ISSN (print): 1067-8212, ISSN (online): 1934-970X Editor-in-Chief: Publisher: Pleiades Publishing Indexed in: RUS White List (level 3), Scopus, Web of Science (SCIE)
An Increase in Process Characteristics of Flotation of Low-Grade Fine-Disseminated Scheelite Ores
The results of investigations into increasing the contrast of process properties of calcite and scheelite due to the combined application of water glass with salts such as sulfates of aluminum, zinc, iron, magnesium; mixtures of water glass and calcium chloride; sodium carboxymethyl cellulose (CMC); combinations of sodium oleate with low-polar compounds (neonol and fatty iso-alcohols); and data on the ultrasonic treatment of the liquid phase and oleate are described. The lowest recovery of calcite during the flotation of a monomineral calcite fraction in the Hallimond tube is attained when jointly using salts of iron(II) and water glass (3(4) : 1). The joint application of water glass and CaCl2 during the flotation of the low-grade scheelite ore with a high carbonate modulus using tap water lowers the calcite flotability. When using recycled water, adding calcium chloride to water glass leads to a certain increase in the yield of the rough concentrate (from 13.8 to 14.1%) with a significant decrease in the recovery of WO3 into the final selection concentrate of scheelite (from 72.7 to 53.3%) and worsens the concentrate quality. The replacement of water glass by CMC showed no satisfactory results. The ultrasonic treatment of the pulp, liquid phase, and collector leads to a certain increase in calcite flotation activity, possibly due to an increase in the liquid phase temperature and in the fraction of the ionic form of oleate. The use of neonols in the reagent flotation mode of the scheelite-containing ore with a high carbonate modulus does not confirm a decrease in the flotation activity of calcite formed when studying monomineral calcite fractions, in contrast with fatty iso-alcohols, which make it possible to fabricate the higher quality concentrates in the selection cycle when compared with one oleate.
Kinetic Evaluation of the Possibility of Aluminum and Magnesium Recovery from Aqueous Solutions of Their Salts as an Alternative to the Electrolysis of Melts
Electrolytic production, which is one of the most power-consuming and environmentally dangerous technologies, occupies a special place in nonferrous metallurgy. For example, aluminum production by the electrolysis of cryolite–alumina melts is accompanied by atmospheric emissions of fluorine-containing substances, sulfur-containing substances, and hydrocarbons, while magnesium production is accompanied by emissions of chlorine and organochlorine compounds. As of now, any proposals in the field of production of metals such as aluminum and magnesium directed at improving the environmental situation near metallurgical enterprises should be considered urgent. Despite the fact that the improvement of occurring production technologies of aluminum and magnesium has favorable developmental tendencies and actual possibilities for incorporation at operating enterprises, there are ideas and proposals on the development of new technologies based on scientific achievements in the field of the electrolytic production of light metals. Magnesium and aluminum were used as the objects of investigation. The interaction of metals with aqueous solutions of their salts—chlorides and sulfates such as MgSO4, MgCl2, Al2(SO4)3, and AlCl3—is considered. It is shown that such interactions always proceed in a diffusion region, which opens up possibilities of using various design solutions when selecting the hardware implementation of the process. The reaction order with respect to the solvent, rate constants, and activation energies are found based on the experimental data. The results prove the preference of applying the chloride media that provide the process behavior based on basic electrode reactions and excluding the appearance of side interactions. It is shown that chloride solutions can serve operating electrolytes and be carriers of ions of recovered metal. Herewith, the electrolyte saturation is the guarantee of the impossibility of the reversible process—the secondary dissolution of metal, which lowers the main characteristics of electrolysis of the cryolite–alumina melts.
Formation of Side Ledge and Bottom Ledge in an Aluminum Electrolyzer
The dynamic behavior (formation/dissolution) of the ledge, depending on the electrolyte overheating temperature, thermal resistance of the lining material, and composite of the cryolite–alumina electrolyte, is studied experimentally using a model installation mimicking the actual conditions of the electrolytic aluminum production. A window that enabled the change of the lining material is mounted into the front wall of the installation case. The ledge formation occurs due to a heat flow formed due to the temperature difference of the electrolyte and electrolyzer walls. The electrolyte cryolite ratio (CR) is varied in a range of 2.1–2.5. The alumina concentration in the electrolyte does not exceed 4.5 wt %. The change in the shape of the working space in the electrolyzer during the electrolysis is determined by the ledge thickness. The active ledge formation in the experimental cell starts upon overheating by 3–4 K. It is shown that a thicker ledge is formed at the same overheating temperature with a decrease in the thermal resistance of the lining material from 16 to 14 m2/W, but a decrease in the thermal resistance in the already formed ledge almost does not affect its thickness. Similarly to the industrial electrolyzer, the ledge profile formed in the experimental cell can be conditionally divided into three zones, notably, bottom ledge, ledge at the metal/electrode interface, and side ledge. The dynamic behavior of the side ledge differs from the bottom ledge; notably, the side ledge is thicker at a high electrolyte CR, while the bottom ledge is thinner. The chemical analysis of components in the dry knock out shows that the CR and Al2O3 concentrations increase over the cell height from top to bottom. It is concluded that the side ledge has a heterogeneous composition that depends on the electrolyte composition and cooling rate.
