Russian Journal of Non-Ferrous Metals最新文献

This work presents comparative studies of structural and mechanical properties of a new β-Ti alloy Ti–10Mo–8Nb–6Zr exposed to conventional cold rotational forging and equal channel angular pressing (ECAP) at 250°C. The main phase in the initial quenched state after forging and ECAP is the BCC β phase. Broadening of X-ray lines of the β phase and TEM data indicate refinement of structure and increase in concentration of lattice defects after deformational treatment. In the initial state, the alloy has ultimate tensile strength of about 700 MPa, the yield stress of 450 MPa, and relative elongation to failure of ~30%. As a consequence of forging, the ultimate strength and yield stress of Ti–10Mo–8Nb–6Zr alloy increase to 1230 and 950 MPa, and after ECAP, they increase to 1280 and 1270 MPa, respectively; also, the relative elongation decreases to 6%. Significant improvement of strength properties of Ti–10Mo–8Nb–6Zr alloy exposed to ECAP makes it more promising for application in the medical field.

The effect of Na₂O on the viscosity, structure, and crystallization behavior of CaF₂–CaO–Al₂O₃–MgO–TiO₂ slag was studied using the rotating cylinder method, differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray diffraction analyses. The analyses demonstrated that with increasing Na₂O content, the viscosity and melting temperature of the slag decreased; however, the crystallization temperature increased. Na₂O acted as a network modifier to decrease the degree of polymerization in the titanoaluminate structure and consequently increased the mobility of ions in the slag structure. The network structures in the [AlO_nF_{4 – n}]-tetrahedral complexes and [AlO₄]-tetrahedra are depolymerized with the addition of Na₂O; however, the depolymerization had a minimal effect on the Ti–O stretching vibration. During the continuous cooling process of the slag without Na₂O, the crystalline phases of 11CaO·7Al₂O₃·CaF₂ were dominant, followed by CaF₂ and CaTiO₃. In addition to the first three phases, a new precipitated phase of NaAlO₂ was observed in the slag when Na₂O was added, and the sequence of crystallized precipitation during the continuous cooling process was 11CaO·7Al₂O₃·CaF₂, CaF₂, CaTiO₃, and NaAlO₂. The effective activation energy of 11CaO·7Al₂O₃·CaF₂ increased with increase in Na₂O content (0–3.9 wt %) and reached a maximum; however, a further increase in Na₂O content (6.6 wt %) decreased the effective activation energy of 11CaO·7Al₂O₃·CaF₂.

The influence of heating and cooling routes prior to aging of the Ti–22Nb–6Zr shape memory alloy (at %) on the intensity of formation of the isothermal ω_iso phase in the temperature range from 250 to 350°C for 1 and 3 h is studied by X-ray diffraction. It is shown that, for intense formation of the ω_iso phase, the most efficient scheme for entering the aging interval includes rapid water cooling water to room temperature from an annealing temperature of 600°C and subsequent rapid heating to an aging temperature of 300°C. All other routes used for entering in the aging interval, including slow cooling and/or heating, do not lead to the formation of an X-ray identifiable amount of the ω_iso phase, whereas, the β → ω_iso transformation in the temperature range from 250 to 350°C has a pronounced C-shaped kinetics with a maximum at 300°C. Aging in the entire range of 250–350°C leads to the dispersion hardening and an increase in the hardness of the alloy compared to the initial state. Moreover, the hardness gradually increases with an increase in the aging temperature from 250 to 300°C and remains constant in the temperature range of 300–350°C. The β-phase lattice parameter of Ti–22Nb–6Zr alloy remains unchanged over the entire aging temperature range of 250–350°C, which indicates the absence of noticeable diffusional redistribution of elements in the solid solution during the formation of the ω_iso phase. The w_iso phase formed during the aging of the Ti–22Nb–6Zr alloy over the entire temperature range of 250–350°C has the ratio c_ω/a_ω = 0.613 ± 0.002, which is similar to the ratio c_ω/a_ω for the shear-type athermal ω_ath phase, which in turn further emphasizes the identity of these two phase varieties.

