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The dependence of the ignition temperature, combustion rate and composition of the resulting products on the concentration of Ti + C in mixtures with powder of a high-entropy alloy (HEA) FeNiCoCrCu and the initial mixture of metals forming it (MIX) has been studied. HEA was obtained by mechanical activation (MA) of a mixture of metal powders in argon. At the melting temperature, the high-entropy FeNiCoCrCu alloy decomposes into several phases, but the basis of the HEA alloy, as well as the alloy obtained by melting and crystallizing MIX, is a 5-component phase with an average formula Cu1.2Fe1.4Ni1.4Co1.4Cr. In addition, 5, 4, and 3-component phases with averaged formulas Cu2Ni2Co2Fe2Cr, Cu3Ni3Co2.9Fe2.5Cr, Cu4.8Ni4.5Co4.6Fe4.2Cr, Cu40Fe2Ni4Co2C, Cr12.5Fe3.2Co2.6Ni and Co3.2 Fe3,5 Cr are present in small amounts in the binder. Experiments on the ignition and combustion of mixtures of MIX and HEA with Ti + C were carried out in argon at atmospheric pressure. The combustion rate, ignition temperature, and maximum temperature reached in the thermal explosion of MIX and HEA mixtures with Ti + C increase with increasing Ti + C concentration. Due to the low exothermicity of the mixtures, the experiments were carried out at an initial temperature of 500 °С. At this initial temperature, the combustion limit of the samples occurs when the Ti + C concentration in the HEA and MIX mixtures is less than 30 %. Based on the results of scanning electron microscopy, the volume concentration of the number of titanium carbide (TiC) particles in molten samples was calculated. In an alloy with a HEA binder, the number of TiC particles per unit volume is 1.5-3.0 times greater than in an alloy with a MIX binder, and their size is correspondingly smaller. With an increase in the concentration of Ti + C from 30 to 40 % in a mixture with HEA, the number of TiC particles per unit volume decreases. In a mixture with MIX, the number of TiC particles per unit volume passes through a minimum. This is due to two opposite processes: on the one hand, the probability of the generation of TiC particles increases, on the other hand, their coagulation occurs.

We have studied the influence of the combustion temperature of Al + AlN mixtures in nitrogen and the cooling time of the synthesis products on the content of oxygen impurities dissolved in the aluminum nitride lattice. The results demonstrate that, in the temperature range 1460–2000°C, surface oxygen is incorporated into the structure of AlN. It has been shown that, with increasing synthesis temperature, the content of oxygen dissolved in aluminum nitride rises. The concentration of dissolved oxygen is higher in the case of a finer particle diluent (AlN). Raising the synthesis temperature leads to aluminum nitride grain growth and coalescence, characteristic of secondary recrystallization. We demonstrate that, to reduce the concentration of oxygen impurities dissolved in aluminum nitride, the starting mixture should contain additives facilitating the reduction of aluminum oxide or surface oxygen vaporization.

This article compares the microstructures of alloys formed upon the sintering of powdered mixtures of tungsten (PV2, average particle size 3.8–6.0 μm) and copper (PMS–11, particle-size fraction 45–60 μm) produced by various methods: the simple mixing of powdered metals, the mechanical activation (MA) of powdered metals, and the deposition of copper from a solution of its sulfate (Cu2SO4·5H2O) on powdered tungsten with simultaneous mechanical activation. The molar ratio in metals in mixtures is Cu/W = 1. The aqueous solution for copper deposition is comprised of diethylene glycol (up to 30%), glycerol (up to 8%), hydrofluoric acid (up to 0.1%), and the OP-10 wetting agent (up to 0.8%). Mechanical activation is carried out in an AGO-2 planetary mill with a drum load of 200 g of steel balls and a drum rotation speed of 2220 rpm for 5 min. Reduced copper in the solution and in air is rapidly oxidized to Cu2O; therefore, the composite powders were washed, dried, and stored in an argon environment. The samples pressed from the powders (tablets with a diameter of 3 mm, height of 1.5–2.0 mm, and density of 7.7–8.0 g/cm3) are sintered in argon at ambient pressure and in a temperature range from 1000 to 1500°C. During the sintering of Cu–W composite particles, it is possible to highlight several regions of the progress of the process. At temperatures below the melting point of copper, solid-phase sintering in the contact points of composite particles occurs. Upon heating from the melting points to 1200°C, the samples from the mixture of powdered metals are sintered according to the liquid-phase mechanism, forming a low porous cake. Sintering of composite powders produced by MA upon copper deposition and the MA of mixtures of powdered metals results in the segregation of samples with the formation of coarse pores extended perpendicularly to the axis of pressing and are partially filled with molten copper. Upon the heating of samples produced by the MA of powders above 1400°C, phase separation occurs and all copper is displaced from the sample to the surface.