Application of Polarization Measurements for the Calculation of the Current Efficiency
A method for determining the Faraday current efficiency (CeF) based on the ratio of partial winning currents of metal and hydrogen is considered. To calculate the magnitude of CeF based on polarization measurements, it is necessary to know the working current density and potential (Ei), at which metal deposits in the corresponding solution, as well as the kinetic parameters of hydrogen evolution for determining the partial current density of hydrogen (\({{i}_{{{{{\text{H}}}_{{\text{2}}}}}}}\)) at this potential. Using the proposed method, the current efficiency for nickel extraction and deposition of the nickel coating from solutions containing nickel sulfate at a current density of 300 A/m2 is calculated. The kinetic parameters of hydrogen evolution are determined from the polarization curve found for the supporting electrolyte solution containing magnesium sulfate in an amount of 120 g/L and boric acid in an amount of 18 g/L at pH 3.9. The equation for the calculation of the partial current density of hydrogen evolution for any potential by kinetic parameters is derived. The use of kinetic regularities allows us to calculate CeF of nickel in sulfate solutions of different compositions with pH 3.0 and 4.1. The calculated values of CeF coincide with the current efficiency determined by the gravimetric method using a copper coulometer in the limits of the statistical error. It is shown that the division of the commercial characteristic of the “total current efficiency” (CeΣ) into Faraday (CeF) and apparatus (Ceap) characteristics in combination with the method of partial polarization curves makes it possible to find additional information on the degree of perfection of the production process.
Fabrication of Binary Niobium Alloys with Low-Melting Metals by the Deposition of Nanoparticles
Binary alloys of niobium with tin, lead, and cadmium are fabricated by the deposition of nanosized metal particles atomized in low-pressure plasma using the thermal-fluctuation melting effect. This effect implies the residence of a small particle in a quasi-liquid state to a certain critical size which, if is exceeded due to vapor condensation or merging (coalescence) with other quasi-liquid particles, leads to the droplet crystallization. Critical sizes are found at which the particles situated in a quasi-liquid state are able to coalescence and formation the alloy–solid solution. They are 2.1–2.2 nm for Nb, 0.4 nm for Sn, 0.6 nm for Pb, and 3.2 nm for Cd. The occurrence boundary of solid solutions of metals in niobium is determined by the following concentrations, at %: Sn 25.5, Pb 23.0, and Cd 64.5. The solid solution is based on the crystal lattice of matrix metal—niobium, in which lead, cadmium, and tin atoms are arranged. In connection with the fact that the sizes of atoms of incorporated metals differ from these for matrix niobium, the lattice parameters of the matrix (Nb) change and additional stresses appear in it up to the lattice destruction. The parameters of the bcc lattice of solid solutions increase with an increase in concentrations of Pb, Cd, and Sn in connection with their atomic sizes more when compared with niobium. The change in the growth rate of the crystal lattice is caused by the change in the schematic of the arrangement of impurity atoms in the matrix niobium lattice for alloys with lead and cadmium. Based on the critical particle sizes of metals, the magnitudes of the surface tension at the crystal–melt boundary are evaluated. They are as follows, J/m2: 1.17–1.22 for Nb, 1.15 × 10–2 for Sn, 1.48 × 10–2 for Pb, and 0.142 for Cd. The fabrication of alloys of refractory niobium with tin, lead, and cadmium is an example of using the size effect when fabricating new materials.
