Magnetic Pulsed Compaction Research Articles

Effect of the method for producing $$\hbox {Cu}$$ Cu – $$\hbox {Cr}_{3}\hbox {C}_{2}$$ Cr 3 C 2 bulk composites on the structure and properties

Copper–chromium carbide composites containing a carbide phase of 20–30 vol% were obtained with the use of solid- and liquid-phase mechanosyntheses, followed by magnetic pulse compaction (MPC) and spark plasma sintering. The morphology, structural-phase composition, density, hardness and electrical conductivity of the composites were investigated. The structure of composites obtained by MPC represents regions of copper matrix hardened by superfine carbide precipitates surrounded by a layer of chromium carbide. In the composites obtained by spark plasma sintering, the copper matrix hardened by superfine carbide precipitates was divided into areas surrounded by a copper–chromium layer. A composite obtained by the MPC of the powders synthesized using solid-phase mechanosynthesis (MS) (copper, chromium and graphite) had the highest values of Vickers microhardness (4.6 GPa) and Rockwell hardness (HRA 69). The best value of electrical conductivity (36% IACS) was achieved using liquid-phase MS (copper, chromium and xylene) and spark plasma sintering. Liquid-phase MS is the only way to synthesize the powder with a small amount of the carbide phase and without contamination.

Preparation of silver-based solder foils by low-voltage magnetic pulsed compaction

Cadmium-free silver-based solder foils were fabricated using mechanically alloyed powders containing 56% silver–22% copper–17% zinc–5% tin by low-voltage magnetic pulsed compaction (LV-MPC) followed by liquid-phase sintering. The effects of processing parameters, such as discharge voltage, capacitance, coil turns, diameter–height ratio and compacting times, of LV-MPC on both the green density and the sintered density of compacts were analysed. The results showed that the green density increased with increasing discharge voltage, capacitance and coil turns. The green density also increased with increasing compacting times and diameter–height ratio, but the effect was relatively small because of the small filling height of the powder. The minimum thickness of solder foils fabricated by LV-MPC was approximately 0·2 mm. After sintering for 0·5 h at 480°C, the changing tendency of sintered density with different processing parameters was similar to that of green density with the same processing parameters. However, antidensification occurred and the sintered density declined slightly. The maximum relative densities of the samples after LV-MPC and liquid sintering were approximately 89 and 87% respectively.

Calculation analysis of magnetic-pulse compaction of explosively formed high-velocity metal elements used for meteoroid protection testing

Accumulation of microdamages as a result of intensive plastic deformation leads to a decrease in the average density of the high-velocity elements that are formed at the explosive collapse of the special shape metal liners. For compaction of such elements in tests of their spacecraft meteoroid protection reliability, the use of magnetic-field action on the produced elements during their movement trajectory before interaction with a target is proposed. On the basis of numerical modeling within the one-dimensional axisymmetric problem of continuum mechanics and electrodynamics, the physical processes occurring in the porous conducting elastoplastic cylinder placed in a magnetic field are investigated. Using this model, the parameters of the magnetic-pulse action necessary for the compaction of the steel and aluminum elements are determined.

Combined Magnetic Pulsed Compaction of Oxide Ceramic Powder Materials

The paper discusses the basic methods of combined magnetic pulse compaction of ceramic powder materials. One important direction is a method that combines axial compaction of the powder, carried out with the help of a hydraulic press, and magnetic pulse compaction (MPC). Experimental studies were carried out on materials such as Al203-Si02. The influence of compaction of specific energy on the compressibility of materials has been shown. It has been established that the combined compaction allows to increase the density of the material, to improve the uniformity of properties in the bulk of the product and to reduce shrinkage during sintering.

Fabrication of Ag–SnO2 Contact Materials from Gas‐Atomized Ag–Sn Powder Using Combined Oxidation and Ball‐Milling Process

Silver–tin oxide (Ag–SnO2) is considered to be an effective alternative to silver–cadmium oxide (Ag–CdO), which is carcinogenic and, therefore, toxic to the human body. In this study, Ag–SnO2 powder was prepared through a combined oxidation and ball‐milling process using gas‐atomized Ag–Sn powder. During oxidation, the Ag3Sn phase disappeared at 800°C and SnO2 was formed without Ag oxidation; this SnO2 formed a layer structure that covered the Ag matrix. The thickness of the oxide layer increased after the composite was subjected to a second oxidation process. Owing to the resultant core (Ag)‐shell (SnO2) structure, the electrical conductivity of the fabricated composite was considerably lower than that of commercially available materials. However, the electrical conductivity increased remarkably after ball milling of the samples, which allowed the SnO2 surface layer to be peeled off and crushed. Following high‐pressure magnetic pulsed compaction, the SnO2 was found to be homogeneously distributed in the Ag matrix, which exhibited a lamellar structure.

