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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.

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.

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.

Various macrokinetic modes of interaction (self-ignition or combustion) of compact samples from nonpassivated (pyrophoric) and passivated iron nanopowders with air are under study. Experiments show that the modes of interaction with air depend on the type of the used gaseous medium (argon or air), previously containing weighting cups with samples, and on how long the bottles remain in air. The possibility of passivation of pressed samples from pyrophoric iron nanopowder is experimentally established for the first time in the case where the weighting cups with samples remain in air. Various experimental methods are used to investigate the sample heating dynamics and the effect of density inhomogeneity along the length of the sample. It is revealed that pyrophoric samples are heated nonuniformly, although heating begins simultaneously over the entire surface of the sample.

The use of nanopowders implies the ability to safely store them without changes in their physicochemical parameters ensured by passivation. In this work, we have determined the thermal stability range in air for compact samples of different diameters prepared from pyrophoric nickel nanopowders and then passivated. The results demonstrate that compact samples prepared from nickel nanopowder can be safely stored in air at temperatures of up to about 200°C without additional oxidation, which points to their high thermal stability. The lack of a noticeable heat release during slow heating to 200°C and the presence of only Ni in both the passivated and heat-treated samples according to X-ray diffraction data suggest that the oxide layer is very thin or that there are noncrystalline oxide phases. The observed uniform oxygen and nickel distributions over fracture surfaces of samples after heating suggests that their interaction with air during both the passivation process and heating to temperatures on the order of 200°C is a bulk process.

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.

The paper studies the effect of mechanical activation (MA) modes when stirring a stoichiometric mixture of titanium and soot powders in a ball mill on the properties of mixtures, combustion parameters, relative density, and the microstructure of consolidated titanium carbide samples obtained by SHS. MA conditions for Ti + C reaction mixtures in a ball mill were determined. An increase in the mass of grinding bodies activates the MA mechanism. It was shown that the greatest effect from MA was obtained with a two-stage preparation of mixtures: firstly, the titanium powder was activated separately, then the components were mixed together, and this process included not only their mixing, but also soot powder activation. It was found that combustion behavior is affected by the activation of not only titanium, but also soot. After MA of both components, an anomalous increase in the burning rate (more than 100 cm/s) was found on pressed samples. At the bulk density, there was no effect of MA on the mixture combustion process, since in this case the burning rate of all mixtures was in the range of 1.5–2.5 cm/s. It was revealed that MA of reagents for pressed samples leads to an increase in the combustion temperature, an increase in the relative density of the consolidated refractory product to 93–95 %, and a decrease in the average size of TiC grains. A decrease in the residual porosity of consolidated TiC is due to an increase in the hot pressing temperature and plasticity of the product synthesized during the reaction mixture combustion after MA. The main reason is an increase in the exothermic interaction rate. It was shown that MA when mixing reagents makes it possible to control combustion parameters, the microstructure of consolidated products and opens up new opportunities for obtaining refractory materials featuring a unique structure and properties by SHS pressing.

Abstract In this paper, we study compact samples of pyrophoric nickel powders with the average particle size of 85 nm, obtained by the chemical-metallurgical method. For the first time, it is experimentally shown that it is possible to passivate compact samples with a diameter of 3 mm from pyrophoric nickel powders with nanosized particles in air. For a relative density of 0.4 to 0.5, the passivation time is only 3–5 s. According to the X-ray phase analysis data, only the Ni phase is observed in passivated samples. It is found that passivated samples retain their thermal stability in air upon slow (

A material based on a (VCr)2AlC solid solution has been obtained for the first time by self-propagating high-temperature synthesis from a powder reaction mixture of vanadium(V) and chromium(III) oxides with aluminum and carbon (graphite). The synthesized material has been studied by X-ray diffraction and microstructural analyses. It has been shown that the product also contains vanadium and chromium carbides and intermetallics. The presence of these phases seems to be associated with the nonequilibrium character of the synthesis process due to a short “lifetime” of melt and its fast cooling and crystallization. The synthesized material is an electrical conductor, which demonstrates a metallic character of conductivity throughout the entire measured temperature range of 300–1300 K. The room-temperature specific resistance of the composite material based on a (Cr,V)2AlC solid solution is 1.14 µΩ m, which is higher than the specific resistance of the materials based on the Cr2AlC and V2AlC MAX phases. The microhardness of the synthesized material is 6.9 GPa.

