Shock Compaction Research Articles

고속 충돌 시 발생하는 평면 충격파를 이용한 산화 나노 분말의 치밀화 및 기계적 특성 평가

Bulk nanostructured copper was fabricated by a shock compaction method using the planar shock wave generated by a single gas gun system. Nano sized powders, average diameter of 100 nm, were compacted into the capsule and target die, which were designed to eliminate the effect of undesired shock wave, and then impacted with an aluminum alloy target at 400 m/s. Microstructure and mechanical properties of the shock compact specimen were analyzed using an optical microscope (OM), scanning electron microscope (SEM), and micro indentation. Hardness results showed low values (approximately 45~80 Hv) similar or slightly higher than those of conventional coarse grained commercial purity copper. This result indicates the poor quality of bonding between particles. Images from OM and SEM also confirmed that no strong bonding was achieved between them due to the insufficient energy and surface oxygen layer of the powders.

Finite Element Simulation of Powder Compaction via Shock Consolidation Using Gas-gun System

Shock consolidation is a promising method for consolidation of nanocrystalline metallic powders since it can prevent grain growth of nanopowders during the process due to very short processing time. However, internal cracks often occurs in powder compacts during the shock consolidation process. In this paper, finite element simulations showed that reflected tensile wave causes spall phenomena resulting internal crack of powder compaction during shock compaction process. To reduce spall phenomena, FEM simulation with changing compaction die's geometry was performed to find out relationship between shape and tensile wave intensity. Based on FEM results, new compaction die was designed and bulk nanocrystalline Cu are obtained using new compaction die.

Explosively driven fragmentation of granular materials

This paper investigates the explosively driven dynamics of dry and wet sand. Contrary to popular belief, wet sand under high strain rate loadings (10(4)s(-1)) is observed to have reduced resistance against flow compared to the dry sand, which is supported by a noticeably enhanced expansion before the breakup followed by an increased number of fragments. Even a small amount of interstitial oil (3.2 wt.%) suffices to substantially reduce the size of fragments whose average mass only amounts to 60% of the mass of the dry sand fragments. To predict the instability onset of the expanding sand shell, a kinetic instability model is proposed based on an instability criterion involving the opposing forces of stabilizing inertial pressures and destabilizing viscous resistance. The interstitial oil leads to a smaller viscous resistance of wet sand by the lubrication effect as well as lessening the degree of shock compaction. The dominance of viscous resistance thus commences later for the wet sand shell until a smaller thickness allows the inertial forces to be overtaken. Moreover, multi-shear localizations rather than interface instability are identified as the dominant mechanism for the instability onset of the expanding sand shells.

Consolidation of Mg<sub>2</sub>Si Powder Using Shockwave Generated by Projectile Impact

A series of shock compaction experiments on as-received and ball-milled Mg2Si powder were conducted. The crystalline size in the shocked compacts obtained from the ball-milled powder was equivalent to that of the compacts obtained from the as-received powder. Although the shock pressure was higher than the phase transition pressure, the crystal structure reverted to its original structure under ambient conditions. For the shocked compact obtained from the ball-milled powder, a MgO peak appeared in the X-ray diffraction pattern.

Production of Sintered α-Alumina by Explosive Compaction from Low Temperature Calcinated Aluminum-Rich Sludge

Up to now the studies performed on alumina nanocrystalline powders using explosive compaction were restricted to the powders produced by specific industrial processes. The research work concerning other sources of alumina, like sludge from industries of aluminum anodizing, only regards to alpha-alumina. This is resulting from a previous heat treatment to high temperatures for which the phase transformation γ → α occurs. In present research is evaluated the possibility to use sludge having, before consolidation, as main phase γ-alumina, that means lower maximum temperature during preliminary calcination. After dried at 110 °C and heat treated at 800 °C during 1 h having as the major phase γ-alumina, the sludge was processed by explosive compaction followed by sintering at 1,200 and 1,650 °C (holding time = 1 h). During shock compaction the γ-alumina was transformed into α-alumina. The role of phase transformation during the explosive compaction followed by sintering is highlighted by the mechanical properties of the bulk material after sintering. The bulk material has hardness values close to α-alumina produced by conventional powder technology. Moreover, it was detected that the sulfur content of 4.5 % (w/w) measured in sludge previously calcinated was further reduced to 0.04 % (w/w), after explosive compaction. This study opens a sustainable possibility to recovery of Al-rich sludge to produce bulk alpha-alumina components/devices.

