Magnetic pulse welding (MPW) employs a strong pulsed magnetic field to accelerate parts against each other, thus forming an impact joint. Single-turn tool coils and field-shapers (FSs) used in MPW operate under the most demanding conditions, such as magnetic fields of 40–50 T with periods lasting tens of microseconds. With the use of conventional copper and bronze coils, intense thermo-mechanical stresses lead to the rapid degradation of the working bore. This work aimed to improve the efficiency of field-shapers and focused on the development of two- and four-slit FSs with a nanocomposite Cu 18Nb brazed wire acting as an inner current-carrying layer. The measured ratios of the magnetic field to the discharge current were 56.3 and 50.6 T/MA for the two- and four-slit FSs, respectively. FEM calculations of the magnetic field generated showed variations of 6–9% and 3% for the two- and four-slit FSs, respectively. The ovality percentages following copper tube compression were 27% and 7% for the two- and four-slit FSs, respectively. The measured deviations in the weld-joining length were 11% and 1.4% in the two- and four-slit FSs, respectively. Compared to the previous experiments on an entirely steel inductor, the novel FS showed significantly better results in terms of its efficiency and the homogeneity of its magnetic field.

The joints of tubes to plugs of STS410 / SUS430, Gr.91 / Gr.91, HT-9 / HT-9 were obtained using magnetic pulse welding (MPW). In MPW, a magnetic field is used to accelerate parts so that they are joined during a high-speed collision, where the contact spot runs at a specified condition. The outer diameter of the steel tubes was 7 to 9 mm, and the wall thickness was 0.5 to 0.6 mm. The MPW experiments were carried out using a 135 kJ / 36 kHz pulsed current generator loaded on a steel single-turn coil. The peak magnetic field reached 38 - 45 T. The impact and contact point velocities Vi and Vc were found from the analytical solution of the one-dimension motion equation of the tube wall. Optical microscopy and scanning electron microscopy with X-ray microanalysis were carried out. A molten interface layer of 2 - 30 inm thick with pores and cracks was found at the joints. Solid-state joining was found on all pairs of materials, however, only in the STS410 / SUS430 pair it had significant dimensions in relation to the size of the joining area and was found in the middle and end areas of the plug at impact and contact point velocities: Vi =310 - 420, Vc = 2750 - 3670 m / s.

The work is devoted to the development of a Cu-Nb composite material and an approach to the design of reliable tool coils, which require a magnetic field of about 40 T with a microsecond duration. A powder method has been applied to obtain homogeneous samples from a fine Cu-Nb composite alloy. The dependence of electrical and mechanical properties on annealing temperature was investigated. Layered sample was produced and tested under conditions of high magnetic field generation in comparison with a commercial wire.

This work focuses on making and studying steel conductors with inhomogeneous surface conductivity. Employing such materials (structures) for engineering the high-field pulsed magnets can provide them with enhanced durability. In this work, monotonically changing resistivity was realized by pack chromizing the medium-carbon steels, 30KhGSA and 40Kh, which were treated at 1000 °C in argon for 150 h under the Cr-load of 20 mg/cm 2 to obtain a diffuse layer with minimal carbides at the surface. An approach to investigate the resistivity distribution across a diffuse layer after steel chromizing is suggested and involves a stepwise surface grinding, resistance measurement, and analytical processing of experimental data. The resistivity profile obtained by this method is well described by the complementary error function. At the near-surface layer, 30KhGSA and 40Kh steels have almost the same values of resistivity, about 110– $115 ~\mu $ Ohm $\cdot $ cm, which is 2.9–4.3 times higher than that in the bulk depending on steel. A strong correlation, almost a linear dependence, of resistivity with the depth-derived chromium concentration in the material was found. The proposed method allows one to measure the depth-varied resistivity for ferrous alloys with proper accuracy, while it does not require complex measuring equipment compared with other ones.

Subject of study. The possibility of using the nonlinear current mode of operation of a photomultiplier tube for measurements of luminescence kinetics was investigated. Aim of study. This study aimed to validate the possibility of using the nonlinear current mode of operation of a photomultiplier tube to determine the kinetic properties of small luminescence signals of condensed media, including the signals that cannot be detected in a linear current mode. Method. The signal arriving at a high-impedance (1 MS?) input of a digital oscilloscope from a photomul-tiplier tube via a coaxial cable was measured. This signal is a convolution of a photocurrent pulse with a kinetic instrument function determined by the discharge of capacitance in the measurement circuit of the photomultiplier tube. The bandwidth of the circuit was determined by the lowest frequency of its elements instead of the character-istic time of the instrument function. The real photocurrent signal was reconstructed by the deconvolution of the digital convoluted array. The pulsed cathodoluminescence method was used to detect the kinetics. Main results. A method for measuring the kinetics of small optical signals in the current mode of operation of a photomulti-plier tube connected to a high-impedance input of a digital oscilloscope was presented. The results of using this method to measure the kinetics of pulsed cathodoluminescence of impurity and intrinsic centers in ceramic and monocrystalline samples of yttrium aluminum garnet were presented. The direct determination of characteristic decay times by approximating the convoluted curves without deconvolution was demonstrated for an exponential luminescence decay profile. Practical significance. The proposed method for the characteristic time detection of luminescence kinetics enables comprehensive analysis of luminescence that can be applied in various sectors of the national economy.(c) 2023 Optica Publishing Group

