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 Russian Journal of Non-Ferrous MetalsJournal Prestige (SJR): 0.281 Citation Impact (citeScore): 1Number of Followers: 23      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1934-970X - ISSN (Online) 1067-8212 Published by Springer-Verlag  [2574 journals]
• Investigation into the Carbothermic Method of Digestion of Titanium Raw
Materials by the Example of Artificially Synthesized Perovskite
• Abstract: The advantages of the carbothermic method of digesting the perovskite concentrate when compared with hydrometallurgical methods are noted. Works in which the carbothermic method was used are mentioned. Data on the known processing methods of perovskite, which had not found application in industry, are given. The results of the investigation into digestion of the titanium raw materials by the example of artificially synthesized perovskite CaO · TiO2 are presented. Artificial perovskite is synthesized in a muffle furnace; herewith, the oxide mixture (41.2 wt % CaO and 58.8 wt % TiO2) is preliminarily stirred for 15 min and briquetted into pellets in a steel mold 15 mm in diameter using a hydraulic press with a force of 147 MPa. The synthesis temperature of CaTiO3 is 1300°C with a holding time of 4 h. Experiments with different carbon excesses (20 and 30 wt % of that stoichiometrically necessary to reduce the perovskite components) are performed. The carbothermic digestion process of artificial perovskite (pellets 4 g in weight) is performed in a vacuum furnace with a graphite heater in two stages: at 1500°C, holding time of 10.1 kPa, and a residual pressure of 10.1 kPa in argon at the first stage and at t = 1750°C, τ = 1 h, and a residual pressure in a chamber of 1.3 Pa at the second stage. Reaction products are studied by X-ray phase analysis using a D8 ADVANCE BRUKER AXS diffractometer. The results of experiments show the practical possibility of recovering titanium and calcium from perovskite by the carbothermic method.
PubDate: 2018-11-01

• Study of the Structural Evolution of a Two-Phase Titanium Alloy during
Thermodeformation Treatment
• Abstract: The behavior of the Ti–3.5Fe–4Cu–0.2B two-phase titanium alloy during thermal-deformation treatment under uniaxial compression is investigated. Boron is introduced to form a fine-grained structure in a cast state. Alloy samples 6 mm in diameter are formed by alloying pure components in a vacuum induction furnace and subsequent accelerated crystallization in a massive copper mold. The tests for uniaxial compression with true deformation of 0.9 are performed using a Gleeble 3800 physical simulation system of thermomechanical processes at 750, 800, and 900°C and strain rates of 0.1, 1, and 10 s–1. The alloy microstructure in the initial and deformed states is investigated using scanning electron microscopy. The tests result in a model of the dependence of the flow stress on temperature and strain rate. It is shown that the recrystallization of the initial cast structure containing solid solutions based on α-Ti, β-Ti, and titanium diboride colonies occurs during pressure treatment. The volume fraction of the solid solution grains based on α-titanium decreases during deformation with an increase in temperature, while the fraction of the β phase, on the contrary, increases. Herewith, the average grain size of solid solutions based on α-Ti and β-Ti varies insignificantly after deformation according to almost all studied modes. It is shown that the preferential mode of the pressure heat treatment for attaining the high complex of mechanical properties in the alloy under study is a temperature range of 750–800°C because the grain size of the α phase increases from 2.2 to 4.5 μm with an increase in temperature up to 900°C.
PubDate: 2018-11-01

• Fabrication of the Nb–16Si Alloy Powder for Additive Technologies by
Mechanical Alloying and Spheroidization in Electric-Arc Discharge Thermal
Plasma
• Abstract: The development of new, more refractory heat-resistant materials for gas-turbine engines is one of most important problems of modern materials science. This is associated with the fact that nickel superalloys currently used for this purpose have a lower melting point of ~1400°C, which limits their own maximal working temperature by a range of 1100–1150°C. The Ni alloys can be replaced by natural composites, in which refractory metals are a matrix, while their silicides are intermetallic hardeners. Only three “refractory metal–silicon” binary systems manifest stability to the Me5Si3 silicide, notably, Nb5Si3, Re5Si3, and W5Si3. From the viewpoint of a combination of a high melting point and a low density, the Nb5Si3 compound is optimal among other silicides. The use of alloys of the Nb–Si system in additive manufacturing machines is of considerable interest. This work presents the results of experimental investigations into the treatment of the Nb–16 at % Si powder fabricated using mechanical alloying of elemental Nb and Si powders in the thermal plasma flux. The Nb–16Si alloy powder is fabricated by the mechanical alloying of powders of pure elements in a Fritsch Pulverisette 4 planetary mill. The powder spheroidization is performed in a plasma installation based on a discharge vortex-stabilized electric-arc thermal plasma generator. Based on the results of experimental investigations, the principal possibility to perform the plasma spheroidization of particles of the Nb–16Si alloy prepared by mechanical alloying is shown. It is shown that the surface of spheroidized particles is rough and reflects the cast material structure. Three phase components Nb5Si3, Nb3Si, and Nbss having different optical contrast are revealed in microslices, which is confirmed by X-ray phase analysis.
PubDate: 2018-11-01

