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The results on thermal stability of the microstructure and mechanical properties of Zr – 1 wt.% Nb and Ti – 45 wt.% Nb ultrafine-grained alloys subjected to long-term thermal annealing at a temperature of 400°С are presented. It is shown that in a Zr – 1 wt.% Nb ultrafine-grained alloy an increase in the annealing duration from 5 to 360 hr leads to a growth of the structural elements (grains, subgrains, fragments) of the α-Zr matrix phase and β-Nb particles. This is a consequence of the recrystallization processes, which gives rise to softening of the alloy and a decrease in their microhardness and yield stress. It is found out that an annealing treatment for as long as 360 hr does not affect the structural element size of β-phase in the Ti – 45 wt.% Nb alloy but favors a noticeable grain growth in α- and ω-phases. It is demonstrated that disordering of the Ti – 45 wt.% Nb alloy and a decrease in its mechanical characteristics are due to the recovery processes at the grain boundaries, an increase in the nanosized grains of α- and- ω-phases, and their decreased contribution to dispersion hardening.

The results for thermal stability of the microstructure and mechanical properties of ultrafine-grained alloys Zr-1 wt. % Nb and Ti-45 wt. % Nb alloys after long-term thermal annealing at temperature of 400°C are presented. It is shown that in the Zr-1 wt.%Nb alloy in the ultrafine-grained state, increase in the annealing duration from 5 to 360 hours leads to growth of the structural elements (grains, sub-grains, fragments) of the matrix phase a - Zr and the particles β-Nb. This fact is due to the processes of recrystallization. It leads to softening of the alloy and decrease of microhardness and yield stress. It was also found that annealing up to 360 hours does not affect the size of the structural elements of the matrix β-phase in the Ti-45 wt. % Nb alloy, but contributes to the noticeable growth of the α-phase and ω-phase grains. According to our results, softening of the Ti-45 wt. % Nb alloy and decrease in its mechanical characteristics are associated with the processes of return at the grain boundaries, as well as with growth of the nanoscale grains of α-phase and ω-phase and decrease in their contribution to dispersion hardening.

The stage-like character of the stress-strain curves and microstructure in the fracture zone of coarse-grained and ultrafine-grained specimens of the VT1-0 and Zr–1Nb alloy specimens under quasistatic loading are investigated using the temperature curves obtained by the method of IR-imaging. New experimental data are obtained, which provide evidence on a considerable influence of the ultrafine-grained state on the evolution of plastic deformation and fracture in the VT1-0 and Zr–1Nb alloys.

The results of investigation of the influence of the structural element size and phase state of the Ti – 45 wt.% Nb and Zr – 1 wt.% Nb binary alloys on their mechanical properties are presented. The structural states of the alloys with the structural elements of different dimensions were formed from the ultrafine-grained state via annealing. The curves of dependence of the yield strength and microhardness on the average size of the structural elements, d –1/2, are obtained using the Hall–Petch relation. It is shown that for the Zr – 1 wt.% Nb alloy, the Hall–Petch relation is fulfilled in the entire range of sizes under study, from ultrafine-grained to finegrained states 0.2–1.9 μm. For the Ti – 45 wt.% Nb alloy, in the analysis of the Hall–Petch relationship within the structural element size range 0.43–45 μm, its phase composition is taken into consideration, specifically, the presence of dispersion-strengthened β-phase grains, α-phase subgrains, nonequilibrium nanosized ω- phase, and the bimodal grain-subgrain structure.

The characteristics of microstructure, deformation and fracture of Zr – 1 wt% Nb and Ti – 45 wt% Nb bioinert alloys in the coarse- and ultrafine-grained states are investigated. It is shown that the ultrafine-grained structure formed in them ensures excellent mechanical properties of the alloys and affects the stages of the stress-strain curves and the behavior of the maximum temperature vs. deformation time plot. The formation of an α-phase in the Ti – 45 wt% Nb ultrafine-grained alloy suppresses the linear stage VI characterized by a constant strain hardening coefficient. In stage VII, the strain hardening coefficient rapidly becomes negative, which indicates the material softening prior to its failure.

Ti–Nb alloy with 40 wt % of Nb is obtained from a composite Ti–Nb powder by means of selective laser melting. The Ti–Nb alloy has a two-phase microstructure. The main β-phase of the solid titanium–niobium solution forms grains ranging in size from ~2 to 20 μm. A nonequilibrium α″-phase is found in the forms of lamellar, globular, and packet martensite inside the grains of the β-phase and along their boundaries.

Experimental data of thermal stability of the microstructure and mechanical properties (exemplified by the microhardness tests) of the ultrafine grained (UFG) Ti–45 wt % Nb alloy after long-term thermal influence were presented in the paper. UFG structure in the alloy was formed with the severe plastic deformation (SPD) method. It was proved that the SPD method including the multiple abc-pressing and multi-pass rolling and further pre-recrystallizing annealing enhances the formation of UFG structures with the mean element size of 0.25 µm. Samples of Ti–45 wt % Nb alloy in UFG state were annealed at 350 and 400°C during 1, 5, 10, 24, 120, 240 and 360 hours. It was shown that the UFG structure was stable after annealing at 350 and 400°C as a result of thermal influence within the time range up to 360 hours. Stability of mechanical properties depended on the temperature and duration of annealing, i.e. microhardness of 3200 MPa was remained during 120 hours of annealing at 350°C, while microhardness of 3000 MPa was remained during 10 hours of annealing at 400°C.

