Showing papers in "Russian Journal of Non-ferrous Metals in 2019"

Influence of a Magnetic Field on Structure Formation during the Crystallization and Physicomechanical Properties of Aluminum Alloys

Abstract: The results of studying the structure and mechanical properties of A356.0 and A413.1 cast aluminum alloy subjected to a pulsed magnetic field of different strength during crystallization are presented. It is established during the experiments that the samples contain two phases each in their compositions which crystallize in definite temperature ranges and remain invariable even with the imposition of the magnetic field of the crystallizing melt. The temperature gradient between the crystallizer wall and outer crucible wall for both alloys, which varies from 14.3 to 16.0°C/mm, and the crystallization time of each phase are determined. The linear crystallization rate of both alloys is found using thermal approaches. It is shown that this rate decreases with a decrease in the temperature gradient, and the crystallization time of phases herewith increases. It is revealed that the magnetic field varies the distribution of dendrites in the bulk of A356.0 and A413.1 alloys, as well as their sizes and orientation in the metallographic specimen plane. A finer structure is formed in the alloy α phase with an increase in the magnetic-field induction amplitude. It homogeneously fills the metallographic specimen plane, which is reflected on the alloy mechanical properties. The hardness of alloys under study increases with an increase in the induction amplitude of the pulsed magnetic field for both alloys by 8–10% due to refining the dendritic structure and the more uniform distribution of dendrites of the α solid solution over the bulk of the crystallizing ingot. In addition, the magnetic field affects the ultimate tensile strength and almost does not vary the relative elongation during the uniaxial tension of the samples of A356.0 and A413.1 cast aluminum alloys.

Mechanical and Tribological Behavior of Powder Metallurgy Processed Aluminum–Graphite Composite

Abstract: In this research, the mechanical and tribological behavior of aluminum–graphite (Al–Gr) composite has been investigated in order to determine the optimum composition of reinforcement. The materials were fabricated by a powder metallurgy process and three different weight percentages of Gr were chosen as a reinforcement in pure Al at 3, 5 and 7 wt % to identify its potential for self-lubricating property under dry sliding conditions. The mechanical properties examined included hardness, tensile strength and flexural strength. The wear tests were conducted by using a pin-on-disc tribometer to evaluate the tribological behavior of the composite and to determine the optimum content of graphite for its minimum wear rate. The results show that the mechanical properties decreased with the addition of Gr. However, 3 wt % Gr reinforced composite offers better mechanical properties as compared to that of other compositions. The wear rate and coefficient of friction also decreased with the addition of Gr and reaches its minimum value at 3 wt % Gr. A smooth graphite layer was observed in the worn surface of the 3 wt % Gr reinforced composite demonstrates superiority in terms of wear properties as compared to base material and other composites compositions.

High-Strength Aluminum-Based Composite Materials Reinforced by Microstructures and Nanostructures (Mini Review)

Abstract: 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.

Studies on Beneficiation and Leaching Characteristics of Rare Earth Elements in Indian Red Mud

Abstract: Bauxite residue (red mud) is a process reject composed of undissolved bauxite phases during digestion in the Bayer process. Rare earth elements present in the bauxite residue could be a potential resource for the extraction of REEs (Sc, La, Ce). It is difficult to recover REEs directly from red mud due to its low concentration and the presence of major minerals. Large amounts of iron in leach solution create problems for further recovery processes, as iron and scandium have some common chemical characteristics. It is, therefore, advisable to remove iron from the mud as much as possible through physical beneficiation. In the present study, physical beneficiation using hydrocyclone, characterization and acid leaching has been exploited. The beneficiation process enhanced the REEs from 200 to 240 mg/kg at a yield of 43%, with a subsequent reduction in the iron oxide content from 37.5 to 29.2%. Further, leaching efficiencies of REEs and impurity (Fe) co-extraction were studied before and after physical beneficiation. It is evident from the data obtained that upgrading minimizes iron co-extraction, which improves the leaching efficiency of REEs.

Powder Metallurgy in Belarus and Global Developmental Trends

Abstract: 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.