• Experimental and Computational Determination of the Heating Temperature of
a Powder Mixture during Explosive Compaction
• Abstract: The results of an experimental determination of the heating temperature of a powder mixture of chromium carbide and titanium binder during explosive loading on a metallic substrate are presented. The compression pressure of a powder mixture in shock waves during explosive compaction is 2.5 GPa. A thermal cycle of a back side of a metallic substrate playing the role of a heat-receiving cell with a coating deposited on it is fixed and the time-independent problem of heat conduction is solved until calculated and experimental thermal cycles coincided. The initial conditions are selected from the assumption that the compacted material is uniformly heated to a certain average temperature upon finishing the shock-wave processes. Thermal properties of the compacted material necessary for calculations are determined by the lased flash method using an LFA 427 installation (Netzsch, Germany). Calculations showed that the heating temperature of a powder mixture was 208 and 225°C when using the adiabatic approximation and allowing for heat emission into the environment, respectively. A comparison of these temperatures with those calculated by an increase in enthalpy during the shock-wave treatment (the density of the monolithic material under standard conditions and final density of the powder material determined after the explosive treatment—199 and 220°C, respectively) shows that they differ insignificantly. Thus, the use of an assumption of the equality of the material density in the shock wave and monolith density does not lead to a substantial error and can be used for practical calculations.
PubDate: 2018-11-01

• Investigation into the X-Radiation Effect on the Structure and
Microhardness of the Tungsten Powder-Filled Composite
PubDate: 2018-11-01

• Regularities of Metallurgical Reactions of Ti 1 – n
$${\text{Me}}_{n}^{{\text{V}}}$$ C 0.5 N 0.5 Carbonitrides with the
Ni–Mo Melt
• Abstract: The influence of alloying TiC0.5N0.5 carbonitride by transition metals of Group V (V, Nb, and Ta) on the contact interaction mechanism with the Ni–25%Mo melt (T = 1450°C, τ = 1 h, rarefaction is 5 × 10–2 Pa) is systematically studied by X-ray spectral microanalysis and scanning electron microscopy for the first time. It is established that the dissolution of single-type Ti1 –n $${\text{Me}}_{n}^{{\text{V}}}$$ C0.5N0.5 carbonitrides (n = 0.05) is an incongruent process (alloying metal and carbon preferentially transfer into the melt), and the relative rate and degree of incongruence of the dissolution process of carbonitrides in a series of alloying metals V–Nb–Ta vary nonmonotonically. An explanation for the discovered effects is proposed. The causal-effect relation between the initial composition of Ti0.95 $${\text{Me}}_{{0.05}}^{{\text{V}}}$$ C0.5N0.5 carbonitride (the grade of the alloying metal) and composition of the Ti1 – n – mMon $${\text{Me}}_{m}^{{\text{V}}}$$ Cx K-phase that is precipitated from the melt upon system cooling is analyzed. It is shown that the factor determining the composition of the forming K-phase is the ΔT factor (the degree of exceeding crystallization temperatures of carbide eutectics Ni/MeVC over the crystallization temperature of the Ni/Mo2C eutectic that is the lowest melting in these systems). The conclusion is argued that the interrelation between the initial carbonitride composition and the composition of the K-phase is a consequence of a microinhomogeneous structure of metallic alloys. It is shown that this interrelation is rather common and manifests itself in all studied systems irrespective of the type of alloying Group V metal and presence or absence of molybdenum in the melt.
PubDate: 2018-11-01

