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.

Cast Mo–Nb–Ta–(Cr,V,Zr,Hf) refractory high-entropy alloys were first prepared via gravity-assisted SHS metallurgy. It was shown that the ingots crystallize from the liquid state, in which a homogeneous distribution of constituting elements is provided. The phase composition of synthesized RHEA ingots was revealed to be doped component dependent. Combined reduction of metals of V (Nb, Ta, V) and VI (Cr, Mo) groups formed single-phase alloys with a bcc crystal structure. MoNbTaCr alloys doped with Zr or Hf having hexagonal crystal structure were found to consist of fcc and hcp phases in addition to bcc solid solution.

High-entropy alloys were produced by centrifugal self-propagating high-temperature synthesis and used as precursors for preparation of catalysts for CO and propane deep oxidation and CO2 hydrogenation. The precursors were converted into catalysts by aluminum leaching and stabilization with hydrogen peroxide solution. Prepared FeCoNiCu, FeCoNiCuMo, FeCoNiCuMn, and FeCoNiCuCr catalysts were characterized by XRD, SEM/EDS, and BET methods and tested in the processes of deep oxidation of CO and propane and methanation of CO2. The highest CO2 conversion, 50.6

Employing centrifugal self-propagating high-temperature synthesis (SHS) metallurgy, complemented by advanced metallurgical processes such as vacuum induction melting (VIM) and vacuum arc remelting (VAR), yielded the alloy formulation denoted as base–2.5Mo–1.5Re–1.5Ta–0.2Ti. This study investigates the effects of various technological modes and additional metallurgical treatments on the alloy's impurity and non-metallic inclusion content, structural characteristics, mechanical behavior under compression, and its oxidation mechanisms and kinetics when exposed to temperatures of 1150 °C for 30 h. With increasing centrifugal acceleration, the proportion of non-metallic inclusions (number of points) drops from 5 to 1–2 points. The best combination mechanical properties, including σucs = 1640 ± 20 MPa, σys = 1518 ± 10 MPa, and residual deformation were observed in alloys processed under conditions of increased gravitational force (g = 50). Within a centrifugal force range of g = 20÷300, the composition of the synthesis products aligned with the theoretical expectations. The total content of impurities is 0.15 ± 0.02 %, with a decrease in gas impurities–oxygen and nitrogen levels reduced to 0.018 % and 0.0011 %, respectively. The structural analysis of the alloys revealed the presence of globular and streaked inclusions of a chromium-based solid solution embedded within the matrix. Inclusions with thickness of 2–8 μm are present in the intergranular space: (Cr)Ni,Mo,Co, (Cr)Mo,Re and (Cr)Re,Mo. The formation of the Ni(Al,Ti) phase at grain boundaries was identified, contributing to an enhancement in plastic resistance and overall strength of the alloy. Oxidation mechanisms varied across different processing modes, with the size of structural components significantly influencing oxidation kinetics. The weight gain observed in SHS samples was 70 ± 10 g/m2 with oxidation predominantly occurring along the NiAl interphase boundaries and penetrating into the depth of the sample. TEM facilitated the identification of phases enriched with Ti microadditions, reducing the levels of dissolved nitrogen and oxygen within the intermetallic phase to a combined weight percentage (ΣO,N) of 0.0223 wt.%.

Alloys based on NiAl-Cr-Co (base) with complex dopants (base+2.5Mo-0.5Re-0.5Ta, base+2.5Mo-1.5Re-1.5Ta, base+2.5Mo-1.5Ta-1.5La-0.5Ru, base+2.5Mo-1.5Re-1.5Ta-0.2Ti, base+2.5Mo-1.5Re-1.5Ta-0.2Zr) were fabricated by centrifugal SHS metallurgy. The phase and impurity compositions, structure, mechanical properties, and the mechanism of high-temperature oxidation at T = 1150 °C were studied; the kinetic oxidation curves, fitting equations and parabolic rate constant were plotted. Al2O3 and Co2CrO4 were the major phases of the oxidized layer. Three layers were formed: I-the continuous Al2O3 layer with Co2CrO4 inclusions; II-the transitional MeN-Me layer with AlN inclusions; and III-the metal layer with AlN inclusions. The positive effect of thermo-vacuum treatment (TVT) on high-temperature oxidation resistance of the alloy was observed. The total weight gain by the samples after oxidative annealing decreased threefold (from 120 ± 5 g/m2 to 40 ± 5 g/m2). The phases containing Ru and Ti microdopants, which reduced the content of dissolved nitrogen and oxygen in the intermetallic phase to the values ∑O, N = 0.0145 wt.% for the base+2.5Mo-1.5Ta-1.5La-0.5Ru alloy and ∑O,N = 0.0223 wt.% for the base+2.5Mo-1.5Re-1.5Ta-0.2Ti alloy, were identified by transmission electron microscopy (TEM). In addition, with the significant high-temperature oxidation resistance, the latter alloy with Ti had the optimal combination of mechanical properties (σucs = 1644 ± 30 MPa; σys = 1518 ± 25 MPa).