Sorption of Scandium from Sulfuric–Chloride Solutions by Activated Carbons
Sorption of scandium by activated carbons of VSK, DAS, and PFT brands of different origin (coconut shell, anthracite, and thermosetting-plastic waste, respectively) from sulfuric–chloride solutions (pH 2) simulating the composition of solutions for the underground leaching of complex ores is studied in batch conditions. It is established that the sorption of scandium by carbons of DAS and VSK brands proceeds with the highest distribution coefficients (133 and 45.8 cm3/g, respectively). Herewith, the sorption of scandium by DAS carbon is also characterized by a large volume coefficient (116 \({{{\text{cm}}_{{{\text{sln}}}}^{{\text{3}}}} \mathord{\left/ {\vphantom {{{\text{cm}}_{{{\text{sln}}}}^{{\text{3}}}} {{\text{cm}}_{{{\text{carb}}}}^{{\text{3}}}}}} \right. \kern-0em} {{\text{cm}}_{{{\text{carb}}}}^{{\text{3}}}}}\)). Sorption isotherms of scandium by these carbons are linear and described by the Henry equation with constants 133 ± 21 and 46 ± 7 cm3/g, respectively. The integral kinetic curves of sorption of scandium are found by the method of the limited volume of the solution, and their linearization according to the kinetic models of the pseudo-first and pseudo-second order, the Elovich model, and the Weber–Morris intraparticle diffusion model evidences that the sorption kinetics of scandium by VSK carbon with a higher correlation coefficient (0.999) is described using the pseudo-second-order model. Processing the kinetic data on the sorption of scandium by DAS carbon showed that, when using all models, the correlation coefficient is low (<0.939) and the highest value is observed when applying the intraparticle diffusion model. It is assumed that the sorption of scandium occurs in the mixed diffusion region. The possibility of eluting scandium from VSK and DAS carbons by the sodium carbonate solution (10%) is studied under the batch conditions and the degree of desorption of scandium for two elution steps is 84.0 and 90.4%, respectively.
Investigation into the Surface Layer Composition Formed on the Ml19 (Mg–Nd–Y–Zn–Zr) Magnesium Alloy during Melting under Protective Gas Atmospheres
The most currently widespread method of flux-free melting of magnesium alloys is melting under a protective gas atmosphere consisting of inert carrier gas with a small additive of active gas. The ML19 (Mg–Nd–Y–Zn–Zr) casting magnesium alloy contains yttrium and neodymium; these metals are rather active. The interaction of similar alloys with protective gas atmospheres is studied poorly and represents considerable practical interest. Sulfur hexafluoride (SF6) strongly affects global warming; therefore, the application of this gas is limited. In connection with this fact, HFC-R134a is used as active gas in several countries. The influence of protective gas mixtures consisting carrier gas (argon or nitrogen) and active gas (SF6 or HFC-R134a) on the composition of protective layer formed on the surface of the ML19 magnesium alloy melt is considered in this work. A special laboratory setup providing the contact of the protective gas mixture with metal during heating, melting, and solidification of the samples, which excluded the influence of surrounding atmosphere, was developed. The loss of alloying elements turned out to be insignificant, but the Y and Nd content in the alloy when applying nitrogen as carrier gas turned out to be lower than when using argon. The zirconium content was lower in alloys melted using SF6 as active gas. The composition and thickness of oxide films forming when using protective atmospheres SF6 and HFC-R134a are similar. The surface film consists mainly of magnesium fluoride (MgF2) with impurities of oxides, fluorides, and nitrides of zirconium, yttrium, and magnesium. The main distinction of the phase composition of the protective film when applying the HFC‑R134a is the presence of a considerable amount of carbon both in the form of compounds and in the free state. It is also established that a thorough dosage of HFC-R134a in protective atmospheres is required because an increase in its fraction in the gas mixture above 1 vol % leads to severe corrosion of the inner crucible surface during melting, which was not observed when using SF6.
Comparative Study of Coatings formed by Electrospark Alloying Using TiC–NiCr and TiC–NiCr– Eu2O3 Electrodes
Coatings formed on steel 40Kh by electrospark alloying (ESA) using TiC–NiCr and TiC–NiCr–Eu2O3 electrodes are investigated. The coatings are deposited using an Alier-Metal 303 installation in argon under a normal pressure in the direct and opposite polarity modes. The structure, elemental composition, and phase composition of electrodes and coatings are investigated using X-ray phase analysis, scanning electron microscopy, energy dispersion spectroscopy, glow discharge optical emission spectroscopy, and optical profilometry. Mechanical and tribological properties of coatings are determined by nanoindentation and testing according to the “pin–disc” scheme, including elevated temperature in a range of 20–500°C. The tests for abrasive wear are performed using a Calowear tester, the impact resistance is studied using a CemeCon impact tester, and gas and electrochemical corrosion resistance are studied. The results show that the electrodes contain titanium carbide, the solid solution of nickel in chromium, and europium oxide in the case of a doped sample. Coating also included these phases, but the solid solution is formed based on iron. Coatings with the Eu2O3 additive are not substantially different in regards to structural characteristics, hardness, and friction coefficient, but exceed base coatings by abrasive resistance, cyclic impact resistance, and heat and corrosion resistance. An increase in impact resistance by a factor of 1.2–2.0, a decrease in the corrosion current more than 20-fold, and an almost twofold decrease in the oxidation index are observed upon the passage to doped coatings.
