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Coatings were produced on the EP741NP nickel alloy substrates by electrospark deposition (ESD) in argon using an MoSi2-MoB-HfB2 electrode. In situ high-resolution transmission electron microscopy and X-ray diffraction analysis studies have identified the temperature above which the strengthening Mo2Ni3Si Laves phase is formed in the coatings. At 25 °C, the coatings with a predominant content of the Laves phase are characterized by enhanced wear resistance, as well as a lower coefficient of friction compared to the non-annealed coatings containing binary silicides. At 700 °C, the EP741NP substrate was characterized by the lowest friction coefficient (Ktr = 0.35), and its wear was approximately at the same level as the wear of both coatings.

Introduction. The paper addresses the problem of the optimal combination of traditional and distance (online) knowledge delivery systems in higher education. The purpose of this study is to identify and describe academic and administrative factors and conditions influencing the integration of traditional and distance learning in a university environment. Materials and Methods. The article reviews and analyses a number of Russian and international studies into distance (online) and traditional learning within the framework of higher education. A survey was conducted at Cherepovets State University (the Russian Federation). Participants of the study were students (n=110) and academic staff (n=20). The observation method was used in order to identify the level of student satisfaction in traditional and distance (online) learning. Results. The authors clarified modern interpretations of distance and traditional education and conducted a historical analysis of these concepts. The study revealed and described academic and administrative factors and conditions contributing to the effective integration of distance and traditional education. The results showed that most of the students and academic staff prefer a traditional education delivery system. In regards to tools and resources of distance (online) learning, most respondents are positive about using Microsoft Teams video conferencing software. Conclusions. The authors identified and clarified the following academic and administrative factors and conditions for the integration of distance and traditional education delivery systems: careful selection of educational online platforms, active use of reflection, a variety of communication channels for feedback, emotional factors, regulations for distance learning, and distance mentoring. Keywords Distance education; Traditional education; Integration; Academic and administrative factors and conditions; Students; Academic staff; Educational online platform

Composites MoSi2–ZrB2–SiC and MoSi2–HfB2–SiC were investigated in this study as the prospective materials for high-temperature industrial heaters. The composites with relative density 97–98% were produced by combustion synthesis followed by hot pressing. The macrokinetic features of combustion, as well as phase and structure formation mechanisms in the combustion waves, were analyzed and their influence on the structure, mechanical properties, and performance of heaters were ascertained. The mechanical and electrical properties of the heating elements produced in this work are considerably higher as compared to conventional MoSi2 counterparts. Among the investigated compositions, the MoSi2–HfB2–SiC demonstrated the highest resistance to high-temperature oxidation. Both compositions featured the formation of a stable continuous oxide layer consisting of crystalline α-quartz (high-temperature modification of SiO2) reinforced by ZrO2, ZrSiO4, HfO2, and HfSiO4 precipitates.

This study covers the elemental synthesis features of Hf–Ta–B–Ti–Si ceramic materials used to obtain promising high-temperature ceramics and analyze its structure and properties. The macrokinetics of self-propagating high-temperature synthesis (SHS) are studied. Combustion temperature and velocity as a function of initial temperature are plotted. It is established that chemical interactions occurring in the liquid phase play a pivotal role in the combustion process. Structure and phase formation processes are studied using the stopped combustion front technique. The mechanism of phase formation in the combustion wave is determined. The primary crystals of hafnium, titanium, and tantalum diborides are precipitated from the super-saturated melt after the Si and Ti contact melting and B, Hf, and Ta dissolution in the melt through the reactive diffusion process. A two-phase structure consisting of complex solid solutions based on diboride and borosilicide is formed due to the similarity of the crystal lattices. Porous synthesis products of the specified composition are milled into powders with the required particle-size distribution for subsequent hot pressing (HP) or spark plasma sintering (SPS). It is found that specimens produced by HP, SPS, and SHS pressing feature a similar phase composition containing solid solutions based on diboride (Hf,Ti,Ta)B2 and borosilicide (Hf,Ti,Та)5Si3В. Specimens of ceramics produced using the above technologies for physical–mechanical testing are made. It is found that the hardness and elastic modulus of the (Hf,Ti,Ta)B2 solid solution are 2–3 times higher than that of (Hf,Ti,Ta)5Si3B borosilicide. Depending on the composition, the density of the ceramics varies from 8 to 6.5 g/cm3, which corresponds to a porosity of less than 5%. Temperature dependences of heat capacity and diffusivity are determined. The heat conductivity of ceramics produced by HP and SPS is 24.05 and 23.1 W/(m K), respectively.