Keywords: composite materials, master alloy, chromium, centrifugal SHS

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.

Centrifugal SHS casting has been used for the production of NiAl–Cr–Co–X alloys, where X = 2.5–15.0 wt % Mo and up to 1.5 wt % Re. The influence of modifying additives on burning has been studied, as well as on the phase composition, structure, and properties of cast alloys. The addition of up to 15% Mo and 1.5% Re in terms of all properties makes the highest improvement of the properties with regard to basic alloy. Molybdenum, while forming the plastic matrix, improves strength properties up to the following levels: uniaxial compressive strength σ ucs = 1730 ± 30 MPa, yield strength σ ys = 1560 ± 30 MPa, and plastic deformation constituent ε pd = 0.95%; annealing at t = 1250°C improves them to σ ucs = 1910 ± 80 MPa, σ ys = 1650 ± 80 MPa, and ε pd = 2.01%. Rhenium modifies the alloy structure and improves its properties to σ u = 1800 ± 30 MPa, σ ys = 1610 ± 30 MPa, and ε pd = 1.10%, whereas annealing improves them to σ ucs = 2260 ± 30 MPa, σ ys = 1730 ± 30 MPa, and ε pd = 6.15%. Using the nanoindentation method, the mechanical properties of NiAl, (Ni,Cr,Co) 3 MO 3 C, Ni 3 Al, (Cr,Mo), and MoRe 2 phases, as well as of Al(Re, Ni) 3 hypothetic phase have been determined. It has been demonstrated that local softening upon annealing from t > 850°C improves the portion of plastic deformation upon compression tests, which is related with the loss of coherency of boundaries of nanosized disk deposits on the Cr base with an oversaturated solid solution similar to the Guinier–Preston structural transformation. The three-level hierarchical structure of the NiAl–Cr–Co–15% Mo alloy has been established: the first level is formed by β-NiAl dendritic grains with interlayers of (Ni,Co,Cr) 3 Mo 3 C and (Mo 0.8 Cr 0.2 ) x B y molybdenum containing phases with cell sizes up to 50 μm, the second level is comprised of Cr(Mo) strengthening submicron particles distributed along the grain boundaries, and the third level is comprised of coherent Cr(Mo) nano deposits (10–40 nm) in the body of β-NiAl dendrites. Using procedures of mechanical grinding of the cast alloy, a powdered precursor has been obtained with an average particle size of D avg = 33.9 μm for subsequent spheroidization.

The study covers the effect of alloying elements on the kinetics and mechanism of oxidation at 1150 °С for 30 hours of heat-resistant nickel alloys obtained using such technologies as centrifugal SHS metallurgy (SHS(M)), vacuum induction melting (VIM), elemental synthesis (ES), hot isostatic pressing (HIP). A comparative analysis was carried out for alloys based on nickel monoaluminide and standard AZhK and EP741NP alloys. It was found that kinetic dependences are described mainly by parabolic approximation. The logarithmic law of oxidation with the rapid (within 3–4 hours) formation of the primary protective layer is typical for alloys doped with molybdenum and hafnium. In the case of AZhK and EP741NP, oxidation proceeds according to a parabolic law at the initial stage (2–3 hours), and then according to a linear mechanism with the voloxidation and complete destruction of samples. Oxygen and nitrogen diffusion proceeds predominantly along the nickel aluminide grain boundaries and it is limited by the Al2O3 + Cr2O3 + Xn O m protective film formation. SHS(M) alloys feature by a positive effect of zirconium and tantalum added as dopants on heat resistance. The Ta2O5 phase is formed in the intergranular space, which reduces the rate and depth of oxidation. The zirconium-containing top layer Al2O3 + Zr5Al3O0.5 blocks the external diffusion of oxygen and nitrogen, thereby improving heat resistance. Doping with hafnium also has a positive effect on oxidation resistance and leads to the formation of submicron and nanosized HfO2 inclusions that suppress the grain boundary diffusion of oxygen. MoO3, Mo3O4, CoMoO4 volatile oxides are formed in alloys with a high content of molybdenum and compromise the protective layer integrity. A comparative analysis of the oxidation kinetics and mechanism for samples consisting of the base β-alloy with Cr + Co + Hf additives showed a significant effect on the heat resistance of the sample preparation method. As the proportion of impurity nitrogen decreases and the Cr2O3 sublayer is formed, the oxidation mechanism also changes.

