Vol 59, No 4 (2018)

In this paper, a sample from Tange-zagh iron mine was characterized by gravity and magnetic separation methods. The mineralogical studies showed that hematite and goethite are the main iron-bearing minerals with insignificant amounts of FeO. The results indicated that spiral separation yields higher separation efficiency than others. The combination of spiral and multi gravity methods showed that the grade and recovery could be obtained 58.7 and 55.6%, respectively. Scrubbing and de-sliming stages increased the recovery in the wet high intensity magnetic process. With a four-stage process of separation, the WHIMS by scrubbing and de-sliming was applied to achieve a final concentrate with grade of 62.6% Fe and recovery of 57.1% Fe.

This article is devoted to one important issue in the development of rare and precious metals industry— analytical control (AC). The current state, importance, problems, and prospects of the development of AC as an integral part of the production of rare and precious metals and quality assurance of products are considered. Modern methods of AC—atomic-spectral, mass-spectral, X-ray fluorescent, combined, and rational fields of their application—are characterized. It is shown scientific-and-technical progress is inextricably associated with a cardinal increase in a nomenclature of materials based on rare and precious metals and an increase in requirements for their quality. This will require the development of new methods of AC and improving existing ones, standardizing them, and metrological support. To carry out this work, it is necessary to attract research organizations of the Russian Academy of Sciences, universities, branch institutes with research laboratories that have survived the dissolution of the Soviet Union, and activate factory science. It is necessary to effectively use the achievements of advanced analytical laboratories abroad and participate in international comparative trials. At the same time, special attention is paid to unsolved problems—a scientifically justified formulation of requirements for new types of products based on rare and precious metals; the development and metrological assessment of sampling techniques; the development of high-quality metrological support for the AC of production of rare and precious metals; improving analytical methods; standardizing analytical methods; the accreditation of analytical laboratories; and the education and training of highly qualified analytical chemists.

The present study investigated the effects of indium (In) addition on the microstructure, mechanical properties, and melting temperature of SAC305 solder alloys. The indium formed IMC phases of Ag₃(Sn,In) and Cu₆(Sn,In)₅ in the Sn-rich matrix that increased the ultimate tensile strength (UTS) and the hardness while the ductility (% EL) decreased for all In containing solder alloys. The UTS and hardness values increased from 29.21 to 33.84 MPa and from 13.91 to 17.33 HV. Principally, the In-containing solder alloys had higher UTS and hardness than the In-free solder alloy due to the strengthening effect of solid solution and secondary phase dispersion. The eutectic melting point decreased from 223.0°C for the SAC305 solder alloy to 219.5°C for the SAC305 alloy with 2.0 wt% In. The addition of In had little effect on the solidus temperatures. In contrast, the liquidus temperature decreased with increasing In content. The optimum concentration of 2.0 wt % In improved the microstructure, UTS, hardness, and eutectic temperature of the SAC305 solder alloys.

Abstract—Regularities of the formation of ultrafine-grained (UFG) and submicrocrystalline (SMC) structures in new nickel-free low-modulus Ti–Nb–Mo–Zr titanium β alloys under the action of plastic deformation have been studied. Temperature–time ranges of the development of dynamic recrystallization processes under the simultaneous action of temperature and plastic deformation are determined. A type-II recrystallization diagram of the Ti–28Nb–8Mo–12Zr alloy is constructed and analyzed. It is shown using scanning electron microscopy and the electron backscatter diffraction method that the UFG structure with an average grain size of no more than 7 μm and high fraction of high-angle grain boundaries is formed in the investigated alloys as a result of longitudinal rolling, followed by annealing for quenching. It is found that the formation of the UFG structure leads to a significant increase in the strength and plastic characteristics of these alloys. The regularities of the formation of UFG and SMC structures in titanium β alloys Ti–28Nb–8Mo–12Zr and industrial VT30 under the action of plastic deformation by the helical rolling method are studied. It is shown that the helical rolling of the VT30 alloy leads to the formation of the homogeneous UFG state as opposed to the Ti–28Nb–8Mo–12Zr alloy, where this method causes structure softening with micropores and microcracks formed in the central region. It is possible to form a nanostructured state with an average grain size of about 100 nm in Ti–Nb–Mo–Zr titanium β alloys using the high-pressure torsion method.

The structure and magnetic properties of model high-cobalt WC–50% Co alloys with different carbon contents and TaC additions in the amount of 1.6–5.6 wt % are studied. Model alloys are fabricated by the liquid-phase sintering of powder mixtures at 1420°C, and their composition is described by the formula 50% Co + 50% WC + x% TaC + y% C, where x = 0, 1.6, 2.6, 3.6, 4.6, and 5.6 wt %; y = 0, 0.2, and 0.5 wt %. It is shown that precipitations of the (Ta,W)C phase are present in all studied alloys and (Ta,W)C precipitations are needle-shaped at a TaC concentration up to 3.6 wt %, while the (Ta,W)C grains become spherical at =3.6 wt %. The (Ta,W)C precipitations are arranged both in a binding phase and along the WC grain boundaries. The lattice parameter of the (Ta,W)C phase in alloys with a low carbon content lies in a range from 0.4438 nm for the alloy with 1.6% TaC to 0.4451 nm for the alloy with 4.6% TaC. It is established by the EDX analysis that the concentration of dissolved tungsten in a cobalt phase is independent of the TaC content and strongly depends on the total carbon content; it is 7, 12, and 17 wt % for alloys with high, elevated, and low carbon contents, respectively. The TaC addition in alloys with a low and elevated carbon content leads to an increase in the coercive force up to 875 A/m and a decrease in the magnetic saturation by 5–10 G m³/g. The experimental results made it possible to put forward a hypothesis on the possibility of formation of dispersed tantalum-containing precipitates in a binder phase.

