A comparative analysis of agglomerates obtained by spray drying and granulation methods and consolidated materials based on them was carried out. The paper provides the results obtained when studying zirconia nanopowders granulated in water medium with an agar agar additive obtained by chemical precipitation with zirconia partially stabilized by yttrium oxide (2.5 mol.%), and TZ-3Y-E powder manufactured by Tosoh Corp. (Japan) that was prepared by spray drying. Agglomerates as well as microsections and fractures of samples were studied by scanning electron, optical, atomic force microscopy, and Raman spectroscopy. The crack resistance coefficient (K_1с) of samples was determined by indenting the polished surface of microsections with a Vickers pyramid. The specific surface of the powders measured by nitrogen thermal desorption during granulation remains unchanged indicating a significant open porosity of agglomerates obtained. With increasing compacting pressure under conditions of semi-dry compaction with an aqueous solution of PVA as a binder, agglomerates and even aggregates of granulated powders are destroyed, K_1с increases with increasing compaction pressure and the accompanying material microstructure grinding. Powders agglomerated using spray drying break up much less intensively, K_1с does not change with increasing pressure. The studies conducted allow us to agree with the authors pointing to the fractal nature of agglomerates obtained from chemically precipitated nanopowders without the use of spray drying. The use of granulated nanopowders in semi-dry compaction with the application of high pressures makes it possible to destroy not only agglomerates, but also aggregates, and to obtain nanostructured ceramics with grain sizes close to the size of initial particles.

CuCr composite particles were obtained using the method of copper deposition from the solution of its sulfate onto chromium powder particles with the simultaneous mechanical activation (MA) of the mixture in an AGO-2 planetary ball mill for 5 minutes. CuSO₄·5H₂O concentration in the solution with complete copper reduction provided a molar ratio of Cu/Cr = 1. Since deposited fine crystalline copper is highly active and rapidly oxidizes to Cu2O oxide in air, the obtained composite powders were washed, dried, and stored in an argon atmosphere. After drying, the mixture was subjected to additional MA for 5 minutes. Composite particles with a laminate structure begin to form in the solution during MA. Tablets were pressed with a diameter of 3 mm, height of up to 1.5 mm, and density of 4.2–4.5 g/cm³ from the powders obtained. Samples were sintered in an argon atmosphere at 700– 1400 °С. For comparison of microstructures, samples were also sintered from mixtures of Cr and Cu metal powders with a volume ratio of chromium to copper of 50 : 50 obtained by simple mixing in a porcelain mortar for 20 minutes and MA for 10 minutes. Three areas of the alloy structure formation can be distinguished depending on the heating temperature. At heating temperatures below the eutectic melting point, composite particles are sintered at certain points. At heating temperatures above the liquidus temperature, the alloy melts with its phases separated; one part of the sample consists of copper enriched in chromium, and the other part consists of chromium enriched in copper. At intermediate heating temperatures, liquid phase sintering occurs accompanied by phase separation. Copper-enriched chromium particles become spherical and are located in a chromium-enriched copper matrix. Comparison of samples sintered under the same conditions from powder mixtures obtained by different methods showed that a more uniform and fine-grained structure is obtained in samples with deposited

The paper presents a theoretical analysis of the single action pressing of powder materials featuring plasticity and compressibility. It takes into account dry external friction between the die material and side walls, which determines the strong nonlinearity of the problem considered. This problem has a number of features that complicate its numerical solution: the presence of external friction, the elastic-plastic law of material behavior description, as well as the calculation of large displacements and, as a consequence, strong geometric nonlinearity. To consider these features, a combination of Fleck–Kuhn–McMeeking and Gurson– Tvergaard–Needleman models was used to consider a wide range of changes in the porosity of materials. The numerical solution of the problem was carried out using finite element analysis with isoparametric elements. The increment of plastic deformations at each step was determined from nonlinear equations of plastic flow. Stresses at the Gaussian points were updated according to the specified increments of deformations to calculate the material behavior during deformation. Unknown density and strain values as functions of coordinate and time were calculated. The influence of the different height-to-diameter ratio of the blank and the value of external friction of the material stress-strain state and compaction kinetics were considered. The distribution of equivalent stresses and the value of volumetric plastic deformations in the material, as well as the nonuniformity of relative density at the end of the pressing period were studied. The theoretical analysis made it possible to study the basic compaction kinetics laws for powder materials with nonuniform density under conditions of dry friction on side walls. The results obtained are relevant for predicting possible negative changes in the blank geometry when implementing the single action pressing scheme for powder materials.

