Magnetic Pulsed Compaction Research Articles

Complex microstructure induced high thermoelectric performances of p-type Bi–Sb–Te alloys

In this research, we have fabricated the complex microstructure features along with the high density of twin boundaries using the combination of magnetic pulse compaction (MPC) and spark plasma sintering (SPS), which are exclusively improved the thermoelectric transport properties of p-type Bi0.5Sb1.5Te3 alloys via effective scattering of carriers and phonons at the grain boundary interfaces. The texture analysis confirmed the formation of bimodal (mixed grains) microstructural features in MPC + SPS specimens sintered at 350 °C, and 400 °C respectively due to the adhesion of fine grains (grain growth) and initiation of recrystallization at high temperatures. In addition to high density of twin structure, high-angle grain boundaries have also been identified. The power factor of 3.53 mW/m.K2 was obtained for the MPC + SPS at 400 °C due to increased Seebeck coefficient and larger electrical conductivity values. The maximum reduced thermal conductivity of 1.14W/mK was recorded due to a significant reduction in lattice thermal conductivity, which is mainly owing to strong scattering of phonons at the formation of mixed grain microstructures with high-density dislocations. As a result, maximum figure of merit, ZT = 1.17was achieved for MPC + SPS at 400 °C temperature.

Synthesis of Titanium-Based Composites by Pulsed Methods

Ti-based composites with advanced properties were fabricated by the explosion of the wires and magnetic-pulsed compaction methods. After the wire explosion the “metal core – oxide (or nitride) shell” structure is formed. Magnetic-pulsed treatment of such poorly conductive powder leads to the destruction of the shells and to the appearance of an electrical conductivity. This conductivity is only 4-7 times higher than that of pure titanium. As a result of the dynamic compaction of 100-150 nm powder the hot-pressed Ti+9TiO2 composition appeared to have the best combination of mechanical properties: relative density – 95 %, microhardness - 4.2 GPa, reduced modulus of elasticity – 143 GPa, creep under constant load – 105 nm. The coefficients of thermal extension of three materials with different titanium oxide content: 6, 9 and 15 wt. % were measured. The nitride-containing composites were ~30% more porous and had low mechanical properties compared to Ti+TiO2 compacts.

Microstructure and properties of a nanostructured W-31 wt% Cu composite produced by magnetic pulse compaction of bimetallic nanoparticles

Nanostructured W-31wt.%Cu composite was for the first time produced via magnetic pulse compaction from bimetallic particles obtained using electric explosion of intertwisted copper/tungsten wires in argon and then characterized for microstructures, mechanical strength and tribological behavior at high temperatures. Microstructure of the composite is characterized by recrystallized copper grains with mean grain size of 59 ± 3 nm and unreacted spherical tungsten particles. The composite density was in the range 93–99%. Flexural and compression strengths were 560 ± 10 and 1035 ± 150 MPa, respectively. Tribological high temperature tests showed that this composite develops reduced wear starting from the testing at 250 °C. Such an adaptation mechanisms is related to generation of copper tungstate CuWO4 on the worn surfaces.

Effect of aspect ratio on the compaction characteristics and micromorphology of copper powders by magnetic pulse compaction

Magnetic pulse compaction (MPC) technology has the advantages of near net shape, high efficiency and density. In this paper, the effect of aspect ratio on the deformation characteristics of copper powders compacted by MPC technology was studied. Specifically, the compaction velocity, volume strain, micromorphology and micro hardness of compacts at various aspect ratios were obtained. Results showed that the compaction velocity and volume strain increased and then decreased with the increase of aspect ratio. The maximum compaction velocity reached 10.28 m/s at aspect ratio of 1.2. At the same compaction moment, the volume strain was decreased as the aspect ratio increased. Then the relationship between compaction pressure and volume strain was revealed. The aspect ratio range of the optimal compaction effect was 0.6–1.0, and the fluctuation degree of relative density was only 1.03%. The aspect ratio had less effect on the micromorphology distribution in the axial direction of the compacts. The micro hardness value of the upper surface was higher than that of the lower surface, and the edge position was greater than the center position.