Phase Composition of D16 and V95 Deformable Aluminum Alloys with the Quantitative Assessment of Metal Burning at Various Stages of Development
New methods to monitor metal burning in D16 and V95 aluminum alloys based on using energy-dispersive X-ray spectral analysis (EDS analysis) are shown. It is known that the reduced properties of aluminum-based materials are often associated with the presence of metal burning in the structure. The structural changes caused by metal burning (partial melting of eutectics and excessive low-melting phases with the subsequent crystallization of molten microvolumes) are often accompanied by the development of porosity and negatively affect the physicochemical, mechanical, and manufacturing properties. The ability to reveal metal burning at early stages makes it possible to reject the defective metal. The characteristics sensitive to the early metal-burning stage are proposed based on the EDS analysis. The induced metal-burning degree in a sheet of the D16 alloy is identified. The structural components of the V95 alloy determining the alloy liability to metal burning are established. It is shown that the EDS analysis makes it possible to reveal the variations in the chemical composition of structural elements of the D16 and V95 aluminum alloys, as well as quantitatively identify the metal-burning stage by the oxygen content. The metal-burning development leads not only to an increase in the oxygen content in the chemical composition of aluminum alloys, but also to a decrease in the electrical conductivity of the material. The correlation between the electrical conductivity of the D16 alloy with induced metal burning and oxygen content is considered. The applicability of the EDS analysis is due to the simplicity of the procedure and the possibility of quantitatively evaluating the development of defects in heat-strengthened deformed aluminum alloys after manufacturing heating. It can be used as an additional method for investigation when metallographic analysis gives an ambiguous answer when revealing early metal-burning stages.
Revisiting Some Prospects for the Further Development of Ideas by Academician V.N. Antsiferov in the Field of Structural Powder Materials
Some developments by Academician V.N. Antsiferov and his scientific school are considered from the viewpoint of their further development when fabricating structural powder materials and products. The prospects of work for the fabrication of concentration-inhomogeneous and trip steels are noted. There is great potential in the possibility of controlling the thickness and volume of the zone of the deformation martensite transformation occurring during the fracture. It is advisable to continue works on the fabrication of fullerene-containing and nitrogen-containing powder compositions, as well as on studying the structural heredity of powder steels. The possibility of synthesizing fullerene-containing phases during the liquid-phase sintering of “iron–cast iron” and “iron–graphite” compositions and their subsequent redistribution in the material bulk during dynamic hot pressing deserves attention. It is reasonable to fabricate nitrogen-containing steels by the mechanical activation of powders with subsequent sintering in dissociated ammonia not only when forming wear-resistant and corrosion-resistant steels, but also heat-resistant materials. Works on studying the decomposition of supercooled austenite in powder steels of various alloying systems having different process prehistories (sintered, hot-deformed, infiltrated, etc.) are promising. Works on studying hot deformed concentration-inhomogeneous materials fabricated, in particular, based on powders of the Distaloy type, are promising. Original procedures developed by the school of Academician V.N. Antsiferov are valuable. This is, in particular, the procedure of determining the concentration variation coefficient, as well as the magnitometric complex and mathematical model providing the possibility to forecast the decomposition of supercooled austenite. Works by V.N. Antsiferov can be in-demand when solving the problem of lean alloyed powder steels with a lower bainite structure, which provide the optimal combination of strength and viscosity.
