Shock Wave Compaction Research Articles

High compaction and physical graphitization of CNT bundles and network via extreme-load compression using laser-induced shockwave

The physical properties of carbon nanotube (CNT) networks, which are one-dimensional assemblies of CNTs, are still far short of the theoretical limits of individual CNTs. These lowered physical properties of CNT networks are mainly due to their high porosity and relatively weak inter-tube load/electron/phonon transfer efficiency at van der Waals junctions between CNTs and their bundles. We present a simple post-treatment technique utilizing high-intensity laser-induced shockwaves of up to ∼3 GPa that effectively densify CNT bundles and networks and physically transform CNT bundles into flattened multilayered graphene nanoribbons. CNT assemblies were selectively modified without chemical agents, and the network properties could be tuned by adjusting the laser compression intensity. After laser shockwave compaction, the CNT network structure showed two and three times higher specific strength and modulus than the as-prepared CNT networks. Furthermore, the thermal and electrical conductivities of the CNT networks were also amplified by 400–500% after laser shock compression. These enhancements can be explained by the substantial densification of CNT networks and physically activated graphitization leading to increased load/electron/phonon transfer between flattened CNTs and their bundles.

Study of Influence of Aluminum Nitride Nanoparticles on the Structure, Phase Composition and Mechanical Properties of AZ91 Alloy

In this work, magnesium-based composites were obtained by shock-wave compaction of a powder mixture of Mg-5 wt.% AlN at a shock-wave pressure of 2 GPa. Their microstructure was investigated and the phase composition was determined, from which it follows that the nanoparticles retain their phase composition and are uniformly distributed in the magnesium matrix. The materials obtained by shock-wave compaction were used as master alloys for the production of magnesium alloys by die casting. The amount of aluminum nitride nanoparticles in the AZ91 magnesium alloy was 0.5 wt.%. Studies of the microstructure of the magnesium alloys showed a decrease in the average grain size of the magnesium matrix from 610 to 420 μm. Studies of mechanical properties have shown that the introduction of aluminum nitride nanoparticles increases the yield strength from 55 to 119 MPa, the tensile strength from 122 to 171 MPa and the plasticity from 4 to 6.5%, respectively. The effect of nanoparticles on the fracture behavior of the magnesium alloy under tension was determined.

The shock wave compaction of ceramic powders

Joint theoretical and experimental investigations have allowed to realize an approach with use of mathematical and physical modeling of processes of a shock wave compaction of ceramic powders. The aim of this study was to obtain a durable low-porosity compact sample. The explosive compaction technology is used in this problem because ceramic powders such as boron carbide and aluminum oxide is an extremely hard and refractory material. Therefore, its compaction by traditional methods requires special equipment and considerable expenses. In order to better understand the influence of the loading conditions and, in particular, to study the effect of detonation velocity, explosive thickness and explosion pressure on the properties of the final sample, the problem of compaction of the powder in an axisymmetric case using the conditions of the above experiments have been numerically solved. Thus, using the technology of explosive compaction, compact samples of boron carbide and aluminum oxide are obtained. On the basis of experimental and numerical studies of shock waves propagation, the optimum scheme and parameters of dynamic compaction of boron carbide and aluminum oxide are determined in order to maximize the density and the conservation of the samples after dynamic loading.

Investigation of Characteristics of Alloys Manufactured by Shock-Wave Compaction on Bimetallic Fe-Cu Powders

The study deals with bulk nanostructured alloys manufactured by the method of shock-wave compaction on bimetallic Fe–Cu powders. The results presented suggest a possible efficient application of shock-wave compaction for the production of high-density compacts from bimetallic powders. The structure and parameters of bimetallic Fe–Cu powders formed by the method of electric wire explosion are investigated. An analysis of the structure and hardness of the bulk nanostructured alloys manufactured from these powders is performed.

Consolidation of Bimetallic Nanosized Particles and Formation of Nanocomposites Depending on Conditions of Shock Wave Compaction

The authors consider and evaluate the physical parameters and regularities of the process of consolidation of Fe–Cu, Cu–Nb, Ag–Ni, Fe–Pb nanoparticles when creating composite materials by means of shock wave compaction. As a result of theoretical consideration of explosive compaction process, researchers established and discussed the physical process conditions, established a number of threshold pressure values corresponding to different target indicators of the state of the compact. The time of shock wave impact on powders for powder consolidation was estimated.

