Copper Compacts Research Articles

Thermal Processes in the Heating of Powder Compacts of Metals and Their Compositions I. Recrystallization Thermokinetics of Copper Compacts

Thermal Processes in the Heating of Powder Compacts of Metals and Their Compositions I. Recrystallization Thermokinetics of Copper Compacts

Analysis of microwave heating of copper powder compacts

The influence of the native oxide films, which is essential for the understanding of the microwave heating of metal powder, is analyzed numerically based on the experimental data on temperature, dilatation and resistance of compacted copper powder samples. The indicative thickness of the oxide films, determined from the resistivity data using an effective medium approximation, is shown to decrease from ≥1 μm to below 1 nm. The effective complex dielectric permittivity and magnetic permeability of the copper powder with oxide films on the particles are calculated within the recently developed models. The dielectric permittivity exhibits a percolation behavior in the temperature range of the oxide decomposition, viz. 210–250 °C when microwave heating is carried out in nitrogen and 330–375 °C – in argon. The efficiency of absorption of the incident 30 GHz microwave radiation in a slab of powder is assessed separately for the electric and magnetic-type losses, the contribution of the latter being predominant until the percolation transition. The energy flux density of the incident microwave radiation required to sustain the prescribed heating rate is shown to increase during the microwave heating process from ∼20 W/cm2 to >1 kW/cm2 due to increasing reflection. The additional microwave energy input required for the completion of the endothermic oxide decomposition reaction is shown to be significant at the initial stage of the process (below 200 °C).

Mechanical Properties of Microporous Copper Powder Compacts Produced by Oxide Reduction

Powder metallurgy (PM) processes for porous copper and alloys have seen some commercial successes, but PM methods have the disadvantage of relatively low porosity or strength that is compromised by stress-concentrating interparticle bonds. To increase porosity without compromising scalability, a Cu-CuO metal matrix composite powder was utilized to produce additional microscale porosity within the particles by oxide reduction. These Cu-CuO powders were pressed at 1, 2, or 3 GPa, and made porous at 600, 800, or 1000 °C to investigate the effects of pressing and sintering parameters on the overall strength and density. It was found that the formation of porosity is weakly dependent on compaction pressure (maximum 6% difference from 1 GPa to 3 GPa), while the final porosity varied by ~16% overall (~40% for 1 GPa and 600 °C to 24% for 3 GPa and 1000 °C). The strength of the porous Cu was highest after being reduced at 600 °C but also exhibited some flaking at the edges at high strain. The 1 GPa, 600 °C samples have a higher specific strength than wrought Cu annealed at the same temperature, as was demonstrated under uniaxial quasi-static compression as well as split Hopkinson pressure bar impact.

Influence of grading and fabric arising from the initial compaction on the geomechanical characterisation of compacted copper tailings

Tailings dams constructed using the upstream method are generally less stable, because of its operational and constructive approach; this presents increased risks, which is the reason why such structures are being closed in Brazil. A feasible option to ensure the safety of closing operations in such dams consists of extracting tailings from behind the dam (reservoir), reducing moisture content through dewatering and compacting it into stable stacks. This demands knowledge of the compacted material's response. Thus, the present research assesses the mechanical response of compacted copper ore tailings extracted from two different sampling locations within the dam reservoir (i.e. about to be de-characterised) from northern Brazil. For this, drained and undrained triaxial compression tests were carried out on compacted dewatered dense, medium and loose specimens, which were assembled using the tailings retrieved from upper and lower beaches to evaluate the influence of grading, as well as the influence of the fabric arising from the initial compaction on the critical state lines (CSLs) of these saturated non-plastic silty sand tailings. The results indicated that the critical state parameters, in the υ–ln p′ space, are dependent on the fabric arising from the initial compaction. Distinct CSLs, which are all curvilinear and parallel to each other, were found in the research.

Three-dimensional multiparticle finite element simulation of dynamic compaction of copper powder by laser shock

A three-dimensional multiparticle finite element method(3D MPFEM) model of laser shock compaction powder was established, and the forming process and densification mechanism of dynamic compaction were studied. The effects of the laser peak pressure(1–5 GPa) on the powder density was studied. The compaction density increased with the laser peak pressure and reached the highest at 5 GPa. A comparison of the different energies of the system revealed that the increase in powder temperature was mainly due to the plastic deformation. In the process of powder springback, large pressure can induce rebound, and the powder may produce an interparticle separation phenomenon due to the difference in particle velocities in different layers. Analysis of the densification process of the inner particles, revealed that the upper layer particles undergo first plastic deformation, and then the second plastic deformation occurs due to the inertia effect, which contributes to the improvement of the powder density. • 3D MPFEM was used to simulate the laser shock powder dynamic compaction process. • Adiabatic temperature rise effect is related to powder plastic deformation. • Laser shock powder has springback phenomenon and large strain rate.