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.

An intermetallic alloy based on the Heusler phase—Cu2TiAl—has been obtained by self-propagating high-temperature synthesis (SHS) in the Cu–Ti–Al system for the first time. The modes of frontal combustion of the green mixtures and the processes of phase formation during synthesis have been studied. The resulting products have been studied by X-ray analysis (including high-temperature diffractometry with step heating up to 900 K), scanning electron microscopy, and differential thermal analysis (DTA), and some physical properties have been studied. Electrophysical and magnetic measurements are also carried out for the alloy. The results of X-ray analysis and scanning electron microscopy using energy-dispersive analysis (EDA) have shown that the content of the Heusler phase in the synthesized product is at least 82%. The product also contains copper (CunineAl4) and titanium (Ti3Al2) aluminides. The temperature dependence of the electrical resistivity of the synthesized product is measured for a wide temperature range of 90–1000 K. The resistivity at T = 300 K is 0.3 μm Ωm. The metallic type of conductivity for obtained samples and the anomalous behavior of the temperature curve of electrical resistance in the region of 770–790 K are revealed. Thermal analysis is used to measure the melting point of the synthesized product and reveal additional heat effects at 788, 848, and 1248 K associated with possible phase transitions in the Cu2TiAl intermetallic compound. One possible mechanism of these phase transitions is considered in accordance with the phase diagram of the Cu–Ti–Al system. Magnetic measurement results show that intermetallic samples of the compound obtained by the SHS method exhibit weak ferromagnetic properties with residual magnetization of 0.069 A m2/kg.

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 multielement carbide (TaZrHfNbTi)С5 has been synthesized via two-step high-energy mechanical processing (HEMP). We have optimized mechanical processing parameters for the formation of the TaZrHfNbTi high-entropy alloy (HEA)—as a precursor for the synthesis of the mixed carbide—from a metal powder mixture. HEMP of a mixture of Ta, Zr, Hf, Nb, and Ti powders in an AGO-2 planetary mill for 15 min at 90g leads to the formation of a TaZrHfNbTi HEA with an imperfect crystal structure. The time needed for obtaining the multielement carbide (TaZrHfNbTi)С5 by milling a mixture of the metallic HEA and carbon black is 30 min. The thermal stability of the resultant carbide has been studied by high-temperature X-ray diffraction. The results demonstrate that the multielement carbide (TaZrHfNbTi)С5 is stable in the range 800–1200°C at an isothermal holding time of 5 h, without precipitation of individual carbide phases. Exposure to temperatures above 1000°C under dynamic vacuum leads to partial oxidation of (TaZrHfNbTi)С5.

For the first time, an intermetallic alloy based on the Heusler phase – Cu2TiAl – was obtained by self-propagating high-temperature synthesis (SHS) in the Cu–Ti–Al reaction mixture. The frontal combustion modes of green mixture compositions and phase formation processes during synthesis were studied. The products obtained were studied by X-ray diffraction analysis including high-temperature diffractometry with stage heating up to 900 K, scanning electron microscopy, differential thermal analysis (DTA), and some physical properties were studied. Also, electrophysical and magnetic measurements were carried out for the obtained alloy. The results of X-ray analysis and SEM using energy-dispersive analysis (EDA) showed that the Heusler phase content in the synthesized product is at least 82 %. The product also contains copper (Cu9Al4) and titanium (Ti3Al2) aluminides. The temperature dependence of the synthesized product electrical resistivity was measured for a wide temperature range of 90–1000 K, which was 0.3 μmm at T = 300 K. The metallic type of the conductivity for the samples obtained and the abnormal behavior of the electrical resistance temperature curve in the region of Т = 770÷790 K were revealed. Thermal analysis was used to measure the melting point of the synthesized product and to reveal additional heat effects at Т = 788, 848 and 1248 К associated with possible phase transitions in the Cu2TiAl intermetallic compound. A possible mechanism of phase transitions is considered in accordance with the Cu–Ti–Al system phase diagram. Magnetic measurements results showed that intermetallic samples obtained by the SHS method feature by weak ferromagnetic properties with residual magnetization of 0.069 A·m2/kg.

