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The results of a study of thermal conductivity and specific heat capacity of Zr – 1 wt.% Nb and Ti – 45 wt.% Nb alloys in coarse-grained and ultrafine-grained states are presented. The influence of the utrafinegrained state on the thermophysical properties and the processes of energy dissipation and accumulation during deformation of the alloys are estimated. It is shown that the formation of an ultrafine-grained state in a Zr – 1 wt.% Nb alloy by abc-pressing and subsequent rolling leads to a decrease in its thermal conductivity and specific heat capacity by 10 and 20%, respectively, due to substructural strengthening under severe plastic deformation. It is found out that thermal conductivity and specific heat capacity of the ultrafine-grained Ti – 45 wt.% Nb alloy increase by 7.5 and 5%, respectively, due to dispersion hardening of the ω phase by nanoparticles and formation of a new α phase. It is established that the ultrafine-grained structure has a significant influence on the energy dissipation and accumulation during plastic deformation, which in turn depend on their thermophysical characteristics and on the structural and phase states.

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 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 evolution of temperature fields and the deformation behavior of samples of VT1-0 titanium and zirconium Zr–1 wt % Nb alloys in coarse-grained and ultrafine-grained states is investigated under quasistatic stretching using infrared thermography. It is shown that the nature of the evolution of the temperature field in the process of deformation and the dependence of the maximum temperature on the strain in the working area differ for VT1-0 titanium and Zr–1 wt % Nb and depend on their structural and phase states, mechanical characteristics, and thermal diffusivity. It has been established that upon transition to the ultrafine-grained state, thermal diffusivity decreases by 6.5 and 9.3% for VT1-0 titanium and Zr–1 wt % Nb alloy, respectively. Differences in the deformation behavior of samples of VT1-0 titanium and Zr–1 wt % Nb alloy in the coarse-grained and ultrafine-grained states are associated with substructural hardening of the matrix phases of α-Ti and α-Zr and solid-solution hardening caused by the dissolution of β-Nb particles as the alloys under study are transferred into the ultrafine-grained state by severe plastic deformation.

The influence of the average size of the structure elements on the deformation and thermal behavior of the Zr-1 wt.% Nb (Zr1-Nb) alloy under quasi-static tension was investigated using the digital image correlation and infrared thermography methods. It is shown that with increasing average size of the structural elements in the range 0.2–2.0 µm the physico-mechanical properties, such as yield strength, microhardness, maximal true strain, and maximal temperature increment during deformation decrease, while longitudinal and transverse strain increase. According to the obtained results, correlations between the mentioned deformation characteristics and the average size of the structural element d–1/2 can be described by linear functions.

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.

In most cases, medical implants are made from titanium alloys or stainless steel with good mechanical properties. However, these materials contain toxic ele� ments such as nickel, aluminum, and vanadium. For medical applications, it would be preferable to use titanium (1, 2), zirconium, niobium and their alloys, with distinctive physicomechanical and biological properties. The widespread use of titanium in implants is mainly hindered by its poor mechanical properties, including its durability under periodic and cyclic loads. This problem may be resolved by using nano� structural (ultrafinegrain) titanium. At present, we are able to produce large blanks of nanostructural tita� nium with good mechanical properties (3). The meth� ods employed are based on intense plastic deformation (3-7): equalchannel angular pressing (3, 4), abc pressing (5-7), and so on. By intense plastic deforma� tion, a nanostructural state may be established over the whole volume of the blank. That ensures mechanical properties matching those of moderately complex tita� nium alloys such as VT6 alloy. The creation of nanostructure permits fundamen� tal change in the mechanical properties of metals: the yield point and strength, the fatigue life, the wear resis� tance, the cyclic durability, etc. Note that at least two successive methods of intense plastic deformation must be used to obtain a nanostructural state of tita� nium (6, 7). Those methods may be combined in a sin� gle cycle (3). Twostage intense plastic deformation was pro� posed in (6, 7): abc pressing in a mold; and multipass rolling. In that approach, the initial upsetting in the mold involves successively changing the compression axis three or four times (analogously to multistage abc pressing (5)). In the first stage, the blank is deformed in a hydraulic press at 10 -3 -10 -1 s -1 . At specified tem� perature, each cycle includes onetime 40-50% upsetting, with subsequent change of the deformation axis by 90° rotation of the blank around the longitudi� nal axis. The temperature of the blank is reduced in stages in the range 700-400°C on passing to the next cycle. In the second stage, the blank is deformed by rolling at room temperature; the rollers may be grooved or smooth. The accumulated strain in rolling is 90%. Rolling produces blanks in the form of rods or plates. The final blanks are annealed in argon at 250 or 300 °C to remove the internal stress and increase the plasticity. As a result of twostage treatment and lowtemper� ature annealing, uniform grain-subgrain nanostruc� ture is formed in the blank (Fig. 1). The mean size of the elements (grains, subgrains, fragments) is less than 100 nm. This nanostructural state ensures plasticity of 6-10%, yield point of 1100 MPa, and strength of 1160 MPa.

The structure of Ti-40Nb alloy prototype obtained by selective laser melting (SLM) on “VARISKAF 100MV” installation was considered by the methods of optical metallography, scanning and transmission electron microscopy. It was revealed that the most of the specimens’ surface is uniform flowed surface with typical banded structure formed by laying-on molten pools. The process of the individual layer formation was followed by drop formation. This leads to the porosity formation on the specimen’s surface. The structure of entire specimen is not homogeneous throughout the transverse section. The porosity of three kinds is observed. They are cavities of not full contact and melting of the layers, drawholes, gas pores. The porosity optimization requires more careful SLM modes selection. The alloy has a grain structure with anisotropy from small (2–8 µm) to medium (8–20 µm) grain size. The anisotropy of the specimen is formed in each layer and is retained during building of the specimen. The grains of microstruct...

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.