Tajikistan has a large amount of gold-bearing dumps making up - 18 tons in gold equivalent. These dumps are tails of amalgamation and cyanidation processes obtained in the processing of ores from the largest deposit in Tajikistan - Tarorskoe and a number of adjacent deposits - Jilau, Khirskhon, Olimpiyskoe. In terms of their mineralogical composition, dumps consist primarily of quartz, feldspar, and clay minerals. Average gold content in them is quite high - 2.4 g/t. Therefore, it is feasible to involve them in processing based on the existing Joint Venture «Zarafshon» plant (Penjikent, Tajikistan) processing ores from the Tarorskoe deposit and having underutilized process capacity. These dumps require no ore preparation for processing as the cyanided gold content is 89.7 % at the existing grain size class (-0.074 mm, 58.11 %). This article presents the results of studies on gold extraction from dumps by thiourea leaching. The paper is aimed at searching for ways to reduce the consumption of an expensive component - thiourea. It was found that dump samples contain sorption-active minerals that lead to the loss of gold with tails. In this regard, it is proposed to conduct gold sorption leaching. It was established that thiourea consumption can be reduced by acid pretreatment of raw materials with Na₂SO₄ added to pulp during the thiourea leaching process. A high degree of extraction (-89 %) is achieved when loading 2 kg/t of thiourea, 7 kg/t of ferrous sulfate (III), 12 kg/t Na₂SO₄ and the initial concentration of sulfuric acid of 0.5 % (at the stage of acid pretreatment). Thus, the thiourea consumption is 0.8 kg/t. A dump processing flow chart is presented that includes the following operations: acid pretreatment, thiourea sorption leaching, desorption, reactivation, electrolysis, and melting.

The paper provides the results obtained when studying the initial charge structure effect on the density, gas content and temperature-time parameters of AK6M2 (Al-6%Si-2%Cu) alloy solidification. Coarse crystalline charge billets (C-charge) were obtained when pouring the melt into ceramic molds with sand filling providing a cooling rate υ_охл ~0.5÷1.0 °C/s. Finely crystalline charge billets (F-charge) were prepared by pouring the melt to cold cast iron molds (υ_охл ~ 5÷10 °C/s). Charge billets obtained were separately remelted with the same temperature-time conditions, rerefined and degassed with samples taken to determine hydrogen content as well as density values in liquid and solid states. It is established that structural information inherited from the initial charge billets is stable in the solid-liquid-solid system. It was found using direct thermal analysis that the melt obtained from C-charge solidifies with a reduction in liquidus temperature by 3 °С and in the temperatures of the beginning and end of eutectic solidification by 10 °C and 3 °С, respectively, as compared to the melt obtained from C-charge. At the same time, α-Al and eutectic dendrites form in the C-charge melt 0.4 and 0.6 min faster, respectively. The results obtained at the Paraboloid-4 unit showed that the F-charge melt has higher density as compared to the C-charge alloy due to a smaller number of pulses passing through it in the studied temperature range of 750 — 450 °C. Temperature values of aluminum and eutectic dendrite formation determined by J—t temperature relationships (where J is the number of γ pulses, t is the temperature) correlate with the results of direct thermal analysis. General practical recommendations on the purposeful conservation of positive structural information in aluminum alloys are formulated in terms of the structural heredity phenomenon.

The paper focuses on the finite element method used to simulate the stress-strain state of a small-diameter bar stock during hot-forming in a combination of radial shear rolling (RSR) and rotary forging (RF). Simulation was carried out using the rheological model of the Ti-6Al-4V titanium-based alloy with the QForm VX software. A combination of radial shear rolling of a workpiece with a diameter of 15 mm to 12 mm bar in one pass and subsequent rotary forging in one, two and three passes to obtain bars with diameters 11, 10 and 8 mm is simulated. During the simulation, step-by-step accumulation of plastic deformation was taken into account in the conditions of its nonuniform distribution. The intermediate and finite fields of plastic deformation, strain rate and average stress are obtained. It is shown that plastic deformation distribution after RSR has an expressed gradient with a maximum value (3 or more) at the periphery of the cross-section and a minimum value (about 1) at the center. As a result of RF, even with small reductions, the stress-strain state becomes much more uniform compared with a workpiece of the same diameter after radial shear rolling only. In addition, residual tensile stresses due to compressive stresses during rotary forging are reduced. Direct experimental testing of the combined deformation method was carried out for a promising medical-grade Ti-Zr-Nb shape memory alloy when manufacturing 7-8 mm diameter rods in experimental production conditions. Qualitative confirmation of modeling results is obtained by metallographic analysis. It is shown that the combination of radial shear rolling and rotary forging is promising for creating industrial technologies for the manufacture of small-diameter rods with a highly uniform finely-dispersed structure.

