The paper is devoted to a detailed study of cathodic processes, their influence on the anode process, and electrolysis performance. The polarization of a steel cathode in a CaCl2–BaCl2–NaCl melt at t = 610 °C was measured. The polarization curve clearly shows the potentials and current densities of the formation of a saturated sodium solution in the electrolyte (Esat = –2.97 V, ic = 0.04 A/cm2, lgic = –1,4), and the occurrence of sodium metal on the cathode (ENa = –3.22 V, iNa = 0.12 A/cm2, lgiNa = –0.92).

The value of Esat was used to calculate the concentration of sodium in the electrolyte at t = 610 °С (1.3·10–4 mol. fr.). The values of Esat, ENa, and their difference (E = 0,25 В) were confirmed by long-term electrolysis. These fundamental characteristics are the basis for process control and management. During long-ter 3 regions close to rectilinear ones were revealed: the discharge of sodium ions from supersaturated solutions at E more negative than Esat (from ENa to Esat), from mixtures of supersaturated and saturated solutions (at a constant E equal to Esat), from diluted solutions (with E more positive than Esat). The activity coefficients of sodium in supersaturated solutions are close to 1, which ensures their increased reducing ability. Maximum degrees of supersaturation (>100) are created at formation and decomposition on the cathode of metallic sodium nuclei, which are sufficient to intensify and prolong electrolysis, to lower the lower temperature limit of its realization from 600 to 350 °С. The formation of metallic titanium in the near-anode layer is explained by the disproportionation of Ti2+ ions entering the near-anode electrolyte from the anode surface and from the near-cathode melt.

The results of the study of the structure and properties of titanium hydride powders obtained from titanium sponge by SHS hydrogenation and mechanical grinding are presented. Hydrogenation was carried out in a reactor at a constant hydrogen pressure of 3 MPa. After passing the combustion wave, the hot titanium sponge was cooled to room temperature in a hydrogenatmosphere. As a result, titanium hydride spongy granules with a hydrogen content of 4.2 wt.% were obtained. Titanium hydride was ground in a ball mill and divided into 4 fractions corresponding to the fractional composition of titanium powder PTK, PTS, PTM and PTOM. Particle size analysis showed that the samples of the PTK and PTOM powders have a narrower particle distribution in comparison with the PTS and PTM ones. Further, obtained powders chemical composition and surface morphology studies were carried out and bulk density, compaction, pycnometric density and specific surface area were determined. According to the chemical analysis results the content of carbon and oxygen impurities decreases during SHS-hydrogenation and the iron content slightly increases during mechanical grinding depending on the grinding time. The study of morphology showed that the hydride titanium particles have an irregular fragmentary shape, such morphology is characteristic of powders obtained by this technology. The surface structure has partially preserved structure of the initial titanium sponge and consists of elongated oriented grains. It is established that with a decrease in the particle size, the bulk density decreases, and the compaction increases. Pycnometric density and specific surface area values are approximately equal for all powder samples.

The synthesis of MAX phase Ti2AlN from several mixtures of Ti, Al, TiN, and AlN powders by vacuum sintering of greensamples in the form of dense compacts, bulk powder in silica tubes, and plain layer in a closed rectangular molybdenum boat was studied upon variation in charge composition and sintering temperature Ts. The sintering of 2 : 1 Ti–AlN mixture was carried out at 1100, 1200, 1300, 1400, and 1500 °С with exposure time of 60 min. The largest MAX phase content (94 wt.%) was reached at Ts = 1400 °С. The sintering of 1 : 1 TiAl : TiN composition at the same temperature gave 93 wt.% Ti2AlN. The best result (singlephase Ti2AlN in a 100-% yield) was achieved upon the sintering of 1 : 1 : 1 Ti–Al–TiN composition at Ts = 1400 °С. The scalability of our process was checked by the fabrication of a large (0.5 kg) and uniform cake of single-phase Ti2AlN. In experiments we used green samples with shielded lateral surface (bulk powder in silica tubes, plain layer in a closed molybdenum boat) and without shield (dense compacts). It has been shown that shielding of Ti–Al–TiN samples restricts the escape of Al vapor from a sintered mixture, thus providing more favorable conditions for the synthesis of single-phase Ti2AlN. Our process can be readily recommended for practical implementation.

The application of the process of self-propagating high-temperature synthesis (SHS) to prepare highly dispersed powder nitride-carbide compositions from the most common refractory nitride (Si3N4, AlN, TiN) and carbide (SiC) compounds with a particle size of less than 1 μm is considered. The advantages of composite ceramics over single-phase ceramic materials and such trends of its development as the transition to nanostructured ceramics and the application of in situ processes of direct chemical synthesis of nanoparticles of components in the composite body are described. The attractiveness of the SHS process as one of the promising in situ processes characterized by simplicity and cost-effectiveness, the possibility of obtaining highly dispersed ceramic powders by burning mixtures of inexpensive reagents is shown. Considerable attention is paid to the consideration of the results of the application of azide SHS, based on the use of sodium azide and gasified halide salts as part of mixtures of initial powders of nitrided and carbidized elements during their combustion in nitrogen gas. The review of publications devoted to the application of SHS to obtain highly dispersed composite powders Si3N4–SiC, AlN–SiC and TiN–SiC, promising for use in sintering of the corresponding composite ceramic materials of submicron and nano-sized structure with improved properties, lower brittleness, good machinability, lower sintering temperatures compared with single-phase ceramic materials made of nitrides or carbides as well as for other applications, is presented. The results of the application of azide SHS are presented in detail both in the form of the results of thermodynamic calculations and the results of experimental research of combustion parameters, combustion product structure and composition. The advantages and disadvantages of using the combustion process for the synthesis of nitride compositions with silicon carbide, the causes of the disadvantages and the directions of further research to eliminate them are discussed.