A new method is proposed for the engineering of SiC-based ceramic-matrix composite materials strengthened by discrete carbon fibers and single-crystal silicon carbide nanowires. Depending on the macrokinetic characteristics of the combustion process, either diffusion layers, particles of silicon carbide, or silicon carbide nanowires with a diameter of 10–50 nm and a length of 15–20 μm can be formed on the surface of carbon fibers. The sequence of chemical transformations and structure formation in the combustion wave of Si–C–C2F4 and Si–C–C2F4–Ta mixtures was studied. Silicon carbide nanowires formed in the combustion wave had high crystallinity and a defect-free TaSi2/SiC interface. The misorientation of the lattices at the interface is about 6%. Nanowires are able to relax the mechanical stresses during growth via the rotation along the growth direction. The optimal combustion temperature for the growth of silicon carbide nanofibers is 1700 K at a ratio of C2F4 : C = 2. The lower temperature threshold for the growth of silicon carbide nanowires is caused by a decrease in the yield of reactive fluorides, while the upper-temperature threshold is caused by a failure of the adsorption blocking mechanism on the surface of the nanofibers and the destabilization of the TaSi2 + Si eutectic droplet. Composites with a SiC–TaSi2 ceramic matrix and a relative density of 98%, a hardness of 19 GPa, a flexural strength of 420 MPa, and fracture toughness of 12.5 MP m1/2 were obtained by hot pressing. An increase in the strength of the carbon fiber-matrix interface has manifested in the suppression of carbon fiber pull-out from the matrix.

The influence of boron on the structure and on the mechanical and tribological properties of protective coatings of the Cr–Al–Ti–N alloys obtained by magnetron sputtering in a closed unbalanced magnetic field using segmented planar ceramic SHS targets has been studied. The obtained coatings were examined using glow discharge optical emission spectroscopy, scanning electronic microscopy, X-ray diffraction phase analysis, nanoindentation, and tribological tests according to the pin-on-disk scheme. It has been shown that the introduction of B results in the suppression of the columnar structure and the reduction of the roughness of the coatings. Hardness, elasticity modulus, elastic recovery, wear resistance, and the coefficient of friction of coatings of the Cr–Al–Ti–B–N alloys have been determined. The introduction of 2.3 at % B leads to a high hardness (H = 15 GPa), stable friction coefficient (f = 0.65), and a decrease of the reduced wear (Vw = 7.5 × 10–6 mm3/(N m)). It has been shown that the hard Cr–Al–Ti–B–N coatings of the optimal composition in their mechanical and tribological properties exceed the coatings without boron addition.

This study proposes a combustion-based ceramic matrix composite processing technique intended on single-step in situ deposition of single-crystal SiC nanowires (SiCnw) on the surface of carbon fibers (Cf) and formation of SiCnw–reinforced SiC matrix. This was accomplished by Ta-catalyzed combustion of poly-(C2F4)-containing reactive mixtures with pre-mixed chopped Cf. Depending on the combustion conditions, carbon fiber surface is subjected either to formation of diffusion layers, ceramic particle incrustation or growth of continuous arrays of carbon-coated single-crystal SiCnw with a nearly defect-free lattice, 10–50 nm diameter and 15–20 μm length. Thermodynamics, phase and structure formation mechanisms are explored, and the optimal conditions are outlined for reproducible Cf/in situ SiCnw dual reinforcement of SiC-based ceramics. Hot pressing at 1500 °C produced Cf/in situ SiCnw-reinforced ceramic SiC–TaSi2 specimens with a relative density of 97%, 19 GPa Vickers hardness, 3-point flexural strength σ = 420 ± 70 MPa and fracture toughness K1C = 12.5 MPa m1/2.

In this study, Mo-(Y,Zr)-Si-B coatings were obtained by direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HIPIMS) using mosaic targets. The results showed that the addition of Y and Zr into the composition of Mo-Si-B coatings led to the suppression of columnar grain growth, a decrease in the crystallite size of h-MoSi2 phase from ~50 to ~5 nm, and an increase in the amorphous to crystalline phases ratio Doping of the Mo-Si-B coating with Y and Zr promoted an increase in oxidation resistance at a temperature of 1000 °C. The introduction of yttrium into the composition of Mo-Si-B contributed to an increase in their crack resistance when heated to 1300 °C. High oxidation resistance of the coatings was provided by a defect-free SiO2 + MoO3 + Y2O3 surface layer. The transition from the DCMS mode to HIPIMS decreased the texture of the Mo-Si-B coatings. The use of an HIPIMS mode led to a decrease in the oxidation rate of Mo-(Y)-Si-B coatings at T = 1000 °C by 1.6–4.5 times compared to DCMS. In the case of Mo-Y-Si-B coatings, the use of HIPIMS led to a decrease of more than 50% in the thickness of the oxide layer at a temperature of 1300 °C.

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).