Fabrication of Silumins Using Silicon Production Waste

Abstract: A survey of occurring methods of silumin production is presented. The possibility of fabricating casting alloys using amorphous microsilica is shown. Various methods of introducing silicon dioxide particles into the aluminum melt are studied and approved, notably, in the form of pelleted “aluminum powder–SiO2” master alloys, by admixing particles into the melt at the liquidus temperature and by introducing SiO2 into the melt jointly with the argon flow. Calculations of the formation enthalpies and variations in the Gibbs energy of the reduction of silicon from its oxide by aluminum are performed. The thermodynamic probability of formation of silumins using amorphous microsilica is shown based on these calculations. The influence of alloying additives and impurities on the process flow of silicon reduction is determined. The possibility of using magnesium as the surfactant additive, making it possible to remove oxygen from the surface of dispersed particles and reduce silicon from its oxide, is revealed. It is determined that the fabrication method of casting silumins by introducing amorphous silica preliminarily heated to 300°C into the aluminum melt (t = 900°C) jointly with the argon flow (with the subsequent intense stirring) jointly with the argon flow (with subsequent intense stirring) possesses the largest efficiency, because it makes it possible to fabricate aluminum–silicon alloys with a Si content higher than 6 wt % and microstructure corresponding to hypoeutectic casting silumins. The industrial implementation of the proposed method will make it possible to increase the efficiency of the occurring production process of silumins due to the economy of resources spent on purchasing commercial crystalline silicon. Moreover, this technology will promote lowering the environmental load to the surrounding medium due to the reduction of volumes and subsequent elimination of sludge fields, which are landfills for storing dust from gas purification systems of silicon production that contain up to 95 wt % amorphous microsilica.

Preparation of Activated Carbon from Cashew Nut Shells for Water Purification

Abstract: The application of the agricultural waste of cashew nut shells (CNSs) from the Ivory Coast is proposed for the production of activated carbon (AC) used in water treatment by the physical activation. Washed and crushed CNSs are carbonized at 800°C. The crushed CNS carbonizate is activated by the physical method in a temperature range from 400 to 700°C. The specific surface (SBET) and porous structure of the AC samples are investigated by low-temperature nitrogen desorption and X-ray structural (X-ray phase) analysis. The results show that an increase in the activation temperature at a fixed time leads to an increase in the material specific surface, the development of a microporous structure, and an increase in the summary volume of mesopores and micropores of AC. The X-ray phase analysis data shows that the degree of graphitization, interplanar spacing, and crystallite sizes vary insignificantly. The possibility of using CNSs to fabricate AC no worse in sorption properties than its analogs currently in use to purify water is proven.

Comparative Study of Coatings formed by Electrospark Alloying Using TiC–NiCr and TiC–NiCr– Eu 2 O 3 Electrodes

Abstract: 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.

Selective Laser Melting of the Intermetallic Titanium Alloy

Abstract: The in situ synthesis of the Ti2AlNb-based intermetallic alloy was studied using selective laser melting of powder materials. The object of research was the Ti–22Al–25Nb (at %) alloy, the main phase of which is the Ti2AlNb intermetallic compound with an ordered orthorhombic lattice (O phase). The Ti–22Al–25Nb alloy has high mechanical properties both at room temperature and at elevated temperatures, as well as a low specific weight, and is considered a promising material for use in the aerospace industry. To perform the experiments, a mechanical mixture of pure powders of titanium, aluminum, and niobium in a ratio necessary to synthesize the Ti–22Al–25Nb alloy was used. Selective laser melting relating to additive technologies is most promising to fabricate parts by the layer-by-layer addition of materials. The use of this technology makes it possible to fabricate complexly shaped parts based on the CAD model data. Compact samples for the investigation are performed by selective laser melting. The microstructure, density, phase composition, and microhardness of these samples are investigated. The influence of the thermal treatment in the form of homogenization at 1250°C for 2.5 h and subsequent aging at 900°C for 24 h on the microstructure, phase composition, and chemical homogeneity of the samples is also investigated. It is shown that the compact material formed by selective laser melting contains unmolten niobium particles. Homogenizing annealing makes it possible to attain the complete dissolution these particles in the material; due to this, the material microstructure consists of B2 phase grains of various sizes and needlelike precipitates of the orthorhombic phase.

Influence of Ultrafine-Grained Structure on the Kinetics and Fatigue Failure Mechanism of VT6 Titanium Alloy