We have examined for the first time the feasibility of producing cast Nb-, Si-, and B-doped Mo-based composite materials by a spin-casting self-propagating high-temperature synthesis metallurgy method and obtained new results regarding control over their composition and structure. In synthesis, we used combinations of a highly exothermic (MoO3/Nb2O5/Al/Si/B) and a low-exothermic (Mo/Nb/Si/B) composition. We have assessed the effect of the ratio of the ratio of the highly exothermic and low-exothermic compositions (α) and acceleration (a) on the composition and structure of the cast composite materials. The mixtures have been shown to be capable of combustion at up to 80% low-exothermic composition. The combustion products have cast form in the range 0 ≤ α ≤ 65%. At α in the range from 0 to 40% and accelerations from 40g to 400g, the combustion products have the form of a two-layer ingot: the lower layer (Mo–Nb–Si–B) consists of the required product and the upper layer (Al2O3) is a slag product. The optimal parameters for the preparation of cast Mo–Nb–Si–B materials are α = 20–30% and a > 100g.

The dynamics of interaction with the air of non-passivated pyrophoric nickel nanopowders pressed into cylindrical compacts has been investigated in detail. A method for preventing self-ignition in the air of compacts made of nickel nanopowder has been experimentally established.

It was experimentally shown for the first time that compact samples of pyrophoric nickel nanopowders can be passivated in air for 3–5 s. The passivation of the samples was confirmed by the absence of noticeable heat release during slow heating to 200°C, an insignificant oxygen content according to the data of X-ray powder diffraction analysis and scanning electron microscopy, and the retention of the chemical activity of the samples. The uniform distribution of oxygen throughout the sample suggests the volumetric nature of their interaction with air during the passivation. The critical conditions for heating of passivated samples under which ignition occurs were determined.

An alloy based on the Heusler phase Fe2TiAl is obtained for the first time by self-propagating high-temperature synthesis (SHS). Experiments have shown that the alloy is synthesized in the thermal explosion mode. Features of the structure- and phase formation during combustion in the 2Fe–Ti–Al system are studied and their mechanisms are proposed. The electrophysical properties of the combustion product are studied.

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.

We have studied the combustion process and the phase composition of its products using granulated 70 wt % (Ti + C) + 30 wt % (3Cr + 2C) and 80 wt % (Ti + C) + 20 wt % (3Cr + 2C) mixtures with nickel-containing binders. The results demonstrate that the addition of a nickel binder reduces the chromium content of the (Ti,Cr)C double carbide, because nickel reacts with chromium to form Nichrome. In the case of combustion of the granulated 80 wt % (Ti + C) + 20 wt % (3Cr + 2C) mixture with the addition of Kh20N80 Nichrome, a Nichrome-binder-containing (Ti,Cr)C double carbide essentially free of impurity phases according to X-ray diffraction data has been prepared in a single step. A two-step mechanism of final product formation has been proposed. According to scanning electron microscopy data, the grain size of the combustion products is 2–5 μm, which is an order of magnitude smaller than the initial titanium and chromium particle size. In contrast to powder mixture combustion products, which are difficult to disintegrate, the agglomerate obtained via the combustion of a granulated mixture broke into separate granules, which could be ground to a desired particle size under laboratory conditions.

International audience; Ceramic-metal composites TiC-High-Entropy Alloy (HEA) CoCrFeNiMe (Me = Mn, Ti or Al) were first produced by combustion synthesis method. Self-sustained synthesis occurs due to heat release from exothermic reaction Ti + C = TiC; the binder content was varied between zero and 40-50 wt.%. The combustion velocity and temperature gradually decreased with increasing binder content. Resultant materials consist of TiC grains and two-phase (fcc and bcc) binder. Vickers microhardness (100 g) of compacted cermet materials with 30 wt.% of binder was in the range of 10-17 GPa and increased with increasing bcc to fcc ratio. Based on experimental results and thermodynamic calculations, the mechanism of microstructure formation in TiC-HEA cermets was suggested.

Composition/structure of products formed upon frontal combustion of Si powder in gaseous carbon dioxide at P(CO2) = 0.4–5.0 MPa were characterized by chemical analysis, XRD, and SEM/EDS. Combustion products were found to contain SiC, unreacted Si, and SiO2. Our results may turn interesting to those engaged in fabrication of heat-resistant Si–O–C ceramics.