Effect Of Ti Powder Addition On The Fabrication Of TiO2 Nanopowders

Abstract Sintered samples of Ti added TiO2 nanopowders were fabricated by combined application of magnetic pulsed compaction (MPC) and sintering. The effect of Ti nano powder on density, shrinkage and hardness of the samples were investigated as part of the study. The optimum processing conditions were found to be around 0.5 GPa MPC pressure and 1450°C sintering temperature, illustrating maximum density, hardness and minimum shrinkage. High pressure compaction using MPC was found to enhance density with increasing MPC pressure up to 0.9 GPa, and significantly reduce the total shrinkage (about 16% in this case) in the sintered bulks compared to other general processes (about 18%). While sintered samples blended with micro Ti showed presence of microstructural cracks, the samples with 1-2% nano Ti had less or no cracks on them. Overall, the inclusion of nano Ti indicated improvement in mechanical properties of TiO2 nanopowders sintered preforms as opposed to micro Ti-added TiO2.

Conventional sintering of WC with nano-sized Co binder: Characterization and mechanical behavior

In this study, WC particles of 1–3μm were blended with two different sizes of Co particles and sintered conventionally at two different temperatures. Compaction of initial powders was carried out using a relatively new dynamic compaction method called Magnetic Pulsed compaction (MPC). The maximum Vickers hardness for the samples found was around 1353HV (13.27GPa), while the maximum fracture toughness was observed at 4.6MPa·m1/2. The marked changes in density, hardness, fracture toughness and crack behavior observed in the samples indicate strong correlations among particle size, sintering process and mechanical properties of cemented carbides. In addition, the nature of crack initiation and propagation, which is indicative of the trend in fracture toughness of materials, was observed and analyzed.

A study on mechanical properties and microstructure of tetragonal zirconia-based composites

The relative density, bending strength, fracture toughness, and fracture surface microstructure of tetragonal zirconia (t-ZrO2)-based composites prepared using magnetic pulsed compaction were investigated. The relative density and bending strength of the composites increased with increasing sintering temperature, whereas the fracture toughness increased with the addition of monoclinic zirconia (m-ZrO2) and Al2O3 particles. Scanning electron microscopy images indicate that the m-ZrO2 particles in the t-ZrO2 matrix induce residual stress and micro-cracking. Al2O3 particles act as barriers to crack growth in t-ZrO2/m-ZrO2/Al2O3 composites.

Difference of Magnetic Pulse Compaction from Traditional Uniaxial Pressing of Alumina Nanopowders

Processes of pressureless sintering of alumina nanopowders, subjected to traditional uniaxial pressing or magnetic pulse compaction, were investigated with the use of X-ray diffraction, scanning electron microscopy, thermal analysis and dilatometry. In this study sintering mechanisms, initiated by magnetic-pulse compacting and absent in the classical compaction, for the first time were found.

Nanopowders in dynamic magnetic pulse compaction processes

A theoretical study of the magnetic pulse compaction of nanosized powders is carried out. The uniaxial pressing and the radial (biaxial) compaction of powders using z- and θ-pinch setups are analyzed. The objects of study are two model systems that correspond to alumina-based nanopowders. System I corresponds to powders not inclined to strong aggregation and system II corresponds to powders in a strong aggregate state. Owing to the inertial effects under the radial pressing of conductive shells, high pressures are reached that exceed the initial “magnetic pressure” several times. A dimensionless number is found for the z-pinch that determines the process dynamics; its value range is established where most effective, “resonance,” conditions are realized.