This paper focuses on the study of the structure and mechanical properties of CoCrCuxFeNi high-entropy alloys and their adhesion to single diamond crystals. CoCrCuxFeNi alloys were manufactured by the powder metallurgy route, specifically via mechanical alloying of elemental powders, followed by hot pressing. The addition of copper led to the formation of a dual-phase FCC + FCC2 structure. The CoCrCu0.5FeNi alloy exhibited the highest ultimate tensile strength (1080 MPa). Reductions in the ductility of the CoCrCuxFeNi HEAs and the tendency for brittle fracture behavior were observed at high copper concentrations. The equiatomic alloys CoCrFeNi and CoCrCuFeNi demonstrated high adhesion strength to single diamond crystals. The diamond surface at the fracture of the composites having the CoCrFeNi matrix had chromium-rich metal matrix regions, thus indicating that chromium carbide, responsible for adhesion, was formed at the composite–diamond interface. Copper-rich areas were detected on the diamond surface within the composites having the CoCrCuFeNi matrix due to the predominant precipitation of the FCC2 phase at the interfaces or the crack propagation along the FCC/FCC2 interface, resulting in the exposure of the Cu-rich FCC2 phase on the surface.

The hard wear-resistant nanocomposite Ti–Al–Ni–C–N coatings were deposited by direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HIPIMS) in the Ar, Ar+15%N2, and Ar+25%N2 atmospheres. The structure of coatings was analyzed using the X-ray diffraction analysis, glow discharge optical emission spectroscopy, and scanning electron microscopy. Mechanical and tribological properties were measured using the nanoindentation and scratch testing as well as by tribological testing using the “pin-on-disc” scheme. Electrochemical corrosion resistance and oxidation resistance of coatings were investigated. The results suggest that the coatings are based on the FCC phases TiCN and Ni3Al with crystallites size ~3 and ~15 nm, correspondingly. DCMS coatings with optimal composition were characterized by hardness 34 GPa, stable friction coefficient

In this work, the influence of modifications of SHS-process on the microstructure and performance characteristics of composite ceramics MoSi2-HfB2-MoB with two-level structure was studied. Partial texturing of MoSi2 grains in samples obtained by force SHS pressing technology was revealed. The effect of preliminary mechanical activation on the macrokinetic parameters of combustion and on the microstructure of the synthesized ceramics was studied. A significant grinding of the synthesized ceramics grain and an increasing of physical-mechanical properties are achieved by increasing the velocity and lowering the combustion temperature of the activated mixtures. The sample obtained by hot pressing of SHS powder from MA reaction mixture showed the most optimal combination of hardness (19.5 GPa), porosity (0.4%) and oxidation resistance (1.82∙10-6 mg/(cm2∙s)).

The study covers coatings obtained on 40Kh steel substrates by electro-spark deposition (ESD) using TiC–NiCr and TiC–NiCr– Eu2O3 electrodes. Coatings were deposited by the Alier-Metal 303 unit in argon environment under the normal pressure using direct and opposite polarity. The structure, elemental and phase composition of electrodes and coatings were studied using X-ray phase analysis, scanning electron microscopy, energy dispersive spectroscopy, glow discharge optical emission spectroscopy, and optical profilometry. Mechanical and tribological properties of coatings were determined by nanoindentation and testing according to the «pin-disk» scheme including high-temperature conditions in the range of 20–500 °C. The tests conducted include abrasive wear tests using the Calowear tester, impact resistance tests using the CemeCon impact tester, and tests for gas and electrochemical corrosion resistance. Test results showed that electrodes contain titanium carbide, nickel-chromium solid solution, and europium oxide in case of a doped sample. Coatings exhibit the same phase composition but solid solution is formed on the iron base. Coatings with the Eu2O3 additive do not differ significantly in structural characteristics, hardness, friction coefficient, and exceed the base coatings in terms of their abrasive resistance, repeated impact resistance, heat and corrosion resistance. There was an increase in impact resistance by 1.2–2.0 times, a decrease in corrosion current by more than 20 times, and an oxidation index by almost 2 times during the transition to doped coatings.

The structure and properties of coarse-grained WC–6% Co carbides with carbon deficiency from 0.11 to 1.31% relative to the stoichiometric ration prepared from narrow-fraction tungsten carbide powder with a grain size of 5–15 μm are studied. It is established by the results of metallographic analysis that sintering temperatures in a range of 1390–1420°C provide the pore-free state of the alloy with the normal carbon content, but the samples have considerable porosity at its lowered concentrations. It is revealed that sintering temperatures of 1450–1475°C, irrespective of the carbon content, make it possible to prepare carbides with residual porosity lower than 0.02%. It is shown that alloys with a carbon deficit of 0.11–0.91% had a two-phase structure, while the alloy with a carbon deficit of 1.31% contained inclusions of the η phase in addition to WC and γ phase. It is established that the retardation of the growth of tungsten carbide grains is observed with a decrease in the carbon content during liquid-phase sintering. The concentration of dissolved tungsten is established by electron probe microanalysis. It was 10, 12, 15, and 19 wt % for carbides with a normal, low, mid, and high carbon deficit, respectively. The use of narrow-fraction tungsten carbide powders makes it possible to fabricate carbides with rounded grains having a shape factor of about 0.77. The alloy with a carbon deficit of 0.91% relative to the stoichiometric ratio had the best combination of hardness and crack resistance:11.1 GPa and 16.0 mPa m1/2.