• Prediction of Misruns in ML5 (AZ91) Alloy Casting and Alloy Fluidity Using
Numerical Simulation
• Abstract: Predicting the misrun formation in thin-walled castings of magnesium alloys is a critical task for foundry. The computer simulation of casting processes can be used to solve this problem. Adequate results of simulation can be attained in the presence of the correct thermal properties of the alloy and a mold in a wide temperature range, interface heat-transfer coefficient between the casting and a mold, and the critical solid fraction (at which the melt flow in a mold is stopped). In this work, the interface heat-transfer coefficient between the ML5 (AZ91) magnesium alloy and a no-bake sand mold is found by comparing simulation spiral test lengths with experimental spiral test lengths under the same pouring conditions. Its values above the liquidus temperature are hL = 1500 W/(m2 K) at pouring temperatures of 670 and 740°C and hL = 1800 W/(m2 K) at 810°C. Below the solidus temperature, hS = 600 W/(m2 K). The critical solid fraction for the ML5 (AZ91) magnesium alloy was also determined for no-bake mold casting (with a cooling rate of ~2 K/s)—its value was 0.1–0.15. The critical solid fraction is refined by comparing the position of misruns by the results of simulation and in an actual “Protective cap” ML5 (AZ91) alloy casting poured into the no-bake mold. Castings are poured at temperatures of 630 and 670°C, and the critical solid fraction is 0.1 in both cases.
PubDate: 2018-11-01

• Comparative Study of the Structural-Phase State and Mechanical Properties
of Ni–Cr(X) and Fe–Cr(X) Heat-Resistant Alloys Fabricated by Additive
Technologies
• Abstract: Comparative studies of peculiarities of the formation, thermal stability of the structure, and mechanical properties of heat-resistant alloys based on iron and nickel and fabricated using additive technologies (ATs) by laser metal deposition and selective laser melting are performed. It is established that a cellular structure is formed in alloys fabricated by the laser metal deposition and small pores up to 200 nm in size are present. The structure of alloys fabricated by selective laser melting contains elements with a globular and lamellar morphology and incompletely melted regions, as well as large pores on the order of 5 μm in size. The possibility of manifestation of the nanophase hardening effect due to the presence of nanodimensional particles of chromium silicides is shown. A comparative analysis of mechanical properties of materials under study is performed. It is shown that iron-based alloys possess higher strength and lower ductility when compared with nickel alloys. All studied samples fabricated by selective laser melting have higher strength characteristics when compared with alloys fabricated by laser metal deposition. Short-term annealing at 900–1000°C for 1 h noticeably decreases both strength and plasticity in tensile and compression tests at room and elevated temperatures. Alloys based on iron and nickel fabricated by laser metal deposition and subjected to compression tests at t = 900°C have similar strength characteristics. In contrast with iron-based alloys, additional annealing of the nickel-based AT alloy almost does not decrease its strength characteristics.
PubDate: 2018-11-01

• Conductive TiB 2 –AlN–BN-Based Composite SHS Ceramics
• Abstract: The structure, phase composition, and electrical conductivity of TiB2–AlN–BN-based ceramics fabricated by self-propagating high-temperature synthesis (SHS) are investigated. The temperature dependence of the specific electrical conductivity was measured in range T = 300–1300 K in vacuum of 2 × 10–3 Pa according to the standard four-probe dc-current procedure. It is established that the TiN and BN contents in the synthesis products increase while those of TiB2 and Al decrease with an increase in the TiB2 content in the initial mixture from 60 to 80 wt % and a decrease in the Al concentration from 40 to 20 wt % because of the reaction of TiB2 with nitrogen. A decrease in the Al concentration in the initial mixture leads to a decrease in the AlN content in the synthesis products. The results showed the mismatch of electrical resistance curves ρ(T) during the heating–cooling cycle for all ceramics compositions, which is associated with the variation in the length of the contact zone of conducting phases in range T = 800–1200 K. Three characteristic temperature regions are found: (I) from 300 to 800 K, when ρ monotonically increases with an increase in temperature; herewith, heating and cooling ρ(T) curves coincide completely; (II) the behavior of electrical resistance varies at T = 800–1200 K—its values depend strongly on the heat treatment mode of the sample; and (III) heating–cooling curves coincide completely at T > 1200 K.
PubDate: 2018-11-01