Cu-Fe3C(Cr3C2) Bulk Nanocomposites Prepared by Mechanosynthesis Followed by Magnetic Pulse Compaction

The Cu Fe3 and Cu Cr3C2 bulk nanocomposites are prepared by consolidation of the mechanically alloyed powders. The structure and properties (density, Vickers microhardness and electrical conductivity) of them have been studied. It is shown that microhardness is equal to 236 HV and 470 HV for a Cu 5 vol.% carbide phase and for a Cu 30 vol.% carbide phase, respectively. The microhardness which can be in uenced by the heat treatment temperature depends on the grain size of the Cu matrix. The electrical conductivity values of 38 44% IACS (International Annealing Copper Standard) at room temperature have been found.

Magnetic Pulse Compaction of Oxide Powders of the (ZrO<sub>2</sub> – Y<sub>2</sub>O<sub>3</sub>) – Al<sub>2</sub>O<sub>3</sub> System

Technology for manufacturing products by magnetic pulse compaction from oxide powders of the (ZrO2 – Y2O3) – Al2O3 system is presented in the paper. Diagram of the magnetic-pulse press with its operating principle being based on Ampere's law is given. Physical and mechanical properties of the obtained compacts are determined. The main feature of the designed technology is the reduced sintering temperature (200 °С) and the acquired fine-grained structure of the products. Another significant advantage achieved by applying the technology is the possibility for manufacturing fine-grained structure ceramic products with high mechanical properties.

Influence of Technological Factors on Structure and Properties of Alumina-Zirconia Ceramics

The article is devoted to the investigation of alumina-zirconia ceramics properties depending on its production technology. Analysis of the technological factors that allow acquiring fine-grained structure as well as high physical and mechanical properties of alumina-zirconia ceramics is presented in the paper. It is shown that when using magnetic pulse compaction due to the pulse impact and adiabaticity of the process the most compact structure is formed. It is possible to obtain pressings with the density of up to 68% of the theoretical value. The obtained compact structure secures high physical, mechanical, and operating characteristics of the finished product.

Thermoelectric properties of n-type Bi2Te3 alloys produced by a combined process of magnetic pulsed compaction (MPC) and spark plasma sintering (SPS)

In this study, n-type 95 %Bi2Te3-5 %Bi2Se3 thermoelectric materials have been produced by a combined process of gas atomization with subsequent magnetic pulsed compaction and spark plasma sintering, and then we investigated the behavior of transport properties with sintering temperature. The microstructural observation was performed by optical microscopy and scanning electron microscopy. The crystal structures were analyzed by X-ray diffractometer. The mechanical properties were calculated by measuring the density and micro-Vickers hardness of the samples. It was found that with increasing sintering temperature the gaps between powder particles decreases and the grain sizes were coarsened. The mechanical properties shows higher values along the parallel direction compared to the perpendicular direction to the pressing. The transport properties of the thermoelectric material were investigated with variation of the sintering temperatures. The maximum power factor 1.7 × 10−3 Wm−1 K−2 was measured at the sintering temperature of 450 °C.

Effect of Micro Ti and TiO<sub>2</sub> P-25 Nano Powder Addition on Mechanical Properties of TiO<sub>2</sub> Nanopowders

Sintered bodies of TiO2nanopowders were fabricated by magnetic pulsed compaction (MPC) and subsequent 2 step sintering in this study and then, the effect of micro Ti and P-25 nano TiO2 powder addition on density, shrinkage and hardness was investigated. The optimum processing conditions in order to find the maximum density, hardness and shrinkage were found to be 0.5~0.7 GPa MPC pressure and 1450oC sintering temperature, with addition of 6% of TiO2 P-25 nanopowder. High pressure and rapid compaction using magnetic pulsed compaction (MPC) enhanced the density with increasing MPC pressure up to 0.7 GPa without the formation of surface or edge cracks on the consolidates bulks, and significantly reduced the shrinkage rate (about 15 in this case) of the sintered bulks compared to the general process (about 18%). Overall, most of the properties showed gradual changes with increasing MPC-ed pressure and TiO2 P-25 nanopowder content. Keywords: Densification, magnetic pulsed compaction, mechanical properties, rutile, sintering, TiO2 nanopowder.