Shock wave compaction and sintering of mechanically alloyed CoCrFeMnNi high-entropy alloy powders

In this study, mechanically alloyed CoCrFeMnNi high-entropy alloy (HEA) powders were compacted using static and shock wave compaction methods followed by pressureless sintering. The microstructural evolution and the mechanical properties were analyzed using optical microscopy, scanning electron microscopy, finite element method simulations, and tensile tests. The alloy consists of an FCC phase with a minor amount of ZrO2 in the as-milled and sintered condition. The presence of ZrO2 is due to the contamination during milling, and it led to the formation of composite microstructure after sintering. The static compaction of the alloyed powders resulted in an increase in compaction density (~ 85 to 88%) with the increasing pressure (1–3GPa), and the shock wave compaction of the alloyed powders resulted in the high relative density (~ 95%) with relatively fine and isolated pores. After sintering, almost full densification (~ 99.5%) with smaller grain size and better mechanical properties was achieved in the shock wave compacted specimens as compared to the sintering of static compacted specimens. The sintered shock wave compacted specimen exhibited high yield strength of ~ 630MPa and uniform strain distributions.

Structural and mechanical properties of aluminium-based composites processed by explosive compaction

Al based materials including Al-nanodiamonds and Al-Al2O3 processed by explosive compaction are considered in this paper. Improvements of composite properties were obtained by the introduction of diamond and ceramic nanoparticles (10wt% of each) into the mixture of aluminium nanopowder. Various schemes and conditions, including a theoretical calculation of the explosion process, were suggested and discussed. Physical and mechanical properties of composites reinforced with nanoparticles are determined and discussed with special consideration paid to process conditions. The results show an increase in the hardness, compressive strength and elastic modulus of the composites after explosive compaction with the introduction of nanoparticles into the powder mixture. Improvement of mechanical properties of composites compared to pure aluminium is determined by dispersion strengthening, small material grain size and internal compressive stresses caused by dynamic shock-wave compaction processing.

Structure, phase content and mechanical properties of aluminium with hard particles after shock-wave compaction

The possibilities to combine metal and metal oxide powders in various compositions open a broad range of mechanical and thermal behavior. When using in nanostructured components the resulting materials might exhibit even more interesting properties, like product effectiveness, tensile strength, wear resistance, endurance and corrosion resistance. Intermetallics like TiAl could be obtained as TiAlx in a quality similar to that obtained from melting where only eutectic mixture can be produced. Similar effects are possible when compacting nanoceramic powders whereas these can be combined with intermetallics. Currently, it is very difficult to produce wires and special shaped parts from high temperature superconducting materials. The compacting by explosives could solve this problem.The present paper uses explosion compacting of Al nanoparticles to create nanocomposite with increased physico-mechanical properties. Russian civil explosive Uglenit was chosen as high energy material (HEM) for shock-wave compaction. The different schemes and conditions were suggested to run the explosion process. Al nanoparticles as produced by electric wire explosion contain 8-10% of aluminum oxide. That aluminum oxide can serve as strengthening material in the final nanocomposite which may be generated in various compositions by explosive compacting. Further modifications of nanocomposites were obtained when including nanodiamonds into the mixture with aluminum nanoparticles with different percentages. The addition of nanodiamonds results in a substantial strengthening effect.The experiments with compacting aluminum nanoparticles by explosives are described in detail including the process variations and conditions. The physico-mechanical properties of the nanocomposites are determined and discussed by considering the applied conditions. Especially, microstructure and phases of the obtained nanocomposites are analyzed by X-ray diffraction.

Structure, Phase Composition, and Mechanical Properties of Aluminum Alloys Produced by Shock-Wave Compaction

Results of an x-ray phase analysis and investigations into the structure and mechanical properties of aluminum-base alloys produced by shock-wave compaction are presented. The method under study makes it possible to obtain samples with density approaching the theoretical value and improved mechanical characteristics.

Preparation of nano-Al2O3 dispersion strengthened coating via coating-substrate co-sintering and underwater shock wave compaction

Abstract This paper aims at developing a process technology to fabricate an aluminum dispersion strengthened coating on a copper substrate. First, nanostructured Cu–Al 2 O 3 powder was prepared by hydrogen-reduction of mechanical alloyed Cu and Al 2 O 3 mixed powders. Low-density coating was then achieved through die pressing and pre-co sintering. Finally, dynamic consolidation by underwater shock wave was used to densify the Cu–Al 2 O 3 sintering body, ensuring strong bonding between the coating and substrate. The compressing process was simulated using the commercially available package LS-DYNA. Numerical simulation gave deformation of the coating layer and pressure distribution during the compressing process. Microstructure characteristics indicate that the coating layer has a uniform and fine-grained composite structure and a strong surface bonding between coating layer and copper substrate. The fracture surface, analyzed by SEM, showed intergranular fracturing. Measurement of hardness showed a high hardness value, indicating sound mechanical properties of the coating layer. This method has thus been proven feasible for preparation of aluminum dispersion strengthened coating on copper substrate.