Abstract: The kinetics and mechanism of fatigue failure of the VT6 titanium alloy (composition, wt %: 5.95 V, 5.01 Al, 89.05 Ti) in the initial (hot-rolled) coarse-grained (CG) state and after equal-channel angular pressing (ECAP) in the ultrafine-grained state (UFG) are investigated. ECAP is performed using billets of the mentioned alloy 20 mm in diameter and 100 mm in length preliminarily subjected to homogenizing annealing. Then, quenching in water is performed from 960°C with holding for 1 h, tempering at 675°C for 4 h, and ECAP at 650°C (route Bс, φ = 120°, number of passes n = 6). The fine alloy structure after ECAP is investigated by transmission electron microscopy at an accelerating voltage of 200 kV. To determine alloy hardness, a Time Group TH 300 hardness meter is used. Static tensile tests are performed for round samples 5 mm in diameter using a Tinius Olsen H50KT universal testing machine. The extension velocity is 5 mm/min. Fatigue tests are performed using prismatic samples 10 mm in thickness at 20°C according to the three-point bending test using an Instron 8802 installation. It is shown that, under the same loading conditions, the fatigue life of alloy samples (the number of cycles before failure) in the initial CG state is higher than that of the alloy samples in the UFG state. It is shown that the number of cycles before fatigue-crack nucleation was at a level of 19–23% of the total sample longevity, regardless the alloy state. The straight-linear segment in kinetic diagrams of the alloy fatigue failure is approximated by the Paris equation. It is revealed that the propagation rate of the fatigue crack in the alloy with an UFG structure is somewhat higher than in the alloy with a CG structure. The microrelief of fatigue cleavages of the VT6 alloy both in the CG and UFG state can be characterized as scaly with fatigue grooves on the scale surface. A low-relief region 4–6 μm in length can be observed in the failure region of the samples with an UFG structure. The microrelief of the rupture region is pit, irrespective of the alloy state.

Mechanical Alloying with the Partial Amorphization of the Fe–Cr–Co–Ni–Mn Multicomponent Powder Mixture and Its Spark Plasma Sintering to Produce a Compact High-Entropy Material

Abstract: The results of studying the influence of mechanical alloying (MA) on the surface morphology, microstructure, and atomic–crystalline structure of particles of the Fe–Cr–Co–Ni–Mn multicomponent powder mixture are presented. The initial components are as follows: the R-10 radio-engineering carbonyl iron powder with average particle size d = 3.5 μm, the NPE-1 nickel powder with d = 150 μm, the PK-1u cobalt powder with d < 71 μm, the PKh-1M chromium powder with d < 125 μm, and the MR0 manganese powder with d < 400 μm. The MA of the prepared mixture was performed in an AGO-2 water-cooled mechanical activator using 9-mm steel balls with an acceleration of 90 g in air. The alloying time varies from 5 to 90 min. The ratio of the ball weight to the mixture weight is 20 : 1. X-ray diffraction patterns of the initial and alloyed mixtures, as well as of the sample formed by sintering, are recorded using a DRON 3M diffractometer in FeKα radiation at 2θ = 30–100°. The microstructure of the mixture particles and the compact sample metallographic specimen after sintering are investigated by scanning electron microscopy. It is established that the peaks of initial components are absent in the X-ray diffraction pattern after mechanical activation for 90 min, and peaks corresponding to the phase representing the γ-Fe-based solid solution having a face-centered crystal lattice are presented. Herewith, the fraction of the amorphous phase increases to 20%. A compact single-phase material is formed from the mixture prepared after 90-min alloying by spark plasma sintering at 800°C for 10 min. Its density is 7.49 kg/cm3, resistivity is 0.94–0.96 × 10–6 Ω m, and microhardness is 306–328 kg/mm2. The phase is uniformly distributed over the volume.

La–Ni Based Alloy Modification by Ce and Fe for the Next Hydrogen Storage in Low-Temperature Metal Hydrides

Abstract: La–Ni based alloys have been established as suitable materials for reversible hydrogen storage. Low-temperature metal hydrides (LT MH) facilitate hydrogen storage at ambient temperatures and pressure of 1–1.5 MPa. Nevertheless, further research and modifications of these alloys are needed. In this paper, the parent LaNi5 alloy was modified by partially replacing La with Ce and Ni with Fe. The alloys were prepared in two different ways: conventional melting of pure powder metals, and thermochemical reaction using corresponding metal chlorides. Steps were taken to optimize the time-temperature parameters of alloy synthesis. A comparative analysis of the obtained alloy samples followed. Hydrogen sorption isotherms were obtained for the unmodified LaNi5 and modified (La0.5Ce0.5)Ni5 samples made from pure powder metals. Due to strong oxidation of the alloys prepared from metal chlorides, sorption isotherms for these alloys were not obtained.

