FeCoNiCu(Cr, Mn, La, Ce)-Al high-entropy alloys (HEAs) were prepared via a combined centrifugal casting–self-propagating high-temperature synthesis process to serve as multifunctional catalyst precursors. The findings indicated that even with aluminum content reaching 50 wt %, the typical bcc structure inherent to HEAs was preserved. Doping additions (Cr, Mn, La, and Ce) led to pronounced microstructural changes, including alterations in morphology, porosity, and elemental distribution, while the primary phase constituents of the FeCoNiCuAl-based alloys remained consistent. It was found that La and Ce exhibited poor bulk incorporation into the HEAs, evidenced by a low surface content. Aluminum leaching and hydrogen peroxide stabilization converted these precursors into catalysts. These catalysts demonstrated high activity in the deep oxidation of propane and CO. The FeCoNiCu catalyst achieved the best results for CO oxidation, reaching 100% CO conversion at 250 °C. For propane oxidation, the FeCoNiCuCrMn catalyst was the most active, yielding 100% CO conversion at 300 °C and 97% propane conversion at 400 °C.

Layered composite materials based on niobium and cermet were produced via self-propagating high-temperature synthesis of pre-structured samples using metal foils (Ti, Nb, Ta, Ni) and reaction tapes (Ti + 1.7B) and (5Ti + 3Si). Reaction tapes for synthesis were produced by rolling process of powder mixtures. The microstructure, elemental and phase compositions of the synthesized multilayer composite materials were studied by scanning electron microscopy and X-ray phase analysis. Particular attention was paid to the formation of intermediate layers and surface modification occurring during combustion. The strength characteristics of synthesized materials were determined according to the three-point loading scheme at temperatures of 1100°C. The analysis of obtained materials showed that joining in the combustion mode of metal foils and reaction tapes is provided due to reaction diffusion, mutual impregnation and chemical reactions occurring in the reaction tapes and on the surface of metal foils. The formation of thin intermediate layers in the form of cermet and eutectic solutions provides the synthesized multilayer materials with good strength properties up to 87 MPa at 1100°C. These results are of interest for the development of structural materials operating under extreme conditions.

For the first time, an intermetallic 2Ni–Mn–Al-based alloy is prepared by self-propagating high-temperature synthesis (SHS) combined with centrifugal casting. According to X-ray diffraction data, the main phase of the SHS product is the (Ni,Mn)3Al nickel aluminide solid solution with the partial substitution of manganese for nickel. The study of the microstructure shows a low aluminum content at the boundaries of the (Ni,Mn)3Al main phase. The averaged microhardness of the synthesized alloy is 8500 ± 45 MPa and the peak hardness is 11500 MPa. The alloy exhibits soft magnetic properties. The maximum magnetization in a field of 796 kA/m (10 kOe) is Js = 1.1 (A m2)/kg (emu/g) and the coercive force is Hc = 14.3 kA/m (179.7 Oe).

A thermoelectric Co2TiAl alloy was obtained by the SHS-metallurgy method for the first time. The microstructure and the magnetic and thermoelectric properties of the synthesized alloy were investigated. The maximum value of the Seebeck coefficient and thermoelectric power at room temperature were ‒29.5 μW/K and 1230 μW m–1 K–2, respectively. The comparison of the influence of the SHS-method modifications on the properties of the synthesized alloy was made. It has been shown that the alloy synthesized by SHS pressing has higher thermoelectric characteristics than the alloy obtained by the SHS-metallurgy method.