The electrospark deposition of coatings onto SPKhN–60 white cast iron samples has been undertaken in two stages. A barrier sublayer has been deposited at the first stage, using chromium and nickel electrodes, and a multifunctional protective coating was deposited at the second stage. The effect of the sublayer on coating properties upon application of STIM–40NAOKn (TiC–NiAl + $${\text{ZrO}}_{2}^{{{\text{nano}}}}$$ ) and STIM-11OKn (TiB2–NiAl + $${\text{ZrO}}_{2}^{{{\text{nano}}}}$$ ) electrodes is studied. The coating structures are investigated. The grain size of the refractory phase is found to be smaller than 100 nm. The application of double-layer coatings increased the wear and heat resistances of white cast iron samples. Pre-deposition of a nickel sublayer enhanced the heat resistance of STIM-11OKn coating over eightfold. The full-scale tests of the rolls strengthened using SHS electrodes were carried out and positive results were obtained.

This work is devoted to the fabrication of heterophase powder and consolidated ceramics based on hafnium and molybdenum borides and silicides by combining self-propagating high-temperature synthesis (SHS) and hot pressing (HP). Composite ceramic HfB2–HfSi2–MoSi2 SHS powders are fabricated according to the magnesium-thermal reduction flowsheet from oxide raw materials, in which the combustion wave has temperatures of 1750–2119 K and rather high mss combustion rates of 8.4–9.3 g/s. The structure of synthesized SHS powders consists of relative coarse MoSi2 grains up to 10 μm in size, submicron elongated HfB2 grains mainly located inside the MoSi2 grains, and rounded Si precipitates. The composition with a lower boron concentration contains numerous polyhedral HfSi2 grains smaller than 10 μm in size. The resulting powders have an average particle size of ~6 μm with a maximal size up to 26 μm. The phase compositions of the ceramics consolidated by the HP method and synthesized SHS powders are identical. The microstructure of compact samples consists of faceted elongated HfB2 grains 0.5–10.0 μm in size, polyhedral HfSi2 and MoSi2 grains up to 8–10 μm in size, and silicon interlayers. The consolidated ceramics have a high structural and chemical homogeneity, low residual porosity of 1.1–1.7%, high hardness of 11.7–12.6 GPa, and thermal conductivity of 62–87 W/(m K).

Electrospark deposition on samples made of SPHN-60 white cast iron is carried out in two stages. During the first stage, a barrier sublayer was applied, and during the second stage, a multifunctional protective coating was applied. Two materials for the electrodes, Ni and Cr, were chosen to form a sublayer according to the calculations of Palatnik’s criterion. The impact of a sublayer on the features of the formation of electrospark coatings is studied using hard-metal electrodes of SHIM-40NАОKn (TiC–NiAl + $${\text{ZrO}}_{2}^{{{\text{nano}}}})$$ and SHIM-11ОKn (TiB2–NiAl + $${\text{ZrO}}_{2}^{{{\text{nano}}}})$$ . The phase composition and the surface roughness of the formed coatings are studied. It is found that deposition of a sublayer contributes to an increase in the fraction of refractory phases in coatings. The surface roughness (Ra) varies from 3.37 to 8.20 μm. The adhesion strength of the two-layer electrospark coatings to the substrate exceeds 100 N.

The kinetics and mechanism of high-temperature oxidation of dense heterophase ZrSi2-MoSi2-ZrB2 ceramics at a temperature of 1650 °C are studied. The ceramics were fabricated by hot pressing of composite powders prepared by self-propagating high-temperature synthesis with magnesiothermic reduction. The oxidation kinetic curve is described by the power-law function, which indicates that the evolutionary changes in the structure of the formed oxide films significantly affect the course of the oxidation process. The oxidation mechanism involves formation of a multi-layered structure of heterogeneous oxide film, partial dissociation of the ZrSiO4 phase, and formation of secondary MoB and Mo5Si3 compounds. The influence of the ZrSi2, MoSi2 and ZrB2 phases on the structural and morphological features of the formed oxide films and the efficiency of their protective action are shown. Silicon is reduced and zirconium is simultaneously oxidized to ZrO2 in the ZrSi2-ZrSiO4 system at temperatures above 1620 °C in the absence of oxygen or in low-oxygen environment.

The possibility of increasing the mechanical properties of the ceramic material of the TaSi2–SiC system by reinforcing it with silicon carbide nanofibers forming in situ in the combustion wave of the SHS system is investigated. To fabricate nanofibers, as well as to increase the exothermicity of reaction mixtures, an energetic polytetrafluoroethylene (PTFE) additive C2F4 was applied. The 70%TaSi2 + 30%SiC ceramic, in which silicon carbide is situated in two types of morphology—in the form of rounded grains and discrete nanofibers—was fabricated with the help of self-propagating high-temperature synthesis when using the mechanical activation of initial reaction mixtures. Reinforced ceramic samples sintered using hot pressing have a relative density up to 98%, hardness of 19.0–19.2 GPa, and crack resistance of 7.5–7.8 MPa m1/2 (which noticeably exceeds the crack resistance of the ceramics of the close composition formed without the PTFE additive).