Electron probe microanalysis (EPMA) was used to obtain concentration curves and calculate bulk diffusion coefficients in solid solutions of the copper-tin system in the tin concentration range of less than 13.9 wt.% (7.96 at.%) and temperature range of 500 to 650 °С. Diffusion couples were made of pure copper (99,995 %) and two-component alloy obtained by direct alloying of metallic copper with chemically pure tin in Ar—H atmosphere at 1100 °C in the quartz reactor during 2 hours. Diffusion coefficients were calculated using the Matano-Boltzmann method and the method proposed by Grube, i.e. in the tin concentration range from 6 to 8 at.% (D₁) on the top of the concentration curve, and from 2 at.% to zero (D₂) on the bottom of the concentration curve. It is shown that tin diffusion coefficients in the concentrated solution were several times greater than in the diluted one. It is shown that diffusion activation energy values virtually coincide with isotope measurement data on tin diffusion in pure copper (187 kJ/mol). A qualitative interpretation is proposed for the tin diffusion acceleration effect in the concentrated solid solution of the copper-tin system.

Composite materials (CM) exhibit high hardness, strength and wear resistance with slightly limited processing properties. The most popular reinforcing components for discretely reinforced composites are carbide, nitride or oxide particles. Amorphous metal materials can be used as an alternative reinforcing component since reinforcement with these particles can ensure improved properties due to higher strength of interfacial bonding between the particles and matrix as compared to traditional reinforcements. A metal matrix composite sheet was obtained based on the Al—5%Zn—5%Ca alloy reinforced by particles of Co₄₈Cr₁₅Mo₁₄C₁₅B₆Tm₂ amorphous metallic glasses with the AA5083 cladding layer. The central layer thickness of the Al—5%Zn—5%Ca alloy reinforced by metallic glass particles covered 60 % of the sheet thickness, and the cladding layer covered 40 % in total. Composite material granules were obtained by mechanical alloying with their subsequent consolidation by hot-roll bonding in the cladding shell at the temperature below the amorphous component devitrification temperature. X-ray and differential thermal analysis showed that metallic glasses retain their amorphous structure after processing in the planetary mill and further consolidation during hot rolling. The microstructure at different steps of composite material production was studied by scanning electron microscopy. Mechanical properties were evaluated by uniaxial tension tests at room temperature. The volume fraction of amorphous particles in the as-rolled state was about |0 %, and their size varied between 2 and 187 pm. The hardness of the obtained composite was 25 % higher as compared to the Al—5%Zn—5%Ca matrix alloy. At the same time, yield strength of the cladded composite material was two times higher than that of the matrix and cladding alloy samples.

The study covers the composition and crystal structure of compounds produced by self-propagating high-temperature synthesis (SHS) from the 5Ta—2Ni—3Al (at.%) powder mixture followed by vacuum remelting at 3000 °C. The SHS product contains the following phases: TaNiAl (Laves τ₁-phase), NiAl, Ni₂Al₃, and Ta. Its microstructure features by the presence ofternary phases with the composi­tion Ta₈₅Ni₇Al₈, Ta₅₂Ni₂₀Al₂₈ and Ta₅₃Ni₂₅Al₂₂ according to elemental analysis. The X-ray diffraction pattern of the remelted material revealed reflections that do not belong to any of the known ternary phases in the Ta—Ni—Al system considered. Based on the homological approach, it was found that these reflections belong to three phases with the structural types W₆Fe₇ (R3m), Ti₂Ni (Fd3m) and Ta3Al (P4₂/mnm). It was possible to define them as reflections of three compounds — Ta_6,5Ni_6,5, Ti₂Ni and Ta_2,84Al_0,91 with unit cell parameters different from those for the same compounds with the retained structural type. The increase in the unit cell parameters for all the phases identified was noted as compared to the known binary intermetallics. It may be associated with the presence of Al atoms in the crystal lattice for the Ta_6.5Ni_6.5 phase and Al and Ta atoms in the phase with the structural type Ti₂Ni. X-ray diffraction analysis and crystal-chemical modeling made it possible to identify Ta_6.5Ni_6.5 and Ti₂Ni phases as Ta₆Ni₆Al and Ta₂Ni_0.5Al_0.5, to determine their structural type, composition and unit cell parameters. Full-profile analysis was conducted to specify the structure and composition and determine unit cell parameters of the phases and their quantitative ratio in the material. The material phase composition is 47 wt.% Ta₆Ni₆Al, 16 wt.% Ta₂Ni_0.5Al_0.5 and 37 wt.% Ta₃Al.

