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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.

It is shown that ∼ 10 % of the total dark matter mass can be transformed into gravitational radiation by primordial blackhole (PBH) mergers inside the compact clusters. If the mass transformation occurred after recombination, but at redshiftsz ≥ 10, the generated gravitational radiation do not contribute to the current density of the Universe. This effect increasesthe rate of cosmological expansion in the era of recombination compared to models without the mass transfer. Accordingly,the Hubble constant, obtained from measurements in the early Universe, changes, which can provide a solution to the“Hubble tension” problem.

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 results of studying the thermal conductivity and specific heat capacity of Zr-1 wt.% Nb and Ti-45 wt.% Nb in coarse-grained and ultrafine-grained states are presented. The influence of the utrafine-grained state on the thermo physical properties and the processes of dissipation and accumulation energy during deformation of the alloys are estimated. It is shown that formation of the ultrafine-grained state in the 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 hardening under severe plastic deformation. It is found that thermal conductivity and specific heat capacity of the ultrafine 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 regularities of the dissipation and accumulation energy during plastic deformation, which in turn depend on their thermo-physical characteristics and on the structural and phase state.

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 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 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 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.

The paper deals with the study on the impact of grain refinement by severe plastic deformation upon the microstructure, as well as deformation and fracture behavior under tensile loading of technical grade titanium. The microstructure of coarse- and ultra-fine grain technical grade titanium was investigated by optical, transmission electron microscopy and X-ray diffraction. In situ monitoring of deformation behavior was conducted by means of acoustic emission and digital image correlation. Scanning electron microscopy was employed for fracture surface observation. The results of the tensile tests have revealed significant growth in ultimate strength and decrease of ductility due to grain-boundary strengthening. The experimental data obtained allow one to get the appropriate understanding of the mechanisms responsible for variation of mechanical properties and fracture patterns as well as to attain quantitative estimation of strain localization induced by the grain refinement.

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 electrochemical behavior of coarse-grained and nanostructured titanium in various media is studied by the methods of potentiodynamic polarization and impedance spectroscopy and by the analysis of the etching curves. It is found that the dissolution rate of nanostructured titanium increases in a Ringer-Locke solution at 37°C in comparison with the coarse-grained state owing to a more defective structure of the natural oxide layer on the surface of nanostructured titanium and its lower polarization resistance. It is demonstrated that the etching of nanostructured titanium in a mixture of hydrofluoric and sulfuric acids occurs mostly via the mechanism of local destruction, whereas overall uniform etching occurs in the case of coarse-grained titanium, which is considerably displayed in a range from 40 to 75°C.

The paper presents the results of studies of the kinetics of accumulation of fatigue damages in titanium VT1-0 and titanium alloy OT4 by acoustic emission method (AE). Identification of the sources of acoustic emission (dislocations, micro- and macro-cracks) is based on the methodology developed by the authors. According to the activity of various types of acoustic emission sources, the stages of fatigue are identified in conditions of flat cantilever bending. The data of the acoustic emission analysis were experimentally confirmed by the results of microstructural studies.The paper presents the results of studies of the kinetics of accumulation of fatigue damages in titanium VT1-0 and titanium alloy OT4 by acoustic emission method (AE). Identification of the sources of acoustic emission (dislocations, micro- and macro-cracks) is based on the methodology developed by the authors. According to the activity of various types of acoustic emission sources, the stages of fatigue are identified in conditions of flat cantilever bending. The data of the acoustic emission analysis were experimentally confirmed by the results of microstructural studies.

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 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.

The dependence of the depth of penetration of implanted aluminum atoms into polycrystalline titanium on the grain size of initial target samples is analyzed. The irradiation was carried out by a pulse-frequency ion beam of a Diana-2 source. The increase in the modified layer thickness to 250 nm with decreasing grain size in the initial material is revealed. In the interpretation of the observed regularities, we take into account the energetically inhomogeneous composition of a beam represented by three components and probable intense sputtering of the target surface by ions. In terms of the simulation, it is found that, in samples with relatively fine grains, a significant contribution to the formation of the depth profiles of implanted atoms comes from the radiation-induced diffusion; in samples with coarse grains, it comes from the diffusion along migrating extended defects, which appear and rearrange themselves in the process of ion implantation.

The research is involved in producing a Ti-Nb alloy surface layer on titanium substrate by high energy beam method, as well as in examining their structures and mechanical properties. Applying electron-beam cladding it was possible to produce a Ti-Nb alloy surface layer of several millimeters, where the niobium concentration was up to 40% at. and the structure itself could be related to martensite quenching structure. At the same time, a significant microhardness increase of 3200-3400 MPa was observed, which, in its turn, is connected with the formation of martensite structure. Cladding material of Ti-Nb composition could be the source in producing alloys of homogeneous microhardness and desired concentration of alloying niobium element.

The paper studies the kinetics of fatigue damage accumulation in VT1-0 titanium by the acoustic emission (AE) method. Technical grade titanium VT1-0 in various structural states was tested under cyclic bending. Submicrocrystalline Ti-specimens (SMC, with subgrain size of 200–300 nm) were fabricated by equal channel angular pressing (ECAP) from polycrystalline titanium. Ingots with ultrafine grain structure (UFG, with structure element size of 1–2 µm) and coarse grain structure (CG, with structure element size of 20–30 µm) were prepared by annealing at different temperatures. Fatigue stages were identified by analyzing the AE signal parameters with their classification by the source type (dislocations, micro-and macrocracks). It was revealed that the specimens with a smaller grain size are of higher fatigue durability, while AE signals at the stages of yielding and microcracking are detected later because of their low energy.

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.