A centrifugal SHS casting technology was used to obtain NiAl–Cr–Co–(X) alloys where X = 2.5÷15.0 wt.% Mo and up to 1.5 wt% Re. The study covers the effect of modifying additives on the combustion process as well as the phase composition, structure, and properties of cast alloys. Alloying up to 15 % Mo and 1.5 % Re provided the highest improvement of properties in relation to the base alloy in terms of overall performance. Molybdenum formed a plastic matrix and improved strength properties to the following values: uniaxial compressive strength σ ucs = 1730±30 MPa, yield strength σ ys = 1560±30 MPa, plastic component of deformation ε pd = 0.95 %, and annealing at t = 1250 °С improved them to: σ ucs = 1910±80 MPa, σ ys = 1650±80 MPa, ε pd = 2.01 %. Rhenium modified the alloy structure and improved its properties to: σ ucs = 1800±30 MPa, σ ys = 1610±30 MPa, ε pd = 1.10 %, and annealing further improved them to: σ ucs = 2260±30 MPa, σ ys = 1730±30 MPa, ε pd = 6.15 %. The mechanical properties of the NiAl, (Ni,Cr,Co) 3 Mo 3 C, Ni 3 Al, (Cr, Mo) and MoRe 2 phases, as well as the hypothetical Al(Re,Ni) 3 phase, were determined by the nanoindentation method. According to the Guinier–Preston structural transformation, local softening upon annealing at t > 850 °С increases the proportion of plastic deformation during compression tests due to the lost coherence of the boundaries of nanosized plate-shaped Cr-based precipitates with a supersaturated solid solution. A hierarchical three-level structure of the NiAl–Cr– Co–15%Mo alloy was established: the first level is formed by β-NiAl dendritic grains with interlayers of molybdenum-containing phases (Ni,Co,Cr) 3 Mo 3 C and (Mo 0.8 Cr 0.2 ) x B y with a cell size of up to 50 μm; the second one consists of strengthening submicron Cr(Mo) particles distributed along grain boundaries; the third one is coherent nanoprecipitates of Cr(Mo) (10–40 nm) in the body of β-NiAl dendrites. The cast alloy mechanical grinding techniques were used to obtain a precursor powder with an average particle size of D av = 33.9 μm for subsequent spheroidization.

We investigate the melting ranges of the base Zr–Si mixture (eutectic composition) depending on the content of the heterophase powder component in the ZrB2–ZrSi2–MoSi2 and the HfB2–HfSi2–MoSi2 systems in the amount of 30–90 wt % obtained by self-propagating high-temperature synthesis (SHS). The range of the melting point of the Zr–Si mixture was 1420–1440°C; addition of the ZrB2–ZrSi2–MoSi2 SHS powders resulted in an increase of the melting onset temperature Tm0 to 1460–1560°C and in the complete melting temperature Tmelt to 1480–1670°C. Addition of the HfB2–HfSi2–MoSi2 powders influenced only slightly the Tm0 value (1390–1430°C), but resulted in the increase in Tmelt to 1510–1550°C. The X-ray phase analysis shows that the remelted samples contain the following phases: ZrB2/HfB2, ZrSi2/HfSi2, MoSi2, and Si; here, the number of phases was directly proportional to the SHS powder content in the Zr–Si mixture. The ingots are characterized by a homogeneous structure consisting of the silicon matrix and ZrSi2/HfSi2 and MoSi2 grains, with inclusions of ZrB2/HfB2.