Influence of Gas Atomization Parameters of the KhN60M Alloy on the Powder Characteristics for Laser Surfacing
Powders of the KhN60M alloy (EP367, 06Kh15N60M1) are investigated. An overview of manufacturing methods of products of the KhN60M alloy is presented with the analysis of their advantages and disadvantages. It is shown that, when compared with the casting technology and hot pressing of powders of high-alloyed special steels and alloys, additive technologies enable fabricating complexly shaped products with a high level of physicomechanical properties and material utilization factor. The low casting properties of the alloy under study are the reason for the research into atomization to meet the requirements for size, shape, morphology, and fluidity of powders for additive technologies. The goal of this work is to study the influence of the argon pressure during gas atomization on the physical, chemical, and process properties of powders for laser surfacing formed from the KhN60M alloy. The gas atomization technology of the liquid melt by argon using a VIGA 2B laboratory atomizer was used to fabricate the metallic powder of the KhN60M brand at 1560°C and varying the atomizing gas pressure in a range of 22–25 mbar. To select the atomization parameters, the values of the melt viscosity are calculated using the ProCast system for the computer simulation of casting processes by the finite element method and the temperature dependence of viscosity is constructed. The shape and size of the particles and their granulometric composition are studied using laser sedimentation and electron and optical microscopy. The quantitative metallography data are processed using the VideoTest 4 software. The fluidity of powders is measured. It is established that the fraction of spherical particles increases and fluidity of powders improves with an increase in the atomizing gas pressure; the Feret diameter, average particle size, and d50 values vary insignificantly. An experimental dependence of an increase in the yield of the target fraction powder (40–60 μm) with a decrease in the atomizing gas supply is found. The inversely proportional dependence of the fraction of spherical particles on the desired cut fraction is established. The results of the study make it possible to predict the output parameters of powders when atomizing KhN60M steel. Characteristics of powders of the fraction –80 + 40 μm with a shape factor of 0.99 and fluidity of 14–15 g/s make it possible to use them for manufacturing products using additive technologies.
Fabrication of Metal Powders for Energy-Intensive Combustible Compositions Using Mechanochemical Treatment: 2. Structure and Reactivity of Mechanically Activated Al–Modifier–SiO2 Mixtures
The results of studying the particles of the aluminum–modifier–quartz composites after mechanochemical treatment (MCT) in a planetary centrifugal mill by various physicochemical methods are presented. Graphite (C), polyvinyl alcohol (PVA), and stearic acid (SA) are used as modifiers. To increase the dispersive ability of plastic metallic powders (metal–modifier), MCT was performed in the presence of quartz, the weight fraction of which in the composite varies from 5 to 20%. The largest grinding of aluminum particles is observed with an increase in the graphite content from 5 to 20% and SiO2 content from 5 to 10% in the composition of aluminum–modifier–quartz composites. The particle decreases, while that of crystallites increases with the MCT of the Al–SA–SiO2 system with an increased quartz content in the composite. The maximal imperfection of aluminum after MCT is characteristic of the Al–SA–5%SiO2 samples. An increase in the particle size and, correspondingly, a decrease in the specific surface with rather small crystallite sizes are observed after MCT for the Al–PVA–SiO2 composition. It is shown that the imperfection of the crystalline structure of aluminum particles increases with an increase in the quartz content in the system. The synthesized powder material is a composite formation of aluminum and quartz particles bound by polymer formed based on polyvinyl alcohol in this case. The MCT of the Al–modifier–SiO2 mixtures results in an increase in the powder activity both due to the accumulation and redistribution of defects in aluminum particles and due to the change of the surface structure due to the incorporation of modifying additives into the destructed oxide layer. The conceptual model of transformation of the surface layer and subgrain structure of aluminum particles during MCT is presented.
Influence of Aluminum Additives on the Content and Parameters of the Fine Structure of Titanium Silicon Carbide in SHS Powders
The dependence of the phase composition and parameters of a fine structure of titanium silicon carbide in powders formed by the self-propagating high-temperature synthesis on the aluminum concentration in the 5Ti/2Si/1C reaction mixture is investigated. The aluminum content is varied in a range of 0.1–0.4 mole fraction with the conservation of the total carbon content. It is established that the additives of aluminum not only affect the yield of titanium silicon carbide, but also promote the preferential formation of Ti5Si3 in synthesis products instead of TiSi2 identified in powders containing no aluminum. The introduction of a small amount of aluminum (0.1 mole fraction) leads to the formation of the Ti3Si1 – xAlxC2 solid solution and makes it possible to decrease the content of impurity phases in SHS powders by 6%. The silicon carbide concentration in SHS powders decrease at a higher aluminum content in the reaction mixture, while that of binary compounds (TiC, Ti5Si3, TiAl) correspondingly increases. No noticeable effect from the introduction of aluminum on the parameters of the crystal lattice of titanium silicon carbide in SHS powders is found in concentration limits of 0.1–0.25 mol %. A noticeable increase in parameters of a and c for Ti3Si1 – xAlxC2 (from a = 3.067 Å, c = 17.67 Å to a = 3.07 Å, c = 17.73 Å) with the conservation of the c/a ratio in limits of known values (c/a = 5.78) is observed only with the aluminum concentration of 0.4 mole fraction. The crystallite size of titanium silicon carbide depends, first and foremost, on the combustion parameters. At the same time, the deformation of the crystal lattice of Ti3Si1 – xAlxC2 in SHS powders increases monotonically with an increase in the aluminum content in the reaction mixture in the concentration range under study.