The microstructures of alloys formed during the sintering of tungsten powder mixtures (PV2, 3.8–6.0 μm average particle size) and copper (PMS-11, 45–60 μm fraction) prepared by various methods were compared. The methods included simple metal powder mixing, mechanical activation (MA) of metal powders, copper precipitation from the solution of its sulfate (CuSO4·5H2O) on tungsten powder with simultaneous mechanical activation. The molar ratio of metals in mixtures Cu/W = 1. An aqueous solution for copper deposition included diethylene glycol (up to 30 %), glycerin (up to 8 %), hydrofluoric acid (up to 0.1 %), wetting agent OP-10 (up to 0.8 %). Mechanical activation was carried out in an AGO-2 planetary mill with 200 g of steel balls charged into the drums rotating at 2220 rpm for 5 min. Reduced copper in the solution and in the air rapidly oxidizes to the Cu2O oxide, so the composite powders obtained were washed, dried, and stored in an argon atmosphere. Samples pressed from the powders obtained (tablets 3 mm in diameter, 1.5–2.0 mm in height with a density of 7.7–8.0 g/cm3) were sintered in argon at atmospheric pressure and temperatures from 1000 to 1500 °C. During the sintering of Cu–W composite particles, several areas of the process can be distinguished. «Solid phase» sintering occurs at the contact points of composite particles at temperatures lower than the copper melting point. When samples are heated from the melting point to 1200 °C, samples are sintered by the liquid-phase mechanism from the conventional mixture of metal powders to form a low-porous cake. When composite powders obtained by MA during the copper deposition and MA of metal powder mixtures are sintered, samples are delaminated with the formation of large pores elongated perpendicular to the pressing axis and partially filled with copper melt. When samples obtained by powder MA are heated above 1400 °C, phase separation occurs and almost all copper is displaced from the sample to the surface.

CuCr composite particles have been obtained using copper deposition from the solution of its sulfate onto chromium powder particles with the simultaneous mechanical activation (MA) of the mixture in an AGO-2 planetary ball mill for 5 min. The CuSO4·5H2O concentration in the solution with complete copper reduction provides a molar ratio of Cu/Cr = 1. Since deposited fine crystalline copper is highly active and rapidly oxidizes to Cu2O oxide in air, the composite powders are washed, dried, and stored in an argon atmosphere. After drying, the mixture is subjected to additional MA for 5 min. During MA, composite particles with a laminate structure start forming in the solution. The powders are used to press tablets with a diameter of 3 mm, height of up to 1.5 mm, and density of 4.2–4.5 g/cm3. Samples are sintered in an argon atmosphere at 700–1400°С. To compare microstructures, we have also sintered samples from mixtures of Cr and Cu metal powders with a volume ratio of chromium to copper of 50 : 50, which were obtained by simple mixing in a porcelain mortar for 20 min and MA for 10 min. Three regions of the alloy structure formation can be distinguished depending on the heating temperature. When temperatures are heated below the eutectic melting point, composite particles are sintered at separate points. With heating temperatures above the liquidus temperature, the alloy melts with its phases separated; one part of the sample consists of copper enriched in chromium, and the other part consists of chromium enriched in copper. With intermediate heating temperatures, liquid phase sintering accompanied by phase separation is observed. Copper-enriched chromium particles become spherical and are located in a chromium-enriched copper matrix. A comparison of samples sintered under the same conditions from powder mixtures obtained by different methods showed that samples with deposited copper have a more uniform and fine-grained structure.