Mathematical Model of Magnetic Hydrodynamics and Heat Transfer in an Aluminum Reduction Cell

Abstract: A new nonstationary three-dimensional mathematical model of an aluminum reduction cell which makes it possible to perform coupled thermoelectric and magneto-hydrodynamic calculation while taking into account sideledge formation is presented. The model takes into account the nonlinear dependence of the coefficients of electrical conductivity and thermal conductivity of materials on temperature, as well as, for ferromagnetic materials, the nonlinear dependence of magnetization on the magnetic field strength. The heat-transfer coefficients on the outer surfaces include radiant and convective components of heat transfer and are functions of the ambient temperature and the local surface temperature. In the energy equation, internal sources of heat are taken into account due to the flow of electric current, exothermic reactions, and additional thermal effects associated with the raw material loading and phase transitions. To obtain a numerical solution, the control volume method is applied. Experimental testing of the developed mathematical model is performed on the S8BME aluminum reduction cell. This paper presents the calculated and experimental data of magnetic, electric, thermal, and hydrodynamic fields. A comparison of the calculation results with the results of industrial experiments shows that the model reflects the physical processes taking place in the aluminum reduction cell with accuracy sufficient for engineering calculations. The calculated values of electrical voltage, magnetic induction, and temperature practically coincide with the measured ones. Values obtained from calculating the direction of velocity in the metal pad and the shape of the sideledge profile differ insignificantly from the experimental values. This model can be used to estimate the performance and design parameters of the operation of new and modernized aluminum electrolysis cells. Further studies will be aimed at clarifying the calculated results by improving the mathematical model.

Nickel Effect on the Structure and Properties of Adaptive Wear-Resistant Arc-PVD Ti–Al–Mo–N Coatings

Abstract: Comparative investigations of the structural characteristics and functional properties of Ti–Al–Mo–N and Ti–Al–Mo–Ni–N coatings fabricated by the ion-plasma-vacuum-arc deposition (arc-PVD) method are performed to study the influence of nanostructuring nickel additives. Coatings have a multilayered architecture with alternating layers of titanium and molybdenum nitrides. The molybdenum concentration is about 22 at % and that of nickel is 7 at %, which corresponds to optimal amounts for the best strength and tribological properties. It is shown that, when introducing nickel, the coating modulation period decreases from 60 to 30 nm with a simultaneous increase in hardness from 37 to 45 GPa. Herewith, the fracture toughness of coatings, which was judged from the relative work of plastic deformation and parameter H/E and H3/E2, increases. Ductile nickel added to the structure of the hard nitride coating promotes a decrease in the level of compressing macrostresses in the material from –2.25 to –0.58 GPa, which, however, does not lead to a decrease in hardness and wear resistance, as is shown by scratch tests. It is concluded that the factor determining the physicomechanical characteristics of the coating is the refinement of the grain structure of the material rather than the macrostress level. The introduction of nickel positively affects the heat resistance of the coating, which successfully protects the substrate material against the oxidation at temperatures up to 700°C, which can be conditioned by the probability of the formation of Ni-containing oxides NiMoO4 and NiTiO3 on the surface. Herewith, their appearance, fracture, and effect as abrasive particles can be the reason for the variation in the wear mechanism under friction at high temperatures.

Synthesis of TiC–NiCrBSi Binder Alloy Composite Powders for Cladding and Deposition of Wear-Resistant Coatings

Abstract: TiC–NiCrBSi binder metal matrix composites are fabricated by self-propagating high-temperature synthesis (SHS) in reaction powder mixtures of titanium, carbon (carbon black), and NiCrBSi alloy. It is established that stable combustion in a steady-state mode is possible with the content of a thermally inert metal binder in reaction mixtures up to 50%. Porous SHS cakes are crushed easily for subsequent separation by screening the composite-powder fraction necessary for the coating deposition. The synthesis products are studied by optical and scanning electron microscopy, X-ray diffraction (XRD), and electron probe microanalysis (EPMA). It is found that the average size of carbide inclusions in the composite structure depends on the content of thermally inert alloy powder in reaction mixtures and can be intentionally controlled in a wide range. The microhardness of granules of the composite powder formed by crushing SHS cakes decreases monotonically with an increase in the content of the metal binder softer than titanium carbide. The crystal lattice parameter of titanium carbide determined by XRD turned out considerably smaller than known values for equiatomic titanium carbide. It is established using local EPMA of carbide inclusions in the composite structure that the carbon-to-titanium weight ratio is 0.21 instead of 0.25 for equiatomic titanium carbide. Iron and silicon concentrations in carbide are negligibly low, those of oxygen and nickel are lower than 1%, and that of chromium is 2.5 wt %. It is concluded based on the analysis of the known data on the influence of all listed impurities on the titanium carbide lattice that the deficit of carbon is the main cause of a decrease in the lattice parameter.

