Vol 7, No 5 (2016)

Samples of rapidly -quenched ribbons and wires with a diameter of metal core of d_с= 50–200 μm within the ternary eutectic system Fe₇₅Si₁₀B₁₅–Co₇₅Si₁₀B₁₅–Ni₇₅Si₁₀B₁₅ were obtained by the melt spinning and Ulitovsky–Taylor methods. The liquidus surface and crystallization surface of the amorphous alloys were constructed on the basis of the results of investigations of the thermal, mechanical and magnetic properties of the system alloys; the concentration ranges of amorphous alloys with various crystallization mechanisms and the ranges of amorphous alloys with the positive and negative Villari effect were determined. The concentration range of compositions favorable for obtaining amorphous wires with high glass-forming ability was determined. The comparative study of the structure and properties of the “thick” wires samples was carried out for two models alloys: Co₇₁Fe₄Si₁₀B₁₅ and Fe₃₁Co₃₄Ni₁₀Si₁₀B₁₅. It was found that the wires possess a new complex of high strength, ductile, elastic, and soft magnetic properties. The prospects for application of “thick” ferromagnetic amorphous wires associated with the development of new types of structural and functional materials were considered.

Nanocrystalline (8–10 nm) solid solutions on the basis of indium oxide in the systems In₂O₃–ZrO₂ and In₂O₃–HfO₂ are synthesized by hydroxide coprecipitation. It is established that the use of polyvinyl alcohol decreases the degree of agglomeration of precipitates and increases the dispersity of the synthesized powders. The optimal conditions for the consolidation of powders on the basis of In₂O₃ are selected. It is shown that In₂O₃ doping with zirconium and hafnium dioxides significantly increases the electrical conductivity of solid solutions compared to pure indium oxide. The influence of temperature and oxygen partial pressure on the conductivity of solid solutions on the basis of In₂O₃ was investigated.

Characteristics of a prospective method of modification of the structural-phase state and properties of materials in the process of pulsed electrical charges in water are given. Experimental results of the structural- phase changes in steels A-35, 30Kh3NMAF, and 45Kh2MFA and nonferrous metals (copper, titanium, and lead) under periodic discharge in a stream of fluid (PDSF) are presented. Formation of a compression wave with instant transition into an expansion wave creates strong local deformation and warm-up in the processed materials accompanied by formation of domains similar to metal pins in automotive rubber; rebuilding of the material structure and change in the phase state take place. The scope and extent of these changes with a fixed PDSF is determined by the nature of the alloy composition and susceptibility to structural transformations under level of pulsed exposure. Recommendations are given for the PDSF application for hardening of the material of various products, which extends the technological capabilities of modern engineering.

Using methods of hardness measurements, determination of the tensile strength properties, and microstructure observation, the effect of annealing at various temperatures on structure and change in the strength properties of the cold-deformed Al–Mg₂Si alloys alloyed with joint additives of scandium and zirconium is studied. It is shown that the hardness decreases with increasing annealing temperature to minimal values in the interval of 300–500°C and then increases up to 600°C. Such a change in hardness is explained by the recovery process (hardness decrease) and enrichment of the aluminum solid solution in magnesium and silicon followed by its natural aging (hardness increase). Addition of scandium and zirconium to the colddeformed Al–Mg₂Si alloys promotes an increase in their strength properties both after aging of these alloys at 170°C for 16 h and after softening annealing at 400°C for 1 h.

LiNbO₃:MgO crystals, representing important materials for nonlinear optics, laser optics, integrated optics, and optical electronics owing to their high resistance with respect to optical damage, are studied. The crystals of LiNbO₃:MgO were grown from a granulated charge mixture of lithium niobate synthesized using homogeneously doped Nb₂O₅:Mg precursors of different origin. The effect of organic substances used in the technology of lithium niobate charge mixture on the properties of LiNbO₃:MgO single crystals is studied. It is found that the physicochemical and optical characteristics of LiNbO₃:MgO crystals grown from charge mixtures synthesized from Nb₂O₅:Mg precursors obtained using organic solvents and without them differ to a considerable extent. It is suggested that the difference in the properties of LiNbO₃:MgО crystals of different origin is caused by change in the structure of the ion complexes in the melt owing to the presence of traces of organic impurities. Change in the structure of ion complexes in the melt leads to change in crystallization mechanisms and, accordingly, in the chemical composition and the properties of LiNbO₃:MgO crystals. Furthermore, it is shown that the use of homogeneous doping methods as opposed to the method of direct doping provides the distribution coefficient K_eef > 1. That is, the method of homogeneous doping allows one to introduce a substantially greater concentration of an impurity element in the LiNbO₃:MgO crystal compared with the direct method for doping the charge mixture at the same impurity concentration in the starting material.

