A computational and experimental method is proposed to determine the medium model for describing the mechanical properties of powder particles of a high-strength VT-22 titanium alloy obtained by plasma spraying in an inert gas jet. The method is based on the indirect determination of the σs ~ ε strain hardening diagram (yield stress dependence on plastic deformation). A specimen for fullscale tests was prepared as a section of powder particles filled into a special resin. The paper provides the results of Vickers indentation into VT-22 powder particles and the results of computer simulation of this process by the finite element method. The average value of the maximum indentation depth was hmax = 6,56 μm with a maximum loading value of 2 N. The Johnson-Cook elasto-plastic model of a material with nonlinear hardening was used for the volume element considered during the computer simulation. An algorithm for searching coefficients by computational experiment multistage planning was proposed to identify the parameters of the equation sought. Estimated maximum coincidences of experimental and calculated data were chosen as selection criteria, in particular, based on maximum indentation depth. As a result of the study, material model coefficient values that meet search conditions best were chosen from a possible set of such values. According to the algorithm proposed, the result was achieved in 4 calculation cycles. Powder metallographic study was carried out. It was found that particles have a coarse intragranular structure with the dominating b phase formed during plasma spraying. This probably led to a decrease in VT-22 alloy deformation resistance in the powder particles.

The paper presents the results of mechanochemical treatment of aluminum powder particles in a ball mill using various organic modifiers (graphite, stearic acid, polyvinyl alcohol) as a surfactant additive in order to increase powder dispersity and modify the surface layer of initial particles. Scanning force microscopy, X-ray diffraction analysis, IR spectroscopy and EDX methods were used to study the morphology, dispersion, structure, and the average particle size of aluminum powders after mechanochemical treatment, and this study showed significant changes in the surface layer of particles. It is found that mechanochemical treatment of aluminum with organic additives leads to partial recovery of the oxide surface layer with several types of active centers formed capable of chemical reactions using the resulting compositions in various combustible mixtures. The study showed that with an increase in the content of modifiers, i.e. graphite and polyvinyl alcohol, the activity of aluminum rises in the composite with these additives. When the content of stearic acid in the Al composite increases, the activity index decreases. This may be due to the fact that Аl–C17H35COOH mixture milling with a large amount of stearic acid (more than 5 %) forms a dense capsule layer on the surface of aluminum particles that is poorly soluble in alkali. During mechanical action the composition powders under study show both the accumulation and redistribution of defects throughout the particle, an increase in the active aluminum content, generation of active centers, and formation of an encapsulating layer based on organic modifiers on the aluminum surface.

The paper justifies the urgency and efficiency of obtaining bimetallic iron-based materials by two-step isothermal sintering to enable forming the structure of the product bases at the first stage and activating diffusion processes in the wear-resistant layer only at the second stage to eliminate any high-porosity areas and brittle inclusions at interlayer boundaries typical for powder materials doped with carbides, nitrides and borides. The analysis of equation solutions for diffusion in two-component heterogeneous powder systems made it possible to propose an option for determining the time and temperature of homogenizing sintering of bimetallic materials taking into account grain-size distribution of powders, concentration and partial diffusion coefficients of components, charge bulk density, initial and final porosity of the products. Experiments proved that bimetallic materials containing 15– 20 wt.% of chromium carbide, 20–25 wt.% of ferrochromium and iron as the rest component in the wear-resistant layer charge have the best combination of hardness, wear resistance and radial compression strength after sintering in a chamber furnace in protective medium at 1150–1180 °C with a holding time of 1,5–2,0 hours at the first stage, and in an induction furnace at 1350– 1370 °C for 25–35 s with a heating rate of 450–470 °C/s at the second stage. Structure formation peculiarities of the interlayer boundaries and wear-resistant layer during two-step sintering of all-pressed bimetallic materials are shown. It is found that for high-temperature sintering by high-frequency (8 or 16 kHz) heating at the second stage, the depth of chromium diffusion from the wear-resistant layer to the matrix is 120–130 μm, and Cr concentration in various points of interlayer and interparticle boundaries varies between 1 and 30 wt.% thus allowing formation of a transition layer with a structure consisting of a ferritic-austenitic matrix with martensitic colonies and dispersed particles of (Cr,Fe)23C6, (Cr,Fe)7C3 and (Cr,Fe)3C2 ferrochromium carbides uniformly distributed over the volume.