Coatings in a Zr-Mo-Si-B-N system were deposited by the magnetron sputtering of ZrB2-MoSi2 targets in argon and nitrogen. The structure of the coatings was investigated using scanning electron microscopy, X-ray diffraction, energy-dispersive spectroscopy, and glow-discharge optical emission spectroscopy. Mechanical and tribological properties were measured using nanoindentation and pin-on-disc testing. Oxidation resistance and oxidation kinetics were estimated via annealing in air at 1000–1500 °C and precision weight measurements. We found that the coatings deposited in Ar demonstrate a superior combination of properties, including hardness of 36 GPa, elastic recovery of 84%, a friction coefficient of 0.6, and oxidation resistance at temperatures up to 1200 °C. High oxidation resistance is realized due to the formation of the protective (SiO2 + ZrO2)/SiO2 oxide layer, which inhibits the diffusion of oxygen into the coating.

Optical Zr-B-N films deposited by pulsed magnetron sputtering (PMS) at various frequencies are studied. A ceramic ZrB2 target obtained by self-propagating high-temperature synthesis is used for sputtering. It is shown that the increasing the frequency improves mechanical properties, including hardness and elastic recovery. All types of films exhibit a high transparent coefficient in the wavelength range of 350–950 nm.

The effects of using of the HIPIMS technology for deposition of coatings for various purposes, including CrB, TiAlNiC, and MoHfSiB, are studied. Ceramic targets obtained by self-propagating high-temperature synthesis were used for sputtering. It is shown that the transition from DC to HIPIMS modes increases the structure density, hardness, elastic-plastic properties, wear and corrosion resistance, cracking resistance during thermocycles, and oxidation resistance of the coatings. The adhesive strength can be significantly increased if preliminary ion cleaning of substrates is used.

Two schemes for fabricating the composite powder ZrB2–TaB2–TaSi2 by SHS are discussed in this study: (1) elemental synthesis in the Zr–Ta–B and Ta–Si mixtures followed by mixing of the combustion products, and (2) elemental synthesis in the Zr–Ta–Si–B mixture. The macrokinetic features of combustion of the Zr–Ta–Si–B mixtures, the mechanism of structure and phase formation in the combustion wave, and the structure and properties of the combustion products were studied. Primary crystals of tantalum and zirconium diborides were formed in the preheating zone as a result of gas-phase mass transfer of boron onto the surface of metal particles. In the combustion zone, melting of Si–B eutectic and Zr particles took place, followed by the formation of borides and silicides of tantalum and zirconium. In the zones of post-combustion and secondary structure formation, zirconium diboride partially interacted with tantalum diboride and formed solid solution (Ta,Zr)B2. Hot pressing of SHS powders produced bulk ceramics with the relative density of 95–98%. Structure and mechanical properties of the hot pressed ceramics depend significantly on the selected scheme of powder synthesis. The ceramics fabricated using scheme 2 have a specific microgradient grain structure and significantly higher hardness and crack resistance (HV10 =19.2 GPa; K1c=3.5 MPa*m1/2) as compared to the similar composite prepared using scheme 1 (13.9 GPa and 2.4 MPa m1/2).

Powders based on tantalum disilicide and silicon carbide were fabricated by mechanical activation-assisted SHS of reaction mixtures, with SiC concentration varied from 10 to 70%. The single- and double-layer composite targets were produced by hot pressing and further utilized for deposition of Si-Ta-C-(N) coatings by magnetron sputtering. The optimal hot pressing regimes, which allowed the production of dense ceramics with a hierarchical structure at 10 and 30% SiC, were determined. These ceramics were characterized by a relative density of 96–97%, hardness of ~19 GPa, and fracture toughness of 6.5–6.7 MPa × m1/2. The nanocomposite Si-Ta-C-N coatings consisted of fcc Ta(Si,C,N) solid solution (TaSi2–30%SiC target) and Ta5Si3 compound (TaSi2–10%SiC target) embedded in an amorphous matrix. Depending on the elemental composition, hardness and Young's modulus of the coatings were 16–26 GPa and 155–268 GPa, respectively. The coatings are characterized by high thermal stability and oxidation resistance at temperatures up to 800 °C. Tribological tests demonstrated the decrease of the coefficient of friction (CoF) of the coatings with increasing temperature: from 0.38 (25 °C) to 0.28 (600 °C) and 0.23 (800 °C). The low wear rate and CoF of the Si-Ta-C-N coatings at elevated temperatures are explained by the formation of a thin (~100 nm) oxide layer and TaSixOy microfibers on the coating surfaces.

