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In this work, the microstructure, phase state, texture, superelastic and mechanical properties of a Ti–18Zr–15Nb (at. %) shape memory alloy subjected to a combined thermomechanical treatment, including hot rotary forging with either air cooling or water quenching and post-deformation annealing are studied. It was revealed that the main structural component of the deformed and annealed alloy is BCC β-phase. With an increase in the forging temperature from 600 to 700 °C, the average grain size increases from 5.4 to 17.8 µm for the air-cooled specimens and from 3.4 to 14.7 µm for the water-quenched specimens. Annealing at 525 °C after forging at 700 °C with water quenching leads to the formation of a mixed statically and dynamically polygonized substructure of β-phase. In this state, the alloy demonstrates the best combination of functional properties in this study: a Young’s modulus of ~33 GPa, an ultimate tensile strength of ~600 MPa and a superelastic recovery strain of ~3.4%.

Ti-Zr-Nb shape memory alloys exhibit a unique combination of properties that make them suitable for bone implants: low Young's modulus, superelastic behavior, superior corrosion resistance, and non-toxicity of all the constitutive elements. In this study, superelastic Ti-19Zr-14Nb (at.%) alloy was subjected to a combination of radial shear rolling at 900°C and rotary forging in a temperature range from 500 to 700°C to form long-length bar stocks for bone implants fabrication. Features of the grain structure, phase composition, mechanical and functional properties of the long-length bar stocks were analyzed using light microscopy, X-ray analysis, as well as during mechanical and functional tests. It was shown that after radial shear rolling at 900°C, a heterogeneous grain structure was formed over the cross-section of the bar stock, and this structure was inherited after the subsequent rotary forging at 500°C. With an increase in the forging temperature, the structural heterogeneity is eliminated and the grain size increases, while the hardness and strength characteristics of the material decrease. After rotary forging at 700°C, the alloy manifests the best combination of structural, mechanical, and functional characteristics. In this state, the long-length bar stock demonstrates a homogeneous grain structure with a certain fraction of a dynamically polygonized substructure of β-phase, a satisfactory strength (UTS ≈ 580 MPa), a low Young's modulus (E ≈ 35 GPa), the high difference between dislocation and phase yield strength (Δσ ≈ 280 MPa), and a relatively large amount of superelastic recovery strain (ε r SE max ≈ 3.1%).

Improving the post-processing of metallic porous tissue scaffolds is an essential step to create a new generation of superelastic implants for the replacement of damaged bone tissue. In this study, the dynamic chemical etching technique is applied to improve the permeability and to optimize the porous structure of Ti-Nb-Zr scaffolds fabricated by the powder metallurgy-based space holder technique. The etched scaffolds are characterised in terms of their porous structure geometry, permeability, and mechanical properties. It is shown that an increase in porosity from 49% to 54% during the etching is mainly due to an increase in the number of 100 to 800 µm-diameter pores; from 30 to 50% of them measuring from 100 to 300 µm in size. These changes in the porous structure lead to a significant increase of its permeability, i.e. from (0.1-15)×10−11 m2 before etching to (44-91)×10−11 m2, after etching; these permeability ranges corresponding to those of bone tissues. Furthermore, the etched scaffolds show systematically higher yield compressive stresses as compared to the as-sintered scaffolds of equivalent porosities. Finally, the highly-permeable etched Ti-Nb-Zr scaffolds with a porosity varying from 40 to 60% exhibit an apparent Young’s modulus ranging from 8.6 to 1.9 GPa, and an ultimate compressive strength, from 650 to 190 MPa, which can be considered as a promising balance of properties for the potential use of these scaffolds as bone implants.