Layered composite materials based on niobium and cermet are produced via the self-propagating high-temperature synthesis of preliminarily structured samples using metal foils (Ti, Nb, Ta, Ni) and reaction tapes (Ti + 1.7B) and (5Ti + 3Si). The reaction tapes for synthesis are produced by rolling powder mixtures. The microstructure, and elemental and phase compositions of the synthesized multilayer composite materials are studied by scanning electron microscopy and X-ray phase analysis. Particular attention is paid to the formation of intermediate layers and surface modification occurring during combustion. The strength characteristics of the synthesized materials are determined according to the three-point loading scheme at temperatures of 1100°C. Analysis of the obtained materials shows that joining in the combustion mode of metal foils and reaction tapes is provided due to reaction diffusion, mutual impregnation, and chemical reactions occurring in the reaction tapes and on the surface of the metal foils. The formation of thin intermediate layers in the form of cermet and eutectic solutions provides the synthesized multilayer materials with good strength properties up to 87 MPa at 1100°C. These results are of interest for the development of structural materials operating under extreme conditions.

Ceramic composite material Al2O3–Cr2O3 + TiC was prepared by metallothermic self-propagating high-temperature synthesis (SHS) under 5 MPa of Ar pressure from green mixtures containing TiO2, Al, and C powders, and additive of CrO3 + Al blend. An increase in the mass fraction α of CrO3 + Al in the general charge was found to raise the synthesis temperature. For α < 0.2, sintered multiphase products were formed. In case of high additive content (α > 0.2), the combustion products were separated into two layers: carbide and oxide phases. Optimum synthesis conditions for forming the cast product consisting of Al2O3–Cr2O3 solid solution ("ruby") and uniformly distributed TiC particles were found. In order to evaluate the possibility of using this material as a cutting tool, physical and mechanical properties were determined. SHS-prepared Al2O3–Cr2O3 + TiC composite after 24-h milling in a planetary mill, pressing under a pressure of 200 MPa, and sintering at 1460°С was found to possess density of 4.55 g/cm3, hardness of 20 GPa, flexural strength of 680 MPa, and crack resistance of 4.2 MPa m1/2.

Keywords: combustion, self-propagating high-temperature synthesis (SHS), Mo-based cast ceramic, gravity forces

Copper and lanthanum promoted cobalt catalysts for CO2 hydrogenation to higher hydrocarbons are described. The catalysts were prepared by the self-propagating high-temperature synthesis followed by alkaline leaching. They are active in CO2 hydrogenation at 200 °C under 10 bar pressure (CO2 : H2 = 1 : 3) with selectivity to C2+ alkanes up to 39%; no alkenes and alcohols are formed under these experimental conditions.

Cox-CrNbWMoAlC cast high-temperature materials were prepared from mixtures containing Co3O4/Cr2O3/Nb2O5/WO3/MoO3/Al/C and additive of 5% Al2O3 by centrifugal self-propagating high-temperature synthesis (SHS). As Co3O4 + Al was added, the burning velocity grew by five times. CrNbWMoAlC alloy was shown to have a multiphase structure consisting of NbC, Cr23C6, and Cr0.53Mo0.14Al0.33. Introduction of Co3O4 and Al was found to yield Cox-CrNbWMoAlC alloy with a dendritic structure containing Co and NbC phases as a basis.

Regularities of combustion of Co3O4/Cr2O3/WO3/MoO3/C/Al mixtures with additive of Ti under the action of artificial gravity were studied. At the centrifugal acceleration of more than 40 g, combustion products were obtained as two-layer ingots of target CoTiCrWMoCAl alloy (lower) and Al2O3 slag (upper). Variation in the amount of additive (up to 17 wt %) affected the composition and structure of cast CoTiCrWMoCAl alloy. SHS-produced alloys were characterized by XRD, SEM, and EDS. CoCrWMoCAl alloy containing 5% Ti was used for preparing powder by vacuum induction melting followed by inert gas sputtering. It was shown that the chemical compositions of powder and its precursor are the same.