Effect of Clay Slime on the Froth Stability and Flotation Performance of Bastnaesite with Different Particle Sizes

Abstract: To investigate the effect of kaolin particles on the flotation performance and froth stability of different particle sizes of bastnaesite, batch flotation tests and froth stability experiments were performed. The results demonstrated that poor froth stability of the coarse particle size bastnaesite led to poor flotation recovery. The medium particle size led to appropriate froth stability and also improved the recovery of bastnaesite. The fine particle size yielded an excessively stable froth, yet did not increase the adherence of bastnaesite particles to the bubbles, but it may have increased the entrainment of kaolin. A longer flotation time may have contributed to improving the recovery of the fine size fraction bastnaesite due to its greater flotation rate. Yet, it had little impact on the recovery of the coarse-grained bastnaesite. In addition, a low proportion (20%) of kaolin improved the recovery and flotation rate of the coarse size fraction bastnaesite. In general, however, the presence of kaolin was detrimental to the flotation performance of bastnaesite. Moreover, the presence of kaolin increased the froth stability of the bastnaesite and resulted in more hydrophilic kaolin particles being entrained into the concentrate products.

Production of Cast Materials Based on the Cr 2 AlC MAX Phase by SHS Metallurgy Using Coupled Chemical Reactions

Abstract: It is known that materials based on MAX phases possess a large potential for use in aerospace, automobile, and industrial spheres because they have a unique combination of features of both metals and ceramics with high mechanical, chemical, thermal, and electrical properties In this work, the experimental results of fabricating cast materials in the Cr–Al–C system with different ratios between the Cr2AlC MAX phase and chromium aluminides and carbides by SHS metallurgy are presented The experiments were performed in an SHS reactor 3 L in volume at an initial inert gas (argon) pressure of 5 MPa The synthesis was performed based on chemically coupled reactions: weakly exothermic (heat acceptor)—Cr2O3/3Al/C and strongly exothermic (heat donor)—3CaO2/2Al The experimental results have good correlation with the preliminary thermodynamic calculations It is shown that, when varying the composition of initial mixtures, it is possible to substantially affect the calculated and experimental synthesis parameters, as well as the phase composition and microstructure of final products Optimal synthesis conditions of the material providing the maximal yield of the Cr2AlC phase in the ingot composition are established The determining factor affecting the Cr2AlC content in the product is the occurrence time of the liquid phase under the synthesis conditions It is shown that the maximal content of the Cr2AlC MAX phase and target product yield are attained at the 30% content of the strongly exothermic additive (3CaO2/2Al) in the initial charge

Arsenic Removal from Cu–As-Containing Filter Cakes by Na2CO3 Leaching

Abstract: In the present study, a process for selective removal of arsenic from Cu–As-containing filter cakes using Na2CO3 leach was examined. When decreasing the weight percentage of arsenic in Cu–As-containing filter cakes, environmental problems can be eliminated while valuable metals will be recycled. The effect of α(Na2CO3) (where α represents excess coefficient), temperature, L/S ratio and leaching time were investigated. the optimal leaching conditions were achieved as follows: α(Na2CO3) = 2.7, L/S ratio 6 : 1 (mL/g), temperature 75°C, leaching time 3 h, where the leaching efficiency were 96.47% for As, 0.41% for Cu with final As and Cu concentrations of 11.72 and 0.02 g/L respectively. Further analysis showed that the Cu content in the leach residue increased to 51.42% with CuS as the major Cu phase. Notably, only 0.92% of As remained in the leach residue. The leaching solution was treated by sodium persulfate oxidation and arsenic precipitation which eliminated As 99%, leaving 0.5 mg/L As in the solution. Therefore, the proposed process is a viable method for the effective separation of Cu and As in Cu–As-containing filter cakes. Broadly, the results of this paper provide a reference for the treatment of arsenic sulfide from nonferrous metallurgy cyclic leaching process.

Effect of High-Power Ion Beams on the Surface Topography and Structure of the Subsurface Layer of Submicrocrystalline Titanium Alloys

Abstract: The influence of high-power beams of carbon ions (the ion energy is 250 keV; the pulse duration is ~100 ns; the current density in the pulse is 150–200 A/cm2; the surface energy density of a single pulse is j ~ 3 J/cm2 under the irradiation of the samples of the VT1-0 titanium alloy and j ~ 1 J/cm2 for the treatment of the samples of the VT6 titanium alloy; and the number of pulses is 1, 5, 10, and 50) on the surface topography and structure-phase state of the subsurface layer of submicrocrystalline titanium alloys VT1-0 and VT6 is studied. The sample surface before irradiation is preliminarily mechanically grinded and polished. It is shown that surface defects are formed on the alloy surface after irradiation. These are craters of various shapes and geometry with diameter from fractions of micrometer to 80–100 μm. Herewith, the grain structure in the subsurface layer becomes more uniform in size and degree of grain equiaxity. A rather homogeneous structure is characteristic of the state of the VT1-0 titanium alloy; the average grain size is ~0.31 μm, while that one the VT6 alloy is ~0.9 μm. The grain growth in the transverse direction to 0.54 μm is observed after one irradiation pulse in the subsurface layer of the VT1-0 alloy (at j ~ 3 J/cm2), while the grain size for the VT6 alloy (j ~ 1 J/cm2) decreases to ~0.54 μm. The average grain size in the subsurface layer after 50 pulses reaches ~2.2 μm for the VT1-0 alloy and ~1.6 μm for the VT6 alloy. It should be noted that a rather homogeneous grain structure with equiaxial grains is formed for both alloys already after the effect of one pulse of the high-power ion beam.