Experimental studies were carried out with theoretical calculations of wave synthesis in the Ni–Al–Cu system were performed using the mathematical model developed. Approximate analytical formulas were obtained for synthesis performance evaluation. The inverse problem method was used to get kinetic constants that determine process dynamics based on the experimental data and analytical relationships. It is shown that the combustion front propagation velocity increases monotonically with an increase in the reaction sample relative density in the range of relative density values of 0.4 to 0.6. The depth of copper melt penetration from the center of the sample into the nickel-aluminum matrix depends on the relative density of the sample and copper wire diameter: higher densities and larger diameters lead to an increase in the liquid-phase impregnation area. The rate of nickel and aluminum powder frame wetting with copper melt is limited by the synthesis wave speed. Based on the experimental data and analytical ratios, we estimated the effective kinetic constants describing the high-temperature synthesis of the Ni + Al reaction mixture in the presence of copper additives. The thermal effect of the NiAl intermetallic formation reaction and the preexponential factor in the chemical transformation equation are calculated, the exponent value in the ratio for the mixture thermal conductivity is established; a constant determining the process of nickel-aluminum matrix impregnation with copper melt is found. The macroscopic approach used to analyze the NiAl intermetallic synthesis makes it possible to determine all the desired physicochemical characteristics and model parameters. The mathematical model is suitable for predictive estimates and experimental data analysis in the macroscopic approximation. Approximate analytical formulas are obtained for calculating the NiAl intermetallic synthesis characteristics. They allow for calculating the through channel characteristics and can be used in the design of NiAl products.

The paper studies the influence of mixing modes for titanium and boron powder mixtures with the 81.5 % Ti + 18.5 % B composition in a ball mill on the process characteristics of mixtures, combustion parameters, and microstructure of SHS composites. It is shown that the dependence of the electrical resistivity on the density of charge compacts for the composition under study can be used as a criterion for mixing quality, mixture uniformity. It is noted that an increase in the grinding media mass includes the mechanism of mechanical activation (MA) of mixtures. Dependences of the burning speed and temperature on density were obtained for all the mixtures under study. Burning speeds for mixtures subjected to mechanical activation (М_ch/М_ball = 1 : 7; 1 : 12) and without it (М_ch/М_ball = 1 : 4) differ significantly. Mechanically activated mixtures feature by differences in burning speeds depending on the charge compact thickness. Thin compacts burn at a higher speed. The burning speed of mixtures without MA (in case of smaller grinding media masses) does not depend on the compact thickness. Maximum burning temperatures of all the mixtures studied have insignificant differences depending on the density, mixing time and grinding media mass. There was also no any effect of the compact thickness on the burning temperature observed. The structure of SHS composites depends on mixing modes. The finely dispersed structure of composites with titanium diboride grains (less than 1 μm) and a titanium-based binder phase can be obtained only from MA mixtures. Alloys with a structure consisting mainly of elongated titanium monoboride grains (up to 40 μm) and a binder phase of a solid solution of boron in titanium were synthesized of the mixtures for which mechanical activation processes are not essential.

Hard alloys are popular materials widely used in the toolmaking industry. Refractory carbides included in their composition make carbide tools very hard (80 to 92 HRA) and heat-resistant (800 to 1000 °С) so as they can be used at cutting speeds several times higher than those used for high-speed steels. However, hard alloys differ from the latter by lower strength (1000 to 1500 MPa) and the absence of impact strength, and this constitutes an urgent problem. We studied the influence of thermal cycling modes on the mechanical and tribological properties of VK8 (WC–8Co) hard alloy used in the manufacture of cutters and cutting inserts for metal working on metal-cutting machines. As the object of study, we selected 5×5×35 mm billets made of VK8 (WC–8Co) alloy manufactured by powder metallurgy methods at Dimitrovgrad Tool Plant. The following criteria were selected for heat treatment mode evaluation: Vickers hardness, flexural strength, and mass wear resistance (as compared to the wear of asreceived samples that were not heat treated). Plates in the initial state and after heat treatment were subjected to abrasion tests. Wear results were evaluated by the change in the mass of plates. Regularities of the influence of various time and temperature conditions of heat treatment on the tribological properties of products made of VK group tungsten hard alloys were determined. An increase in the number of thermal cycling cycles improved such mechanical properties of the VK8 hard alloy as strength and hardness. When repeating the cycles five times, an increase in abrasive wear resistance was obtained compared to the initial nonheat-treated sample. The elemental composition of the VK8 hard alloy changed insignificantly after thermal cycling, only a slight increase in oxygen was observed on the surface of plates. The grain size after thermal cycling increased in comparison with the initial VK8 hard alloy. It was found that VK8 hard alloy thermocyclic treatment leads to a change in the phase composition. X-ray phase analysis showed the presence of a large amount of α-Co with an hcp-type lattice on the surface of a hard alloy and a solid solution of WC in α-Co. A change in the cobalt modification ratio causes a decrease in microstresses. An analysis of the carbide phase structure state showed that the size of crystallites and microstresses changed after thermal cycling. The lattice constant of the cobalt cubic solid solution decreased, which may indicate a decrease in the amount of tungsten carbide and carbon dissolved in it. Statistical processing of experimental results included the calculation of the average value of the mechanical property, its dispersion and standard deviation in the selected confidence interval.

