The volume of silicon waste generated annually in the Irkutsk Region is 20 thousand tons per year, and the volume of waste accumulated in three sludge fields of JSC «Silicon» exceeds 3 million m3. The main type of crystalline silicon production waste is dust from gas cleaning systems of electric ore smelting furnaces. In this regard, this paper studies its chemical composition and the possibilities of using valuable components (amorphous silica, carbon nanotubes (CNT)) included in its composition. The study demonstrates that it is possible to separate this product by flotation into 3 components — sand fraction, flotation tailings enriched in SiO₂, and froth enriched in carbon in the form of CNT. The structure of carbon nanotubes was studied and their physical and mechanical properties were determined: elastic modulus (2000 GPa), tensile strength (75 GPa), and thermal conductivity (4000 W/(m·K)). The amount of heat required to obtain 1 kg of CNT in electric ore smelting furnaces was calculated. Based on the material balance of commercial silicon electric smelting, it was found that 153 kg of CNT and 336 kg of flotation tailings are formed per ton of crystalline silicon during the endothermic process. Flotation tailings consist of 75 % amorphous microsilica particles. According to heat effect and Gibbs energy calculations made for amorphous microsilica formation reactions, it was found that all processes are exothermic, and the process of solid silicon carbide particles (2SiC + 3O₂ → 2SiO₂ + 2CO) oxidation with air oxygen has the highest thermodynamic probability. The economic efficiency of using amorphous silica to produce casting silumins was calculated, and its results clearly demonstrate a quick payback period (6 months), as well as a high level of its profitability (USD 819672).

Hysteresis alloys based on the Fe–Cr–Co system are of scientific and practical interest, primarily due to their high manufacturability, high level and temperature stability of magnetic properties, which provide the required hysteresis magnet performance including residual magnetic induction, coercive force, and loop squareness ratio. The research was aimed to control and stabilize the Fe–Cr–Co ridge alloy magnetic properties using reageing. The 22Kh15K4MS hard magnetic powder alloy was investigated after quenching and multistage aging. Billets were obtained by cold pressing at a pressure of 600 MPa and subsequent sintering in vacuum. The samples obtained by sintering in the α phase in the presence of the liquid phase formed during contact melting had a porosity of up to 1 %. The concentration heterogeneity of chromium and cobalt distribution was 0.06–0.08. The alloy magnetic structure parameters were determined by electron microscopy. The relationship between the magnetic structure formation kinetics during aging and the level of magnetic properties was established. After aging, the fine structure of the 22Kh15K4MS alloy was represented by elongated α₁ phase sections in the α₂ phase matrix. The average particle sizes of the α₁ phase were »124 nm in length and »44 nm in width after the first stage of aging, and they remained the same after final aging. It was shown that it is possible to control magnetic properties by reaging without repeated quenching. A slight change in the size and morphology of magnetic phase particles was observed during aging. The influence of the number of reaging cycles on the stability of magnetic properties over time was determined.

One of the main problems limiting further growth in the production of parts by the hot forging of porous performs (HFPP) is that the obtained materials are prone to brittle fracture due to the poor quality of interparticle jointing formed during hot deformation, as well as the presence of impurities in the composition of initial powders. The paper studies the possibility of increasing the mechanical properties and endurance performance of hot-deformed powder steels by doping them with sodium or calcium microadditives and using thermomechanical treatment. Sodium bicarbonate and calcium carbonate were used for microalloying. Carbon was added as pencil graphite powder. The temperature of heating porous preforms before hot forging and the carbon content in steels were varied; the content of microalloying additives was, wt.%: 0.2 for sodium, and 0.3 for calcium. Mechanical properties as well as contact and low-cycle fatigue life were tested on 5 × 10 × 55 mm and 10 × 10 × 55 mm prismatic specimens, as well as ∅ 26 × 6 mm cylindrical specimens. In comparison with carburizing and thermal treatment, thermomechanical treatment improves the impact strength and endurance performance of hot-deformed powder steels with Na or Ca microadditives under the contact and low-cycle fatigue loading, and the hot repressing temperature of porous preforms is reduced without compromising the mechanical properties of powder steels obtained. It may be associated with the formation of a more fine-grained structure and higher microstresses of the crystal lattice. The cooling down of preform surface layers during hot forging process operations creates conditions for ausforming in them.

