This paper provides the data on the composition and structure of nanocrystalline particles formed during the plasmachemical synthesis of mechanical mixtures containing TiC, Mo, and Co according to the plasma-induced Ostwald ripeningscheme. The paper was mainly intended to study the structural features and localizations of Mo₀.₄₂C₀.₅₈ carbide in TiC–Mo and TiC–Mo–Co nanocrystalline «core–shell» structures. As a result of X-ray diffraction and high resolution transmission electron microscopy (HRTEM) studies, it was found that the Mo₀.₄₂C₀.₅₈ carbide of orthorhombic modification is present in all fractions of TiC–Mo and TiC–Mo–Co mechanical mixtures after Ostwald ripening. Nanocrystalline TiC–Mo fractions and the TiC–Mo–Co mixture subjected to one-time Ostwald ripening from a baghouse filter were used in the electron microscopy study to illustrate the presence of «core–shell» structures where refractory cores are represented by Ti1–nMonCx titanium-molybdenum carbides, and high-contrast metal shells contain Mo, Mo₀.₄₂C₀.₅₈ and Co. Electron microscope images also showed the localization of orthorhombic Mo₀.₄₂C₀.₅₈. According to the results obtained, it can be concluded that «core–shell» structures are formed during the extreme exposure in the form of plasma-chemical synthesis of TiC–Mo and TiC–Mo–Co mechanical mixtures in a low-temperature nitrogen plasma. At the same time, it should be added that nanocrystalline compositions with the «core–shell» structure are crystallized in a tangential nitrogen flow at a cooling rate of 105 °C/s with the subsequent separation of products into ultra- and nanodispersed fractions in a vortex-type cyclone and a baghouse filter.

The paper studies the effect of particle sizes of hexagonal ferrite powders on their electrodynamic properties. SrTi₀.₂Co₀.₂Fe₁₁.₆O₁₉ and BaSc₀.₂Fe₁₁.₈O₁₉ hexaferrites were used as the objects of research. Grinding in a high-energy planetary mill for up to 60 minutes made it possible to obtain hexaferrite powder particles with the average size successively decreasing from 1.5–2 μm to 0.05–0.15 μm. A scanning electron microscope was used for the analysis. Samples were prepared in a mixture with a polymer binder (70% ferrite + 30% polymer), and their electromagnetic radiation (EMR) absorbing capacity was studied in the microwave range from 30 to 50 GHz. It was shown that there is practically no peak corresponding to ferrimagnetic resonance in the composite with ferrite, with a decrease in the average particle size of BaSc₀.₂Fe₁₁.₈O₁₉ hexaferrite powders to 50–150 nm. The dependences of the real and imaginary parts of the magnetic permeability and dielectric constant are given in the frequency range from 107 to 109 Hz. There was no domain wall resonance in the frequency dependence of magnetic losses for a ferrite-based composite mechanically activated for 60 min. SrTi₀.₂Co₀.₂Fe₁₁.₆O₁₉ ferrite was milled in a bead mill to particles with an average size of 150–300 nm, and then to drying, pressing, sintering at 1360 °С and subsequent grinding to a size of 200–500 μm to obtain similar composites in a bond with a polymer. It was found that the properties of compositions change significantly with a change in the magnetic component synthesis technology: no resonant pattern of EMR absorption was observed. The Curie temperature was measured using the Faraday method. It was shown that it is ~340 °С for the studied material. Therefore, the effect of precursor milling on changes in magnetocrystalline anisotropy was identified.