Magnesiothermal Synthesis and Consolidation of the Multicomponent Powder Ceramics in the Zr–Si–Mo–B System
This work is devoted to the fabrication of ZrB2–ZrSi2–MoSi2-based composite powder ceramics by self-propagating high-temperature synthesis (SHS) according to the scheme of magnesium thermal reduction from oxide feedstock and its subsequent hot-pressing (HP) consolidation. The combustion of reaction mixtures has rather high adiabatic temperatures in a range of 2060–2120 K and burning rates in a range of 8.3–9.4 g/s. The end product yield of the magnesiothermal reduction is 34–38%. The resulting powder contains 13–47% ZrB2, 21–70% ZrSi2, 2–32% ZrSi, and 10–18% MoSi2, depending on the composition of the initial reaction mixture; has high structural homogeneity; and consists of composite polyhedral particles with an average size on the order of 8 μm. The structure of ceramics consolidated by HP from the SHS powder is homogeneous and includes needle ZrB2 grains distributed in the ZrSi2 matrix, MoSi2 inclusions of various morphologies, and inclusions of ZrSiO4 silicate distributed over the ZrSi2 grain boundaries. The HP-formed samples have a high degree of homogeneity of the chemical composition and residual porosity of 2.5–7.4%.
High-Strength Aluminum-Based Composite Materials Reinforced by Microstructures and Nanostructures (Mini Review)
This mini review is devoted to analysis of the latest advances in the development of aluminum-based composite materials (CMs) reinforced by microstructures and nanostructures. The fabrication methods of CMs, various reinforcing additives (Al2O3, AlN, SiC, CuO, B4C, Li3N, C, and BN), and their morphological types (nanotubes, nanoplates, microparticles, and nanoparticles), as well as the structure and properties of CMs, are considered. The importance of theoretical modeling methods for studying the strength of interfaces in CMs is shown.
Influence of the Concentrate of Rare-Earth Elements on the Stabilization of High-Temperature Phases and Properties of the ZrO2–7Y2O3-Based Ceramics
Powders based on the ZrO2–7 wt % Y2O3 system, into which oxides of rare-earth elements (REE)—La, Nd, and Pr—were introduced in the form of the concentrate in an amount from 5 to 15 wt %, are prepared by chemical coprecipitation from inorganic precursors. It is established that an increase in the concentrate content leads to a shift in the temperature maxima of thermal effects into the range of high temperatures from 450 to 505°C. The influence of the annealing temperature in a range of 600–1200°C on the phase transformations of the ZrO2–7% Y2O3–REE systems is investigated using Raman spectroscopy. These studies show that the phase composition of powders includes tetragonal zirconium dioxide ZrO2, regardless of the concentrate content. The influence of the sintering temperature on the compaction of synthesized powders and ceramic phase composition and microstructure is investigated. It is revealed that ceramics with the 10% REE concentrate has the largest compaction rate during sintering, while an increase in the concentrate content to 15% leads to the retardation of compaction during sintering. The largest open porosity at all sintering temperatures is inherent to ceramics with 15% REE. It is noted that a decrease in intensity of the peaks of the Raman spectra and their broadening are observed with an increase in the sintering temperature for the samples with 10 and 15% REE concentrate, which is associated with the formation of the tetragonal modification of another type. The results of atomic force microscopy show that the isolation of a new phase having faceting and layered structure occurs in the structure of ceramics containing 15% REE concentrate after sintering at 1350°C.
Investigation into the Influence of the Structure Dispersion and Homogeneity on the Properties of Powder Metastable Austenitic Carbide Steels and Diamond Tools
Diffusion and homogenization in “iron (5 μm–nickel (5 μm or 50 nm)” powder systems of various degrees of dispersion during sintering (900 and 1000°C), as well as spark plasma sintering, are investigated using the Matano–Boltzmann method. Calculated diffusivities in pairs of micron powders sintering without applying pressure (900°C, 6 h) and by the spark plasma method (900°C, 5 min) in these systems are equal to 7 × 10–10 cm2/s. It is shown that the use of nanodispersed nickel powder in diffusion pairs based on finely dispersed iron powder promotes a twofold increase in diffusivity at 900°C in contrast to the pair with the microdispersed nickel powder. Constants in the Ivensen sintering kinetics equation are calculated for the “iron–nickel” powder systems, by which the factors activating sintering of these systems are established. The dependences of the structural phase composition and physicomechanical properties of carbide steels of the Fe(base)–14 wt % Ni–8 wt % TiC system on the sintering temperature in range t = 900–1200°C and structure dispersity and homogeneity are determined. The dependences of the grain size, porosity, hardness, microhardness, fracture toughness, and bending ultimate strength on the sintering temperature are shown. Dependences of tribotechnical properties on the degree of homogeneity of the solid solution and volume of the phase transformation of metastable austenite into deformation martensite during abrasive friction turn out similar for carbide steels and diamond tools based on carbide steel. Optimal values of the variation coefficient of the nickel concentration in austenite and carbide steels of the same chemical composition but with different degrees of dispersity, which provide the maximal volume of the austenite decomposition and high values of the diamond-tool grinding coefficient, turn out equal to 5 in both systems, but the sintering parameters are different. It is shown that the physicomechanical properties of the studied systems depend on the structure porosity and dispersity, while tribotechnical properties depend on the structural homogeneity of steels.