This study was conducted to obtain nanostructured mechanically activated composite particles from immiscible metals Cu, Cr and 5÷70 wt.% W, nanostructured bulk materials based on them and Cu / Cu—Cr—W nanostructured gradient material with different tungsten content by combined short-term (up to 150 min) high-energy ball milling (HEBM) and spark plasma sintering (SPS). Cu— Cr—W mechanically activated composites were obtained by HEBM of Cu + Cr + (5÷70 wt.%)W powder mixtures in the Activator-2S ball planetary mill at the rotating speed of 1388 rpm for the grinding chamber and 694 rpm for the planetary disk in an argon atmosphere for 150 min. Cu—Cr—W mechanically activated composite particles were consolidated by SPS in the temperature range of 800— 1000 °C at a pressure of 50 MPa for 10 min. The nanostructured gradient sintered material based on Cu—Cr—W pseudo alloys was pressed layer by layer in the following sequence (from pure copper to pseudo alloy with increasing tungsten content): Cu / Cu—Cr—5%W / Cu—Cr—15%W / Cu—Cr—70%W and sintered at 800 °C for 10 min. The crystal structure, microstructure, and properties of Cu— Cr—W mechanically activated composites and consolidated materials based on them were studied depending on production conditions. It was shown that the nanostructure formed in mechanically activated composites at the short-term HEBM stage (up to 150 min) was preserved for all Cu—Cr—W (5÷70 wt.% W) compounds after SPS. Based on SEM and EDX, refractory particles of W (d ~ 20÷100 nm) and Cr (d ~ 20÷50 nm) were uniformly distributed in the material volume (in the copper matrix). The hardness of Cu—Cr—W (15 wt.% W) bulk samples obtained from nanostructured powder mixtures (after 150 min HEBM) by SPS at 800 °C was approximately 6 times higher than the hardness of samples sintered from the mixture of starting components (without HEBM). For the Cu—Cr—70%W nanostructured compound (t_sps = 1000 °С) the hardness value was ~3 times higher than that for microcrystalline analogues. The highest re­lative density of 0.91 was achieved for Cu—Cr—15%W and Cu—Cr—70%W samples. Electrical resistivity for nanostructured Cu—Cr—W composites were 2 times higher than for microcrystalline samples. Apparently, this is due to an increase in grain boundaries and various defects accumulated in the material at the HEBM stage. The obtained results show that combined short-term HEBM and subsequent SPS is a promising way to produce nanocrystalline Cu—Cr—W composites and gradient materials based on them.

The paper considers formation conditions for stable and metastable aluminides Al_n(Zr_1-xNb_x) obtained in the crystallization of superheated Al—Zr—Nb melts. At the close zirconium content in the alloys of 0.23—0.25 at.%, the niobium content varied from 0.05 to 0.21 at.%. Alloys were prepared in a resistance furnace at 1230 °C in an argon atmosphere in graphite crucibles. Alloys were cast into a bronze mold where the cooling rate was estimated at 200 °C per second. The structural features, distribution pattern, morphology, the composition of the matrix, dendritic cells and aluminides, as well as the structural type of intermetallics in the investigated alloys were studied using scanning electron and optical microscopy, X-ray phase analysis, X-ray diffraction analysis, electron microprobe analysis including inductively coupled plasma atomic emission spectroscopy. It was shown that the growth forms of stable aluminides (D0₂₃ structural type) change from the faceted to dendritic one, and primary metastable aluminides (L1₂ structural type) begin to form during the Al—Zr—Nb melt overheating at 360—365 °C above the liquidus temperature. Only metastable aluminides with both polyhedral and dendritic growth forms are formed in the alloys when overheated by 390 —395 °C and higher. The near-peritectic niobium composition of the Al—Zr—Nb alloy (at the zirconium content more than seven times higher than the peritectic one) are crucial factors in the formation of a large fraction of metastable Al_nZr aluminides having a cubic L1₂ structure. It was shown that, in accordance with isomorphism rules, Nb replaces Zr at equivalent positions of the crystal lattice of aluminides. The intensity of isomorphism of the Al₄(Zr_0.79Nb_0.21) intermetallics formed increases with the increasing melt overheating temperature.

Single- and two-layer coatings were deposited on 5140 steel substrates by electrospark alloying (ESA) and a combination of ESA technology and pulsed cathodic arc evaporation (PCAE) using TiCNiCr and TiCNiCr Dy₂O₃, electrodes obtained by powder metallurgy. The structure, elemental and phase composition of electrodes and coatings were studied using scanning electron microscopy, energy dispersive spectroscopy, and X-ray phase analysis. Tribological properties of coatings were determined as a result of tests according to the «pin-on-disk» scheme in contact with the Al₂O₃ counterbody at loads of 1, 5, and 10 N. The temperature during the tests was 20 °C. The potential and density of corrosion current were determined using a three-electrode cell with a VoltaLab 50 potentiostat. The results showed that electrodes consist of 12 pm TiC grains, a solid solution of Ni in Cr, and Dy₂O₃ up to 5 μm in size in case of a doped electrode. ESA coatings had a low-defect fine-grained structure consisting of regions of a solid solution of Ni and Cr in Fe and TiC grains with a maximum size of 0.3 μm. Coatings with the addition of Dy₂O₃ had a lower friction coefficient at loads of 1, 5, and 10 N. All coatings during the tests in the H₂SO₄ 1N solution were in a stable passive state and featured high corrosion resistance: corrosion current density of the coatings was at least 4 times lower than the values obtained for the 5140 steel substrate.