Thermodynamic Analysis of the Shock Compaction of W/Cu Granular Mixture Based on the Mesoscale Simulation

Shock compaction is an important industrial manufacturing technology for metal powder mixture. In order to analyze the thermodynamic response of W/Cu powder mixture during the shock compaction process, numerical simulation is conducted based on the mesoscale model. The model is generated randomly according to the real morphology distribution statistics regularity. Shock wave is achieved by introduce a rigid wall moving towards the model. Therefore, effects of deformation morphology, temperature distribution and pressure distribution under different shock velocities are presented and discussed. This work could provide a detail understanding of thermodynamic response during shock compaction process in granular-level.

Equation of State and Evidence of Enhanced Phase Transformation for the Shock Compression of Distended Compounds

Shear stress and deformation is inherent to shock-wave compression. Shear deformation is enhanced when the material subject to shock compression is in an initial distended state. Shock Hugoniot data for full-density and porous compounds of boron carbide, silicon dioxide, tantalum oxide, uranium dioxide and playa alluvium are investigated for purposes of equation-of-state representation of intense shock compression. Hugoniot data of distended materials reveal evidence of accelerated solid-solid phase transition as a consequence of shock compaction and accompanying enhance shear deformation. A phenomenological thermo-elastic equation-of-state model is constructed that accounts for both deformation- induced phase transformation and the extreme shock compaction of distended solids, and applied to the compounds studied.

Equation of state and evidence of enhanced phase transformation for shock compression of distended compounds

Shear stress and deformation is inherent to shock-wave compression. Shear deformation is enhanced when the material subject to shock compression is in an initial distended state. Shock Hugoniot data for full-density and porous compounds of boron carbide, silicon dioxide, tantalum pentoxide, uranium dioxide and playa alluvium are investigated for purposes of equation-of-state representation of intense shock compression. Hugoniot data of distended materials reveal evidence of accelerated solid–solid phase transition as a consequence of shock compaction and accompanying enhanced shear deformation. A phenomenological thermo-elastic equation-of-state model is constructed that accounts for both deformation-induced phase transformation and the extreme shock compaction of distended solids, and applied to the compounds studied.

Room-temperature fast deposition and characterization of nanocrystalline Bi0.4Sb1.6Te3 thick films by aerosol deposition

P-type nanocrystalline Bi0.4Sb1.6Te3 thick films were directly deposited on copper substrates by aerosol deposition (AD) involving shock compaction of the starting powder at room temperature. The film deposition rate was over 700 μm/min. The relative density of the films was above 95%. Films with a thickness of over 2 mm were obtained. They consisted of nanocrystals with grain sizes of several tens of nanometers. The crystal structure of the films was the same as the bulk materials prepared by spark plasma sintering (SPS) using the same starting powder. We measured the electrical conductivity, carrier concentration, Hall mobility, and thermal conductivity of the films and compared them with those of the bulk materials. The thermal conductivity of the AD film was 20-30% lower than that of the bulk materials, which is attributed to the increased number of grain boundaries and some defects in the AD films.

Preparation of Bi Superconducting Grains Including Seed Crystals by Shock Compaction

ABSTRACTWe have fabricated Bi2212 and Bi2223 bulk samples by shock compaction technique. Seed crystals were added to the starting materials in order to promote crystallization. The grain size of the prepared sample was increased by the addition of seed crystals to the starting material.

High-pressure equation of state properties of bismuth oxide

The high pressure equation of state response of hot pressed bismuth trioxide (Bi2O3) powder compacts is determined through a series of parallel plate impact gas-gun experiments. Loose powders of Bi2O3 are hot-pressed to an average density of 9.202 g/cm3, corresponding to 96% theoretical maximum density. Shock compaction of the compacts to pressures between 4-17 GPa reveal full consolidation occurring at pressures above ∼ 8 GPa. Using the experimentally determined Hugoniot of the 96% dense compact, calculations are performed to obtain the equation of state parameters for solid density Bi2O3.

Research on Initiation Sensitivity of Solid Explosive and Planer Initiation System