Physicochemical Processes of Fabricating Ceramic Materials Based on Nanopowders of Zirconium, Yttrium, Cerium, and Aluminum Oxides
When studying nanoceramics, it is necessary to constantly keep in mind the closest interrelation of their fabrication method, structure, and properties. Nanoceramic materials are used in various branches of technology as structural and functional materials. Nanoceramics are also widely used in medicine. They are harmless, stable, and have great affinity to living organisms. ZrO2-based nanoceramics have a lower elastic modulus than other oxide materials. The specificity of their application lies in their high rupture strength, thermal shock resistance, and chemical stability at high temperatures. However, it is necessary to solve the problem of increasing the fracture toughness of ZrO2-based ceramic materials. The complex alloying of ZrO2 with yttrium and cerium oxides and the use of the Al2O3 additive leads to an increase in the fracture toughness and lowering of the negative effect of materials in the biological medium. In this work, the physicochemical properties of ceramic powders and materials of the ZrO2–2Y2O3–4CeO2–Al2O3 system synthesized by the chemical deposition of inorganic precursors when applying the sol-gel technology are considered based on scientific data and experimental studies. Alloying pure zirconium oxide by stabilizing Y2O3 and CeO2 oxides and thermal hardening of Al2O3 ensure the conservation of the tetragonal structure at room temperature, which makes it possible to retard and control the crack resistance of the material under the load. Investigations into the influence of the sintering temperature and aluminum oxide content on the microstructure and grain size, as well as physicomechanical properties of ceramic materials of compositions ZrO2–2Y2O3–4CeO2 + 1 wt % Al2O3 and ZrO2–2Y2O3–4CeO2 + 3 wt % Al2O3, are carried out.
Growth Features of Diamond Films on the Tungsten Carbide Surface with a Copper Sublayer
The surface preparation is a prerequisite for ensuring the required properties of a diamond film formed by gas-phase deposition. The influence of the temperature and concentration of the CuSO4 etchant on the structural and phase compositions of the surface of hard-alloy materials is considered in this work, and the structural and phase compositions of a continuous polycrystalline diamond film at its growth stages is also considered. The adhesion of the diamond films to the surface of hard-alloy materials is determined qualitatively. It is established that the treatment of the hard-alloy surface in the CuSO4 solution at t = 23°C leads to the inhomogeneous removal of a cobalt binder with chipping WC grains and the formation of the porous structure in the surface layer of the WC–6% Co alloy. The treatment by the CuSO4 etchant at t = –2°C provides the homogeneous etching of the Co binder over the boundaries of WC grains and the formation of a chemically homogeneous surface. The orientation growth and adhesion of the diamond film depend on the elemental composition of the WC–Co alloy surface after treatment by the CuSO4 solution. If the treatment was performed at tsln = 23°C, then the removal of copper from the defect surface WC layer is complicated during the synthesis, which provides the multidirectional growth of diamond crystals in the film along two directions, 〈111〉 and 〈110〉, which causes critical biaxial compressive stresses (2.5 GPa) and leads to low film adhesion to the hard alloy surface. If the treatment is performed at tsln = –2°C, then the orientational growth of diamond crystals in the film occurs in one preferential crystallographic direction 〈111〉, which lowers the biaxial compressive stresses (1.7 GPa) and increases the adhesive bond of the film to the hard alloy surface. The structure imperfection calculated from the ratio of the lines of integrated intensities I1333/I1580 using the Raman spectroscopy method decreases with an increase in concentration at negative temperatures and increases at positive temperatures of the CuSO4 solution during surface preparation.