The NiAl–Cr–Co–X alloys were produced by centrifugal self-propagating high-temperature synthesis (SHS) casting. The effects of dopants X = La, Mo, Zr, Ta, and Re on combustion, as well as the phase composition, structure, and properties of the resulting cast alloys, have been studied. The greatest improvement in overall properties was achieved when the alloys were co-doped with 15% Mo and 1.5% Re. By forming a ductile matrix, molybdenum enhanced strength characteristics up to the values σucs = 1604 ± 80 MPa, σys = 1520 ± 80 MPa, and εpd = 0.79%, while annealing at T = 1250 ℃ and t = 180 min improved strength characteristics to the following level: σucs = 1800 ± 80 MPa, σys = 1670 ± 80 MPa, and εpd = 1.58%. Rhenium modified the structure of the alloy and further improved its properties. The mechanical properties of the NiAl, ZrNi5, Ni0.92Ta0.08, (Al,Ta)Ni3, and Al(Re,Ni)3 phases were determined by nanoindentation. The three-level hierarchical structure of the NiAl–Cr–Co+15%Mo alloy was identified. The optimal plasma treatment regime was identified, and narrow-fraction powders (fraction 8–27 µm) characterized by 95% degree of spheroidization and the content of nanosized fraction <5% were obtained.

Проведен обзор результатов, полученных авторами по синтезу литых жаропрочных сплавов методами СВС-металлургии. Основное внимание уделено синтезу жаропрочных сплавов на основе интерметаллидов никеля и титана, кобальта и силицидов ниобия. Определены параметры, позволяющие управлять процессами горения исходных смесей термитного типа, гравитационной сепарацией в расплаве продуктов горения, формированием состава и структуры литых жаропрочных сплавов.

A promising approach to the development of advanced metallic materials is based on a fundamentally new concept of avoiding the use of the main component but mixing several metal elements simultaneously. Such multicomponent alloys are called high-entropy alloys, the most studied of which is the Co-Cr-Fe-Ni-Mn alloy with attractive mechanical properties. The single-phase fcc structure is stable in this alloy, which allows it to be used as a "model" high-entropy alloy or a single-phase multicomponent solid solution. This paper is the first to experimentally evaluate the possibility of synthesizing strengthened high-entropy alloys with the basic system (Co-Cr-Fe-Ni-Mn) and strengthening precipitates based on borides and silicides of refractory metals (Mo and Nb), formed in situ during the combustion of thermite-type SHS systems. The microstructural analysis of the synthesized NiCrCoFeMn alloys with the complex modifying Mo(Nb)-Si-B additive showed that, at a higher content of the additive, the microstructure of the synthesis products exhibits the high-entropy alloy matrix and precipitates of new structural elements based on borides and silicides of refractory metals (Mo and Nb). The morphology and concentration of such precipitates depends on the concentration of the additive in the green mixture. The strengthening precipitates are of endogenous origin as they are formed in situ during SHS and are the result of chemical reactions occurring both directly in the combustion wave and during cooling of the high-temperature melt of the synthesis products. Control of SHS processes opens up new possibilities for the formation of metal-matrix composites based on high-entropy alloys.

The influence of different methods of producing alloys of the Fe–Cu system from immiscible components is studied. Alloys with limited solubility (LS) in liquid and solid states are impossible to fabricate by conventional metallurgy. This is why developing low-cost and simple technologies for fabricating such alloys and materials based in them, making it possible to specify the necessary level of physicomechanical properties, is currently a relevant problem. Energy-effective SHS metallurgy is used for the first timchemical scheme of the synthesis ofe in this work to prepare a pseudoalloy with a composition, wt %, of 70Cu–30Fe from oxide materials. This technology offers the use of chemical energy liberated during the interaction of highly exothermic thermite compositions (in a combustion mode), which makes this method one of most energy-efficient for cast material production. The short synthesis time (tens of seconds) and protection of the top ingot surface by the oxide melt (Al2O3) against oxidation make it possible to perform the process in atmospheric conditions. Rods with the same composition have been fabricated by vacuum induction smelting from pure (impurity-free) components Fe and Cu for a comparative analysis of structural components of alloy samples. It is revealed that the high temperatures of the melt of the SHS alloy provide an increased solubility of Cu in Fe. Then structural components are isolated during the crystallization in the form of finely dispersed particles over the entire volume, forming the hierarchical structure characteristic for the SHS alloy only. The 70Cu–30Fe alloys formed in the combustion mode (SHS) have a uniform homogeneous structure with a uniform distribution of all structural components over the sample volume, which can be of great practical interest, in particular, when developing isotropic and anisotropic hard-magnetic materials with high magnetic energy.