• Contact Interaction Peculiarities at the Boundary of Layers of Structural
Steel–High-Speed Steel Hot-Forged Powder Bimetal
• Abstract: The main problem in the production of bimetals (BMs) is the necessity to ensure adhesive interaction at the contact boundary of the layers, preventing their delamination during the operation. Hot forging of porous preforms (HFPP) offers the possibility of fabricating high-density powder BMs with a minimal amount of pores both in the bulk of the layer material and at the boundary between the layers, which promotes an increase in the adhesion strength. When fabricating hot-forged powder BMs, it is possible to mix materials of charges of a working layer and a substrate, which can lead to uncontrollable interface “spread.” In this work, to fabricate porous BM performs of the structural steel–high-speed steel type, the previously proposed method foreseeing the preliminary prepressing of the powder of the hard-to-deform material is used. In order to determine mechanical properties and perform a structural analysis, bilayer cylindrical samples 20 mm in diameter and 30 mm in length are prepared. The BM base material is steel PK40 and that of the working layer is atomised high-speed steel M2 powder with satisfactory compressibility characteristics. Porous preforms of BM samples are pressed in a specially designed mold using a hydraulic press, enabling one to perform two-side pressing of bilayer powder moldings with the specified distribution of density and strength of layers. Cold-pressed BM preforms were sintered in a protective atmosphere and then subjected to hot repressing using a laboratory drop hammer. Some preforms are examined as sintered. In addition, hot repressing of cold-pressed green preforms is performed. The satisfactory process strength of the working layer material is observed at its porosity of 34% < Pwl < 45%. The powder is not molded at Pwl > 45% and delaminates at Pwl < 34%. It is established that the maximal layer bonding strength and BM thermal-shock resistance is provided by the application of a flowsheet foreseeing the preliminary sintering of cold-pressed preforms and subsequent hot forging. The optimal repressing pressure of the working layer is 145 MPa.
PubDate: 2018-11-01

• Experimental and Kinetic Study of Magnesium Extraction and Leaching from
Laterite Nickel Ore by Roasting with Ammonium Sulfate
• Abstract: Laterite-nickel ore was roasted with ammonium sulfate to extract magnesium by a single-factor experiment, and an orthogonal test was employed to optimize the conditions. The optimum roasting conditions were: calcination temperature, 450°C; calcination time, 120 min; molar ratio of reactants, 2 : 1; granularity <80 µm. The kinetics of the roasting process were also studied. The experimental results showed that the extraction rate of magnesium increased as the calcination temperature increased. The reaction rate of magnesium is in accordance with the shrinking non-reacted nuclear model for the solid product formation reaction. The roasting reaction is controlled by internal diffusion. The apparent activation energy is E = 18.96 kJ mol–1. The kinetic equation is $${\text{1}} + {\text{2}}\left( {{\text{1}} - {\alpha\text{}}} \right) - {\text{3}}{{\left( {{\text{1}} - {\alpha\text{}}} \right)}^{{{{\text{2}} \mathord{\left/ {\vphantom {{\text{2}} {\text{3}}}} \right. \kern-0em} {\text{3}}}}}} = {\text{0}}{\text{.05061exp}}\left[ { - {{{\text{18}}{\text{963}}} \mathord{\left/ {\vphantom {{{\text{18}}{\text{963}}} {\left( {RT} \right)}}} \right. \kern-0em} {\left( {RT} \right)}}} \right]t.$$ A single factor experiment and orthogonal test were carried out to optimize the magnesium leaching process reaction conditions. The optimum conditions of the leaching process were: leaching temperature, 60°C; leaching time, 60 min; liquid to solid ratio, 2.5 : 1; stirring intensity, 400 r min–1. The kinetic equation is 1 – (1 – α)2/3 = 0.3991exp(–8632/RT)t. The apparent activation energy is E = 8.63 kJ mol–1. The reaction rate of the leaching process was controlled by external diffusion.
PubDate: 2018-11-01