Mechanical Properties of WC-Co Alloys with Various Mixing and Milling Conditions using High Energy Ball Miller

This study aims to understand the changes in mechanical properties when WC-7.5wt%Co and WC-12wt%Co compositions were experimented with various mixing, milling and consolidation conditions. Magnetic Pulsed Compaction (MPC) was used to consolidate WC-7.5wt% Co and WC-12wt% Co powders where high-energy ball milling with varying duration was employed for generating various powder types. Mechanically alloyed milled, non milled and mixed (non milled and milled powders in certain proportions) powders with compositions of WC-7.5wt% Co and WC-12wt% Co were used, followed by applying high pressures to form the bulks. Maximum densities for mixed milled and non milled WC-Co bulks after MPC were found to be around 60-65%, which later turned nearly 82% after sintering, while a maximum hardness of over 1400 Hv was observed in WC-12wt%Co sample. Density, hardness and other microstructural behavior did not illustrate substantial changes when mixed powders were used, although variations were noticed when non-milled powders were used for consolidation. Keywords: Carbides, compaction, high-energy ball milling, mechanical properties, microstructure, sintering.

Influence of the Dopants on the Mechanical Properties of Alumina-Based Ceramics

In the present study the mechanical properties of dense alumina-based ceramics obtained by two processing routes are investigated. The application of magnetic-pulsed compaction or hot pressing of the powder leads to a comparable combination of microhardness, elastic modulus, and fracture toughness. The insertion of Al into Al2O3 powder increases the microdistortions of the crystalline lattice, resulting in the sufficient decrease of indentation wear-resistance. The usage of ZrO2 or TiCN as dopants to alumina matrix improves slightly the mechanics of the composites with a noticeable decrease of the material lost by 30% compared to pure alumina at closely spaced arrays of indents. Regardless of the synthesis method, the ceramic grains were formed completely with the fracture travelling along the grain boundaries.

Uniaxial compaction of nanopowders on a magnetic-pulse press

Uniaxial magnetic-pulse compaction of nanosize powders is studied experimentally and theoretically. Experiments are carried out with powders based on aluminum oxide. The theoretical model of the process includes the consistent solution of equations describing the dynamics of the pulsed magnetic field as well as the dynamics of the mechanical system (movable parts of the press and the powder being compacted). The behavior of the powder is described using the phenomenological theory of a plastically compacted porous body. Direct comparison with experimental data makes it possible to determine all input parameters required for theoretical calculations. A wide range of pressing conditions is investigated and the effect of parameters such as the mass of the powder being compacted and the mass of the parts of the press being accelerated is analyzed. The conditions are determined for the most effective use of inertial properties of the press, which must result in high-density products of compacted powders.

Modeling and optimization of uniaxial magnetic pulse compaction of nanopowders

An experimental and theoretical study of the process of the uniaxial magnetic pulse compaction of nanopowders is conducted. The experimentation is carried out using aluminum oxide powders. The developed theoretical model includes the integrated description of the pulse magnetic field and of the dynamics of the mechanical system (of the moving pressing tooling and of the densified powder). The powder constitutive behavior is considered in the framework of the phenomenological theory of plastic porous bodies with hardening. The direct experimental data input enables the introduction of all the parameters necessary for the theoretical calculations. Based on the developed model, the influence of a broad range of pressing conditions and parameters (the densified powder mass, the mass of the accelerated press equipment parts, specimen diameter, etc.) on the final specimen density and on the effectiveness of the magnetic pulse compaction is studied. The process conditions, under which the optimal inertia properties of the pressing device lead to the fabrication of high-density components, are determined.

Sliding wear resistance of fine Co powders compacted by the magnetic-pulsed compaction method

The microstructural and wear properties of consolidated Co powders prepared by non-pressure sintering and magnetic pulse compaction (MPC)+sintering methods were investigated. The relative densities were found to be 94.4% and 96.2% for non-pressure sintered and MPC+sintered bodies, respectively. Some holes, arising from the removal of weakly bonded particles, were observed on the surface of non-pressure sintered sample while the surface of MPC+sintered sample was very smooth and consisted of homogeneously distributed Co particles. MPC+sintered sample exhibited a lower wear rate than non-pressure sintered sample. SEM observations from the worn surfaces and corresponding longitudinal sections implied that the abrasive and fatigue were two dominating mechanisms responsible for the wear behavior of samples. The high wear resistance of MPC+sintered sample can be ascribed by the strongly bonded particles originating from the high packing ability of MPC method.