A relatively new approach to obtaining metal materials containing several principal elements in equiatomic concentrations which look promising for replacing commercially used alloys is proposed. Such materials are called high-entropy alloys (HEAs). Studies show that HEAs tend to form a simple solid-solution structure and can also contain ordered intermetallic phases. Such a method of forming metal materials can be regarded as a background for producing new HEAs with elevated performance characteristics. Most studies focus on the relationship between microstructure and measured properties; significantly less attention is paid to studying and developing new effective methods for creating HEAs. In this paper, we study the possibility of obtaining CoCrFeNiMn–(X) HEAs by centrifugal metallothermic SHS. Chemical and technological modes of modifying cast CoCrFeNiMn alloy during synthesis (in situ) by introducing alloying components into the starting exothermic compositions are tested for the first time. The microstructure and phase composition of NiCrCoFeMn alloys synthesized from mixtures containing Ti–Si–B(C) or Al are characterized. The microstructure of CoCrFeNiMn–(Ti–Si–B(C)) HEAs is found to consist of an HEA-based matrix and new structural inclusions of carbides and borides of titanium. High-Al CoCrFeNiMn–Al HEAs are represented by a composite structure containing NiAl as a basis and dispersion nanoprecipitates (~100 nm) of a Cr- and Fe-based solid solution.

A comprehensive comparative study of the structure, phase composition, and mechanical properties of heat-resistant nickel-based Ni–Cr–(X) alloys produced by the methods of traditional metallurgy and self-propagating high-temperature synthesis (SHS metallurgy) is carried out. With the purpose of formation of the submicrocrystalline structure, a longitudinal rolling and post-deformation annealing of the cast alloy is performed. The microstructure of the heat-resistant alloys is investigated by the SEM and TEM methods. It is shown that the cast alloy has a recrystallized structure with the mean grain size of ~1 μm and the particles of chromium carbides have a size of ~1–3 μm. After rolling and subsequent annealing (750°C/1 h), the average grain size is reduced to 0.43 μm and the formation of dispersed particles of carbides 100 nm in size is observed. The structure of the alloy obtained by SHS metallurgy is dendritic, and particles of W and Cr are absent. When 0.1 wt % carbon powder is added to the initial powder mixture for SHS synthesis, formation of the network of W and Cr particles is observed along the boundaries of dendrite colonies. It is found that the SHS Ni-based heat-resistant alloy similar in composition to commercial cast alloy is characterized by improved mechanical properties and increased heat resistance compared to the cast alloy in both the coarse-grained and the submicrocrystalline state. Adding the carbon powder to the powder mixture for SHS leads to a further increase in the resistance to high-temperature deformation owing to formation of the carbide phase impeding the movement of dislocations and grain boundary creeping processes.

Mo-Ni-B-Al as-cast alloys containing 35.5-58.7 wt% Mo, 23.0-57.6 wt% Ni, 3.3-5.2 wt% B, and 2.2-13.5 wt% Al were synthesized by Self-Propagating High-Temperature Synthesis (SHS) using a mixture of MoO3, NiO, B2O3 and Al powders in order to obtain low-cost Mo2NiB2 containing hard materials. The first series of experiments were performed using 1.05 times the stoichiometric amount of Al. In the second series of experiments, FactSage thermochemical modeling software was used to minimize Al increasing the Mo2NiB2 formation in the as-cast alloys. The products were characterized by using atomic absorption spectrometry (AAS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-hardness techniques.

The possibility of utilizing the industrial wastes of metallurgical production and secondary raw materials (aluminum) by organizing self-propagating high-temperature synthesis (SHS) and obtaining cast ferroalloys (Fe–Si; Fe–Si–Al, and Fe–Si–Al(Cr, Mn)) was investigated. The main production operations of the preliminary preparation of the starting raw materials were worked out and cast ferroalloys providing high concentration Si, Al and B were revealed. The possibility of processing the industrial wastes of metallurgical production and obtaining cast ferroalloys was shown.