Experimental data on the explosive compaction of powder mixtures of chromium carbide (Cr₃C₂) with metals (Ti, Ni, Cu) are presented, their theoretical explanations are given, and scientifically substantiated principles of the composition selection and development of the explosive fabrication of wear-resistant antifriction chromium carbide hard alloys and coatings are formed on this basis. The explosive pressing of powder mixtures was performed according to the scheme with the use of a plane normally incident detonation wave in a broad range of loading parameters (the powder heating temperature in shock waves was varied in experiments from 200 to 1000°C, while the maximal pressure of the shock-wave compression varied from 4 to 16 GPa). To analyze the phase transformations, the numerical thermodynamic simulation of the phase equilibrium was performed applying the Thermo-Calc software complex. The microstructure and the chemical and phase compositions were investigated using an Axiovert 40 MAT optical microscope (Carl Zeiss, Germany), Versa 3d and Quanta 3D FEG scanning electron microscopes (FEI, United States), BS 540 (Tesla, Czech Republic) and Titan 80–300 and Techai G2 20F (FEI, United States) transmission electron microscopes, and a Solver Pro atomic force microscope (OOO NT-MDT, Zelenograd). The temperature stability and oxidation resistance at elevated temperatures of materials formed by the explosion were investigated by thermogravimetric analysis using an STA 449 F3 Jupiter device (NETZSCH, Germany) in synthetic air upon heating to 1500°C. Tribotechnical tests were performed using an MI-1M friction machine (MEZIMiV, Moscow) according to the pin–ring scheme with digging in distilled water. Mechanisms of compaction and formation of strong boundaries between the particles of powder materials during the explosive pressing are described. It is shown that chromium carbide hard alloys with a titanium binder formed by explosion retain their phase composition invariable, do not oxidize to 600°C, and have considerably better antifriction properties and wear resistance when compared with SGP-0.5 and KKhN-20 materials lubricated with water, which have been applied in friction pairs until now.

Additive manufacturing (AM) offers a fully integrated fabrication solution within many engineering applications. Particularly, it provides attractive processing alternatives for nickel-titanium (Ni–Ti) alloys to overcome traditional manufacturing challenges through layer by layer approach. Among powder-based additive manufacturing processes, the laser beam melting (LBM) and the electron beam melting (EBM) are two promising manufacturing methods for Ni–Ti shape memory alloys. In these methods, the physical characteristics of the powder used as raw material in the process have a significant effect on the powder transformation, deposition, and powder-beam interaction. Thus, the final manufactured material properties are highly affected by the properties of the powder particles. In this study, the Ni−Ti powder characteristics are investigated in terms of particle size, density, distribution and chemical properties using EDS, OM, and SEM analyses in order to determine their compatibility in the EBM process. The solidification microstructure, and after built microstructure are also examined for the gas atomized Ni–Ti powders.

ZrB₂-mullite composite was synthesized by combustion synthesis (CS) from two different reactant systems: commercial ZrSiO₄-B₂O₃-Al, and zircon sand (mineral tailing)-B₂O₃-Al. The reactant mixture was activated by high-energy ball milling for 2 hours. The reaction was carried out under an air atmosphere and initiated with an oxy-acetylene flame. The standard Gibbs energy minimization method was used to calculate the equilibrium composition of the reacting species. The effects of different starting materials on the resulting combustion products were investigated and discussed. The as-synthesized products were characterized by X-Ray diffraction (XRD) and scanning electron microscope (SEM) coupled with energy dispersive X-Ray (EDS) detector. Examination of the self-propagated velocity showed that the reactivity was marginally higher when using commercial ZrSiO₄. The results also showed that both reactant systems successfully produced ZrB₂-mullite composite by the combustion reaction but that the commercial ZrSiO₄-B₂O₃-Al reactants system exhibited fewer undesirable phases than zircon sand-B₂O₃-Al due to a better conversion of the reactants into combustion products.

In this study, a nano-composite composed of gelatin as the matrix and Si-Mg-FA nano-particles as an additive was deposited on the AZ31 Mg alloy via dip coating method. In addition, a coating composed of MgO, MgSiO₃ and Mg₂SiO₄ phases was applied on the AZ31 Mg alloy by anodizing process. It was found that the Nano-composite coating with a uniform distribution of nano-particles within the gelatin matrix with the thickness of about 9 µm was dense, crack-free and uniform whereas the surface of anodized layer was relatively coarse due to the presence of flaws and micro-cracks. The surface morphology, EDS analysis and FTIR results revealed the ability of nano-composite coated specimen to form the bone-like apatite. Due to the presence of aforementioned phases and special surface features, the anodized specimen possessed higher and lower corrosion resistance than uncoated and nano-composite coated specimens, respectively. The passive coating resistances (R_CT) of nano-composite, anodized specimen and uncoated samples were 2164, 1449 and 1024 Ω cm², respectively.