This work focuses mainly on making and study steel conductors with inhomogeneous surface conductivity and its effect on material behavior under generation of high pulsed magnetic fields. Monotonically changing resistivity was realized by pack chromizing steel grades 30KhGSA and 40Kh which were treated at 1000°C in argon under different conditions. An approach to investigate the resistivity distribution across diffuse layer after steel chromizing is proposed and some results are presented. To achieve a discrete change in resistivity., a powder technology is proposed that involves the use of a base steel powder., e.g. ., 30KhGSA., and compositions based on it with chromium addition to form a layered structure. The results obtained on single layer samples made of powders are discussed.

Iridium is rather difficult to process due to its brittleness and sensitivity to impurities. It is better treated while it is clean and fine-grained. Therefore, it should be promising to use fine powders. At the same time, the pressing and sintering of iridium nanopowders has not been studied well. This paper describes a method for manufacturing thin-walled iridium tubes using powder technology. Iridium powder of 99.997% purity with an average particle size of 42 nm (BET) was obtained by the electrolysis of molten salts. It was subjected to radial magnetic pulsed compaction in copper shell, which was subsequently chemically removed. The resulting pressure on the powder here strongly depends on the parameters of the magnetic field pulse and other initial conditions, such as the properties of the shell, the thickness of the charge and the rheological properties of the powder. Therefore, the properties of green and sintered samples were investigated depending on the amplitude of the magnetic pressure, without changing the other parameters. Green bodies with a relative density of up to 50% were obtained with an amplitude of magnetic pressure of 85 - 190 MPa. The green density slightly increased with increasing magnetic pressure. Sintering at 1000 degrees C in a hydrogen atmosphere yielded thin-walled tubes with a grain size of 0.3 mu m and a density of up to 22.3 g/cm(3), close to the theoretical density of iridium, 22.56 g/cm(3). The sintered density was insensitive to the green density in the studied range. Solid sintered tubes were obtained by an amplitude of magnetic pressure between 85 and 122 MPa.

The work concerns the realization of a conductor material with monotonically changing conductivity with depth and theoretical description of magnetic and thermal effects in such systems under high magnetic fields. Thick-walled cylindrical single-turn coil of steel was used as model inductor for theoretical and experimental studying. Surface modification of medium carbon steel 30KhGSA was made by pack chromizing. Characterization of modified surface layer depending on chromizing conditions has been made. The full-scale testing the inductors made of this steel with modified surface was carried out using an inductor system with magnetic flux concentrator as a test subject under generation a magnetic field of 50 T in amplitude and 15 mu s in half-period. The results are discussed.

The paper concerns processes of high-speed compaction of nanosized powders. The processes of uniform and uniaxial compaction have been simulated by the granular dynamics method. Nanoparticles interaction, in addition to known contact laws, includes dispersive attraction, formation of a strong interparticle bonding as well as the forces caused by viscous stresses in the contact region. For different densification rates, the densification curves (pressure vs. density) have been calculated. Relaxation of the stresses after the compression stage has been analyzed. The densification curves analysis allows us to suggest the dependence of compaction pressure as a function of strain rate in the form of p proportional to v(1/8). The rate dependence obtained has been applied for interpretation of experimental data concerning high-speed processes of magnetic pulsed compaction of nanopowders.

The work was aimed to study the influence of plasma nitriding on electrical and mechanical properties of steels, meant for pulsed magnets production, and their durability in pulsed high magnetic field. For this purpose single-turn coils of several domestic steel grades, including 30KhGSA, 40Kh, 50KhGA, 38Kh2MYuA, 3Kh2V8F, 4Kh5V2FS, and U8A, have been produced and examined. Steel inductors had an inner channel surface modified by ion plasma nitriding at low temperature (400, 500°C). The coils without plasma treatment were also studied for comparison. Temperature dependence of electrical resistivity of nitrided steels has been investigated. A microstructure and microhardness profiles across near-surface layer of treated and untreated inductors, applied for high magnetic field generation, has been studied. The full-scale testing of the coils was performed using an inductor system with magnetic flux concentrator as a test subject. Magnetic field of about 50 $T$ in amplitude and rising time of 6 microseconds inside the concentrator was generated by the outer coil. The concentrators of different steels with and without plasma treatment were compared on durability in high pulsed magnetic field and their destruction features were studied.

