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For this paper, studies of the microstructure as well as the mechanical and biological properties of bioinert titanium, zirconium, and niobium alloys in their nanostructured (NS) and ultrafine-grained (UFG) states have been completed. The NS and UFG states were formed by a combined two-step method of severe plastic deformation (SPD), first with multidirectional forging (MDF) or pressing into a symmetrical channel (PSC) at a given temperature regime, and then subsequent multi-pass groove rolling (MPGR) at room temperature, with pre-recrystallization annealing. Annealing increased the plasticity of the alloys in the NS and UFG states without changing the grain size. The UFG structure, with an average size of structural elements of no more than 0.3 μm, was formed as a result of applying two-step SPD and annealing. This structure presented significant improvement in the mechanical characteristics of the alloys, in comparison with the alloys in the coarse-grained (CG) or small-grained (SG) states. At the same time, although the formation of the UFG structure leads to a significant increase in the yield strength and tensile strength of the alloys, their elastic modulus did not change. In terms of biocompatibility, the cultivation of MG-63 osteosarcoma cells on the polished and sandblasted substrates demonstrated high cell viability after 10 days and good cell adhesion to the surface.

Bioinert Zr-1Nb alloy, which is a prospective material for the fabrication of implants for different applications, is studied. Annealed billets of the alloys are subjected to severe plastic deformation including multi-cycle abc-pressing and multipass rolling in grooved rolls. The abc-pressing stage involves three cycles of pressing within the temperature range 500 -400°C with one pressing in each cycle at a given temperature. In the second stage, the billets are deformed through rolling in grooved rolls at room temperature. Rolling in grooved rolls provided the formation of a homogeneous structure throughout the bulk billet volume and additional grain refinement. After annealing the alloy had a fine-grained structure consisting of 2.8 µm sized equiaxial α-Zr matrix grains and 0.4 µm sized β-Nb particles distributed on the boundaries and interiors of α-Zr matrix grains. As a result of severe plastic deformation, a binary ultrafine-grained alloy with 0.2 µm size of structural elements was obtained. Transmission electron microscopy shows that the microstructure of the alloy consists of α-Zr grains, while β-Nb phase grains are not identified structurally or via X-ray diffraction. Only the diffraction identification analysis reveals the presence of β-Nb in the alloy. Ultrafine-grained structure enhances the mechanical properties of the alloys: yield stress 450 MPa, ultimate tensile strength 780 MPa, and microhardness 2800 MPa are obtained while keeping a low value of Young's modulus (51 MPa) comparable to the Young's modulus of bone tissue.