Influence of carbon nanotubes (CNT), hexagonal boron nitride (h-BN) and tungsten carbide (WC) nano-reinforcement on the mechanical and tribological properties of the Cu-Ni binder alloy was investigated experimentally and numerically. In situ TEM and multiscale micromechanical finite element (FE) modeling were used to study the mechanisms of deformation of the nanomodified binder. Сomplex reinforcement by 0.1% CNT + 0.1% hBN + 0.69% WC increases the tensile strength of the materials from 155 to 346 MPa, bending strength from 420 to 832 MPs, hardness from 2.1 to 2.4 GPa and elastic modulus from 98 to 123 GPa. The complex reinforcement changes the wear mechanism and significantly enhanced the tribological properties of the binders, decreasing the coefficient of friction from 0.47 to 0.28 and wear rate from 12.3 to 6.7·10−6 mm3/N/m. The failure of the nanomodified binder was found to be caused by the emergence and propagation of microcracks along the interface between hBN particles and the matrix. Carbon nanotubes inhibit the propagation of cracks, significantly increasing the mechanical and tribological properties of Cu-Ni binders.

This study focuses on the investigation of the macrokinetic features of SHS (combustion synthesis) of elemental mixtures Mo–Hf–Si–B, in particular the mechanisms of structure and phase formation in the combustion front as well as the structure and properties of consolidated ceramics. Two routes for the fabrication of the composite SHS powder in system MoSi 2 –HfB 2 –MoB were used: (1) synthesis using Mo–Si–B and Hf–B mixtures followed by mixing of the combustion products and (2) synthesis using the four-component Mo–Hf–Si–B mixture. Dense ceramic samples with a homogeneous structure and low residual porosity (0.8–3.6%) were prepared by hot pressing of SHS powders. Although the particles size distribution and phase composition of SHS powders are similar for both synthesis routes, the structure and properties of both the composite SHS powders and hot-pressed ceramics differ considerably. Synthesis using the four-component Mo–Hf–Si–B mixture allows one to produce hierarchically ordered nanocomposite material with improved mechanical properties: hardness up to 17.6 GPa and fracture toughness up to 7.16 MPa m 1/2 .

The microstructure and properties of spherical composite powders produced from the β-(Fe, Ni)Al-based alloy by plasma rotating electrode process (PREP) using a steel-shelled electrode were studied. Parameters of the selective laser melting (SLM) mode (laser power density, laser intensity, scan speed and regime) were optimized to ensure the minimal porosity of

The novel technology of multilayer coating deposition combining electric-spark alloying (ESA), pulsed arc evaporation (PAE), and magnetron sputtering (MS) in one vacuum process is presented. Layers can be deposited using a single electrode material at operating pressures from 0,1 Pa to atmospheric pressure. The lower ESA layer provides increased substrate toughness, perfect adhesion and a relatively high (up to 100 μm) coating thickness. The upper PAE or MS layer up to 10 μm in thickness provides high mechanical and tribological characteristics. The technology of double-layer PAE–ESA and MS–ESA coating deposition was tested on substrates made of structural and tool steels, titanium alloys using electrodes of cemented carbides (WC–Co, TiCNiAl) and carbon (low-porous graphite).

Spheroidization of micropowders of a heat-resistant alloy based on nickel aluminide with a particle size of 20 to 45 μm was studied. The alloy was produced by calcium hydride reduction (CHR) and elemental synthesis (SHS). The spheroidization was carried out in a flow of argon–hydrogen thermal plasma generated by a direct-current (DC) plasma torch. The degree of spheroidization of the micropowders reached 98.5%, and the flowability was 20 s/50 g.

Powders of new CompoNiAl M5-3 heat-resistant alloy were prepared by mechanoactivated SHS from (Ni–Al–Cr–Co–Hf)–NaCl mixtures. Ni dissolution in Al melt was found to be the motive force of combustion. Unlike the binary Ni–Al system, NiAl is formed not in the melt but in the post-combustion zone as a result of diffusion-controlled processes. Conditions for MASHS were optimized toward fabrication of a superalloy with homogeneous composition/structure and low content of gas impurities. As-prepared combustion product was disintegrated into a powder and the latter was subjected to plasma spheroidization, keeping in mind the needs of additive manufacturing. The attained degree of spheroidization was 98%. The structure and phase/chemical compositions of spherical powders did not differ from those of the synthesized powders. After plasma treatment, the content of gas impurities (О2 and N2) decreased.

