Ana L. C. Garcia,¹ Angelo L. Gobbi,² Valmor R. Mastelaro,³ Conrado R. M. Afonso,¹ Pedro A. P. Nascente¹

¹Federal University of Sao Carlos, Department of Materials Engineering and Graduation Program in Materials Science and Engineering, Sao Carlos, SP, Brazil
²Brazilian Center for Research in Energy and Materials, Brazilian Nanotechnology National Laboratory, Campinas, SP, Brazil
³University of Sao Paulo, Sao Carlos Institute of Physics, Sao Carlos, SP, Brazil

Titanium and its alloys present better characteristics for biomedical applications, such as mechanical properties, corrosion resistance, and biocompatibility, than stainless steel (SS) and cobalt-based alloys, which are traditionally used in orthopedic implants. The β (body-centered cubic – BCC) phase Ti alloys are more adequate for biomedical applications due to their low elastic modulus, which is an intrinsic property associated with the charge transfer between the implant and the tissue around it, shape memory effect, and superelastic characteristics. Among the β-Ti alloys, the Ti-Nb-Zr system is attractive since Ti, Nb, and Zr are non-toxic and non-allergenic biocompatible metals, and the addition of Nb and Zr to Ti favors stabilizing of the β phase [1]. A main disadvantage of bulk β-Ti-Nb-Zr alloys is that they are much more costly than SS and Co-Cr alloys. An economical option is to coat an implant with a β-Ti-Nb-Zr thin film with adequate thickness and composition, and magnetron sputtering is suitable for producing alloy coatings for biomedical applications.

To the best of our knowledge, Tallarico et al. [2, 3] were the first who mentioned biomedical applications for Ti-based alloy thin films. They investigated tri-layered films of TiNbZr deposited on Si(111) and stainless steel (SS) substrates by direct-current magneton sputtering (DCMS) [2]. The TiNbZr/Si(111) thin film was used as model surfaces of biomaterials. The formation of a tri-layered film on Si(111) was confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiles, with each metal in a distinct layer, separated by sharp interfaces between the layers, while the film grown on SS presented a slight intermixing at the interfaces [2]. The TiNbZr/SS thin film presented morphological, chemical, and mechanical characteristics that might improve the biocompatibility and extend the lifetime of SS implants [3].

Gonzalez et al. [4-6] studied the influence of Nb content on the composition, structure, morphology, and nanostructure of Ti-Nb coatings deposited on AISI 316L SS by DCMS. The substrate temperature during the deposition was kept at 200° in order to help the formation of the β phase for Nb amounts greater than or equal to 15 at. %. Four compositions were produced (at. %): Ti₈₅Nb₁₅, Ti₈₀Nb₂₀, Ti₇₀Nb₃₀, and Ti₆₀Nb₄₀. These alloy coatings presented lower elastic modulus values and equal or higher hardness values as compared to commercially used alloys. They also presented high values for joint plastic deformation between the coating and substrate [5]. Gonzalez et al. [7] studied the influence of Zr content on the nanostructure, mechanical, and tribological properties of Ti-Nb-Zr alloy coatings deposited on AISI 316 substrate by DCMS. They detect the presence of small quantities of the ω phase for the coating with the lowest amount of Zr (Ti₇₅Nb₂₀Zr₅); this ω phase is metastable and can have either trigonal or HCP structures. Only the β phase was detected for higher amounts of Zr. The coating with higher Zr content (Ti₄₀Nb₂₀Zr₄₀) presented lower elastic modulus and hardness values, which were related to increases in both the lattice parameter and mean grain size. The Ti-Nb-Zr coatings presented high ductility and high adhesion, indicating a high combined plastic deformation of the coating/substrate system. No coating delamination was observed.

The ideal amounts of the constituent elements in the Ti-Nb-Zr ternary system are undetermined. Combinatorial strategies allow for simultaneous production and characterization of many alloys simultaneously. This work has aimed to identify the optimal composition of the Ti-Nb-Zr system. Ti, Nb, and Zr targets were positioned in a triangular configuration below a Si(100) wafer substrate, and a composition gradient was formed over the substrate area by magnetron co-sputtering. Five samples were cut from different patches of the coated wafer, and the compositions, structures, and morphologies were evaluated by energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscopy (AFM). The combination of physicochemical characteristics and elastic modulus values suggest that the Ti-Nb-Zr coatings are good candidates to be used in dental and orthopedic prosthetic devices that are not subjected to wear.

References:
[1] E. D. Gonzalez, L. V. G. Gil, C. L. Kugelmeier, V. Amigó-Borras, V. R. Mastelaro, C. A. D. Rovere, P. A. P. Nascente, Mater. Today Commun. 32, 104069 (2022).
[2] D. A Tallarico, A. L. Gobbi, P. I. Paulin-Filho, A. Galtayries, P. A. P. Nascente, J. Vac. Sci. Technol. A 30, 051506 (2012).
[3] D. A Tallarico, A. L. Gobbi, P. I. Paulin-Filho, M. E. H Maia da Costa, P. A. P. Nascente, Mater. Sci. Eng. C 43, 45-49 (2014).
[4] E. D. Gonzalez, T. C. Niemeyer, C. R. M. Afonso, P. A. P. Nascente, J. Vac. Sci. Technol. A 34, 021511 (2016).
[5] E. D. Gonzalez, C. R. M. Afonso, P. A. P. Nascente, Surf. Coat. Technol. 326, 424-428 (2017).
[6] E. D. Gonzalez, C. R. M. Afonso, P. A. P. Nascente, Thin Solid Films 661, 92-97 (2018).
[7] E. D. Gonzalez, N. F. Fukumasu, C. R. M. Afonso, P. A. P. Nascente, Thin Solid Films 721, 138565 (2021).