The combustion of highly exothermic multicomponent mixtures of Co3O4/Cr2O3/Nb2O5/Al with additives of MoO3, WO3, and carbon (graphite) under overload up to 200 $$g$$  has been studied. It has been shown that the introduction of carbon into the initial mixture has a marked effect on the combustion, formation of chemical composition, and structure of combustion products. When the weight percentage of carbon in the initial mixture increases from 0 to 3.9%, the burning rate decreases by more than half and the rate of dispersion of combustion products and the mass loss increase markedly. Under the action of overload, the two-phase melt of combustion products is stratified into two layers, which crystallize upon cooling. The lower metal layer contains Co, Nb, Cr, W, Mo, C, and impurity aluminum, and the upper layer contains mainly Al2O3. With an increase in the carbon content above 4.0%, the separation of the metal and oxide phases ceases, and with a further increase, the flammability limit is reached. With an increase in the carbon content in the mixture from 0 to 3.9%, its concentration in the cast composite material reaches 5.4%, the Al content is about 4.0% and the content of Co, Nb, Cr, W, and Mo changes slightly. The combustion slag contains reducing metal oxide (Al2O3) and impurity Cr2O3 dissolved in it.

Co–Al and Co–V–Al intermetallics produced by centrifugal self-propagating high-temperature synthesis (SHS) were used as precursors for preparation of catalysts for deep oxidation and hydrogenation of CO2. Leaching in NaOH solution and stabilization with H2O2 solution of precursors were carried out in permanent magnetic field (MF) (0.24 Т) and alternating magnetic field (0.13 Т, 50 Hz). Prepared Co и Co–V (95Co–5V, 90Co–10V) granular catalysts with size of 100–300 µm were characterized by XRD, SEM, EDS, and BET method and revealed to have a scaly surface structure. It was shown that the type of MF affects phase composition and surface morphology, as well as specific surface and activity in deep oxidation of CO and hydrocarbons as an important part of the neutralization of gas emissions, and hydrogenation of CO2, the processing of which would reduce atmospheric pollution with this greenhouse gas. Catalysts obtained in alternating MF was found to possess higher activity in the process of deep oxidation.

4 1 2 3 0 α, % Xi, % Heat resistant Сo-based superalloys are used in aerospace engineering to strengthen shroud shelves of turbine blades [1, 2]. Industrial Co alloy (KhTN 61) containing alloying agents (Cr, Nb, W, Mo, Al) and 1.95–2.35% of bound carbon is currently produced by induction melting and is known [1] to have a non-uniform coarse-grained structure. The latter drawback can be overcome by synthesizing similar alloy by centrifugal metallothermic SHS [3]. In this communication, we report on the preparation of Co-based superalloys—analogs of KhTN 61 with larger carbon contents (up to 5.4 wt %)—by centrifugal SHS.

High-temperature lightweight alloys based on TiAl intermetallic are promising for manufacturing low-pressure turbine blades. Various methods of additive manufacturing (AM) from such alloys are being developed. AM is attractive because of its flexibility and its potential to reduce the number of assembly and machining operations. However, the issues of defect and microstructure formation at AM of TiAl alloys have not been sufficiently studied to ensure an industrial application. In the present work, a Cr- and Nb-doped TiAl alloy is obtained by self-propagating high-temperature synthesis under an overload necessary for better separation of slag impurities. Samples of the alloy are processed with a laser beam in the conditions typical of AM by selective laser melting (SLM) in scanning speeds ranging from 5 to 4000 mm/s, laser power from 10 to 165 W, and preheating temperatures from 25 degrees C to 800 degrees C. It is shown that cracking can be avoided in laser processing with preheating up to 800 degrees C in the range of the scanning speed from 10 to 200 mm/s. The formed material microstructure is studied by SEM and related to the cracking ability. A strategy for theoretical assistance in the SLM parameter optimization is proposed based on a model of heat transfer in the laser-interaction zone. This strategy is validated by comparison with the experimental data. It is shown that several experiments are sufficient to predict the integrity of optimal combinations of the following process parameters: laser power, scanning speed, and preheating temperature.

