properties and density of all the program alloys.
Alloy | Young’s Modulus, GPa | Yield Strength, MPa | δ,% | Microhardness, HV | Density, g/cm3 |
---|
Ti30Nb20 | 77.7 ± 0.1 | 1090 ± 50 | 24 ± 2 | 321 ± 5 | 7.24 ± 0.04 |
Ti40Nb10 | 68.8 ± 0.1 | 930 ± 45 | 29 ± 3 | 280 ± 6 | 6.26 ± 0.04 |
Ti50Nb0 | 57.5 ± 0.1 | 690 ± 40 | 25 ± 2 | 244 ± 5 | 5.99 ± 0.04 |
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