Effect of isochronal annealing on the magnetic and mechanical properties of Ti-Al-Co and Ti-Al composites

Ti-Al and Ti-Al-Co metal composites have been produced by shock-wave compaction using hexogen and ammonite explosives. The microstructure, microhardness, and temperature spectra of the real part of the complex magnetic susceptibility χ′(T) have been studied. The measurements have been performed in the course of isochronal annealings of the samples at temperatures progressively increasing in steps of 50 K. The values of χ′, which correspond to the isothermal sections of the spectra at 140 K and 400 K, as a function of the isochronal annealing temperature, χ′(T), have the form of asymmetrical bell-shaped curves. The maxima of these curves are in the region of the temperature of the α → β polymorphic transformation of cobalt. Possible reasons for this behavior of χ′ have been discussed.

Effect of the metal structure on the loss of stability of a thin plate separating a powder compressed by a shock wave

Results of an experimental and theoretical study of the problem of shock-wave compaction of a metallic powder enclosed into a metallic container with a transverse partition are presented. It is demonstrated that internal stresses in the partition generate disturbances, which evolve under explosive loading and compression of the partition together with the powder. In addition to the loss of stability in the powder, which occurs owing to filling of voids, wave formation on the partition is observed.

Enhanced microhardness of nanocrystalline carbon nanotube-reinforced Cu composite using planar shock-wave compaction

Planar shock-wave compaction (SWC), at a peak pressure of ∼15 GPa, was used to fabricate 90% dense carbon nanotube-reinforced–Cu composite (SWC-CNT/Cu). Transmission electron microscopy analysis of SWC-CNT/Cu revealed retention of nanoscale size Cu grains, and the presence of shear bands and homogeneous dispersion of CNTs in the Cu matrix. These findings explain the significantly enhanced hardness observed. A Vickers hardness and nanoindentation test for SWC-CNT/Cu indicated enhanced microhardness of 1190 and 1794 MPa, respectively, proving the efficiency of the SWC technique.

Explosive compaction of tungsten powder using a converging underwater shock wave

Tungsten and tungsten-based alloys have wide applications in industries. Powder metallurgy is one of the major processes for production of tungsten parts, but tungsten parts with high density cannot be produced by this method. Two explosive compaction processes using converging underwater and no-water shock wave, were applied to compact tungsten powder in the present investigation. C4 as an explosive material with a detonation velocity of 8.2 km/s applied to consolidate amorphous powder with a mean grain size of 5 μm. The density and hardness of consolidated tungsten parts were determined and by scanning electron microscope (SEM) analyzed their fragment surfaces. In addition to explosion experiments, a numerical simulation of compaction processes conducted by use of LS-DYNA program. Finally, the experimental results of two processes and numerical simulation results of the same processes compared. The results indicated that the tungsten parts without cracks and with a hardness equal to 570 Vickers and a density equal to 18.5 g/cm 3 can be obtained by underwater shock wave compaction method.

Shock-wave compaction of the granular medium initiated by magnetically pulsed accelerated striker

The experimental and theoretical investigation of the granular medium shock-wave compaction process is made. The striker acceleration in the experiments is realized by pulsed magnetic field force action. The granular medium is alumina nanopowder. The mathematical model of the process describes the energy dissipation, which is stipulated by the work made to compact the powder, considering the loss for the non-ideal reflection of the shock wave from the discontinuity surfaces on the borders of the body being compacted. There is a satisfactory fit of the theoretical calculations and the final compact’s density experimental data. In terms of the low-energy shock front approximation the problem of the time dynamics calculation of the granular medium state is narrowed down to the system of ordinary non-linear differential equations. The limitation the striker to low energies linearizes the system, allowing to take its rigorous solution. The influence of such parameters as starting voltage of the capacitor, powder and striker masses and wave resistances of contacting materials on the compaction process is analyzed.