Alumo-matrix dispersion-hardened composite materials are widely used in engineering due to the combination of high strength and low density, allowing the production of lightweight endurable structural elements for various purposes. They are used for manufacturing abrasive, triboengineering products, parts of the internal combustion engine cylinder-piston group, airframe and other special products. The paper is aimed to study the fracture mechanism of a layered dispersion-hardened Al–Al₂O₃–Al₄C₃ composite on static loading and impact. Specimens were obtained by liquid phase sintering of PAP-2 powder blanks in a vacuum. The liquid phase was formed due to Al–Al₄C₃ eutectic melt. The layered structure appeared due to the liquid-phase splicing of PAP-2 scaly particles along the contacting planes. Dispersion hardening of aluminum matrix was achieved due to nanosized lamellar alumocarbide crystals precipitated from the eutectic melt on cooling. The synthesis of alumina crystals – δ-Al₂O₃ – occurred due to the interaction of aluminum with residual oxygen molecules of the air on sintering at the furnace rarefaction of 10^–5 mm Hg. The stable destruction of samples by the «shear stratification» mechanism was found to occur under static loading accompanied by the formation of cavities due to tearing of layered blocks under the action of shear stresses (σ_b = 430÷500 MPa, K_1s = 14.0÷ ÷15.5 MPa·m^1/2) At shock loading, a significant amount of material is involved in the fracture accompanied by the formation of cleavage steps between layered blocks and extended regions of ductile fracture dimples. Thanks to this mechanism, a high KCU (1.1·10⁵ J/m²) is achieved comparable with that of the VT-5L titanium alloy. The developed composite can be used for manufacturing lightweight structural elements operated under dynamic loading.

This paper is intended to continue the studies of magnesium effects on the structural phase composition, physical and mechanical properties of the nanostructured strain-hardened aluminum-magnesium alloys modified with C₆₀ fullerene [1]. Previously obtained mechanically alloyed composite powders [1] were consolidated by direct hot extrusion method. Consolidation parameters were chosen based on previous studies of the structure and phase composition formation during mechanical alloying and heat treatment. It was found that an increase in magnesium concentration improves mechanical properties of extruded nanosructured composite materials, and additives modified by C₆₀ fullerene stabilize the grain structure and slow down decomposition of α solid solution of magnesium in aluminum to 300 °C. Under similar thermobaric treatment Al₈₂Mg₁₈ (AMg₁₈) not modified with C₆₀ demonstrates a reduced α solid solution lattice constant and an increased average crystallite size. These processes are accompanied by sequential formation of γ, β′, and β phases, while γ and β′ are intermediate phases. The grain structure of extruded samples is typical for materials obtained in this way – grains are closely packed, elongated and oriented along the extrusion axis. The grain structure of extruded samples inherits the morphology of mechanically alloyed powders. Thus, mechanical alloying methods followed by intense plastic deformation (extrusion) improved mechanical properties significantly. Materials with ultimate tensile strength of 880 MPa; ultimate bending strength of 1100 MPa; microhardness up to 3300 MPa; and with the same density of 2.4–2.6 g/cm³ were obtained. This result demonstrates the prospects for using powder metallurgy techniques in the production of new nanostructured composite materials modified by C₆₀ fullerene with improved physical and mechanical properties.