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Biomedical Ti-22Nb-6Zr, Ti-18Zr-15Nb, and Ti-41Zr-12Nb (at.%) shape memory alloys were subjected to cold rolling (CR) and subsequent post-deformation annealing (PDA). The evolutions of phase and structure states, crystallographic texture, and crystallographic limit of recovery strain were studied using EBSD, TEM, and XRD analyses. The study found that CR (e = 1.5) and PDA at 800 °C for 30 min results in fine- and coarse-grained structures. Severe CR (e = 3.0) and PDA at 550 °C for 5 min results in a recrystallized, equiaxed, predominantly ultrafine-grained structure of the β-phase with a small amount of low-angle boundaries. Increasing the degree of CR from moderate (e = 0.3) to severe (e = 3.0) results in a favorable strong {111}β<110>β recrystallization texture. Alloys with low Zr content are more susceptible to this type of crystallographic texture formation during TMT, primarily due to a higher Nb content. The Ti-41Zr-12Nb alloy shows the highest crystallographic limit of recovery strain (εrmax ≈ 6%). The limit decreases to ≈5% (for Ti-18Zr-15Nb) and ≈3% (for Ti-22Nb-6Zr) when transitioning from high- to low-Zr alloys. The transition of Ti-Zr-Nb alloys from coarse-grained to ultrafine-grained structures of the β-phase and a decrease in grain size do not affect the crystallographic limit of recovery strain in the studied grain size ranges. [ABSTRACT FROM AUTHOR]

Superelastic biocompatible alloys attract significant attention as novel materials for bone tissue replacement. These alloys are often composed of three or more components that lead to the formation of complex oxide films on their surfaces. For practical use, it is desirable to have a single-component oxide film with a controlled thickness on the surface of biocompatible material. Herein we investigate the applicability of the atomic layer deposition (ALD) technique for surface modification of Ti-18Zr-15Nb alloy with TiO2 oxide. It was found that a 10–15 nm thick, low-crystalline TiO2 oxide layer is formed by ALD method over the natural oxide film (~5 nm) of the Ti-18Zr-15Nb alloy. This surface consists of TiO2 exclusively without any additions of Zr or Nb oxides/suboxides. Further, the obtained coating is modified by Ag nanoparticles (NPs) with a surface concentration up to 1.6% in order to increase the material's antibacterial activity. The resulting surface exhibits enhanced antibacterial activity with an inhibition rate of more than 75% against E. coli bacteria. [ABSTRACT FROM AUTHOR]

Metastable Ti-Nb-based shape memory and superelastic alloys are known to be strong candidates for bone implant applications. The issues of the materials’ biochemical and biomechanical compatibility and its characterization are reviewed. Thermomechanical treatment is conventionally applied to these alloys in order to obtain supreme functional properties; the processing scheme comprises cold rolling and post-deformation air annealing. The structure and electrochemical characteristics of annealing-induced oxide films were studied by scanning electron microscopy, open circuit potential measurement and voltammetry. It is shown that the samples after the annealing treatment exhibit higher steady-state potential value and lower anodic dissolution current density in simulated biological solution, compared with the samples with mechanically removed oxide films. At the same time, the samples with thermal oxide films exhibited lower rate of passive layer recovery than those subjected to mechanical renewal of the oxidized surface. This fact underlies the recommendation to remove the annealing-induced oxide film from the implants operating under friction conditions.

Metastable near‐beta Ti‐21.8Nb‐6Zr and Ti‐19.7Nb‐5.8Ta (at%) alloys were subjected to a thermomechanical treatment comprising cold rolling (CR) with a true strain of e = 0.3 and post‐deformation annealing (PDA) in the 500–900°C temperature range to ensure the superelastic behavior which is important for bone implants. It was found that PDA resulted in formation of about 1–2 μm‐thick oxide layer on the Ti‐Nb‐Zr and Ti‐Nb‐Ta alloy samples; the layer was mainly composed of TiO2, in rutile and anatase modifications. The structure, the phase and chemical compositions, and some surface‐sensitive properties of the alloys were compared to those of Ti‐50.7Ni and Ti‐Grade2 reference materials. These surface layers (especially that of the Ti‐Nb‐Zr alloy) demonstrated a promising combination of high cohesion strength (load causing surface layer fracture is over 25 N), hardness (∼12 GPa), and hydrophilicity (contact angle ∼40°). Surface modification by controlled oxidation during air annealing increases corrosion resistance and enhances in vivo osteoinductive properties of Ti‐Nb‐Zr alloys by changing the surface microrelief, increasing the surface wettability, and improving the mechanical characteristics, thus laying the foundation for the development of medical implants with prolonged service life. So, it was confirmed that the same thermomechanical treatment, which creates conditions for the superelastic behavior of the bulk metal (CR: e = 0.3 + PDA = 500–700°C for 1 hr), would also create a strong, protective and biocompatible layer on the implant surface. [ABSTRACT FROM AUTHOR]