Considered in the article, α’-phase growth and coagulation stages under 500°С thermal aging of Fe–22% Cr binary alloy have been investigated on the atomic scale level, with atom probe tomography being applied. α’-phase appearing precipitates are shown to be separated in space. In addition, after 100-hour thermal aging the nucleation stage evolves into the growth and coagulation stage of α’-phase precipitates, with their number density being decreased simultaneously. Deviation of time dependences from Lifshitz-Slezov theory is revealed in Fe–22% Cr supersaturated solid solution alloy.

The effect of high-power nanosecond pulsed fluxes of deuterium ions and dense deuterium plasma (10⁸ W/cm²) generated in the Plasma Focus apparatus on the mechanical properties of chromium steel is investigated. It is found that the replacement of carbon in composition of the ferrite 12 Cr–2 W–0.1 C steel by nitrogen leads to dramatic embrittlement and softening of the steel caused apparently by formation of brittle nitrides of iron and/or tungsten. Irradiation with powerful pulses of hot plasma improves the mechanical properties of nitrous ferrite steel owing to dissolution of the brittle precipitations of nitride phases and formation of nanoscale particles of W, which is confirmed by X-ray analysis of irradiated steel. Ferrite chromium steels without nitrogen and austenitic manganese steels show a high stability of the mechanical properties under irradiation with powerful pulses of deuterium plasma.

This article presents an investigation of the influence of modification of Al₂O₃–(Ce-TZP) with alkaline earth elements Ca⁺² and Mg⁺² on the phase composition, microstructure, and strength characteristics of composites. It is established that modification of Mg⁺² compositions leads to a decrease in the strength parameters of composites, while introduction of Ca⁺² contributes to an increase in the strength parameters of the respective composites owing to aggregation of effects of transformational and dispersive hardening. The obtained high-strength composites can be applied as constructional materials in engineering and medicine.

For the purpose of improving the technology of manufacturing artificial cardiac pacemaker heads (connector blocks) (ACPHs), the traditional PEO-113K epoxy compound (produced by the St. Petersburg State Institute of Technology) was replaced by polyurethane (PU) Estate 58144 compound from Lubrizol (Germany) on the basis of 4,4-methylene diphenyl diisocyanate, 1,4-butanediol, and polytetramethylene oxide. To assess the safety of using ACPHs made of thermoplastic PU, sanitary chemical studies of products made in accordance with the technological regulations and ACPHs processed in the accelerated aging regime in Ringer–Locke solution at 80°C for 1785 h, which simulates a long stay (7.5 years) in the body, were performed. It was proved that potentially hazardous substances (the components of PU composition, functional and technological additives, impurities in raw materials, and products of their transformation that were analyzed by chromatographic and integral methods were absent in the water extracts from ACPHs. On the basis of the gas chromatography/mass spectrometry method, admixtures of compounds that can be attributed to oligomers of polytetramethylene oxide, which is one of the components of the polyurethane compound, were detected among the products of migration. Similar or identical values of the registered parameters of initial ACPHs and ACPHs processed in the accelerated aging regime indicate that the properties of ACPHs remain almost the same even after their processing in the accelerated aging regime simulating a long stay in body. As a result of toxicological studies, the biocompatibility of ACPHs made of PU with the body was proved. Histological examination of the area of ACPH implantation showed that the tissue reaction to the implantation was weaker than that to the control implantation of a sample made of NS-3 medical glass (GOST 19808-86). The possibility of using plastic Estane 58144 PU from Lubrizol (Germany) for ACPH production was substantiated as a method to significantly reduce the time of the technological process of manufacturing both ACPHs and pacemakers as a whole.

The structure and phase composition of ZrO₂–MgO powders with the MgO content from 9 to 43 mol % obtained by the plasma chemical method after annealing at 700–1400°С are studied. Differential scanning calorimetry and powder thermogravimetric analysis are carried out. It is found that, in the course of heating, the mass loss and the endothermic reactions energy increase with the increase in the MgO content. In the initial state, the powders containing more than 25 mol % of MgO are supersaturated solid solutions of cubic ZrO₂. Water desorption processes and decomposition of residual nitrates are observed in powders up to 420°С. The endothermic peak at high temperatures is due to the dehydration process and decomposition of the cubic ZrO₂ solid solution.