A synthetic route for metal–ceramic interpenetrating phase composites

A novel synthetic route for metal–ceramic interpenetrating phase composites (IPCs) is proposed. The method excludes infiltration operations and eliminates the problem of closed pores and low wettability between ceramic and metal phase. We suggest using two-stage processing including preparation of composite powder precursors by reaction in a metal matrix and subsequent compaction of as-synthesized nanostructured powders. The appropriate choice of compaction technique allows obtaining dense nanostructured bulk IPCs. Bulk interpenetrating phase TiB 2–Cu nanocomposites were fabricated by Spark Plasma Sintering (SPS) and shock wave compaction of powder precursors.

衝撃波圧搾法で成形した高特性Ｆｅ‐Ｓｉ‐Ａｌ系圧粉磁心

Fe-Si-Al powder cores were made by shock wave compaction in order to obtain high compacted density, and their electromagnetic properties were investigated. The compacted density with shock wave was higher than that compacted conventionally. The initial permeability and also the permeability under DC bias increased with increase of the green density. Demagnetizing factor of the core was estimated large compared to that of conventionally pressed core, and the reason is supposed that the longitudinal direction of the particle is orientated to the shock wave direction. On the other hand, the resistivity of compaction by shock wave was lower than that of conventional pressing. It is guessed that the surface insulator was broken by the shock wave. The eddy current loss decreased with increase of the resistivity, and over about 0.01Ωm it showed approximately constant. It is suggested that eddy current generates only inside the particle over about 0.01Ωm, however below the critical resistivity it runs inter-particle due to the contact between particles.

Effect of Wave Formation during Shock-Wave Compaction of Powders

The problem of shock-wave compaction of a metal powder enclosed in a metal container with a transverse partition is solved. A model of wave formation on the partition and in the compact adjacent to the partition is proposed; the model is based on the loss of strength in the powder due to collapsing of pores and to development of instability of the partition being compressed in the shock wave.

Comparative Study of Al/SiC<sub>p</sub> Composites Manufactured by Direct and Underwater Explosive Compaction

Abstract. Aluminum matrix composites containing of 10, 20 and 30 vol% SiC particles were processed by direct and underwater explosive compaction methods. Optical microscopic examination hardness and bending strength measurements were carried out. It is observed that there was different distribution of SiC particles in recovered compacts by direct and underwater explosive compaction. In direct method, distribution of SiC particles at center and at periphery of the cross-section was different but in underwater (except some insignificant area at top and corners of the compact samples) microstructure was uniform. The micro hardness of compacts increased with increasing SiC particle volume fraction in both method and highest bending strength obtained for composite including 10-20 vol% SiC particles. Introduction Aluminum-matrix composites (AMCs) possess many advantages such as high strength, high stiffness and excellent wear resistance, which make them increasingly being cited as candidate materials in many industrial applications [1-3]. Particulate-reinforced aluminum matrix composites are most promising and also economically viable [4-6]. There are many methods for fabrication of AMCs. Dynamic consolidation, such as explosive compaction is a route that involves a very rapid and intense deposition of shock energy at powder particle surfaces and used to produce densification to a solid piece and has been intensively attractive method for the compaction of powdered materials and composites since 1980s[7,8]. This process offers several unique advantages over the static compaction methods in conventional powder metallurgy [9]. Among advantages achieved is high density (or full theoretical density) and prevention of undesirable microstructural changes such as reaction between the constituents in silicon carbide- aluminum composites. Shock wave can be gnerated by the detonation of an explosive that surrounds the powders (direct method)[10] or by explosive capsule that put on a water container as transmitting medium above powder container (underwater method)[11]. Normally researchers have studied shock wave compaction of favorite powders by one of these routes. In this investigation we tried compare some microstructure characteristics of Al/SiC

Shock-wave sintering of nanodiamonds

A two-stage technology of compaction of ultrafine-dispersed diamonds (UDDs) is developed and successfully applied for ampoule-free sintering of dense UDD granules in lead under a pressure of up to 100 GPa. Standard strength tests of polycrystals (fractions 80/63, 125/80) thus obtained showed a wide spread in strength (from grade AS4 to AS80), which is indicative of highly inhomogeneous sintering conditions. A single-crystal diamond is obtained for the first time by using shock-wave compaction; the crystal is a transparent twinned octahedron 0.6 mm in size with an impurity content of less than 0.05%. This result is unexpected and encourages us to believe that this method can be used to manufacture jewellery-grade diamonds (larger than 2 mm in size). The pressure and temperature conditions of sintering are analyzed.