This paper presents the results of studying the mechanical alloying (MA) effect on the surface morphology, microstructure and atomic-crystal structure of multicomponent Fe–Cr–Co–Ni–Mn powder mixture particles. The following materials were used as initial components: radio-engineering carbonyl iron powder (R-10 with an average particle size d = 3,5 μm), nickel powder (NPE-1, d = 150 μm), cobalt powder (PK-1u, d <71 μm), chromium powder (PH-1М, d <125 μm) and manganese powder (MR0, d <400 μm) were used. MA of the prepared mixture was carried out in the AGO-2 water-cooled mechanical activator using 9 mm steel balls with an acceleration of 90 g in air. Alloying time varied between 5 and 90 minutes. The ratio of ball mass to the mass of the mixture was 20 : 1. X-ray patterns of the initial and alloyed mixtures and the sample obtained by sintering were made on the DRON 3M diffractometer on FeKα radiation in the range of angles 2θ = 30°÷100°. The particle microstructure of the mixtures and compact sample section after sintering was studied by scanning electron microscopy. It is found that no peaks of the initial components are present on the X-ray pattern of the mixture after 90 minutes of mechanical activation, but there are peaks corresponding to the γ-Fe-based solid solution phase having a face-centered crystal lattice with an amorphous phase content increased by 20 %. A compact single-phase material was obtained by spark plasma sintering at 800 °С for 10 minutes from the mixture after 90-minute alloying. Material density was 7,49 kg/cm3, specific electrical resistivity was 0,94÷0,96·10–6 ·m, microhardness was 306÷328 kg/mm2, and the phase was distributed uniformly throughout the volume.

TiC + NiCrBSi binder metal matrix composites were obtained by self-propagating high-temperature synthesis (SHS) in the reaction powder mixtures of titanium, carbon (carbon black) and NiCrBSi alloy. It has been found that steady combustion in a stationary mode occurs when the content of the thermally inert metal binder in reactive mixtures does not exceed 50 vol.%. Porous SHS cakes were crashed and resulting granules were separated to fractions by screening to get the composite powder fraction necessary for coating application. Synthesis products were studied by optical and scanning electron microscopy, X-ray diffraction and electron microprobe analysis. It has been found that the average size of carbide inclusions depends on the content of thermally inert alloy powder in the reaction mixtures and can be purposefully regulated in a wide range. The microhardness of composite powder granules obtained by crushing the SHS conglomerates decreases monotonically with an increasing content of the metal binder having hardness less than that of titanium carbide. According to X-ray diffraction data, the titanium carbide lattice parameter turns out to be considerably less than values known for equiatomic titanium carbide. It has been found by electron microprobe analysis of carbide inclusions in the composite structure that the ratio of carbon and titanium mass contents is 0,21 as compared with 0,25 in equiatomic titanium carbide. Iron and silicon contents in the carbide are negligible, oxygen and nickel contents are below 1 wt.%, and chromium content is 2,5 wt.%. The analysis of known data on the effect of all the above-listed dopants on the titanium carbide lattice allows for a conclusion that the carbon deficit is a main reason of the lattice parameter reduction.

Relationships between ignition and product structure formation in W–Teflon (Tf)–Al powder mixtures was explored by thermodynamic and structural analyses. The use of tungsten as one of mixture components was dictated by the need to obtain high-density condensation products. Aluminum was used as a heat-generating agent to reduce ignition temperature and increase mixture combustion temperature. Combustion experiments used compositions with a fixed tungsten-to-Teflon ratio, while aluminum content varied according to the formula: (1 – x)(0,8W + 0,2Tf) + xAl = const. After intermixing in the AGO-2 planetary mill in hexane environment, the powders were compressed into 0,01–0,02 g samples and then heated in a BN crucible in argon environment under atmospheric pressure at a variable crucible heating rate. The sample temperature increased sharply on the thermogram once the ignition temperature was reached. It is shown that as the heating rate increases, the ignition temperature of systems grows, and this may be due to transfer from thermal explosion mode to ignition mode. Low-aluminum mixtures yielded large amounts of gaseous products during ignition and combustion, and this results either in defragmentation of combustion product or in formation of porous cakes. The analysis of products obtained with high-aluminum systems indicated WAl4 as a main product. For higher aluminum content results of thermodynamic calculations strongly differed from experimental ones owing to the lack of thermodynamic data for tungsten aluminides in the Thermo software and to the strong mismatch between the actual reaction conditions and adiabatic equilibrium ones. Calculated and experimental results suggest that the formation of fused high-density products (ρW2C = = 17,2 g/cm3) is possible at an optimal aluminum content ≈10 wt.%. When this value is exceeded, the main product, WAl4, has a much lower density (ρWAl4 = 6,6 g/cm3), which is inadequate for practical implementation.