Firstly, recently, there are a lot of techniques being demanded for complex process, various explosive initiation method and highly accurate control of detonation are needed. In this research, the metal foil explosion using high current is focused attention on the method to obtain linear or planate initiation easily, and the main evaluation of metal foil explosion to initiate explosive was conducted. The explosion power was evaluated by observing optically the underwater shock wave generated from the metal foil explosion. Secondly, in high energy explosive processing, there are several applications, such as shock compaction, explosive welding, food processing and explosive forming. In these explosive applications, a high sensitive explosive has been mainly used. The high sensitive explosive is so dangerous, since it can lead to explosion suddenly. So, for developing explosives, the safety is the most important thing as well as low manufacturing cost and explosive characteristics. In this work, we have focused on the initiation sensitivity of a solid explosive and performed numerical analysis of sympathetic detonation. The numerical analysis is calculated by LS-DYNA 3D (commercial code). To understand the initiation reaction of an explosive, Lee-Tarver equation was used and impact detonation process was analyzed by ALE code. Configuration of simulation model is a quarter of circular cylinder. The donor type of explosive (SEP) was used as initiation explosive. When the donor explosive is exploded, a shock wave is generated and it propagates into PMMA, air and metallic layers in order. During passing through the layers, the shock wave is attenuated and finally, it has influence on the acceptor explosive, Comp. B. Here, we evaluate the initiation of acceptor explosive and discuss about detonation pressure, reactive rate of acceptor explosive and attenuation of impact pressure.

Fabrication of bulk AlN–TiN nanocomposite by reactive ball milling and underwater shock consolidation technique

Reactive milling of aluminum nitride and titanium powders corresponding to the stoichiometric reaction Ti + AlN resulted in the formation of the ceramic matrix composite AlN–TiN. Prolongation of the milling process led to a microstructure with nanosize range of crystallites of both AlN and TiN, evidenced through XRD measurements, SEM and TEM observation. Further, underwater shock compaction with a pressure level of about 10 GPa was applied to the nanocomposite powders to obtain bulk nanostructured sample. The effect of this shock compaction on the prolonged milled powder resulted in a 22% reduction in crystallite size. The average microhardness of the consolidated nanocomposite was 656 HV and 840 HV for 40 h and 100 h MA samples, respectively, with densities 98% of theoretical values in both cases as well as no change in chemical composition.

Deposition mechanism of dry sprayed ceramic particles at room temperature using a nano-particle deposition system

The nano-particle deposition system (NPDS) is a new dry spray process used to deposit metal and ceramic particles at room temperature. Low temperature deposition techniques for metals and ceramics that involve particle spraying include the NPDS, cold spray, and aerosol deposition methods. These are widely used to minimize thermal damage to the substrate when fabricating metal or ceramic layers. To optimize the process conditions for the intended applications and improve the deposition quality one must understand the mechanism of particle deposition at room temperature. The bonding mechanism in metal particle deposition by the cold spray method has already been researched. Adiabatic shear instability near the particle/substrate interface due to plastic deformation was reported to be the bonding mechanism for metal particles below the melting temperature. However, the bonding mechanism of ceramic particles has not been fully determined. This study assessed the bonding of ceramic particles by NPDS using numerical analysis and experimental results. A bonding mechanism is suggested after considering the experimental results for shock compaction, which is a process similar to that of the NPDS. The suggested deposition mechanism for ceramics involves the fragmentation of submicron ceramic particles into nanoparticles and the successive impact of submicron particles, which provides sufficient bonding energy, with heat and high pressure, to nanoparticles fragmented by the shock wave.

Numerical Simulation of the Shock Compaction of W/Cu Powders

A numerical simulation approach is used to study the deformation and temperature distribution of W/Cu powders under shock compaction. A two-dimensional micromechanical model is employed where only a few particles are considered. The simulation is performed using plane strain element and Lagrange formulation. Shock compaction is achieved by bringing in the W/Cu powders an intense compression wave using a high-velocity rigid wall. The effects of compact velocity, particle size and friction on the particle deformation and temperature distribution are discussed based on the results of simulations. The study provides a detailed understanding of the micromechanical behavior of metal powders during shock compaction process.

Microstructural, crystal structure and electrical characteristics of shock-consolidated Ga 2O 3 doped ZnO bulk

Ga 2O 3 (5 wt.%) doped zinc oxide (ZnO, 95 wt.%) bulk was fabricated by underwater shock compaction technique. The microstructural, crystal structure and electrical properties of shock-consolidated samples were investigated and compared to a commercially available sintered Ga 2O 3 (5 wt.%) doped ZnO (95 wt.%). The relative density of shock-consolidated sample was about 97% of the theoretical density, and no grain growth and lattice defects were confirmed. The grain boundary resistance was remarkably higher than that of commercial sintered Ga 2O 3 doped ZnO and nonlinear current–voltage (I–V) characteristics of shock-consolidated ZnO and Ga 2O 3 doped ZnO were very lower than that of commercial ZnO varistor.

