The behavior of compacted mixtures of metal powders (Al, Ti) and recycled metalworking wastes (Fe + Fe₂O₃ + C) during vacuum sintering under controlled heating was investigated to assess the possibility of producing in situ metal–matrix composites containing oxide strengthening particles. The starting materials were titanium and aluminum powders (particle size <160 μm and <100 μm, respectively) and a powder produced from recycled steel chips (<300 μm). The resulting samples exhibited a heterogeneous phase composition, which was examined by X-ray diffraction (CuK_α radiation, XRD-6000 diffractometer) and optical microscopy (Axiovert 200MAT). A pronounced difference was observed between the aluminum- and titanium-based systems: the former exhi­bited a distinct thermal peak, whereas the latter showed smooth temperature behavior without thermal spikes. A thermokinetic model describing the multi-stage reactions in both systems was developed. The model incorporates metallothermic reduction and intermetallic formation reactions. Formal kinetic parameters were estimated using a semi-empirical approach and refined by comparison with experimental data. The governing equations, including the heat balance equation and the system of kinetic rate equations, were solved numerically using a semi-implicit Euler method, while mass conservation and atomic balance were verified. The initial composition of the samples was varied in the calculations – accounting for oxygen, carbon, and the Fe/Fe₂O₃ ratio in the steel-chippowder – to reproduce the experimentally observed product compositions. The calculated and experimental results showed qualitative agreement.

Refractory high-entropy alloys (RHEAs) based on refractory metals exhibit a combination of outstanding properties, such as high strength and thermal stability at elevated temperatures. These alloys typically contain costly refractory elements, including Mo, Nb, Ta, W, and Hf. In addition to their high cost, RHEA production is associated with a number of technological challenges. Well-established commercial methods used for nickel-based superalloys are generally unsuitable due to the higher melting points and increased chemical reactivity of the components. To address this issue, the present study explores the feasibility of synthesizing cast RHEAs using centrifugal self-propagating high-temperature synthesis (SHS) metallurgy – a technolo­gical approach within the broader field of SHS. For the first time, cast RHEAs based on the Mo–Nb–Ta system, alloyed in situ with 3d metals (Cr, V, Zr, Hf), were successfully synthesized via SHS. It was demonstrated that crystallization of the ingots occurs from the molten state, ensuring homogeneous distribution of Mo, Nb, Ta, Cr, V, Zr, and Hf. The phase composition of the synthesized RHEAs was found to depend on the alloying elements. Co-reduction of group V (Nb, Ta, V) and group VI (Cr, Mo) metals resulted in nearly single-phase alloys with a body-centered cubic (BCC) structure typical for these elements. The addition of Zr and Hf – metals with a hexagonal crystal structure – to the quaternary MoNbTaCr alloy significantly altered the phase composition of the ingots. In addition to BCC-phase reflections, the X-ray diffraction patterns exhibited intense reflections of face-centered cubic (FCC) phases and weak reflections of two hexagonal close-packed (HCP) phases. The proposed synthesis method considerably simplifies the otherwise complex technological process of producing cast, multicomponent RHEAs with a desired composition. Oxidation resistance tests revealed that the Mo–Nb–Ta–Cr–V composition is the most promising for further investigation. Compared to other compositions, this alloy demonstrated superior oxidation resistance, making it a competitive candidate for high-temperature applications.

Silicon carbide (SiC) and titanium nitride (TiN) are widely used non-oxide ceramics characterized by low density and high melting point, hardness, wear resistance, high-temperature strength, and corrosion resistance. However, single-phase silicon carbide ceramics have a number of drawbacks that limit their wider application. The main reason for developing TiN–SiC composite ceramics lies in the introduction of an electrically conductive TiN phase into the electrically non-conductive silicon carbide phase, which makes it possible to significantly reduce the high specific electrical resistivity of SiC while improving the sinterability, as well as the physical and mechanical properties of SiC-based composite ceramics. This study focuses on improving a simple and energy-efficient method of azide self-propagating high-temperature synthesis (SHS) for producing highly dispersed (<1 μm) TiN–SiC powder compositions from charge mixtures consisting of sodium azide (NaN₃), titanium, silicon, and carbon powders, through the use of powdered polytetrafluoroethylene (PTFE) as an activating and carbiding additive. The bulk and pressed charges were combusted in a reactor under a nitrogen pressure of 3 MPa. The maximum pressure and the yield of solid combustion pro­ducts were measured. The morphology and phase composition of the combustion products were determined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The use of the PTFE additive eliminated the shortcomings of the traditional azide SHS of TiN–SiC compositions involving halide salts ((NH₄)₂TiF₆, Na₂SiF₆, and (NH₄)₂SiF₆). While maintaining the high dispersity of the synthesized TiN–SiC powder compositions, their phase composition became much closer to the theoretical one: the silicon carbide content in the synthesized TiN–SiC product increased substantially, while the amount of the secondary phase of silicon nitride (Si₃N₄) decreased or was completely eliminated.