Preparation of Zinc Powders by Acid Electrowinning

Abstract: During the electrowinning of zinc in a mixture electrolyte of zinc sulfate and ammonium sulfate, the effects of current density, Zn2+ mass concentration and electrolytic additives on the morphology and current efficiency of Zn powders were evaluated. Finer Zn powders were obtained at high current density and low Zn2+ mass concentration. However, the current efficiency decreased. Adding a proper amount of sodium dodecyl sulfate generated spherical Zn powders, and adding ethanol produced dendritic ones.

Fabrication, Microstructure and Properties of the Mid-Fraction SiC Particles/6061Al Composites Using an Optimized Powder Metallurgy Technique

Abstract: Commercial F500 SiC powder and 6061Al powder were chosen to fabricate the mid-fraction SiC particles (SiCp)/6061Al composite of 30 vol % (volume fraction) SiC using a pressureless sintering technique. Decantation of the SiC powder and optimization of the sintering temperature were performed to improve the microstructure and properties of the composite. The results show that near full-densification of the 30 vol % SiCp/6061Al composite sintered at 680°C is achieved, and no SiCp/Al interfacial reaction occurs. The composite possess the following set of properties: relative density of 98.2%, bending strength of 425.6 MPa, thermal conductivity (TC) of 159 W/(m K) and coefficient of thermal expansion (CTE) of 12.5 × 10–6/°C (20–100°C). The fracture of the composite occurs via cleavage of the SiC particles and ductile tearing of the Al alloy matrix, indicating a strong SiCp/Al interface bonding.

Research into the Influence of Process Parameters on the Efficiency of Zinc Electrolysis from Alkaline Solutions

Abstract: The effect of the main zinc electrolysis parameters from an alkaline zincate solution on the current efficiency and power consumption is studied in laboratory conditions. The zinc concentration (initial and final), current density, and temperature are chosen as variable parameters. Both model (prepared from standard reagents) and actual electrolytes are used. The latter is prepared by leaching the calcined middling product of zinc-bearing dusts processing of ferrous metallurgy. It is shown that the current efficiency can be rather high (higher than 90%) even at the initial zinc concentration in the alkaline electrolyte of 10 g/dm3. However, low current loads (100–400 A/m2) are required in this case, the use of which is unreasonable for industrial electrolysis with the formation of powdered metal, because the actual current density decreases with the development of a cathode deposit surface even lower than the limiting diffusion current of complex ions. The growth of enlarged dendrites with the formation of short-circuited segments in the interelectrode space is expected in this case, which will decrease the current efficiency of zinc. Large-scale laboratory studies on zinc electrolysis from the actual zincate solution make it possible to determine the most power-efficient (with the highest current efficiency of zinc and lowest power consumption) process parameters; notably, the current density is 1000–2000 A/m2, the electrolyte temperature is 50–80°C, the initial zinc concentration is 20–50 g/dm3, and the residual zinc concentration is no lower than 15 g/dm3. A high current efficiency (85–95%) and applied power consumption (2.28–3.20 kW h/kgZn) will be provided under these conditions. The maximal current efficiency (higher than 90%) for the “depleted” zincate solution with a zinc content of 10 g/dm3 is implemented at current density j = 125 A/m2 close to the diffusion current density (of about 95.7 A/m2). The current efficiency considerably decreases at j > 500 A/m2, which is caused by intense hydrogen evolution. When performing studies for the enlarged electrolysis cell, the formed cathode deposit is evaluated qualitatively (by visible crystal sizes).