The study covers the method of azide self-propagating high-temperature synthesis (SHS-Az) to obtain a highly dispersed TiN–SiC ceramic composite with a theoretical ratio of nitride and carbide phases from 1 : 4 to 4 : 1 (in moles) using the combustion of the corresponding composition of powder reagent mixtures: NaN₃ sodium azide, (NH₄)₂TiF₆, (NH₄)₂SiF₆ and Na₂SiF₆ halide salts, titanium, silicon and carbon in a nitrogen gas atmosphere. Thermodynamic calculations using the Thermo computer program showed that the optimum nitrogen pressure in the reactor is about 4 MPa, and the final composition of SHS-Az products can be completely different depending on the composition of reagents: it may include only target phases (TiN–SiC), contain silicon nitride and free carbon phases impurities (TiN–SiC–Si₃N₄–C) along with the target phases or consist only of nitride and free carbon phases (TiN–Si₃N₄–C). It was found that only target TiN and SiC phases are formed when using halide salt (NH₄)₂TiF₆, at any ratio of nitride and carbide phases in the final powder composition. In cases where halide salts (NH₄)₂SiF₆ and Na₂SiF₆ are used, target  TiN and SiC phases are synthesized with an increased titanium content in reagents, i.e. only when composites of the 2TiN–SiC and 4TiN–SiC with an increased content nitride phase are obtained. Experimental studies of combustion products using scanning electron microscopy, energy dispersion analysis and X-ray phase analysis showed that they differ significantly from the theoretical compositions of products by the completely absent or significantly reduced SiC phase content in the final composition of powder composites synthesized during the combustion of bulk charge with carbon, and at the same time the absence of free carbon in the final composition of powder composites obtained. This difference is explained by the fact that when the combustion of a silicon and carbon powder mixture is initiated, silicon nitride is synthesized at the first stage with the temperature rising to high values of about over 1900 °C, at which the synthesized Si3N4 dissociates, and then at the second stage the resulting silicon reacts with carbon to form SiC that is more stable at high temperatures. But during combustion, very small light particles of carbon black (soot) may be removed (blown out) from a burning highly porous charge sample of bulk density by gases released at the first stage of combustion and not participate in the transformation of Si₃N₄ into SiC. In this regard, in case of low-carbon charge combustion, silicon carbide either does not form at all, or it is formed in small quantities compared to the theoretically possible amount, and Si₃N₄ silicon nitride remains the main component of the composite. A noticeable amount of SiC is formed only when burning high-carbon charges, but this amount is significantly less than the possible theoretical one, and the difference between them is replaced by the silicon nitride content. Therefore, it was experimentally shown for the first time that the SHS process can be used to obtain composites of highly dispersed ceramic powders TiN–Si₃N₄ and TiN–Si₃N₄–SiC consisting of a mixture of nanoscale (less than 100 nm) and submicron (100 to 500 nm) particles with a relatively low content of free silicon admixture (less than 1.4 %).

This study focuses on the combustion kinetics and mechanisms of reaction mixtures in the Mo–Al–B ternary system taken so that the MoAlB MAB phase was formed. The effect of the initial temperature on the key combustion parameters was demonstrated. Reaction mixture preheating was found to weakly affect the maximum combustion temperature. The effective activation energy of self-propagating high-temperature synthesis (SHS) was calculated. Phase diagrams in the Mo–Al–B system were built using the AFLOW and Materials Project databases. The phase composition and structure of the synthesized ceramics with MoAlB lamellar grains 0.4 μm thick and ~2–10 μm long as a main component were studied. The DXRD lines of MoB and Mo₂B₅ intermediate borides with their total content of ≤3 % were also identified. Scanning electron microscopy and energy dispersive spectroscopy studies revealed that the Al₂O₃ phase was present in the intergranular pores. A sequence of chemical transformations in the combustion wave was studied, and a hypothesis about the structure formation mechanism was put forward. MoO₂ and Al₂O₃ can be the primary phases during SHS, and the MoAlB phase is formed from the boron-containing aluminum–molybdenum melt. Submicron-sized MoB precipitates are formed in the post-combustion zone due to the partial oxidation of aluminum by the dispersion strengthening mechanism.

The effect of activation energy on phase transformations (transitions) in the W–C system during the synthesis induced by an external heat source was investigated by electrothermal explosion (ETE) under pressure. The ETE technology combines self-propagating high-temperature synthesis (SHS) with additional sample heating by Joule heat – electric current passing through the synthesized mixture, and it makes it possible to determine the chemical reaction rate that is highly susceptible to external impacts such as pressure, concentration, sample shape, any film present on combustion products, etc. The chemical reaction rate, i.e. external source current, may be controlled by changing the activation energy. The study was conducted in the following conditions: temperature Т = 293÷3700 K; carbon concentration of 49.8–50.2 at.%; quasi-static compression at P = 96 MP_a; external source voltage and current density V = 10 V, I = 20 МА/m², respectively; samples 8 mm in diameter weighing 6 g. The Т–τ thermogram of the W–C system was used to determine the following parameters: four stages of the synthesis process, temperatures of special points of phase transformations, temperature boundaries of phases and process activation energy. Thermograms of intermediate states are presented as isothermal plateaus of phase transformations. The analysis of experimental results and the physical representation of the process make it possible to assert that temperature plateau parameters are the effective value of activation energy for synthesis mode maintenance. Each of the 4 W–C mixture synthesis stages is described. Pre-explosion stage I – sample heating in the temperature range of Т = 293÷563К, endothermic reaction, effective activation energy for synthesis mode maintenance Q = 2.96 kJ, and taking into account 1-mole mass Е_а = 111.6 kJ/mol. Low-temperature (563–1190 К) stage II – ignition, Q = 5.46 kJ, Е_а = 109.2 kJ/mol. High-temperature stage (III) in the range of Т = 1190÷2695К, order–disorder transformation, Q = 14.25 kJ, Е_а = 424 kJ/mol. Finally, Stage IV occurs in the range of Т = 2695÷3695К, Q = 14.31 kJ, Е_а = 143.2 kJ/mol. It was shown that the limiting stage with the highest activation energy is the melting process.