Combustion and the formation of structures and phases in a 2Co–Ti–Al system during self-propagating high-temperature synthesis in a thermal explosion are under study. It is determined that a single-phase product (a Co2TiAl Geissler compound) can be obtained in this system. Morphology, microstructure, and physical-magnetic properties of combustion products of the system are investigated.

Nanostructured mechanical composites of immiscible metals Cu, Cr, and 5–70 wt % W; nanostructured consolidated materials based on them; and Cu/Cu–Cr–W nanostructured gradient material with various W contents are fabricated in this work by combining short-term (up to 150 min) high-energy ball milling (HEBM) and spark plasma sintering (SPS). To fabricate Cu–Cr–W mechanical composites, HEBM of Cu + Cr + (5–70 wt %)W is performed using an Activator-2S planetary ball mill with a revolution rate of drums of 1388 rpm and a planetary disc of 694 rpm in argon for 150 min. The Cu–Cr–W mechanical composites are consolidated by SPS at temperatures of 800–1000°C and pressure of 50 MPa for 10 min. The nanostructured gradient sintered material based on Cu–Cr–W pseudoalloys is compacted layer-by-layer in the following sequence (from pure copper to pseudoalloy with an increase in the tungsten weight fraction): Cu/Cu–Cr–5% W/Cu–Cr–15% W/Cu–Cr–70% W and sintered at 800°C for 10 min. The crystal structure, microstructure, and properties of Cu–Cr–W mechanical composites and consolidated materials based on them are investigated depending on fabrication conditions. It is shown that the nanostructure formed in mechanical composites at the short-term HEBM stage (up to 150 min) is retained after SPS for all Cu–Cr–W (5–70 wt % W) compositions. The SEM and EDS data evidence that W (d ~ 20–100 nm) and Cr (d ~ 20–50 nm) refractory particles are homogeneously distributed in the material bulk (in a copper matrix). The hardness of consolidated Cu–Cr–W samples (15 wt %) formed from nanostructured powder mixtures (after 150-min HEBM) by SPS at t = 800°C exceeds the hardness of samples sintered from the mixture of initial components (without HEBM) by a factor of ~6. The hardness for the nanostructured Cu–Cr–70% W composition (tSPS = 1000°C) is higher by a factor of ~3 than for microcrystalline analogs. Samples Cu–Cr–15% W and Cu–Cr–70% W have the largest relative density up to 0.91. The resistivity of nanostructured Cu–Cr–W compositions exceeds this characteristic for microcrystalline samples approximately twofold. This can be caused by an increase in grain boundaries and the accumulation of various defects in the material at the HEBM stage. These results show the prospects of using the combination of short-term HEBM and subsequent SPS for the formation of consolidated nanocrystalline Cu–Cr–W composites and gradient materials based on them.

Molybdenum is a refractory metal, with a melting point of 2900 K. Its alloys with B and Si, obtained via powder metallurgy, have high heat resistance and have potential use in aircraft engine building. In this paper, the authors examined the possibility of using centrifugal SHS-metallurgy for the production of Mo–Si–B. To synthesize Mo–Si–B, a combination of a highly exothermic mixture (MoO3/Al/Si/B) and a moderately exothermic mixture (Mo/Si/B) were used. In a wide range of ratios, the combustion temperature exceeds 3000°C, which makes it possible to obtain combustion products in a cast form. Studies have shown that variation in the composition of the mixture and the magnitude of the centrifugal effect allows the parameters of combustion to be controlled, along with the composition and structure of molybdenum silicoborides.

A cermet material based on the system Ni–Al–SiO2 with different SiO2 weight content (0 – 50%) in the mixture was obtained by means of self-propagating high-temperature synthesis (SHS) with preliminary mechanoactivation (MA). It is shown that preliminary mechanoactivation of the powder mixture strongly affects the morphology of the final product. Depending on the composition of the initial mixture, the phases NiAl, Al2O3, Ni2Si, and NiSi2 can form in the final product of synthesis.

A Ti + Ni powder mixture has been subjected to high-energy mechanical processing (HEMP) and then characterized by X-ray diffraction. The results demonstrate that, with increasing milling time, the crystallite size of both titanium and nickel drops to 10 nm. The internal stress rises with increasing HEMP time, reaching a level near the yield stress of the metals studied. HEMP in the Ti–Ni system leads to the formation of an essentially amorphous material after 40 min of milling time processing.

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.