Combustion of mechanically activated mixtures in 2Co–Ti–Al and Co–2Ti–Al is investigated, and alloys based on them are obtained by self-propagating high-temperature synthesis (SHS). Microstructural, X-ray, and differential-thermal studies are performed. A Heusler phase Co2TiAl-based alloy is obtained for the first time by means of mechanical activation. Conditions for the mechanical activation of a reacting powder mixture for the formation of a single-phase material is experimentally selected.

Results are given for synthesis of AlN–Al2O3–Y2O3 composites in a combustion regime in an industrial reactor. The effect of synthesis temperature on formation of the microstructure, phase composition, and impurity oxygen content dissolved in the crystal lattice of aluminum nitride is studied. The optimum synthesis temperature is determined. Experimental batches of composite powders are produced for the manufacture of dielectric ceramics with high thermal conductivity.

The results of studies on the synthesis of AlN‒Al2O3‒Y2O3 compositions in the combustion mode in an industrial reactor are presented. The influence of synthesis temperature on the formation of microstructure, phase composition of compositions and oxygen content of impurities dissolved in the crystal lattice of aluminum nitride was studied. The optimal synthesis temperature is determined. Experimental batches of composite powders were produced for the production of dielectric ceramics with high thermal conductivity.

To fabricate Cu–Ti composite particles, the method of copper deposition from its sulfate solution on titanium powder particles with the simultaneous mechanical activation (MA) of the mixture in an AGO‑2 planetary ball mill for 5 min is used. The CuSO4 ⋅ 5H2O concentration in solutions is 10 and 16%, which provides molar ratio Cu/Ti = 0.85 and 1.36, respectively, with the complete reduction of copper. The rapid reduction of copper in the form of highly dispersed partially amorphized powder occurs during MA, and composite particles with a thin laminate structure and high reaction ability are formed. Prepared composites are rinsed and stored in argon because reduced copper possesses high activity and rapidly oxidizes in air to oxide Cu2O. After drying, the additional MA of the mixture is performed for 5 min. Pellets 3 mm in diameter and up to 1.5 mm in height are compacted from prepared powders and heated in argon to 700–1200°C. An intense reaction with heat liberation (heat explosion) and the formation of TiCu, Ti2Cu3, and Ti2Cu intermetallic compounds starts upon sample heating. The critical inflammation temperature for composite powders formed by MA with simultaneous copper deposition from the solution is 480°C, which is 400°C below the inflammation temperature of the usual powder mixture of titanium and copper. The alloy has a dendritic structure at a heating temperature close to the melting point, while, if it is exceeded by more than 100°C, the phase distribution in the alloys becomes more uniform and their size decreases.

Shock-induced chemical transformations in Ti–B–Ni and Ti–C–Ni powder blends were explored by XRD and EDS methods (flyer velocities 1000 and 1500 m/s). The blends based on Ti–C showed lower sensitivity to shock compression compared to those based on Ti–B. Synthesized products comprised of TiC or TiB2 grains in a Ti–Ni binder. Preliminary mechanical alloying of reactive mixtures was found to elevate their sensitivity to shock compression. The obtained results may turn helpful in designing and optimizing the processes for fabrication of layered cermets.

The effect of the composition of iron-containing compounds on the production of Si 2 N 2 O when burning a mixture of Si + SiO 2 in nitrogen was studied. It was established that the phase composition and morphology of the crystals of combustion products depend on the composition of the iron-containing compound. The powder of Si 2 N 2 O not containing impurity phases was obtained in the form of polycrystalline fibers consisting of ultrafine crystals in the presence of FeCl 3 ·6H 2 O. Ill. 6. Ref. 14.

The effects of iron-containing compounds on Si2N2O production during burning in N2 of an Si + SiO2 mixture were studied. It was established that the phase composition and morphology of the crystalline combustion products depended on the iron-containing compound. Si2N2O powder without impurity phases was obtained in the presence of FeCl3·6H2O and formed polycrystalline fibers consisting of ultrafine crystals.

TiZrNiCuAl and TiNbNiCuAl alloys were prepared by thermal explosion and high-energy ball milling, characterized by SEM, XRD and tested for their thermal stability.