Combustion of powders of transition metals of titanium PTS (average particle size 57 μm), zirconium PCRK-1 (12 μm), tantalum Ta PM-3 (8 μm), hafnium GFM-1 (4 μm), niobium NBP-1a (21 μm) with carbon black grade P-803 dispersion 1–2 μm was studied. The combustion process of the compressed samples (mass 2.5–6.9 g, height 1.2–1.7 cm, relative density 0.55–0.61) was performed in an inert argon medium at a pressure of 760 mmHg in the constant pressure chamber.  Combinations were studied, Me1 + Me2 + Me3 + Me4 + 4C, Me1 + Me2 + Me3 + Me4 + Me5 + 5C. XRD patterns of the mixtures were recorded on a DRON-3М diffractometer (CuKα-radiation). Combustion product sections were studied using a LEO 1450 VP scanning electron microscope (Carl Zeiss, Germany). The fractional composition and particle size distribution of the mixture were determined according to standard procedure using a Microsizer-201C laser particle size analyzer. Combustion velocity, elongation of samples, phase composition of products were determined. The maximum combustion temperature of the mixture (Ti + Hf + Zr + Nb + Ta) + 5C was measured experimentally for the first time. The morphology and microstructure of the reaction products were also observed. Combustion products of mixtures (Ti + Zr + Nb + Ta) + 4C and (Ti + Zr + Nb + Hf) + 4C contain high entropy carbides, which are solid solutions with the same structural type B1 (space group Fm-3m) and having different cell parameters. Product samples of mixtures (Ti + Zr ++ Hf + Ta) + 4C and (Ti + Hf + Zr + Nb + Ta) + 5C contain high entropy and medium entropy carbides, also representing solid solutions with the same structural type B1 (space group Fm-3m). The results of this work can be used in the production of high-entropy and medium-entropy multicomponent carbides.

In this work, using the methods of X-ray phase analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy, the features of the impact of annealing in air within the temperature range of t = 200÷÷550 °C on the morphology, elemental and phase composition, chemical state and structure of primary particles of nanopowders obtained by grinding natural diamond and the method of detonation synthesis are studied. It is shown that heat treatment in air at given values of temperature and heating time does not affect the elemental composition and atomic structure of primary particles of nanopowders obtained both by the methods of detonation synthesis (DND) and natural diamond grinding (PND). Using XPS, Raman spectroscopy, and transmission electron microscopy, it has been found that annealing in air within the temperature range of 400–550 °C results in the effective removal of amorphous and graphite-like carbon atoms in the sp2- and sp3-states from diamond nanopowders by oxidation with atmospheric oxygen. In the original DND nanopowder, containing about 33.2 % of non-diamond carbon atoms of the total number of carbon atoms, after annealing for 5 h at a temperature of 550 °C, the relative number of nondiamond carbon atoms in the sp2-state decreased to ~21.4 %. In this case, the increase in the relative number of carbon atoms in the sp3-state (in the lattice of the diamond core) and in the composition of oxygen-containing functional groups ranged from ~39.8 % to ~46.5 % and from ~27 % to ~32.1 %, respectively. In the PND nanopowder, which prior to annealing contains about 10.6 % of non-diamond carbon atoms in the sp2-state of the total number of carbon atoms, after annealing under the same conditions as the DND nanopowder, their relative number decreased to 7.1 %. The relative number of carbon atoms in the sp3-state  increased from 72.9 % to 82.1 %, and the proportion of carbon atoms in the composition of oxygen-containing functional groups also slightly increased from 10.2 % to 10.8 %. It is demonstrated that the annealing of PND and DND nanopowders in air leads to a change in their color, they become lighter as a result of oxidation of non-diamond carbon by atmospheric oxygen. The maximum effect is observed at a temperature of 550 °C and an annealing time of 5 h. In this case, the weight loss of PND and DND nanopowders after annealing was 5.37 % and 21.09 %, respectively. The significant weight loss of DND nanopowder compared to PND is primarily caused by the high content of non-diamond carbon in the initial state and the high surface energy of primary particles due to their small size.

Using the SLM method in a nitrogen blanket with heating to a temperature of 200 °C, samples were obtained at a position of 0° against the build plate. The effect of the hot isostatic pressing (HIP) and heat treatment (HT: hardening + aging) on the structure and mechanical properties of maraging steel CL50 WS was studied (the Russian analogue is ChS4 grade). To analyze the effect of post-processing on the strength characteristics (σb, σ0,2, δ, ψ), tensile tests were conducted. Their results indicated high values of strength and ductility. It has been established that as a result of HT in the steel structure, in addition to α-Fe, γ-Fe, dispersed precipitates of the NiTi3 strengthening phase are formed, the identification of which was carried out by high-resolution transmission electron microscopy. Through the NiTi3 intermetallic phase, the steel has acquired increased tensile strength and yield strength required for the production of critical components and parts for highly loaded turbomachine disks. The change in the porosity of the samples before and after the HIP was analyzed. The microstructure of the samples and the changes that occur under the influence of various post-processing options are studied. The fine-grained homogeneous structure obtained by combining the SLM, HIP and HT provided optimal strength and ductility. Analysis of fractures after mechanical testing showed that the samples after postprocessing are destroyed according to the viscous-pitting mechanism with the formation of a neck.