In this study, a Mg22Al/10MgO composite could be produced at nearly full density by the field-assisted sintering technique at relatively low temperatures and for short time such as 400°C and 15 min under the vacuum-argon atmosphere. The Mg22Al matrix consists of 22 wt % Al, produced by mechanical alloying for 18h and then mixed 2 h with 10 wt % MgO as a reinforcement material. The microstructure of the sample was analysed using an optical microscope, SEM, EDS and XRD. Mechanical properties such as micro hardness, density and compression strength are also obtained. With a compression strength of 314.4 MPa and a hardness value of 137 HV, the composite obtained nearly theoretical density-TD of 0.99. The crystal distortion was measured and calculated by using XRD results. Furthermore, minor amounts of fine intermetallic compounds and oxides such as Al₃Mg₂, AlMg, γ-Al₁₂Mg₁₇ Al₂O₃ and MgO were detected. The field-assisted sintering technique, which allows rapid and low-temperature sintering, is used in this study to show that the mechanical properties of the mechanically alloyed microstructure are likely to be preserved during sintering. Furthermore, it demonstrates that when Al and Mg are mechanically alloyed, the alloying pair is a very suitable metal matrix material for composites in which a reinforcing phase, such as MgO, forms an insufficient interface.

Simulation model accuracy of quench induced residual stress in wrought magnesium alloy Mg‒Gd–Y–Zr–Ag–Er is tested by applying both isotropic and anisotropic criteria models in residual stress FEM simulation. Both hexagonal close-packed (HCP) lattice structure and asymmetry are considered in the manufacturing process. The distributions of residual stress in isotropic and anisotropic criteria models differ both in distribution and in value, which is due to stress-strain nonuniformity in extrusion direction (ED) and long transverse direction (LTD). Comparing the experimental and predicted errors of the two models, the anisotropic model improves the prediction accuracy by 8.3% in ED and 4.8% in LTD. Residual stress in LTD is always larger than that in ED by the XRD method, and the average deviation between the XRD method and the hole-drilling method is reduced through electropolishing.

Agglomeration of fine particles to produce agglomerates with desired properties (e.g., size distribution, internal pores, and stability) is a critically important precursor to heap leaching. In this work, the effect of the properties of agglomerates prepared by geopolymerization on column bioleaching was investigated. The agglomerates were prepared with different metakaolin addition and alkali activator composition. Reducing the metakaolin addition and increasing the sodium silicate content in the alkali activator was beneficial to increasing agglomerate size. With the increase of agglomerate size, size distribution uniformity also improved. NMR analysis showed that agglomerates prepared with minor metakaolin addition and alkali activator composed of fewer Na₂SiO₃ had more and larger pores. Column bioleaching experiments showed that the agglomerates with more and larger pores had lower permeability and higher copper extraction. For more efficient leaching, the added alkali activator did not need to contain NaOH. This study’s results can guide the agglomeration operation based on geopolymerization to prepare agglomerates that better meet the requirements of heap leaching.

The article presents technical solutions for the creation of deforming devices with a power drive made of a material with a shape memory effect. As an example, the designs of a press, a press stamp, and a hardness tester, in which new designs of multilink power drives are used, are considered. A method of designing a universal multilink power drive is proposed, the power elements of which are made of thermally thin material with a shape memory effect. The analysis of thermal processes in power elements of various shapes and geometric sizes and using different methods of their heating (current transmission heating, convective and radiant heat exchange) is given, which makes it possible to determine the efficiency of the devices being created. The technological and operational properties of thermally thin power elements of a multilink power drive are investigated. To determine their qualitative and quantitative indicators, a measuring stand has been created that allows recording the current strength, temperature change, displacement, and developed forces on a single time scale. On the basis of the calculations performed, a line of universal power drives with a developed deformation force of 500–10 000 N and a displacement of 1.0–8.0 mm was created; the results of their testing and use in existing models of deforming devices are presented.