Conventional sintering of copper powder with and without addition of different weight percentage of aluminium powder

Cu-Al powder for different weight percentages of 5, 10 and 15 was ball milled for 30 min. The compacts of pure Cu, Cu- 5 wt.% Al, Cu-10 wt.% Al and Cu-15 wt.% Al was compacted using metallic die by applying 70 kN force. The compacts were kept in a heat treatment electrical resistance furnace at 600oC for 8hr for conventional sintering. The conventional sintered compacts were tested to measure the behaviour of the alloy. The density of the sintered compact of Cu, Cu-5 wt.% Al, Cu-10 wt.% Al and Cu-15 wt.% Al were calculated using water displacement method. The surface topography of the sintered compacts were analysed using optical metallurgical microscope for the magnifications of 100x. The microstructure of the copper is exhibited cellular structure. The quantity of the secondary phase increases with increasing Al content. The hardness values of respective compacts were measured using Wilson micro Vickers hardness testing machine. The micro Vickers hardness values of Cu, Cu-5 wt.% Al, Cu-10 wt.% Al and Cu-15 wt. % Al were measured as 38.78 ± 1.2, 21.22 ± 2.0, 24.54 ± 3.7 and 39.44 ± 3.5 HV1 respectively. The compression strength of the sintered compacts of pure copper, copper with 5, 10 and 15 wt.% Al were determined using universal testing machine. The compression strength of Cu-15 wt.% Al is higher than copper and other sintered Cu-Al compacts.

Experimental Study on Dynamic Compaction of Copper Powder by Laser Shock Wave

Experimental Study on Dynamic Compaction of Copper Powder by Laser Shock Wave

Experimental study on drop penetration and wetting characteristics of sintered copper powders with nanostructures

In this study, nanostructures were fabricated on sintered copper powders through alloying-dealloying method for investigating and analyzing drop penetration and wetting characteristics. Based on the high-speed video imaging, the kinetics of droplets immersing process were studied for multi-scale composite compact (MCC), featured with the microns for copper particle sizes and nanometers for the surface structures. The comparisons of various sizes of copper powders and different initial falling heights were conducted to explore the effect of porous structures. The results indicated that the nanostructures, with pore size and ligament size of approximately 30 nm and 50 nm respectively, could effectively enhance the hydrophilic performance for the sintered copper compacts. Moreover, larger powder size could lead to faster penetration, while the higher initial falling height facilitated the increase of the maximum spreading diameter of droplet, resulting in lower penetration time.

Study on mechanical characteristics, microstructure and equation of copper powder compaction based on electromagnetic compaction

Electromagnetic powder compaction technology had the advantages of high efficiency and strong impact during the powder forming. The mechanical characteristics of copper powder compaction were investigated through digital image correlation technology under different discharge energies. The microstructure was analyzed by the metallography and electron microscopy. The results showed that the force-displacement curves had a bimodal tendency during the compaction of copper powders. The compaction force and velocity of copper powders gradually increased with the increase of discharge energy. The microstructure distribution of copper compacts was more and more dense as the discharge energy increased. However, the microstructure distribution of the axial direction of compact center was not much different overall at the same discharge energy. There was a tendency that the microhardness values at the center of the upper end faces were gradually larger than that of the lower end faces. The electromagnetic compaction equation of copper powders was established by Gaussian fitting. It had been verified that the error between the predicted and actual values of equation was only 0.47%.

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%.

Particulate Scale Multiparticle Finite Element Method Modeling on the 2D Compaction and Release of Copper Powder

Herein, two‐dimensional (2D) single‐action die compaction process of copper (Cu) powder was simulated by the multiparticle finite element method (MPFEM) at particulate scale. The initial packing structure, generated by the discrete element method (DEM), was used as an input for the FEM model, where the mesh division of each particle was discretized. The evolution of macro‐ and microscopic properties, such as relative density, stress distribution, particle deformation, void filling behavior, and force transmission, during compaction and pressure release processes have been systematically studied. The results revealed that the force is mainly concentrated on largely deformed regions of the particles during compaction and formed a contact force network, which hindered the densification process. In the compact, the shorter side of the large void edges rendered higher stress than the longer side. On the other hand, the stress distribution of small void edges remained uniform. After pressure release, large residual stress was observed at the contact area of the adjacent particles and the maximum stress was observed at the particles’ edges. Moreover, the residual stress did not proceed to the interior of the particles. Meanwhile, the stress of large void edges has been completely released but exhibited a nonuniform distribution. The smaller fraction of void filling resulted in a larger reduction of the released stress after pressure removal. Also, the particles closer to the upper die exhibited higher average equivalent von Mises stress inside the particles during compaction and pressure release processes.