• Structure, Mechanical Properties, and Oxidation Resistance of MoSi 2 ,
MoSiB, and MoSiB/SiBC Coatings
• Abstract: Single-layer MoSi2, MoSiB, and multilayer MoSiB/SiBC coatings are fabricated by magnetron sputtering. Coating structures are investigated using X-ray diffraction, a scanning electron microscopy, and glow-discharge optical emission spectroscopy. Mechanical properties of coatings are determined by nanoindentation. The thermal stability of coatings is studied in a temperature range of 600–1200°C and oxidation resistance is studied upon heating to 1500°C. It is established that single-layer MoSiB coatings possess a hardness of 27 GPa, elasticity modulus of 390 GPa, and elastic recovery of 48%. They can also resist oxidation up to 1500°C inclusively, which is caused by the formation of the SiO2-based protective film on their surface. The MoSi2 coatings can have hardness comparable to the hardness of MoSiB coatings, but they are somewhat worse than them in regards to oxidation resistance. Multilayer MoSiB/SiBC coatings have hardness 23–27 GPa and oxidation resistance restricted by 1500°C, but they herewith have higher elastoplastic properties when compared with MoSiB.
PubDate: 2018-11-01

• Study on Pure Mercurous Chloride Leaching with Sodium Thiosulfate
• Abstract: Mercurous chloride (Hg2Cl2), also known as Calomel, is a typical mercury-containing mineral found in nature. In this work, the leaching behaviour of pure mercurous chloride dissolved in pure water and in thiosulfate solution was investigated. The mercurous chloride hardly dissolved in sulfuric acid solution at pH of 3 and pure water at pH of 6.4, with the corresponding maximum Hg extraction percentage at 3.1 and 7.5% respectively. However, the Hg extraction percentage increased to 45.8% in sodium hydroxide solution at pH of 11.2. The mercury extraction percentage reached a high of 62.6% in thiosulfate solution, and the leaching kinetics results show that the activation energy is 6.6 kJ/mol. This study indicates that the thiosulfate solution can efficiently extract mercury from mercurous chloride.
PubDate: 2018-11-01

• Simulation of the Final Stage of the Direct Extrusion Method of Large-Size
Rods at Small Elongations
• Abstract: A simulation of the direct extrusion method of large-size rods with diameters of 188, 214, 252, 283, 326, and 560 mm made of alloy 7075; coefficients of friction of 0 and 0.5; and die cone angles of 80° and 90° from a container with a diameter of 800 mm using a 200-MN press with the help of the DEFORM-2D software package is performed. The distribution of radial velocities of metal flow on a working surface of a pressure pad depending on the contact friction, die cone angle, and elongation ratio at the main and final stages of extrusion is found. The butt-end height at the beginning instant of funnel formation is accepted equal to the distance between the pressure pad plane and input plane of extruded metal into a screw channel of flat or cone dies. The combined effect of the elongation ratio, coefficient of friction, and die cone angle on the butt-end height, extrusion force, intensities of strain rates and stresses, and temperature on the die orifice edge is investigated. Numerical experiments are performed according to the complete factorial plan 23 for variability intervals of parameters: Х1 = 3–9, Х2 = 0–0.5, Х3 = 80°–90°. Friction between the tool and the billet at the final stage of extrusion plays a negative role, noticeably decreasing the radial velocity. This leads to the earlier onset of the formation of the central funnel. Extrusion into a conical die and an increase in the elongation ratio, on the contrary, increase the radial flow velocity and provide the later onset of formation of a central funnel. The main factor that determines the butt-end height is the elongation ratio. A mathematical model is proposed to select the butt-end thickness for concrete extrusion conditions of large-dimensioned rods with small elongation ratios.
PubDate: 2018-11-01