Aluminum-Matrix Natural Composite Material Based on the Al–Ca–Ni–La–Fe System

Abstract: The primary crystallization concentration region of the aluminum solid solution (Al) is refined using computational analysis in the Thermo-Calc program, including the construction of liquidus surfaces and polythermal sections of the Al–Ca–Ni–La–Fe system, as well as experimental microstructural analysis using scanning electron microscopy. This region can be considered promising for the formation of new aluminum-matrix natural eutectic-type composite materials containing above 20 vol % of intermetallic particles in the structure. The investigation into the microstructure of a promising composition with the formula, wt %, Al–4Ca–2Ni–1La–0.6Fe revealed that it contains up to 23 vol % of Al4Ca and Al9FeNi intermetallic phases of a eutectic nature according to the calculation. Separate crystals of these phases in the eutectic composition have submicron sizes, notably, a length of 250–400 nm and a thickness of 100–200 nm. It is also established that no formation of the Al4La intermetallic phase predicted by the thermodynamic calculation is observed, while lanthanum itself is completely dissolved in the Al4Ca calcium-containing phase. An analysis of the microstructure and hardness during stepped annealing has shown that codoping of the Al–4Ca–2Ni–1La–0.6Fe alloy by zirconium and scandium (0.2% Zr and 0.1% Sc) leads to precipitation hardening due to the decomposition of the (Al) solid solution and further formation of coherent nanoparticles of the L12 phase—Al3(Zr, Sc) up to 20 nm in size. The results of studying the mechanical properties under uniaxial tension testing of cylindrical castings of the Al–4Ca–2Ni–1La–0.6Fe–0.2Zr–0.1Sc alloy show a relatively high level of strength characteristics (σв of 265 MPa and σ0.2 of 177 MPa) with the conservation of the elongation acceptable for the composite material (~2%). Thus, it is shown based on these results that the Al–Ca–Ni–La–Fe system is promising for the fabrication of new aluminum-matrix natural composite materials.

Prospects of Nanotechnology and Design of Materials Based on Refractory Compounds

Abstract: The prospects for the development of high-temperature ceramic materials science are considered as a matter of discussion. The substantiation of the development of hetero-modulus ceramic composites as the possibility to implement unique physicochemical features of refractory compounds (carbides, nitrides, borides, etc.) under their application conditions at high and ultrahigh temperatures is presented. The prospects for a nanotechnology-based approach to the fabrication of such materials in engineering are shown.

Micromechanical Investigation of the Fatigue Crack Propagation and Damage Development in Al/Al2O3/SiC Hybrid Metal Matrix Composite

Abstract: In this study, the micro-mechanisms involved in fatigue crack propagation are investigated qualitatively in a Al/Al2O3/SiC hybrid metal matrix composite (MMC) and the results are compared with Al2O3 fibre reinforced MMC and monolithic Al alloy. The three-point bending fatigue test was carried out in a rectangular notched specimen and crack propagation was monitored until the fracture of the specimen. The crack profile on the surface of the specimen was analyzed via optical microscope. The fracture surface and the crack-path profile in the fracture surface were analyzed by scanning electron microscopy (SEM) and three dimensional (3D) surface analysis respectively. The hybrid MMC shows higher crack propagation resistance than that of fibre reinforced MMC and Al alloy in the low ∆K region. In the threshold region, the crack in hybrid MMC is directed by the reinforcement–matrix debonding, followed by void nucleation in the Al alloy. Additionally, the crack propagation in the stable-crack-growth region is controlled by reinforcement-matrix interface debonding caused by the cycle-by-cycle crack growth along the interface, as well as by the transgranular fracture of particles and fibres. The presence of large volumes of inclusions and the microstructural inhomogeneity reduces the area of striation in hybrid MMC, leading to unstable fracture.

Temperature Dependence of Heat Capacity and the Variation in Thermodynamic Function of the AZh 4.5 Alloy Doped with Tin

Abstract: It is known that technical aluminum with an elevated content of iron, silicon, and other impurities cannot find application in industry because of its low performance characteristics. Therefore, the development of new alloy compositions based on such a metal is very urgent. Eutectic (α-Al + Al3Fe) in the Al–Fe diagram and hypereutectic alloys are promising because, having a minimal crystallization range, they correspond to an iron content of 2–5 wt %. The alloy of the composition Al + 4.5% Fe (AZh4.5) is accepted in this study as a model alloy and is subjected to modification with tin. The temperature dependence of heat capacity of the tin-doped AZh4.5 alloy is determined and the variation in its thermodynamic functions is calculated. Investigations are performed in the cooling mode using a computer and the Sigma Pilot program. The polynomials of the temperature dependence of heat capacity and varying the thermodynamic functions (enthalpy, entropy, and Gibbs energy) of the tin-doped AZh4.5 alloy and reference sample (Cu) are established with correlation coefficient Rcorr = 0.999. It is established that the heat capacity of the initial alloy decreases with an increase in the tin content and increases with an increase in temperature. Enthalpy and entropy of the AZh4.5 alloy increase with an increase in the tin content and temperature, while the Gibbs energy decreases.