The paper concerns the nanopowder high-speed, 10 – 10 s, compaction processes modelling by a two-dimensional granular dynamics method. Nanoparticles interaction, in addition to known contact laws, included dispersive attraction, the formation of a strong interparticle bonding (powder agglomeration) as well as the forces caused by viscous stresses in the contact region. For different densification rates, the "pressure vs. density" curves (densification curves) were calculated. Relaxation of the stresses after the compression stage was analysed as well. The densification curves analysis allowed us to suggest the dependence of compaction pressure as a function of strain rate. It was found that in contrast to the plastic flow of metals, where the yield strength is proportional to the logarithm of the strain rate, the power-law dependence of applied pressure on the strain rate as 1/4 p v  was established for the modelled nanosized powders.

The microtubular design of solid oxide fuel cells (SOFCs), which are promising electrochemical power sources, has a number of significant advantages over traditional planar and tubular designs: increased resistance to the cell (stack) heating rate and packing density of cells in a stack. The paper presents results on the development of a microtubular SOFC (MT-SOFC) fabrication method based on compaction and co-sintering a set of films. The formation of an anode-supported MT-SOFC having a Ni-cermet collector (support) and functional layers of about 300 and 50 μm thick, respectively; a Zr0.84Y0.16O2–δ solid electrolyte layer (40 μm); and a cathode based on La0.7Sr0.3MnO3–δ has been developed. The outer diameter and length of the MT-SOFC were 3.9 and 12 mm, respectively. The maximum specific power generated by the MT-SOFC at 850°C was 0.21 W/cm2.

y The work was aimed to study the influence of plasma nitriding on electrical and mechanical properties of structural steels and their durability in pulsed high magnetic field. The plates and cylindrical magnetic flux concentrators were made of several steel grades (30KhGS, 40Kh, 50KhGA, 38Kh2MYuA, and U8A), heat-treated, and subjected to the low-temperature (400, 500 degrees C) plasma nitriding. Electrical and mechanical properties of materials, phase composition of steel surface layer, microstructure and microhardness profiles were investigated on the plates before and after plasma treatment. Microstructure and microhardness profiles across the subsurface layer of plasma treated and untreated concentrators applied for high magnetic field generation were also studied. Magnetic field of 50 T under tens of microseconds in duration inside the flux concentrators was generated by long-life outer coil.

The results of tests of a self-heated hollow cathode made by magnet-pulse pressing of the mixture of TiN (90 %) and Ti (10 %) powders with further high-temperature annealing and fusing during operation of the compact as a cathode in high-current (10 - 45 A) discharge are presented. It was found that the rate of the cathode mass loss during operation in Ar/N2 mixture made 2.3*10-7 g/C. The possibility of the cathode use for oxygen-argon plasma generation at separated gas feeding (argon – through cathode cavity, and O2 – to anode area of discharge) was shown. Testing of massive tubular cathodes with the increased thickness of the wall (up to 2.5 mm) and large inner diameter (up to 12 mm) possessing an enhanced resource (300 - 500 h) was carried out.

A method for the formation of a tubular hollow self-heated cathode using magnetic-pulse pressing of a mixture of TiN (90%) and Ti (10%) powders with subsequent annealing and sintering during operation of the compact as a cathode in a high-current (5–45 А) discharge at temperatures of 2000–2200°C is described. Massive tubular cathodes with a 2.5-mm-thick wall and a large (up to 12 mm) inner diameter were manufactured. The erosion rate of a TiN cathode was 2.3 × 10–7 g/C for the operation in an Ar/N2 mixture and increased by a factor of 1.6 in the oxygen–argon plasma generation mode with separate feeding of gases.

Direct transformation of chemical energy of fuel to energy with use Solid Oxide Fuel Cells (SOFC) is perspective technology of highly effective, non-polluting power. Individual fuel cells are multilayered heterostructure on a basis ionic conductivity the solid electrolyte, consisting of materials with various properties and type of conductivity. It the material of electrolyte should possess high only ionic conductivity and to be gastight materials of electrodes should have high electronic and ionic conductivity, catalalyic activity and possess sufficient porosity for delivery and to tap of reagents on three-phase, where are basic reactions to not create diffuses difficulties and to not limit course of a current.

The influence of small additions (1, 3, 5 mol %) of transition metal (Co, Cu, Mn, Zn) oxides on the properties of solid electrolyte Ce0.9Gd0.1O2–δ (GDC) have been investigated. It has been shown that the addition of dopants results in intensification of GDC sintering and reduction of the shrinkage end temperature by 300–400°C, which decreases in the sequence Zn–Mn–Co–Cu. The ultimate dopant concentration above which the further activation of GDC sintering does not occur is about 3 mol % for Co, Cu, and Mn and about 1 mol % for Zn. It has been shown that Co and Cu increase the total conductivity of GDC, while Mn and Zn decrease it.