Effect of aluminum content on the mechanochemical synthesis of in-situ TiN in the Al–Ti–AlN system and subsequent shock consolidation

To determine the effect of aluminum content on the formation of in-situ TiN in the Al–Ti–AlN system, a mixture of aluminum, titanium and aluminum nitride powders was subjected to high energy milling. Al content of the mixture was changed according to the following stoichiometric reaction: Ti+AlN+ XAl→TiN+(1+ X)Al. The value of X was varied from 5.35 to 19.65 based on the stoichiometric calculation of the molar mass of each component expected to result in aluminum matrix composite with TiN weights of 30%, 20% and 10%, respectively, in addition to reaction corresponding to X=0(Ti+AlN→TiN+Al). Thermodynamic factors determine that the amount of Al in the mixture plays a key role in the formation of in-situ TiN. XRD and EPMA results showed that at lower Al content ( X=0, 5.35), reaction proceed through a gradual mode. By increasing Al content ( X=19.65), no mechanochemical reaction occurred between Ti and AlN. Continuation of the milling process allowed acquisition of in-situ TiN in the designed compositions of AlN–TiN, Al–Ti–AlN–30%TiN, and to some extent, of Al–Ti–AlN–20%TiN. A nanocrystalline solid solution evolved by mechanical alloying (MA) was sustained for prolonged milling time. The mean TiN crystallite size obtained was 10 nm for the AlN–TiN composition. The end product milled powder after 40 h of milling time, equating to the Al–Ti–AlN–30%TiN composition was consolidated into bulk compact using the underwater shock compaction method. The milled specimens were characterized by XRD, scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and microhardness testing. The sample had a uniform and fine-grained composite structure with 99% theoretical density and average microhardness of 434 HV0.1. The results confirmed the possibility of fabricating reliable bulk nanostructured materials by imposing shock compaction on submicron sized powders.

Shock-compression response of magnetic Fe 3O 4 nanoparticles

The shock-compression response of magnetic nano-Fe 3O 4 powders of ∼12 nm and ∼6 nm, and their bimodal mixture (∼12 nm + ∼6 nm in a 4:1 ratio), was investigated to determine the densification behavior of nanoparticles and properties of the consolidated magnets. Compacts recovered following shock compaction using a three-capsule, plate-impact, gas-gun setup at impact velocities of ∼800 m s −1 and ∼1100 m s −1 showed maximal densification of ∼80% theoretical maximum density (TMD) for ∼12 nm particles, ∼70% TMD for ∼6 nm particles, and ∼75% TMD for the bimodal mixture (∼12 nm + ∼6 nm in a 4:1 ratio) nanoparticles. Pressure–volume compressibility (Hugoniot) plots of nano-Fe 3O 4 powder compacts were constructed to assess their dynamic densification behavior. Scanning electron microscopy imaging of the recovered compacts showed the presence of a laminar structure, with inter-layer voids and microscopic gaps between nanoparticle agglomerates, which were responsible for the incomplete consolidation. X-ray diffraction and transmission electron microscopy analyses showed the retention of nanostructure in the recovered compacts, although the shock-energy deposition caused some grain growth. Hysteresis loop measurements revealed that the magnetic properties were retained, and shock compaction did not cause any magnetic transition. The potential causes for the lack of complete densification observed in the recovered shock-consolidated compacts of nano-Fe 3O 4 particles are discussed in light of the shock-consolidation mechanisms and interparticle bonding in nano-sized powders.

Magnetization, magnetic transition and magnetic entropy changes of bulk MnAs1−xSbx fabricated by underwater shock compaction

MnAs 1− x Sb x ( x = 0.068, 0.073) materials were fabricated by means of underwater shock compaction technique. A peak shock pressure of water acting on the powders was about 16 GPa. It was confirmed that underwater shock compaction leads to the compositional inhomogeneity, broad magnetic transition and lower magnetization and magnetic entropy changes of MnAs 1− x Sb x . However, these problems were improved by a post-annealing. Consequently, the post-annealed samples after the shock compaction exhibit the sharp magnetic transitions and high magnetic entropy changes of in a field of 1 T.

Electric and microstructural characteristics of bulk ZnO fabricated by underwater shock compaction

An underwater shock compaction of pure zinc oxide (ZnO) powder has been performed. This technique uses an underwater shock wave generated by detonation of an explosive. Shock pressure used in this work was about 10 GPa. The morphology and structure of shock-consolidated ZnO was investigated by X-ray diffraction (XRD) method and scanning electron microscopy (SEM). The density and impedance characteristics of shock-consolidated ZnO were measured by Archimedes method and Nyquist plot method, respectively. The shock-consolidated ZnO without visible cracks was successfully obtained. It was confirmed that the shock-consolidated ZnO had 99% of theoretical density without grain growth and high grain boundary resistivity in comparison with the commercial sintered ZnO.