Influence of the Concentrate of Rare-Earth Elements on the Stabilization of High-Temperature Phases and Properties of the ZrO 2 –7Y 2 O 3 -Based Ceramics

Abstract: 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.

Production of the 70% Cu–30% Fe Alloy by SHS Metallurgy and Electrometallurgy: Comparative Analysis of Microstructures

Abstract: The influence of different methods of producing alloys of the Fe–Cu system from immiscible components is studied. Alloys with limited solubility (LS) in liquid and solid states are impossible to fabricate by conventional metallurgy. This is why developing low-cost and simple technologies for fabricating such alloys and materials based in them, making it possible to specify the necessary level of physicomechanical properties, is currently a relevant problem. Energy-effective SHS metallurgy is used for the first timchemical scheme of the synthesis ofe in this work to prepare a pseudoalloy with a composition, wt %, of 70Cu–30Fe from oxide materials. This technology offers the use of chemical energy liberated during the interaction of highly exothermic thermite compositions (in a combustion mode), which makes this method one of most energy-efficient for cast material production. The short synthesis time (tens of seconds) and protection of the top ingot surface by the oxide melt (Al2O3) against oxidation make it possible to perform the process in atmospheric conditions. Rods with the same composition have been fabricated by vacuum induction smelting from pure (impurity-free) components Fe and Cu for a comparative analysis of structural components of alloy samples. It is revealed that the high temperatures of the melt of the SHS alloy provide an increased solubility of Cu in Fe. Then structural components are isolated during the crystallization in the form of finely dispersed particles over the entire volume, forming the hierarchical structure characteristic for the SHS alloy only. The 70Cu–30Fe alloys formed in the combustion mode (SHS) have a uniform homogeneous structure with a uniform distribution of all structural components over the sample volume, which can be of great practical interest, in particular, when developing isotropic and anisotropic hard-magnetic materials with high magnetic energy.

Peculiarities of the Microstructure and Properties of Parts Produced by the Direct Laser Deposition of 316L Steel Powder

Abstract: The direct laser deposition of metal powders is one additive method of producing functional materials. It consists of the melting of metallic powders by a laser beam in inert gas. The main process parameters are the laser-beam power, laser-beam speed and scanning trajectory, and powder consumption. Each parameter is selected depending on the alloy type, which in totality affects the structure and defect formation in products. In this study, experimental rectangular samples of 316L austenitic steel are fabricated by the direct laser deposition of the powder. The microstructure and fractures of samples are investigated using scanning electron microscopy in order to determine the structural features and reveal the defects (pores, holes, crystallization cracks, and oxide inclusions). Uniaxial tension tests and hardness tests are performed. The analysis of the influence of the laser beam scanning trajectory on the microstructure and properties of samples during melting is performed. It is found that a dispersed structure with an average crystallite size of 1.3–1.9 μm is formed at a laser power of 250 W and scanning rate of 16 mm/s, which results in a high level of mechanical properties of experimental samples. It is shown that, when using the lengthwise laser-beam trajectory (along the largest sample size), the tensile strength reaches 730 MPa with a relative elongation of 25%, which exceeds the level of mechanical properties of 316L steel by 110 MPa.

Computer Simulation of Mannesmann Piercing of Aluminium Alloy Ingots

Abstract: The piercing of aluminium ingots (made by permanent mold gravity casting) is done in a Mannesmann rolling mill with supporting shoe using plugs of various shapes with a spherical working part: an entire plug, a plug with cavity, and a hollow plug. The calibrating segments of the plugs have identical diameters. The piercing is carried out at an ingot temperature of 400°C. The influence of the plug shape on the variation in the outer hollow shell diameter and wall thickness along the shell length, as well as shell density over the length, is investigated. Hollow shells were cut into 15 equal rings to measure density using hydrostatic weighing. Experimental investigations are simulated with the help of the finite-element method (FEM) computer software. Ingot fabrication by permanent mold gravity casting is simulated using the ProCAST software and piercing—using the QForm software. The variation in the hollow shell diameter, wall thickness, and shell density along the length is also evaluated by computer simulation. Experimental and simulation data are compared to verify the adequacy of acquired models in the QForm. The difference in density does not exceed 2% and, for hollow shell dimensions, 20%. These results make it possible to establish the influence of the piercing plug shape on the accuracy of the shells and their density. It is most preferable to use a hollow plug or a plug with a cavity from the viewpoint of dimension accuracy of fabricated shells. Each of these piercing schematics makes it possible to densify the entire hollow shell volume to the true density, except for the near-edge domains, where the density is lower by 1%.