In this study, hybrid composites based on β-alloy Ti−xNb and oxide nanotubes (NTs) have been successfully prepared. NTs of different sizes were grown on Ti−Nb substrates with different Nb contents (5, 25, and 50 wt %) via electrochemical anodization at 30 and 60 V. Scanning electron microscopy imaging revealed that vertically aligned nanotubular structures form on the surface of Ti−Nb alloy substrates and influence Nb content in alloys based on NT length. X-ray diffraction analysis confirmed the formation of the anodized TiO 2 layer and revealed several phases as the Nb content increased, starting with α′ for low Nb content (5 wt %), the martensite α″ for intermediate Nb content (25 wt %), and the β phase for the highest Nb content (50 wt %). Nanoindentation testing was used to evaluate the changes in mechanical properties of oxide NTs grown on Ti−Nb alloys with different compositions. NT arrays showed wide variations in Young's modulus and hardness depending upon the anodization voltage and the Nb content. The hardness and Young's modulus strongly correlated with NT morphology and structure. The highly dense morphology formed at a lower anodization voltage results in increased elastic modulus and hardness values compared with the surfaces prepared at higher anodization voltages. The nanostructurization of Ti−Nb surface substrates favored improved surface properties for the enhanced adhesion and proliferation of human mesenchymal stem cells (hMSCs). In vitro adhesion, spreading, and proliferation of hMSCs revealed the improved surface properties of the NTs prepared at an anodization voltage of 30 V compared with the NTs prepared at 60 V. Thus it can be concluded that NTs with diameters of ∼50 nm (at 30 V) are more favorable for cell adhesion and growth compared with NTs with diameters of 80 ± 20 nm (at 60 V). The surfaces of Ti−25Nb substrates anodized at 30 V promoted enhanced cell growth, as the further increase in Nb content in Ti−Nb substrate (Ti−50Nb) led to reduced cell proliferation. The application of NTs on Ti−Nb substrates leads to significant reductions in mechanical properties compared with those on the Ti−Nb alloy and improves cell adhesion and proliferation, which is vitally important for successful application in regenerative medicine.

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High-current pulsed electron-beam (PEB) treatment was applied as a surface finishing procedure for Ti–35Nb–7Zr–5Ta (TNZT) alloy produced by electron beam melting (EBM). According to the XRD results the TNZT alloy samples before and after the PEB treatment have shown mainly the single body-centered cubic (bcc) β-phase microstructures. The crystallite size, dislocation density, and microstrain remain unchanged after the PEB treatment. The investigation of the texture coefficient at the different grazing angle revealed the evolution of the crystallite orientations at the re-melted zone formed at the top of the bulk samples after the PEB treatment. The top-view SEM micrographs of the TNZT samples treated by PEB exhibited the bcc β-phase grains with an average size of ~85 μm. TEM analysis of as-manufactured TNZT alloy revealed the presence of the equiaxed β-grains with the fine dispersion of nanocrystalline α and NbTi4 phases together with β-Ti twins. Meanwhile, the β phase regions free of α phase precipitation are observed in the microstructure after the PEB irradiation. Nanoindentation tests revealed that the surface mechanical properties of the melted zone were slightly improved. However, the elastic modulus and microhardness in the heat-affected zone and the deeper regions of the sample were not changed after the treatment. Moreover, the TNZT alloy in the bulk region manufactured by EBM displayed no significant change in the corrosion resistance after the PEB treatment. Hence, it can be concluded that the PEB irradiation is a viable approach to improve the surface topography of EBM-manufactured TNZT alloy, while the most important mechanical parameters remain unchanged.

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