A cast material based on the Nb2AlC MAX phase is formed by SHS metallurgy. The synthesis is performed using the Nb2O5–Al–C mixture with the CaO2–Al high-energy additive. The results of thermodynamic calculations correlate with the experimental data. The substantial influence of the CaO2–Al additive on the thermodynamic parameters and phase composition of the product is established. It is shown that the synthesis using mentioned mixtures occurs in a stationary mode with the formation of a steady combustion wave. The combustion rate increases from 6 to 12 mm/s with an increase in the additive content, and the product yield into the ingot increases from 30 to 47% (up to 15 wt % additive) and then decreases. The variation in the composition of initial mixtures can substantially affect both the synthesis parameters and the phase composition of products. The optimal synthesis conditions of the materials that provide the maximal yield of the Nb2AlC MAX phase in the ingot composition are established. The determining factor that affects the Nb2AlC content in the product is the liquid-phase lifetime under the synthesis conditions. It is shown that the maximal amount (67 wt %) of the Nb2AlC phase is attained with the content of the high-energy additive in the initial charge of 15 wt %.

International audience; A powder of equiatomic CoCrFeNiCu high entropy alloy (HEA) was prepared by shortterm (120 min) high energy ball milling (HEBM). Our structural and chemical analysis showed that microsized particles of fcc CoCrFeNiCu with a grain size of 8 nm were obtained after 120 min of HEBM at 694/1388 rpm. The structural/phase evolution of CoCrFeNiCu HEA powder and its thermal stability were explored by high-temperature XRD at 600 °C, 800 °C and 1000 °C, by DSC up to 1500 °C, through the consolidation by SPS at 800 °C and 1000 °C, and characterized using XRD, SEM and EDX analyses. In-situ HT XRD analysis during 5.5 h of annealing showed the involvement of transient phases: the bcc phase that appeared in 1 h of annealing at 600 °C and disappeared at higher temperatures; and the fcc 1 phase (Cu-rich) arising in 2 h of annealing at 800 °C and disappearing at 1000 °C in 3 h of annealing. SPS consolidation at 1000 °C and annealing at 1000 °C for 5.5 h were found to result in the formation of singlephase fcc 2 CoCrFeNiCu alloy with a lean amount of Cu. The melting points for Cu-rich and Cudepleted HEAs were found as 1118 °C and 1288 °C (Calphad calculations) and 1115 °C and 1365 °C (DSC measurements), respectively. SPS consolidation at 1000 °C under a pressure of 50 MPa yielded the single-phase fcc CoCrFeNiCu 0.5 alloy that turned thermodynamically more favorable than the equiatomic one. Thus, we can suppose thereupon, that the equiatomic fcc phase that appears after 120 min of HEBM is metastable because of the excess of Cu atoms. During annealing in the temperature range 800-1000 °C, the Cu-rich fcc 1 phase precipitates from the initial single-phase alloy, while the "mother phase" transforms into the more stable Cudepleted fcc 2 phase. The chemical compositions of Cu-depleted and Cu-rich phases for the SPSconsolidated HEA CoCrFeNiCu alloy (at 800 °C) were determined from TEM-EDX analyses. Optimal combination of short-term HEBM and SPS consolidation can be recommended as a facile route to fabrication of single-phase fcc equiatomic CoCrFeNiCu HEA powders and bulk materials with good structural/elemental homogeneity.

The laws and mechanism of combustion of TiO2 based thermite systems with a complex reducing agent (Al and Ca) under the influence of overload are revealed. The thermite system includes a basic composition whose combustion products are target elements (Ti, Al, Nb, and Cr) and a high-energy additive (CaO2, Al, and Ca) for ensuring high-temperature combustion. With the introduction of an energy additive, the system acquires the ability to burn. With a sufficient content of this additive, the combustion products (TixAly and Al2O3 and CaO oxide solutions) can melt. As the fraction of Ca in the base mixture composition increases, the burning rate drops and the reduction completeness of the target oxides increases. With an optimal ratio of Ca and Al in the mixture, the yield of the target elements in the ingot is close to the calculated value.

Large-sized plates (120×80×8 and 80×40×8 mm) were obtained from a material based on titanium monoboride by the method of free SHS-compression using press equipment with a force of up to 120 kN. The structural features of the obtained materials, their physicomechanical properties were investigated, the samples were annealed in an oxidizing environment for 10 hours at 1100 ° C.

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.