Phase Transformations and Properties of Concentration-Inhomogeneous Magnetic Materials Based on the Fe–30% Cr–27% Co System
The phase and structural transformations of a powder hard magnetic alloy of the Fe–30% Cr–27% Co–1% Si–0.07% B system with a metastable α1 + α2 phase composition, elevated cobalt content, and high level of magnetic properties are studied. The density and variation coefficient of the concentration of main elements of sintered billets at a level of deformable analogs are attained by sintering in the α phase with contact melting in the presence of a “vanishing” liquid phase formed due to the addition of silicon and boron ferroalloys. A kinetic approach to the development of a competitive hard magnetic alloy with a high fraction of a strong magnetic phase is proposed. The influence of boron additives on the incubation period of the formation of the undesirable σ phase and the temperature range of the concentration stratification of the α solid solution into the strong magnetic α1 phase and weak magnetic α2 phase are established. Optical microscopy, X-ray phase analysis, and differential scanning calorimetry are used to determine the temperature–temporal parameters of the thermal treatment of the alloy, including quenching, thermomagnetic treatment (TMT), and final aging, which provide the required combination of Hc and Br due to an increase in stability of a metastable α phase up to 20 min in a temperature range of spinodal decomposition α → α1 + α2. The largest increase in magnetic properties after TMT observed at the first and second stages of final aging is associated with the supplementary decomposition of the α solid solution and the formation of subgrain boundaries. Elements of the formed structure have submicron and nanometer sizes that correlate with the results of studying the deformable alloys based on the Fe–Cr–Co system. The anisotropic α1 + α2 structural state attained by thermomagnetic treatment provides an increase in characteristics of magnetic properties of the studied 30Kh27KSRA powder alloy to 30% and squareness ratio of the magnetic hysteresis loop of 0.82.
Structure and Properties of Corrosion-Resistant Steels Fabricated by Selective Laser Melting
The objects of the investigation are the powder of 12Kh18N10T stainless steel of the 20–63 μm powder and experimental samples formed based on it by selective laser melting (SLM). The powder was fabricated by argon atomization at a temperature of 1640°C and pressure of 27 bar. The particle structure is dendritic–cellular, and the cellular structure prevails with a decrease in the particle size (<35 μm), while the dendritic almost disappears. The characteristic particle size is d50 = 37 μm and d100 = 67 μm. The differential distribution is close to the Gaussian form, while asymmetry is associated with the satellite character and the presence of innumerous particles smaller than 20 μm in size. The powder fluidity is 3.27 g/s, while the apparent density is 4.41 g/cm3. The density of the samples of the 12Kh18N10T steel samples grown using a Concept Laser M2 installation under a laser power of 180 W and speed of 700 mm/s is 7.89 g/cm3 on average. Since the density of compact steel is 7.95 g/cm3, the material is rather high-density. The microstructure of the 12Kh18N10T sample is continuous, has no pores and cracks, and comprises the austenite solid solution. The average size of coherent scattering regions in the grain bulk is 19 nm. The arc-shaped interfaces of parallel semicircular tracks are formed due to the crystallization heat removal during the SLM. The elongated crystallites in the tracks are oriented inwards from the arc-shaped interface. The microhardness of the samples in the transverse plane of the metallographic section is higher than the microhardness of the planar plane. Herewith, the microhardness of the samples formed by the SLM method is higher than that of the standard compact alloy. The ultimate strength and relative elongation are 651 MPa and 47%, respectively. An increase in strength is apparently due to refining structural parameters after SLM. The fracture surface of the samples is characteristic of the clearly pronounced viscous type.
Powder Metallurgy in Belarus and Global Developmental Trends
Trends and prospects for the development of industry according to materials of European and world congresses on powder metallurgy and publications in leading specialized foreign editions are analyzed. Trends of the stable development of the production of powder structural parts for the automotive industry in developed countries, including using assembly technology during joint sintering, are noted. The production of articles using MIM methods is constantly growing, and micro MIM technology has become a separate subindustry, making it possible to manufacture products 0.1 g and less in weight. HIP methods have found a second use; it becomes possible to fabricate large-scale billets from corrosion-resistant steels up to 1000 kg in weight, and post-HIPing technology is used increasingly to improve the quality of products fabricated by additive technologies and important castings. Products up to 100 kg in weight are already being fabricated using additive technologies. The author’s opinion on the developmental prospects of powder metallurgy in Europe and around the world is also formulated, and the developmental directions of industry in Belarus and its influence on the development of global powder metallurgy are determined. In particular, new brands of economically alloyed powder steels are being developed. They make it possible to decrease the prime cost of mass structural parts without worsening their technical characteristics. For the same purpose, the processes of sintering combined with quenching are improved and endogas is used for cooling instead of nitrogen, unlike foreign analogs.