Fabrication and Properties of Densified Tungsten by Magnetic Pulse Compaction and Spark Plasma Sintering

The present study demonstrates the effect of magnetic pulse compaction and spark plasma sintering on the microstructure and mechanical property of a sintered W body. The relative density of green specimens prepared by magnetic pulse compaction increases with increase in applied pressure, but when the applied pressure is 3.4 GPa or more, some cracks in the specimen are observed. The pressureless-sintered W shows neck growth between W particles, but there are still many pores. The sintered body fabricated by spark plasma sintering exhibits a relative density of above 90 %, and the specimen sintered at 1,600 oC after magnetic pulse compaction shows the highest density, with a relative density of 93.6 %. Compared to the specimen for which the W powder is directly sintered, the specimen sintered after magnetic pulse compaction shows a smaller crystal grain size, which is explained by the reduced W particle size and microstructure homogenization during the magnetic pulse compaction process. Sintering at 1,600 oC led to the largest Vickers hardness value, but the value is slightly lower than that of the conventional W sintered body, which is attributed mainly to the increased grain size and low sintering density.

Effect of Discharge Energy of Magnetic Pulse Compaction on the Powder Compaction Characteristics and Spring Back Behavior of Copper Compacts

Magnetic pulse compaction (MPC) technology had unique compaction advantages compared to traditional powder compaction methods. In this study, the pure copper compacts have been consolidated by MPC technique. The effect of discharge energy on the microstructures, relative density, micro hardness, strain and stress of copper compacts were analyzed via optical microscopy, scanning electron microscopy, hardness tester and FEM simulation. The relationship between discharge energy and spring back was analyzed by numerical calculation. Results showed that the MPC method had the advantages to refine powder particles. The relative density of copper compacts reached 96% when the discharge energy was 9 kJ. Stress concentration was occurred at the upper edge of the powder body, and propagated to the upper center, lower edge and middle position of the powder body. The powder body could have a uniform strain distribution in a short period of time when the discharge energy was greater than 7 kJ. There was a linear relationship between the relative density and the logarithm of Vickers hardness. The axial and radial spring back both increased with the increase of discharge energy. When the discharge energy was 9 kJ, the axial and radial spring back was 2.36% and 0.42%.

Sealing and compaction of powder materials in metal shells by a pulsed electromagnetic field

The extended heat elements are widely used in heat exchangers, filters, heating devices, as well as the fuel elements with the dispersion fuel. For use as shells, copper, aluminium and magnesium have proven themselves well. In this paper, a comparative analysis of various manufacturing schemes of long tubular and rod elements using the method of magnetic pulse compaction is given. Experimental studies were carried out on metal powders of iron and powder compositions based on it. The expediency of using the step and combined pressing method is shown.

Structural, Mechanical, and Tribological Characterization of Magnetic Pulse Compacted Fe–Cu Bimetallic Particles Produced by Electric Explosion of Dissimilar Metal Wires

Bimetallic 73 wt.% Fe–Cu nanoparticles have been produced using electric explosion of two immiscible metal wires and then consolidated into disks using magnetic pulse compaction. The compacted disks have been characterized for phase composition, mechanical strength, and high-temperature steel ball-on-disk sliding friction. The sample possessed good flexural and compression strength. Friction and wear reduction were observed during sliding test at 400 °C, which was explained by intense tribosynthesis of cuprospinel CuFe2O4 nanoparticles, which served to reduce adhesion between the ball and disk.

Microstructure Characterization and Properties of Ti Carbohydride/Cu–Ti/GNP Nanocomposites Prepared by Wet Ball Milling and Subsequent Magnetic Pulsed Compaction

Wide application of hard composite materials in modern technologies stimulates a search for new compositions and more efficient and cheaper ways of their obtaining. A novel Ti carbohydride/CuTi/CuTi2/GNP (few-layer graphene or graphite nanoplatelets) composites were produced via magnetic pulsed compaction of Ti, Cu and graphite powders mechanically milled in liquid organic medium for 4 h. Phase composition and microstructure were examined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. Density, microhardness, ultimate compression strength, abrasive wear resistance and sliding wear resistance of the composites were studied. The composites consisted of hexagonal and cubic titanium carbohydrides, CuTi2 and CuTi intermetallics, ~ 5 wt% of GNP and amorphous carbon. The presence of GNP and amorphous carbon resulted in higher wear resistance under conditions of dry friction against steel (1 wt%C, 1.5 wt%Cr) but lower composite density, microhardness, ultimate compression strength and abrasion wear resistance as compared with the GNP-free composites.