• Conceptual Protection Model for Especially Heat-Proof Materials in
Hypersonic Oxidizing Gas Flows
• Abstract: This article is a continuation of the publication cycle of the authors on the subject matter “Multifunctional Protective Coatings for Especially Heat-Loaded Constructional Elements of Hypersonic Systems.” A conceptual physicochemical operation model of the protective coating in a high-speed high-enthalpy oxidizing gas flow taking into account and leveling main surface fracture sources by the gas flow is proposed. The model is successfully implemented when developing a whole series of alloys of the Si–TiSi2–MoSi2–B–Y system intended to form thin-layer coatings from them by any method of the stratified deposition providing the reproduction of the structure, phase composition, and morphological features of the deposited material in the coating. During the deposition, the formation of a microcomposition layer is provided. This layer is a refractory silicide framework with the cells filled by a low-melting (relative to the melting point of framework-forming phases) eutectic structural component. This layer transforms into a multilayer system with a series of functional layers (anticatalytic, reradiative, antierosion, heat-proof, and barrier-compensation layers) of micron and submicron thicknesses during high-temperature interaction with oxygen-containing media (the synergetic effect). The protection ability is provided by the formation of self-restoring oxide vitreous film based on alloyed silica. The self-restoring effect consists of rapid filling of random defects with a viscoplastic eutectic component and protective film formation accelerated when compared with known coatings. The high resistance to the erosion carryover is provided by the presence of a branched dendritic-cellular refractory framework. Coatings MAI D5 and MAI D5U, designed in the scope of the proposed concept, are successfully approved in high-speed high-enthalpy oxygen-containing gas flows affecting the samples and constructional elements made of especially heat-proof material of various classes (niobium alloys, carbon–carbon and carbon–ceramic composite materials, and graphitized carbon materials). The protective ability of coatings of 80–100 μm in thickness in flows with the Mach number of 5–7 and enthalpy of 30–40 MJ/kg is no shorter than 600 s at Tw = 1800°C, 200 s at 1900°C, and 60 s at 2000°C, including the constructive elements with sharp edges.
PubDate: 2018-11-01

• Solvent Extraction of Copper Using TBP, D2EHPA and MIBK
• Abstract: In this research, a synergetic system of solvent extraction process was developed to recover copper from aqueous solutions with tri-n-butyl phosphate (TBP), di-2-ethyl hexyl phosphoric acid (D2EHPA) and methyl iso-butyl ketone (MIBK). The effect of significant parameters such as pH, organic phase composition, aqueous to organic phase ratio (A : O), sodium acetate (CH3COONa) concentration and presence of HCl were studied. The optimum mixing ratio of TBP: MIBK was found to to 7 : 3 for the copper extraction. In addition, the usage of HCl caused a reduction in the extraction percentage due to the instability of the TBP complex with copper in the presence of HCl. The A : O ratio of 1 : 1 resulted in a higher percentage of copper extraction. Finally, MIBK-TBP-D2EHPA-acetate system could extract more than 99% of copper under the optimum condition.
PubDate: 2018-11-01

• Development of the Aluminum Powder Composite Based on the Al–Si–Ni
System and Technology of Billet Fabrication of This Composite
• Abstract: Results of an investigation into the development of the composition and fabrication technology of compact billets of the aluminum powder composite material based on the Al–Si–Ni system for space-rocket hardware are presented. The composite production was performed as follows: initially the powder of the matrix alloy is prepared by gas sputtering, and then a mixture of the matrix alloy powder and alloying dispersed additives is subjected to mechanical alloying in high-energy apparatuses. The method of degassing the mechanically alloyed composition in a thin layer (in order to exclude material ejection from a container when degassing a larger volume of powder) and process regimes of composition compaction are developed using the unique equipment available at OAO Kompozit (Korolev, Moscow oblast)—a vacuum press. Using this technology, cylindrical briquettes up to 100 mm in diameter and up to 120 mm in height are fabricated. Newly developed and patented Kompal-301 composite material has substantial advantages over SAS-1-50 power alloy applied for similar purposes. Its thermal linear expansion coefficient is lower by a factor of 1.5, while the precision limit of elasticity is higher by a factor of 2–3 upon similar strength characteristics. The final structure of a compact briquette is a matrix in which dispersed particles of excess silicon are distributed rather uniformly against the background of the aluminum solid solution. Coarser isolated silicon particles are met in separate regions of the structure. Unfortunately, they are the cause of low plasticity of briquettes, which prevents the formation of semifinished products by plastic deformation; however, such low plasticity does not immediately negatively affect the fabrication of the briquettes themselves.
PubDate: 2018-11-01