Phase composition and microstructure of Ti–Nb alloy produced from the composite titanium and niobium powder by selective laser melting (SLM) method were studied in the present research. Ti-Nb alloy produced by SLM is a monolayer and has zones of fine-grained and medium-grained structure with homogenous elemental composition within the range of 36–38 wt.% Nb. Phase state of the alloy corresponds to the main phase of β- solid solution (grain size of 5–7 μm) and non-equilibrium martensite α″-phase (grain size of 0.1–0.7 μm). Grains of the α″-phase are localized along the boundaries of β-phase grains and have a reduced content of niobium. Microhardness of the alloy varies within the range of 4200–5500 MPa.

The mechanical behavior of coarse- and ultrafine-grained (CG/UFG) Zr–1Nb alloy specimens under quasi-static tensile testing, the distribution of exx, eyy, exy strains and the evolution of temperature patterns have been studied using the techniques of digital image correlation and infrared thermography. The microstructure of the Zr–1Nb alloy in the initial CG and UFG states, as well as after deformation at the prefracture stage, has been investigated. A study of the accumulation and dissipation of energy in these materials under tensile load has demonstrated the influence of the alloy heat capacity on these processes. It has been found that, under tensile testing, the Zr–1Nb alloy in the UFG state is characterized by a stage with constant temperature, which takes place up to e t r u e ≈ 0.04 thus indicating that UFG materials, unlike CG ones, more efficiently use the structural energy absorption channel during deformation. The prefracture stage of the Zr–1Nb in the UFG state is characterized by the sharp temperature increase up to 60 °C. At this stage, the strain hardening coefficient becomes negative reaching values up to -6.5 GPa thus indicating local material softening before fracture. The formation of large local areas with disoriented mesh structure of dislocations is another feature of structural transformations in the Zr–1Nb alloy in the UFG state before fracture that also indicates a local material softening.

The microstructure and mechanical properties of bioinert titanium, zirconium, and niobium alloys in the ultrafine-grain state are investigated. The ultrafine-grain structure is obtained by severe plastic deformation, including multicyclic abc pressing at specified temperatures, multipass rolling in shaped rollers at room temperature, and low-temperature non-recrystallizing annealing. Annealing increases the plasticity of the ultrafine-grain alloys, without changing the grain size. As a result of two-stage treatment—severe plastic deformation and annealing—ultrafine-grain structure with grains and subgrains of mean size 0.16–0.25 μm is formed. That considerably improves the mechanical properties (ultimate strength, yield point, and microhardness) of the alloys. At the same time, the formation of ultrafine-grain structure in the alloys does not change the elastic modulus, even with considerable increase in the ultimate strength and plasticity.

Results of investigation of the microstructure, mechanical properties, and thermostability of bioinert titanium VT1-0 and zirconium E110 in nanostructured and ultrafine-grained states formed by combined methods of severe plastic deformation, including abc pressing in a press-mould or without it and multipass rolling in grooved or smooth rolls, are presented. It is demonstrated that the combined severe plastic deformation method allows titanium and zirconium billets in nanostructured and ultrafine-grained states to be obtained that provides substantial improvement of the mechanical properties comparable to the properties of titanium alloys, for example, VT6 and VT16 ones. The yield strength and the microhardness of titanium and zirconium obey the Hall–Petch relationship.

The microstructure and mechanical properties of titanium are studied in the nanostructured, ultrafine- and coarse-grained structured states. The temperature dependence of the titanium grain size is analyzed, and the Hall-Petch coefficient is determined. A decrease in the grain size in the initial material leads to the penetration of the doping element to a considerable depth as a consequence of radiation-induced diffusion along grain boundaries, which constitute a separate phase for nanomaterials. This can provide a positive effect on the properties of titanium implanted with aluminum ions.

This paper focuses on the development of microstructure of TiNb 40 alloy after severe plastic deformation. Primary billets (blocks) are Ti alloy cast with 40% Nb mass which are exposed to a combined two-stages severe plastic deformation method, including abc-pressing and multi-pass rolling in grooved rolls . An area of less than 0.3 micron grains is about 6% of the total area. It plays a strong role for improving the strength of the material. Microhardness of the alloy increased to 2300MPa. The small-angle grain boundaries (less than 15 °) of the alloy account for 61.1% after the combined processing . It is shown that a relatively large amount of micron grains and subgrains were produced in the processing of the alloy.

The phase composition and microstructure of Ti-Nb alloy produced from composite titanium and niobium powder by selective laser melting (SLM) was studied. Produced monolayered Ti-Nb alloy enhanced the formation of fine-grained and medium-grained zones with homogeneous element composition of 36-38% Nb mass interval. Alloy phase composition responded to [beta]-alloy substrate phase (grain size was 5-7 pm) and non-equilibrium martensite [alpha]"- phase (grain size was 0.1-0.7 [mu]m). [alpha]"-phase grains were found along [beta]-phase grain boundaries and inside grains, including decreased niobium content. Alloy microhardness varied within 4200-5500 MPa.