Effect of Aluminum Oxide Powder Particle Size on Spark Plasma Sintering Results

The results of a comparative study of compacts obtained by spark plasma sintering from nano- and ultradisperse (UD) aluminum oxide powders with spherically shaped particles are reported. It is shown that the compacts obtained from UD-powder have higher density and greater strength, microhardness, and structural uniformity with smaller grains than compacts obtained from nanopowder. Preliminary magnetic-pulse compaction of powders prior to sintering improves the characteristics of both compacts but higher density and strength with smaller grains are achieved in compacts obtained from UD-powder. In both cases of preliminary preparation the UD-powder compacts have advantages over nanopowder compacts.

Advanced methods for consolidation of powder materials by impulse electromagnetic fields

Advanced technologies for the production of new materials and, in particular, nanostructured materials, using powder technologies require fundamentally new approaches for the formation and preservation of a given structural-phase state. Precision control of the state of materials in the process of consolidating powders of nanomaterials can be carried out using pulsed electromagnetic fields. The aim of the project is to study the effect of high-voltage and low-voltage pulsed electromagnetic fields in the technologies of powder consolidation. The experimental devices of spark-plasma sintering, flash-sintering, high-voltage consolidation and magnetic-pulse compaction are used in our laboratory for the production of advanced materials from metal powders, ceramic and composite powders. We can produce boron carbide, silicon carbide, uranium nitride, tungsten carbide - cobalt - diamond composites, tungsten heavy alloys, and others by electromagnetic methods of powder consolidation. Experimental results to consolidation metal powders, ceramic and composites powders by electromagnetic methods presage fruitful results.

Manufacture of products from boron-containing materials by the method of combined static-pulse compaction

In the production of long parts of powder materials, the magnetic pulse method of pressing is of great interest. In this paper a variant of the method combining the radial magnetic-pulse compaction of a powder in a metal shell and longitudinal drawing is considered. Samples were made of boron-containing materials.

Properties of compacts of barium fluoride nanopowder produced by pulsed electron beam evaporation

Abstract Mesoporous crystalline BaF 2 nanopowder with a specific surface area of up to 34.8 m 2 /g was produced by a pulsed electron beam through the evaporation of targets of micro-sized BaF 2 powder with optical purity ( S red = 0.38 m 2 /g). The texture and thermal features of the BaF 2 nanopowder (before and after annealing in air at a temperature of 200 °C) and some properties of compacts made of the BaF 2 nanopowder by magnetic-pulse compaction and static pressing were studied. Glassy, opaque, and black compacts, which are promising materials for use as scintillators and dosimeters, were produced by magnetic-pulse compaction in a vacuum at a temperature of about 425 °C. It was found that heating up to 425 °C is sufficient for removing defects in nanopowders. The effect of pressing methods on the pulsed cathodoluminescence and photoluminescence spectra of the compacts was studied. Luminescent properties were found to depend on pressing technology. It was also determined that surface color centers, the number of which decreases during heating, are responsible for the pulsed cathodoluminescence band near ∼560 nm.

Densification mechanism and its effect on the magnetic properties of Nd-Fe-B bonded magnets through the new high-energy compaction method

Abstract Gas-atomized Nd-Fe-B magnetic powders were subjected to magnetic pulse compaction, which is very high-energy compaction method, can be densified in a short time with various binder contents at different compaction pressures. The powders were rapidly forced together with in an abbreviated period, and formed a well-packed dense sample with full density during the magnetic pulse compaction process. The influence of density on the magnetic properties of the Nd-Fe- B magnet was investigated. The relative density increased with pressure and highest density of 6.9 g/cm3 was achieved at a consolidation pressure of 3 GPa. The optimized binder content and pressure were found to be 1 wt% and 3 GPa, respectively, for achieving the highest density. The remanence and maximum energy product of the Nd-Fe-B magnets gradually increased with increasing density. The significant improvement in density can effectively offers high remanence of 6.635 kG and maximum energy product of 8.5 MGOe.