The structure and properties of pre-alloyed Ni41Al41Cr12Co6 spherical powders (the 40–160 μm fraction) produced using the plasma rotating electrode processing technology were studied. The evolution of the fine structure of pre-alloyed Ni41Al41Cr12Co6 spherical powders under heating at 20, 350, …, 850 °C was investigated. Disk-shaped chromium-rich pre-precipitation zones 5–30 nm in size were detected in the temperature range of 450, …, 650 °C; they precede the formation of the dispersed chromium precipitate. Prism-shaped chromium nanocrystals with the characteristic longitudinal dimension ranging from 15 to 100 nm, whose nucleation process starts at prismatic dislocation loops, were found to be formed at 750, …, 850 °C. The Young's modulus, hardness, and elastic recovery of powder material were determined by nanoindentation measurements. The resulting powders are characterized by bulk density of 3.8 g/cm3, excellent flow rate (3.5 s), and the angle of repose of 19.6°. Keywords: Plasma rotating electrode processing (PREP), Spherical powders, Nickel aluminide, Precipitation hardening, Intermetallic alloys, Nucleation and growth

The influence of mechanical-activation (MA) conditions on the microstructure and phase composition of Ta–Hf–C reaction mixtures and products fabricated from them by self-propagating high-temperature synthesis (SHS) is investigated. The Ta–Hf–C reaction mixtures are mechanically activated in centrifugal planetary mills with various drum revolution rates. It is revealed that an increase in the drum revolution rate from 250 to 900 rpm lowers the heterogeneity scale of the reaction charge, decreases the size of coherent scattering regions of tantalum and hafnium by an order of magnitude, and leads to a rise in the degree of microdeformation of their crystal lattices by a factor of 1.5–2.0. It is established experimentally that it seems impossible to initiate an SHS reaction in the Ta–Hf–C activated mixture at initial temperature T0

The structure, composition, surface area and catalytic activity of Solution Combustion Synthesis (SCS) catalysts are all influenced by the conditions of preparation and in particular, the glycine concentration in the initial SCS solution. NMR was used to monitor the formation of glycine-nickel nitrate complexes in solution before SCS initiates, IR high speed temperature measurements have allowed to elucidate the mechanism of synthesis during SCS, dynamic X-ray analysis and thermogravimetric analysis have clarified the mechanisms of phase formation during SCS, BET analyses have shown the regularity of pore formation and SEM and TEM studies have indicated the regularities involved during microstructure formation. Regular three-dimensional (3D) flowerlike Ni-NiO hierarchical architectures were synthesized by SCS. The results have revealed a three-dimensional percolation network with hierarchical structure on the basis of nano-structured metal oxides and metals synthesized during SCS. Such hierarchically nanoporous catalysts have versatile structural properties such as increased surface area and large overall pore volume that can alleviate diffusional limitations of conventional nanocatalysts with solely microporous framework. This is important for liquid phase heterogeneous catalysis. These new insights provide a valuable capability for optimizing the selectivity and activity of SCS catalysis and will no doubt be of significant interest to a wide range of researchers working in catalysis and other fields.

The structure and magnetic properties of model high-cobalt WC–50% Co alloys with different carbon contents and TaC additions in the amount of 1.6–5.6 wt % are studied. Model alloys are fabricated by the liquid-phase sintering of powder mixtures at 1420°C, and their composition is described by the formula 50% Co + 50% WC + x% TaC + y% C, where x = 0, 1.6, 2.6, 3.6, 4.6, and 5.6 wt %; y = 0, 0.2, and 0.5 wt %. It is shown that precipitations of the (Ta,W)C phase are present in all studied alloys and (Ta,W)C precipitations are needle-shaped at a TaC concentration up to 3.6 wt %, while the (Ta,W)C grains become spherical at =3.6 wt %. The (Ta,W)C precipitations are arranged both in a binding phase and along the WC grain boundaries. The lattice parameter of the (Ta,W)C phase in alloys with a low carbon content lies in a range from 0.4438 nm for the alloy with 1.6% TaC to 0.4451 nm for the alloy with 4.6% TaC. It is established by the EDX analysis that the concentration of dissolved tungsten in a cobalt phase is independent of the TaC content and strongly depends on the total carbon content; it is 7, 12, and 17 wt % for alloys with high, elevated, and low carbon contents, respectively. The TaC addition in alloys with a low and elevated carbon content leads to an increase in the coercive force up to 875 A/m and a decrease in the magnetic saturation by 5–10 G m3/g. The experimental results made it possible to put forward a hypothesis on the possibility of formation of dispersed tantalum-containing precipitates in a binder phase.

The work is dedicated to researching into combustion kinetics and mechanism as well as the stages of the chemical transformations during self-propagating high-temperature synthesis of ZrB2-SiC based ceramics. Dependences of the combustion temperature and rate on the initial temperature (T0) have been studied. It has been shown that the stages of the chemical reactions of ZrB2 diboride and SiC carbide formation do not change within the range of T0 = 298–700 К. The effective activation energy of the combustion process amounted to 170–270 kJ/mol, from which it has been concluded that chemical interaction through the melt plays a leading role. The stages of the chemical transformations in the combustion wave have been studied by dynamic X-ray diffraction. First, ZrB2 phase forms from Zr-Si melt saturated with boron, and SiC phase is registered later. The SHS method has successfully been used in order to obtain ZrB2-SiC composite powders and compact ceramics with a silicon carbide content of 25–75%. The ceramics are characterized by a residual porosity of 1.5%, hardness up to 25 GPa, the elastic modulus of 318 ± 21 GPa, elastic recovery of 36% and thermal conductivity of 54.9 W/(m × K) at Troom.