This study examines the structure and mechanical properties of aluminum-matrix composites (AMCs) with varying contents of the ZrC reinforcing phase, produced by powder metallurgy. Elemental mapping together with hardness measurements indicate a uniform distribution of ZrC particles in the matrix. The effects of mixing time (1–6 h), compaction pressure (636–1910 MPa), and sintering time (1–2 h) on density, porosity, and properties were investigated. With increasing ZrC content, the composite’s mechanical properties improve, and correlations among density, porosity, hardness, and strength are observed. An increase in sintering time has little effect on density and porosity; after sintering, hardness decreases due to annealing. Local agglomeration of ZrC at grain boundaries may weaken interfacial bonding between aluminum and the reinforcement. Strengthening arises from load transfer, Orowan strengthening, and thermally induced dislocations due to the coefficient-of-thermal-expansion mismatch between the particles and the matrix. Efficient load transfer during compression testing requires good particle–matrix interfacial contact; dislocation–particle interactions generate Orowan loops, contributing to the observed strengthening.

Alumina-based composite ceramics containing barium hexaaluminate are promising for various industrial applications, including the fabrication of replaceable cutting inserts. However, reports on such materials produced by spark plasma sintering (SPS) are scarce. This study aimed to evaluate the influence of sintering temperature on the structure and properties of alumina ceramics containing barium hexaaluminate. The materials were fabricated from highly dispersed Al₂O₃ and BaO powders by co-dispersion in an alcohol medium, followed by drying and spark plasma sintering at 1500, 1550, and 1600 °C. X-ray diffraction, scanning electron microscopy, and hydrostatic weighing were used to determine phase composition, microstructure, apparent density, and open porosity. Vickers hardness and fracture toughness were evaluated by indentation. The formation of α-Al₂O₃ and Ba_0.83Al₁₁O_17.33 phases was confirmed. The relative density of alumina ceramics without additive reached 99.72 ± 0.3 %, while that of ceramics containing barium hexaaluminate was 92.45 ± 0.5 %. The average Al₂O₃ grain size decreased from 4.27 ± 1.80 μm (without additive) to 1.49 ± 0.80, 1.89 ± 0.85, and 1.60 ± 0.63 μm at sintering temperatures of 1500, 1550, and 1600 °C, respectively. The barium hexaaluminate plates grew with increasing temperature, from 2.45 ± 0.22 μm at 1500 °C to 5.23 ± 0.46 μm at 1600 °C. The maximum fracture toughness (K_Ic = 5.00 ± 0.10 MPa·m^1/2 ) was obtained for the material containing barium hexaaluminate sintered at 1550 °C, which also exhibited a hardness of 2070 ± 43 HV₂.

Titanium carbide (TiC) coatings were produced on the surface of graphite components using a low-cost liquid-phase technique involving application of a TiO₂-based reaction mixture followed by carbothermal annealing in vacuum at 1900 °C. Typical grades of structural graphite (GMZ, MPG-6, and I-3) commonly used in high-temperature graphite assemblies were employed as substrates for the protective coating. The resulting polycrystalline titanium carbide films (NaCl-type structure) exhibited an axial growth texture [111] and thermal stresses that depended on the graphite grade, caused by the difference in the coefficients of thermal expansion between titanium carbide and graphite. Typical coating thicknesses ranged from 10 to 20 µm. Graphite components with TiC coatings were successfully tested under high-temperature silicon carbide single-crystal growth conditions. The tribological properties of the coatings were also evaluated. The use of denser grades of isostatic graphite (I-3) is preferable due to the formation of a dense two-dimensional structure of the protective layer on the graphite surface.

This article continues the research on α-SiC powder preforms produced by selective laser sintering (SLS) [1]. The study examines the hydrostatic density and microstructure of the surface and internal cross sections of both the porous preforms and the densified specimens obtained through post-processing. Two post-processing routes were tested to increase the density of porous SLS preforms. The first method involved densification by silicon infiltration (liquid silicon infiltration, LSI). The second method was hybrid, combining polymer infiltration and pyrolysis followed by silicon infiltration (PIP + LSI). For conventionally pressed materials, this hybrid treatment forms a higher fraction of silicon carbide in the structure compared to LSI alone, which has a beneficial effect on mechanical and thermophysical properties. The study established the dependence of SiC, Si, and C phase contents and the relative density on the number of infiltration and pyrolysis cycles and on the post-processing route. Specimens were fabricated with different single-layer thicknesses (30 and 50 µm). Specimen with a 30 µm layer thickness had a higher initial density than those with 50 µm layers and required only 2–3 infiltration cycles for carbon saturation, compared with 4–5 cycles for the 50 µm specimens. The final density of the specimens with both layer thicknesses was approximately the same – no higher than 2.88 g/cm³. The density of specimens subjected only to silicon infiltration was 2.52–2.65 g/cm³, which is lower than that of the fully post-processed specimens. This density difference was not due to porosity; in fact, the porosity was lower in the LSI specimens. According to quantitative microstructural analysis, the lower density resulted from nearly twice the content of free silicon, which has a lower density than SiC and thus decreases the overall density of the LSI specimens.