The influence of annealing time on the ductile-brittle transition temperature (embrittlement temperature) Т_f in amorphous Co-based alloy Со₆₉Fe_3.7Cr_3.8Si_12.5B₁₁ with extremely low saturation magnetostriction λ_s (λ_s < 10^–7) is investigated. It is revealed that the embrittlement temperature Т_f dependence on annealing time t_a can be described by the Arrhenius equation. Embrittlement at annealing temperatures higher and lower than 300°С can be described by different kinetic parameters owing to the different states of the amorphous phase. It is shown that, in the studied alloy, the embrittlement proceeds in a very narrow annealing temperature range, not exceeding 5°С. On the basis of experimental data on the evolution of hysteresis magnetic properties during isochronous annealing and isothermal exposure, the thermal treatment mode is investigated, providing rather high values of permeability μ₅ (Н = 5 mOe, f = 1 kHz) of about 50000, without transforming studied alloy into the brittle state.

Special features of fluorination of thermoplastic polyurethane elastomers (TPE) are considered. A dependence of the fluorination level of TPE on the fluorination time and the atomic structure of the modified surface layer is detected. A significant effect of fluorination on the surface morphology of TPE, its physical and mechanical properties, flammability, and resistance to fuels and lubricants is determined and studied. The surface morphology of a fluorinated sample in comparison with a virgin one becomes more developed owing to the emergence of a high-frequency component. The formation of this structure is determined by a more intense fluorination of elastic, less dense polymer regions, to large depth and with partial destruction. A decrease in the swelling rate of the samples in aviation kerosene and motor oil is shown. It was found that surface fluorination reduces flammability of the thermoplastic elastomer with respect to such indicators as ignition time, burning-out height, and maximum flame height. In general, according to the Federal Aviation Regulations FAR-25, fluorination of thermoplastic elastomers shifts them from the category of “burning” into the category of “self-extinguishing.”

A thermohydrolysis process is considered for aluminum chloride hexahydrate as one of repartition stages for a hydrochloric acid technology of alumina production from Russian high-silicon raw materials. A physicochemical study is performed for the burning of AlCl₃ · 6H₂O, and the temperature ranges for the removal of water and chloride ions are determined. It is shown that chloride ion is released mainly as HCl. The effect of burning temperature on the phase composition and the basic physical properties of the alumina powder (specific surface area, porosity, and average particle size) is studied. The results of optical and electron microscopy showed that the alumina particles retain the hexagonal structure of the source of aluminum chloride hexahydrate. It is established that ultrasonic treatment affects the dispersion level of the aluminum oxide powder. The data obtained allow one to produce metallurgical alumina of “sandy” type which can be used to prepare aluminum metal by means of electrolysis.

The regularities for the autowave synthesis (SHS) of a cast oxide composite material (Al₂O₃–Cr₂O₃ · ZrO₂) were studied by example of combustion of thermite-type systems under an inert gas pressure. The ratio of starting reagents with optimal zirconia content was determined for the synthesis of the desired product on the basis of analysis of published data and thermodynamic calculations (Thermo program). In the experiments, it was shown that combustion temperature and sample mass are the most important parameters influencing the composition and microstructure of the final product. Optimal conditions for the process control were defined. The final product includes solid solution Al₂O₃–Cr₂O₃ grains located on the boundaries of ZrO₂ particles. The material is promising for production of machine parts working in conditions of intense wear and shock loads in corrosive environments at elevated temperatures (for example, sintering of ceramic cutting tools).

The typical distortions of the particle size distribution functions are calculated from the smallangle X-ray diffraction for nanoscale transition metal powders and their mutual binary systems. The abnormal negative distribution functions are established to be caused by the presence of a thin nanoscale (oxide or hydroxide) shell at the metal nanoparticle surface with the electronic (scattering) density inferior to the electronic density of the nucleus. The analysis of the intensity and position of the abnormal minimum and maximum of the distribution function using computer modeling of the inhomogeneous particle scattering and experimental methods allows assuming the structure of the diffracting particles and evaluating the nucleus size and the relative outer shell density.