This study demonstrates that homogeneous high-purity micropowders with grain size of 10–45 µm from refractory NiAl-Cr(Co)-Hf alloy can be produced by combustion elemental synthesis and further treated in a thermal plasma flow. The optimal parameters of plasma spheroidization of the synthesized powders are shown at which the resulting spherical alloy particles are characterized by high sphericity (~ 98%) and the absence of satellites or internal porosity. The spherical powders were consolidated by HIP. The alloy structure was investigated by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The fine structure and features of segregation of hardening nanoparticles of Ni2AlHf (the Heusler phase) and hafnium solid solution (ssHf) in the NiAl matrix were thoroughly studied. Furthermore, in situ examination of structural phase transformations occurring in the as-HIP NiAl-based alloy was carried out upon heating in the temperature range of 25–850 °C. The α-Cr phase nanoparticles are formed inside the NiAl grains via two different mechanisms: (1) spinodal decomposition of solid solution at 250–450 °C resulting in segregation of the Guinier-Preston zone rich in Cr and its subsequent transformation into α-Cr precipitates 25–170 nm in size; (2) heterogeneous nucleation and growth of α-Cr nanocrystallites 7–40 nm long on prismatic dislocation loops at 750–850 °C. The thermomechanical properties of the alloy were studied in the temperature range of 596–1100 °C on a Gleeble System 3800 testing system. The correlation between the thermal load and the high-temperature creep rate, as well as the temperature dependences of the Young's modulus (E), the offset yield strength (σ0.2), and the rate sensitivity coefficient (m), were ascertained. The Young's modulus (E), the ultimate tensile strength, the offset yield strength σ0.2, and the proportional limit of the alloy being examined during uniaxial compression test of a cylindrical sample at 750 °C and at true strain rate of ~ 0.01 s−1 were as high as 137.8 GPa, 682, 455 and 358 MPa, respectively.

Comparative study of Ti-C-Ni-Fe, Ti-C-Ni-Al, and Ti-C-Ni-Al/Ti-C-Ni-Fe coatings obtained by electro-spark deposition (ESD) using TiCNi electrode, magnetron sputtering (MS) of TiCNiAl target, and a combination of these methods (MS-ESD) was carried out. The coating microstructures and elemental compositions were studied by means of X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and glow discharge optical emission spectroscopy. The materials were tested in terms of their hardness, elastic modulus, elastic recovery, crack resistance, friction coefficient, and wear resistance under sliding, impact and abrasive conditions, as well as corrosion- and oxidation resistance. The work demonstrated that the utilization of a combined two-step MS-ESD technology permits to obtain bilayers made of Ti-C-Ni-Al/Ti-C-Ni-Fe coatings with improved crack-, wear- and oxidation resistance compared with their single-layered Ti-C-Ni-Al counterparts deposited by MS, and with reduced friction coefficient and enhanced corrosion resistance compared with ESD Ti-C-Ni-Fe coatings.

The goal of this study was to produce biocompatible ceramic materials in the Ti–C–Co–Ca3(PO4)2–Ag–Mg system by combustion mode synthesis. The influence of cobalt on combustion parameters of the mixture, structure, and properties of the products was investigated. Compact ceramics consist of a combined grain frame of nonstoichiometric titanium carbide (TiC0.5–TiC0.6) with the titanium phosphate (Ti3POx) phase homogeneously distributed along grain boundaries and local isolations of calcium oxide (CaO). The introduction of cobalt promotes the formation of a complex phosphide CoTiP and TiCo intermetallic compound. Alloying with silver and magnesium leads to the formation of a silver-based solid solution.

The macrokinetic features of combustion in the Ta-Zr-B system were studied. Combustion is characterized by spin mode, suggesting the limiting role of gas-phase mass transfer of reagents. The mechanism of chemical reactions and phase formation in combustion wave was discussed. Primary layers of tantalum and zirconium borides were detected in the preheating zone at temperatures below the melting point of the reagents. After zirconium and boron melt, the temperature in the combustion zone reaches its maximum and zirconium diboride precipitates out of the oversaturated solution. Powders with a grain size of 1–3 μm were fabricated and hot-pressed into dense ultra-high-temperature ceramics (UHTCs). Boride ceramics with the record-setting hardness of 70 GPa, Young's modulus of 594 GPa, and elastic recovery of 96% were obtained. The measured heat conductivity of the solid solution (Zr,Ta)B2 was equal to 35–42 W/m K. Plasma torch tests demonstrated high oxidation resistance of the obtained ceramics at 2900–3000 °C.