The paper presents the results of a study on the dense titanium carbide production by SHS compaction. It is shown that the use of a mechanically activated reaction mixture of titanium and carbon black powders makes it possible to obtain titanium carbide samples with a maximum relative density of 95 %. A feature of this research is that the mechanical activation of components and Ti + C mixture stirring were carried out in a ball mill. The study covers the influence of process parameters on the combustion properties and structure of the consolidated titanium carbide. It was found that the high-speed reaction mixture combustion is an essential condition for dense titanium carbide production. It was shown that the burning rate and temperature strongly depend on the size, mass and density of charge compacts. With an increase in the diameter (20–58 mm) and weight (10–70 g) of compacts made of mixtures with activated reagents, the burning rate varied from 10 to 100 cm/s, and the burning temperature varied from 2200 to 3100 °C. An influence of the pre-pressing pressure (applied at the combustion stage) on the burning rate and temperature was shown: the burning rate sharply decreases from 100 to 10 cm/s at pressures between 0 and 10 MPa, and the combustion temperature decreases monotonically from 3000 to 2000 °C at pressures between 0 and 40 MPa. A high-speed combustion mechanism was proposed for the titanium and carbon black reaction mixture where the formation of radial (longitudinal) cracks in compacts pressed from the mechanically activated mixture is an important factor. These cracks ensure the propagation of incandescent impurity gases and the exothermic reaction initiation in the sample volume.

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)₃Mo₃C, Ni₃Al, (Cr, Mo) and MoRe₂ 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)₃Mo₃C and (Mo_0.8Cr_0.2)_xB_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.

Many machinery parts working in contact with a fast-flowing fluid flow (e.g. turbine blades of hydroelectric power plants, valves, pump impeller blades, ship propellers, cooling systems for various units, etc.) are subjected to such type of wear as cavitation erosion. An important objective is to eliminate or reduce cavitation erosion so as to achieve a considerable economic effect. This research uses a patented technique developed to evaluate the cavitation erosion resistance of cermet thermal spray coatings (WC–10Co4Cr and WC–20CrC–7Ni). These coatings were prepared using high velocity air fuel thermal spraying (HVAF). The aim of this study is to test a new technique for evaluating coating cavitation resistance, which differs from the standard one by specimen positioning relative to the testing liquid. In addition, scanning electron microscopy (SEM) was used to analyze the initial structure of the coatings prepared and study their behavior after cavitation exposure. The material volume loss criterion during the cavitation test was used to evaluate the coating resistance. The results of cavitation tests showed that the WC–20CrC–7Ni coating has a somewhat higher cavitation resistance than that of WC–10Co4Cr despite its slightly lower average hardness (850±90 HV_0.5 versus 950±60 HV_0.5). The study of coating surfaces and cross-sections showed that they feature by different erosion mechanisms. It can be concluded that the presence of defects (pores) in the coating structure is the main reason for reducing their cavitation erosion resistance. Therefore, the developed technique proved effective in obtaining experimental data to analyze cermet thermal spray coatings for cavitation wear.

In this work, Zr–B–N coatings were obtained by the method of high-power impulse magnetron sputtering (HIPIMS) in Ar, Ar + 15%N₂, and N₂ gaseous media using a ZrB₂ SHS target. Sputtering was carried out at the following parameters: medium power of 1 kW, peak power of 70 kW, peak current of 130 A, frequency of 100 Hz, pulse duration of 200 μs. The working pressure in the vacuum chamber was 0.1–0.2 Pa, the distance between the substrate and the target was 80 mm, and the coating deposition time was 40 minutes. Glass, silicon, and high-speed steel were used as substrates. For comparison with the HIPIMS method, the coatings were also applied by direct current magnetron sputtering (DCMS) at an average power of 1 kW. The composition and structure of the coatings were studied by scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GDOES), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analysis. The mechanical, tribological and optical properties of Zr–B–N coatings, as well as resistance to impact dynamic loading, were studied. All coatings were characterized by a dense structure and the absence of columnar grains. With the help of spectroscopic structural studies of coatings, it was revealed that during deposition in a reaction medium, the BN phase is formed, which has a significant effect on the microstructure and characteristics of the coatings. An increase in the nitrogen concentration in the gas mixture during the deposition of Zr–B–N coatings led to an increase in the optical transmittance of the coatings up to 97 %, resistance to cyclic impact dynamic loads by 40 %, and a decrease starting value of friction coefficient by 60 %. The non-reactive coating had a maximum hardness of 19 GPa and an elastic modulus of 221 GPa.