An effective approach to increasing the fatigue resistance of metal products is to create residual compressive stresses on the surface of the product using surface plastic deformation (SPD) processing SPD. In the present study, with the help of the finite element analysis, one of the effective SPD methods, the process of abrasive-free ultrasonic finishing (AFUF), is studied. Another well-known approach to improving mechanical characteristics, including the fatigue resistance, is the creation of an ultrafine-grained (UFG) structural state in the product. This study is devoted to investigation of the stress–strain state of a UFG workpiece subjected to SPD by the AFUF method using the finite element analysis. Commercially pure Grade 4 titanium in the UFG state obtained by the equal channel angular pressing “conform” method (ECAP-C) is chosen as the workpiece material. In the course of the study, the stress–strain state of the deformation zone after a single impact of an indenter with subsequent unloading is analyzed in the elastoplastic formulation of the problem. The effect of the oscillation amplitude and geometrical characteristics of the indenter on residual radial stresses, including their depth of occurrence, average normal stress, and the accumulated effective strain, has been analyzed. It has been established that, with an increase in the indenter radius, the value of the accumulated effective strain (e) decreases. The behavior of distribution of the e parameter shows a gradient character with its values decreasing from the surface to the center of the workpiece. An analysis of the simulation results shows that the residual radial stresses in the region of the deformation zone are predominantly compressive stresses and, accordingly, allow increasing the fatigue resistance of the final product. It has been established that, with an increase in the indenter oscillation amplitude, the values of residual radial stresses also rise, with their maximum achieving 540 MPa at the amplitude of 75 µm and the depth of occurrence of these stresses reaching 0.3 mm. Increasing the indenter radius, or, in other words, in fact, the contact surface area, leads to an increase in the residual radial compressive stresses, which turns out to be an almost linear increase.

In investigation of the aggregative stability of disperse systems by sediment volumetry, a violation of the structure of water in the contact area causes formation of nanobubbles, whose coalescence leads to appearance of hydrophobic attraction forces. A change in the aggregative stability of aqueous dispersions of particles can be interpreted in such a way that ingress of water molecules having a high potential of interaction with molecules of the medium in the interfacial gap between particle surfaces and outflow of water molecules exhibiting high intensity of interaction with a solid surface from the interfacial gap between particle surfaces is difficult. Excess osmotic pressure between hydrophilic surfaces leads to their hydrophilic repulsion, and excess osmotic pressure of the surrounding water (reduced osmotic pressure between surfaces) leads to hydrophobic attraction of the surfaces. To change the result of flotation, it is sufficient to bring a heat flow to a nanoscale-thick liquid layer, within which action of forces of structural origin is localized, determining the stability of wetting films. To increase the temperature in the interfacial gap between the particle and the bubble using the heat of water vapor condensation, as a gas for flotation, a mixture of air and hot water vapor is proposed. The developed flotation method has been tested in flotation of gold ores. The efficient steam flow rate determined from the results of a factorial experiment is 10.7 × 10^–3 kg/(s m²), with the xanthate flow rate being 1.74 g/t. In the rough flotation operation, the jet method of constructing a flowsheet is used, which provides for combination of the initial feed and rough concentrate. In comparison with flotation of ores according to a factory scheme, the yield of a concentrate sent to hydrometallurgical processing is smaller by 23.4 rel. %, with the achieved level of gold recovery remaining the same.

Insufficient understanding of the nature of the interfacial interaction of reinforcing particles with the matrix alloy during repeated remelting of cast composite materials is one of the problems that limit the increase in the volume of their industrial application. This work is aimed at establishing the effect of repeated remelting of AK12 + 10 vol % SiC aluminum matrix composites on the retention and chemical stability of silicon carbide reinforcing particles. It is shown that an increase in the number of remelting iterations was not accompanied by the appearance of new phases at the interfaces between particles and the matrix, which indicates the stability of the SiC reinforcing phase in aluminum–silicon melts under the considered temperature–time and concentration conditions. During repeated remelting of aluminum matrix composites with silicon carbide, the degree of particle distribution uniformity shifts toward a more uniform distribution (on average 0.81046 at the first iteration of remelting, 0.6901 at the second, and 0.5609 at the third) and some decrease in their average sizes occurs (from 70.74 µm at the first iteration to 65.76 µm at the second and 61.21 µm at the third), apparently owing to particle fragmentation, leading to an increase in the amount of a finer fraction. At the same time, the share of the area occupied by particles in the segments of the section under consideration remains practically unchanged (10.9293, 10.9607, and 11.6483% in the first, second, and third iterations of remelting, respectively). In the course of repeated remelting of aluminum matrix composites of the Al–SiC system, processes of redistribution of reinforcing particles occur, leading to the destruction of agglomerates even in the absence of intensive mixing by an impeller. Because of this, the uniformity of particle distribution in the structure of ingots of secondary aluminum matrix composites can be significantly improved.