This paper discusses the synthesis regularities of new composite materials via combustion processes and their features of physicochemical transformations for task of a modern technology. In early studies, the authors showed the possibility of synthesizing composite materials via centrifugal SHS metallurgy, in which the combustion of thermite mixtures and the chemical transformations were studied. The compositions, structures and mechanical properties of the synthesized materials were also investigated

Graded and layered materials are fabricated by the methods of conventional and powder metallurgy [1, 2], except for joining dissimilar materials such as ceramics and metals. The latter task can be solved by SHS method as it was demonstrated using a Ti/hard alloy pair as an example [3]. This work aimed at the deposition of a protective MoSiB layer strongly joined with a Ti substrate by metallothermic SHS in centrifugal machine.

Cast refractory alloys Mo–Nb–Si–B were prepared by centrifugal self-propagating high-temperature synthesis (SHS) from metallothermic mixtures containing MoO3, Nb2O5, Al, Si, and B powders, and additive of Al2O3 as a temperature-moderating and chemically inert agent. Variation in the centrifugal acceleration and amount of the additive affected the composition and structure of cast Mo–Nb–Si–B alloys. In a wide range of values, the combustion temperature was found to exceed 3000 K, and the combustion products were obtained as two-layer ingots of target Mo–Nb–Si–B alloy (lower) and Al2O3 slag (upper).

— We have studied the potentialities of dispersion and precipitation modification of a cobalt alloy in combustion mode under the effect of centrifugal forces. The starting mixture consisted of Co 3 O 4 , Cr 2 O 3 , Nb 2 O 5 , MoO 3 , and Al, with titanium carbide and a mechanical mixture of titanium powder and carbon black as modifying additives. The basic mixture has been shown to burn in a wide range of titanium carbide additions under normal conditions. The use of a centrifugal force field allows the phase separation limit to be increased from 17.5 to 20% titanium carbide. In the case of precipitation modification, the system has greater potential for both combustion and phase separation, and the structural constituents of the alloy are characterized by a smaller size and finer structure. We have proposed a sequence of chemical reactions involved in the modification by the precipitation mechanism, in which Co 3 O 4 decomposition and subsequent release of active oxygen play a key role.

The effect of PTFE, continuous boron, and tungsten fibers on the combustion behavior and strength of reactive Ni–Al compacts was examined in this study. The introduction of continuous fibers into Ni–Al compacts according to the developed scheme was found to increase the flexural strength from 12 to 120 MPa. Heat treatment (HT), leading to chemical interaction of the starting components, increases the strength of compacts at temperatures not exceeding 550 °C. The combination of reinforcement and HT significantly increases the strength without reducing reactivity. Experimental results showed that strength and combustion rate increase with the reduction in PTFE to 1 wt % in Ni–Al compacts. A favorable effect of the addition of PTFE from 5 to 10 wt % on the reduction of the threshold for the shock-wave initiation of reactions in Ni–Al was established. The obtained results can be used to produce reactive materials with high mechanical and energy characteristics.

Previously, we suggested a new class of polymetallic catalysts based on SHS-produced intermetallic compounds for environment-friendly deep oxidation of CO and hydrocarbons [1]. Among these, Co–La catalyst showed best catalytic activity in the Fischer– Tropsch synthesis [2]. Since Co is also active in oxidation reactions [3], we made an attempt to further improve the oxidative ability of SHS-produced Co–La catalyst upon its modification with copper [4]. Moreover, Co and Cu catalysts exhibited high activity in the hydrogenation of СО2 [5–7]. Cu-doped Co–La catalysts of nominal composition (95 – x)Co–xCu–5La (x = 10, 30, 50 wt %) were prepared by centrifugal SHS from Co3O4–Cu2O–Al– La powder mixtures. As-prepared intermetallics were leached with NaOH, stabilized by processing in H2O2 solution (for details see [1, 2]), and characterized by SEM/EDS (Zeiss Ultra plus microscope + JCXA-733 Superprobe JEOL accessory) and XRD (DRON-3, Fe-Kα radiation). The 100–300 μm fractions of SHSproduced catalyst were tested for their activity in a flow silica reactor as described in [1, 2]. Gas compositions were determined using an Avtotest 02.03P gas analyzer and a gas-liquid chromatograph Model 3700.