Measuring the Changes in Copper Nanopowder Conductivity during Heating as a Method for Diagnosing its Thermal Stability

This work researches the impact of the temperature of compacted copper nanopowder on the amperage of the current flowing through the nanopowder sample. It was determined that upon reaching its oxidation temperature (~ 1900C), the copper nanopowder started conducting electricity, and at 280-320°C electric breakdown of sample was occurring. This is caused to irreversible processes taking place in nanomaterials during heating, such as sintering and mass-transfer, those processes leading to the formation of conductivity channels. This speaks in favor of an evident dependency between copper nanopowder conductivity and the chemical transformations taking place in it; this allows for recommending this research method for instant diagnostics of copper nanopowders.

Preparation and electrical properties of sintered copper powder compacts modified by polydopamine-derived carbon nanofilms

In this study, copper (Cu)/polydopamine (PDA) composite was fabricated by vacuum hot-press sintering of micrometer-sized Cu particles covered with PDA film tailored at the nanometer scale thickness. The resultant compacts exhibited much higher electrical conductivity than the uncoated counterparts. Analyses of sintered samples using scanning and transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy revealed the conversion of PDA into carbonized PDA (cPDA). The increased mass density and grain growth are likely responsible for improved electrical conductivity of the composite material.

Effect of target-fixture geometry on shock-wave compacted copper powders

In shock compaction with a single gas gun system, a target fixture is used to safely recover a powder compact processed by shock-wave dynamic impact. However, no standard fixture geometry exists, and its effect on the processed compact is not well studied. In this study, two types of fixture are used for the dynamic compaction of hydrogen-reduced copper powders, and the mechanical properties and microstructures are investigated using the Vickers microhardness test and electron backscatter diffraction, respectively. With the assistance of finite element method simulations, we analyze several shock parameters that are experimentally hard to control. The results of the simulations indicate that the target geometry clearly affects the characteristics of incident and reflected shock waves. The hardness distribution and the microstructure of the compacts also show their dependence on the geometry. With the results of the simulations and the experiment, it is concluded that the target geometry affects the shock wave propagation and wave interaction in the specimen.

A modified diametrical compression test technique (MDCTT) for mode II fracture toughness of iron powder compact

A sound knowledge of the fracture properties of a powder metallurgy (PM) component is essential for a design engineer to predict or prevent sudden fracture failure. Though iron powder is the most used base material in the PM industries, only its tensile mode fracture toughness (KIC) has been documented. This lack of adequate data can be traced to the non-availability of suitable test technique. In this paper, we present a new test approach for determining the mode II (shear mode) fracture toughness (KIIC) of iron powder compact. This method is known as the modified diametrical compression test technique (MDCTT). The MDCTT combined the qualities of diametrical compression test specimen with the pure shear mode failure of a riveted lap joint. The fracture toughness of copper powder compacts was also studied to corroborate the results of this technique. A comparison of the ratios KIICKIC for both powder compacts with theoretical predictions made using the maximum tangential stress criterion show strong agreement. Hence, the MDCTT is a suitable technique for determination of the KIIC values for iron and other metallic powder compacts.

Effects of particle shape and temperature on compaction of copper powder at micro scale

This study investigated the effects of particle shape and temperature on the compaction of copper powder at micro scale. Copper powder particles were compressed inside a cylindrical die cavity with 2 mm diameter to form compacts with about 3 mm height. Two kinds of particle shapes, spherical and dendritic, and two forming temperatures, room temperature and 400 °C, were considered in the experiments. Some of the produced compacts were further sintered at 600 °C. The study also used simple upsetting tests to investigate the characteristics of the deformation of the compacts under compressive stresses. The results showed that the compacts produced at room temperature demonstrated brittle deformations. However, by increasing the forming temperature to 400 °C, ductile deformations have been observed on the compacts of dendritic particles. Furthermore, the sintering treatment resulted in increases in dimensions, decreases in relative density and hardness, and an increase in ductility. It also led to pore growths which have been seen on scanning-electron microscope images. These phenomena were most significant in the dendritic powder compacts which were produced at 400 °C and treated by the sintering process.