• Investigation into the Structure and Properties of Solders Based on
Aluminum and Zinc in the Form of Cast Rods of a Small Cross Section
• Abstract: Solders of the Al–Cu–Si system (A34 brand) and Zn–Al–Cu system (Welco52 brand) are investigated. It is found that the A34 solder (Al–28% Cu–6% Si) melts and crystallizes in a narrow temperature range (~18°C). Solidus and liquidus temperatures of the A34 solder are ~508 and ~526°С, respectively. Solders of the Zn–Al–Cu system (Zn–4% Al–2.5% Cu) have an eutectic composition that provides melting and crystallization at a constant temperature of ~389°С. Densities of studied solders in liquid and solid states are investigated. Their values for the solder of the A34 brand are 3.02 and 3.32 g/cm3, respectively, and, for the zinc solder, 6.28 and 6.69 g/cm3. The influence of casting conditions on the structure of cast alloys in the form of rods with a cross-section area of 13, 10, and 5 mm2 is investigated. The main structural components of solder alloys refine with a decrease in the cross-section area. Dendrites of the aluminum-based solid solution and CuAl2 phase refine in the microstructure of the A34 solder. Dendrite sizes of the zinc-based solid solution most noticeably decrease in the zinc solder. The largest castability is characteristic of alloys fabricated from rod solders with a cross section of 5 mm2 for studied gaps in the sampling of 2.0, 1.5, and 1.0 mm. The zinc solder of the eutectic composition has the best castability when compared with the A34 solder: this characteristic for the melt formed from the zinc-based solder rod with a cross section of 5 mm2 and a gap width in the sampling of 2.0 mm is 100% (the melt of the A34 solder formed from the rod of the same cross section has a castability of 98%). The results of experiments on soldering plates made of the AK12 alloy and sheets made of the AMts alloy show the presence of a tight boundary in the “solder–base material” system, as well as the absence of discontinuities in the form of pores and unsoldered regions. An insignificant interpenetration of solder alloys into the base material is observed, especially when soldering cast plates made of the AK12 alloy.
PubDate: 2018-11-01

• Features of Microstructure Formation in the Ni–Al–W System
during SHS
• Abstract: New-generation superalloys based on Ni intermetallics possess high thermomechanical stability at high temperatures and are widely used in modern industry. The fabrication of such materials by self-propagating high-temperature synthesis (SHS) is advantageous over traditional metallurgical technologies due to the use of the chemical-reaction energy. The development of coatings and pads based on the NiAl intermetallic on the surface of tungsten articles during SHS is of great practical interest. In this work, experiments on the interaction of the W substrate and the Ni–Al-based melt are performed in the SHS mode. When the W substrate connects with the NiAl intermetallic during SHS, the gradient welded joint 200–400 μm in thickness having a complex structure occurs. The Ni and Al melt is formed during the SHS reaction, and surface layers of the W substrate diffuse into it. The crystallization of the dendrites of the tungsten-based phase (84‒86 at % W and 16–14 at % Ni) and dendrites of the pseudobinary NiAl-based eutectic (β phase), in which precipitates of W-containing phase smaller than 50 nm in size and needle Ni3Al inclusions (γ') are present, occurs during cooling in the near-surface layer. The W + Ni + Ni3Al (α + γ + γ') containing the solid solution particles based on Ni3Al intermetallics of about 100 nm in size is revealed in the transient layer. The modification of the W substrate is modified with the formation of globular precipitations of W (α phase) in it, which considerably increases the surface area.
PubDate: 2018-09-01

• Reducing the Metal Content in PCD Polycrystalline Diamond Layer by
Chemical and Electrochemical Etching
• Abstract: This article is devoted to investigating polycrystalline diamond compacts (PDCs), which find broad application in drilling, tool-and-die, and building branches of industry. They are a complex composition of diamond and cermet phases. The diamond phase consists of diamond grains of various granulometric compositions and shapes and forms a strong hard skeleton. A cermet phase serves as a binder. The presence of catalyst metals in a diamond layer of bilayer PDC composite materials lowers their operational properties, because the difference in thermal expansion coefficients between diamond grains and catalyst can lead to material cracking in the cutting process, while a high temperature when fabricating the diamond tool and its operation in the cutting zone can lead to the reverse diamond–graphite phase transition. In order to increase wear-resistance characteristics of diamond PCD composites formed using catalyst metals (cobalt and tungsten), etching of metals from the surface of the tool working zone is performed by two methods, notably, electrochemical and chemical. Electrochemical etching is performed in sulfuric acid with various current modes and concentration, and chemical etching is performed in a mixture of hydrochloric and nitric acids and a mixture of fluoric and nitric acids. The distribution of the chemical composition over the depth of PCD samples after etching is performed using scanning electron microscopy. It is established that electrochemical etching is more active kinetically, while chemical etching is promising for industrial application. Abrasive tests of PCD samples before and after etching show the absence of a noticeable effect of both electrochemical and chemical etching of their abrasive ability.
PubDate: 2018-09-01

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