The paper studies the microstructure, phase composition, and electrical conductivity of TiB2–AlN–BN-based composite ceramics obtained by self-propagating high-temperature synthesis (SHS). Electrical resistivity dependence on temperature was measured in the range Т = 300÷1300 K in a vacuum of 2·10–3 Pa using a standard 4-point DC technique. It is found that higher TiB2 content in the initial composition (from 60 to 80 wt.%) and lower Al content (from 20 to 40 wt.%) results in increased TiN and BN content in synthesis products, and decreased TiB2 and AlN content as a result of TiB2 reaction with nitrogen. Lower Al content in the initial mixture leads to lower AlN content in synthesis products. According to the results obtained, electrical resistivity curves are inconsistent during the «heating–cooling» cycle for all ceramic compositions due to changes in the contact zone of conducting phases in the temperature range Т = 800÷1200 К. Three specific temperature ranges were identified: (I) 300 to 800 K when ρ values increase monotonically with increasing temperature, while heating and cooling ρ(Т) curves coincide completely; (II) Т = 800÷1200 К when electrical resistivity behavior varies – its values strongly depend on the sample heat treatment mode; (III) Т > 1200 К, when coincidence of heating-cooling curves is observed.

The paper studies the liquid phase sintering features of compacts made of Al–10Zn alloy and Grade PO 2 tin powder mixture as well as the effect of sintering modes on the structure and strength of the (Al–10Zn)–40Sn antifriction composite formed. The porosity of original raw compacts ranged from 5 to 18 %. They were sintered in a vacuum furnace at a residual pressure of gases lower than 10–2 MPa. Sintering temperature varied from 550 to 615 °С, where partial aluminum wetting with liquid tin was observed. Sample holding time at a given sintering temperature was 30–180 min. Structural studies have shown that the particle size of aluminum and tin phases increased with an increase in sintering temperature and holding time. Mechanical properties of sintered composites were determined by the compression test. Test samples were cut from the middle area of sintered compacts. The tests have shown that (Al–10Zn)–40Sn composite samples have high ductility. Moreover, these samples exhibit higher strength in comparison with Al–40Sn sintered composite with a pure aluminum matrix due to more intensive strain hardening of the matrix at high deformation levels. It was found that the composites obtained when sintering samples with a low initial porosity and subjected to pre-exposure at low temperature have the highest strength. Based on the reported results it can be concluded that the liquid-phase sintering method within the specified temperature range allows to obtain the (Al–10Zn)–40Sn composites with a continuous aluminum matrix to effectively prevent localized deformation in the soft Sn interlayers. The optimum sintering temperature should not exceed 600 °С.

The paper studies the effect of temperature fields of heating during continuous laser treatment on T15K6 carbide insert performance. A tool with T15K6 indexable carbide inserts was exposed to laser treatment by heating the working surface with continuous laser radiation using the LK 3015ls07 PM industrial laser according to the KV_OSN program along insert contours with the cutting edge distance ~2 mm. Laser exposure time was 2–3 s in nitrogen as a shielding gas. The study used samples in the form of 12,70×12,70×4,76 mm quadrangular plates (GOST 19052-80) with variable radiation power in the range of q = 300±100 W/cm2, and laser radiation moving speed within VL = 20±10 mm/s. Hardness measured in the laser-hardened zone after laser exposure was Hμ = 15500÷21500 N/mm2. The laser impingement point was tested for cutting and abrasive wear with microstructure analysis. Cutting wear along the front and back surfaces of carbide inserts after laser treatment was up to 5 times reduced. It is shown that further laser power density increase to q = 400 W/cm2 provides no positive trend. Diamond abrasive wear with an increased q value indicates wear reduction to 40 wt.%. Microstructural analysis showed a decrease in the tungsten carbide grain size from 5,6 to 4,3 μm in the continuous laser treatment area.