Mechanosynthesis of TiC(NbC)–Cu composites using liquid hydrocarbons

The high-energy ball milling of Ti, Nb and Cu powders in liquid hydrocarbon and magnetic pulse compaction have been successfully used to produce Ti2CH0.6–(CuTi2,CuTi) and NbC–Cu composites with a density of 94–97% of the theoretical value, a microhardness of 4–5GPa and high abrasive wear resistance

Fabrication of thin-walled iridium tubular articles by radial magnetic pulsed compaction and sintering of nanopowder

Fabrication of thin-walled iridium tubular articles by radial magnetic pulsed compaction and sintering of nanopowder

Structure study of Al+Al2O3 composite by atomic force microscopy

The structure of a metal matrix composite based on aluminum containing 6, 17 and 24 wt % Al 2 O 3 was studied by atomic force microscopy. The composite was prepared by the method of magneticpulse compaction from aluminum nanopowder obtained by the electric wire explosion method. The samples compacted at 400 ◦ C have more clearly expressed grain boundaries than those obtained at room temperature. The structure of a composite subjected to dynamic plastic deformation is studied.

Impact of pressure in static and dynamic pressing of ultrafine plasmochemical ZrO2 (Y)-Al2O3 powders on compact density and compaction efficiency during sintering

The effect of different methods of pretreatment and compacting of ultrafine alumina-zirconia powders of composition (in mass%): 20 Al2O3-80 (ZrO2-Y2O3) on densification processes during pressing and subsequent calcination has been studied. Ultrafine powders were prepared by plasma-chemical method. It was found that the initial nanocomposite is a mechanical mixture made up of zirconia nanoparticles and amorphous alumina in a thermodynamically nonequilibrium state. Grinding of powders did not affect their phase state. Powder compacts were produced by means of uniaxial static pressing and magnetic pulse compaction. The impact of mechanical processing of powders on ceramics density was studied. It was shown that dry grinding of powders in a planetary ball mill does not increase the ceramics density. The best and virtually identical results were obtained using preliminary static pressing of powders at increased pressure P = 900 MPa and their subsequent grinding in a ball mill. Dilatometric studies showed that double-action magnetic pulse compaction provides the maximum shrinkage rate at lower temperatures in comparison to that observed under static pressing. The ceramic density achieved is higher than that obtained using other pressing methods.

Microstructure and Density of Sintered ZnO Ceramics Prepared by Magnetic Pulsed Compaction

Three different sintered ZnO ceramics were prepared by magnetic pulsed compaction (MPC) and other conventional methods. The microstructures of the sintered ZnO ceramics prepared by MPC at sintering temperatures ranging from 900 to 1300°C showed a homogeneous grain growth compared to those of the samples prepared using other methods under the same sintering conditions. This implies that interpowders and/or intergrains can induce the minimization of wall friction effect because of the application of a high compaction pressure for a short process time in the MPC method. In addition, the microstructure of the sample obtained using the cold isostatic pressing method showed the presence of heterogeneous regions, indicating its low quality even though the densities of the three different samples were almost similar in the range of 97–99% at sintering temperatures of 900, 1100, and 1300°C. Therefore, different methods used for the compaction of ZnO ceramics may result in different microstructural and physical properties of the product.

Impact of pressure in static and dynamic pressing of zirconia ultradisperse powders on compact density and compaction efficiency during sintering

This paper studies the impact of pressure in static and dynamic pressing on densification of stabilized zirconia ultradisperse powder compacts and on compaction kinetics during sintering. Ultradisperse powders of 97 ZrO2 + 3 Y2O3 zirconia were synthesized using the plasma chemical method. Dry uniaxial static pressing and double-action magnetic pulse compaction were employed. It is shown that double-action magnetic pulse compaction provides the maximum density of the product in comparison to that obtained through static pressing. The dilatometric studies showed that the increased density of compacts from stabilized zirconia powders obtained in dynamic pressing does not make ceramics less compact during isothermal aging as it typically occurs during static pressing. This increases the density of ceramics and improves its mechanical characteristics.