Mo–Si–B and Mo–Hf–Si–B coatings were produced by magnetron sputtering of a MoSiB ceramic target equipped with 2 or 4 Hf segments. Their structure and composition were studied by scanning electron microscopy, energy dispersive spectro scopy, X-ray diffraction analysis, and Raman spectroscopy. Mechanical properties were determined by nanoindentation at a load of 4 N. The crack resistance of coatings was studied on a microhardness tester at loads of 0.25–1.0 N. The oxidation kinetics was studied at 1000 °C in air with a total exposure of 300 min. The heat resistance of coatings was determined as a result of short-term annealing at 1500 °C. Electrochemical tests were carried out by voltammetry in the 1N H₂SO₄ solution. The results showed that the Mo–Si–B coating and Mo–Hf–Si–B coating obtained using 2 Hf segments feature by a columnar structure. The use of 4Hf segments in coating deposition led to an increase in density and suppression of the undesirable columnar structure formation. It was shown that hafnium introduction into the coating composition increases the growth rate by 20% and reduces the grain size of the main component of the h-MoSi₂ phase by an order of magnitude, while simultaneously promoting HfB₂ formation. Maximum hardness (27 GPa), Young’s modulus (370 GPa) and elastic recovery (62 %) were achieved for the Mo-Si-B coating. The hardness of coatings obtained using 2 and 4 Hf segments decreases by 1.9 and 1.6 times, respectively. During the Mo–Si–B and Mo–Hf–Si–B (2Hf) coating microindentation, radial cracking was observed. The sample obtained with the maximum concentration of hafnium featured by the best crack resistance. Electrochemical tests showed that the corrosion resistance of coatings increases in the Mo–Hf–Si–B (2Hf) → Mo–Si–B → Mo–Hf–Si–B (4Hf) series. All coatings showed good oxidation resistance at 1000 and 1500 °C. However, coating delamination areas were observed on the surface of Mo–Si–B and Mo–Hf–Si–B (2Hf) samples. The Mo–Hf–Si–B (4Hf) coating showed a lower oxide layer thickness and better oxidation resistance due to the dense SiO₂ + HfO_х protective layer formation.

The paper presents the results of studies into the microstructure, chemical and phase composition of coatings deposited on a steel substrate using the sliding explosive loading of Cr₃C₂ chromium carbide and titanium powder mixtures. The equilibrium phase composition of coatings was calculated by computational thermodynamic modeling using the Thermo-Calc software package. The structure and elemental composition were studied using a FEI Versa 3D scanning electron microscope with an integrated EDAX Apollo X system for energy dispersive X-ray microprobe analysis. A Bruker D8 Advance diffractometer was used for X-ray phase analysis. It was shown that when the powder layer is loaded by a sliding detonation wave, it can be shifted along the substrate surface due to the horizontal mass velocity component of compacted material particles. This shift causes the inner layer of the compacted powder and the surface layer of the substrate to melt as a result of friction. The presence of a liquid phase prevents the compacted powder layer deceleration so that the major part of it is removed from the substrate surface. The liquid phase remaining on the surface undergoes rapid quenching due to heat removal into the substrate and forms a deposited coating containing both the components of the initial powder mixture and the components of the substrate to be coated. It was established that the deposited layer structure features by extremely high dispersion (grain size does not exceed 250 nm), and its phase composition turns out to be close to a thermodynamically equilibrium one. When using powder mixtures of chromium carbide with 40% titanium, a coating is formed consisting of titanium carbide with a metal binder based on solid solutions of iron and titanium in chromium.