CFD Simulation and Experimental Analyses of a Copper Wire Woven Heat Exchanger Design to Improve Heat Transfer and Reduce the Size of Adsorption Beds

The chief objective of this study is the proposal design and CFD simulation of a new compacted copper wire woven fin heat exchanger and silica gel adsorbent bed used as part of an adsorption refrigeration system. This type of heat exchanger design has a large surface area because of the wire woven fin design. It is estimated that this will help improve the coefficient of performance (COP) of the adsorption phase and increase the heat transfer in this system arrangement. To study the heat transfer between the fins and porous adsorbent reactor bed, two experiments were carried out and matched to computational fluid dynamics (CFD) results.

AN APPROACH TO IDENTIFY AND ESTIMATE THE BONDING OF COPPER AND ALUMINUM POWDERS

Ultrasonic powder consolidation (UPC) is a novel rapid, full-density powder consolidation process in which metal powders confined in a die under uniaxial loading is subjected to ultrasonic vibration at low temperature for a few seconds or less. In this research, copper powders with dendritic and spherical morphologies and an aluminum powder with spherical morphology were subjected to UPC under various conditions to investigate the effects of the process variables on the densification and metallurgical bonding of the compact. An ultrasonic washing test, developed in this research, was used to determine the extent of densification and bonding achieved in specimens consolidated under systematically varied UPC conditions. Hardness testing was also employed as a supplementary means for the assessment of compact density in both as-consolidated and ultrasonically washed states. The degree of metallurgical bonding was also qualitatively assessed from the fracture surfaces of manually broken specimens. With the dendritic and spherical copper powders, the minimum consolidation temperature, time and uniaxial pressure required for nearly full densification were determined to be 450 °C, 4 s and 84 MPa, respectively. The best conditions were 500 °C, 4 s and 100 MPa for both copper powders. Dendritic-powder specimens exhibited better] Densification and bonding than spherical-powder specimens above 450 °C. However, below 450 °C, the spherical powder produced better results, due probably to its higher packing geometry and repacking under the ultrasonic vibrations. With the spherical aluminum powder, specimens with best densification and bonding were obtained under the conditions of 400 °C, 2.5 s and 80 MPa. Compact densification generally requires a good amount of powder deformation. In UPC, this occurs very quickly in a fraction of a second if consolidation temperature is sufficiently high. However, a high degree of compact densification does not necessarily assure good metallurgical bonding. Bonding must be preceded by the formation of nascent metal-to-metal contact of powder particles, which requires good compact densification. Thus, densification is only a necessary condition for bonding. For the copper compacts, metallurgical bonding, at a given temperature, increased with increasing consolidation time, indicating that bonding is a thermally activated

Finite Element Modeling on the Compaction of Copper Powder Under Different Conditions

Single-action die compaction of copper powders with initial loose natural packing and vibrated random dense packing structures was carried out numerically by finite element method and physically for validation. Furthermore, the compaction under various cyclic loadings was modeled to identify its effects on the compact properties. The results were analyzed and compared between compacts formed at different initial packing structures and different forming conditions, which indicate that at the same pressure, single-action die compaction on the dense uniform initial packing can produce compacts with high relative density, uniform density and stress distributions, which implies the necessity to improve initial packing density and uniformity in forming high performance compacts. Meanwhile, by using cyclic loading on such dense initial packing structures, compacts with higher packing density and more uniform density and stress distributions can be created. The numerical and physical results are comparable and in good agreement with the proposed double logarithmic equation.

Cold Compaction of Copper Powders Under Mechanical Vibration and Uniaxial Compression

Physical experiments were carried out to study the cold compaction of copper powders under uniaxial compression using our self-designed equipment. Two kinds of copper powders with different particle sizes and distributions were considered. One-dimensional vibrations were utilized before compaction to systematically study the effect of parameters such as vibration frequency ω, amplitude A, and vibration intensity Г on the initial packing density. The macro-property and corresponding microstructures of compacts obtained from initial packings with and without vibrations were compared and analyzed. The results show that higher packing density can be obtained in the compaction of coarse powders with broad size distribution when other experimental conditions are fixed. For each powder, the evolution of packing density vs pressure takes on exponential correlation with high R 2 value. Much denser and more uniform compacts can be realized with the aid of vibration which can improve the particle rearrangement and result in the filling of macro pores formed in initial packing, and the characterization on the microstructure identifies that the particles inside the compact become polyhedrons with regular shape and uniformly distributed.