Shock Compaction Research Articles

Evacuation Effect on Products during Underwater Shock Compaction

Evacuation Effect on Products during Underwater Shock Compaction

Bulk nanocomposite magnets produced by dynamic shock compaction

Exchange-coupled R2Fe14B/α-Fe (R=Nd or Pr) nanocomposite bulk magnets with nearly full density have been successfully produced by shock compaction of melt-spun powders. X-ray diffraction and transmission electronic microscopy analyses of the shock-consolidated compacts showed no grain growth upon compaction, in fact, a decrease in the crystallite size of both the hard and soft phases was observed. As a consequence, magnetic properties were retained and even improved after compaction. Hysteresis loops of the shock-consolidated powder compacts showed a smooth single-phaselike behavior, indicating effective exchange coupling between hard and soft magnetic phases.

Dynamic compaction domain (shock compaction energy vs. ρ0/ρ) for a Fe-15 atomic % Cu nanometric alloy obtained by mechanical alloying

A Fe-15 atomic percentage Cu mixture was processed by Mechanical Alloying, in a Spex 8000D, and Dynamically Compacted, in a light gas gun. The MA as-powder product was a supersaturated solid solution with a BCC structure (a=0.28736 nm). Nanometric grain sizes between 6 to 30 nm were obtained. Different impact velocities on precompacted cylindrical specimens were used to obtain bulk specimens. The energy used for compaction was between 6 to 10% of the impact energy. XRD and TEM showed no structural changes after DC. We are proposing a Dynamic Compaction Domain in the shock compaction energy vs. ρ 0 /ρ plane, were consolidation of nanometric powders can take place.

Dynamic compaction domain (shock compaction energy vs. ρ0/ρ) for a Fe-15 atomic % Cu nanometric alloy obtained by mechanical alloying

Dynamic compaction domain (shock compaction energy vs. ρ₀/ρ) for a Fe-15 atomic % Cu nanometric alloy obtained by mechanical alloying

Hot shock compaction of nanocrystalline alumina

An experimental investigation of hot shock compaction of a nanocrystalline alumina powder was performed. The effects of variations in shock pressure and compaction temperature on the properties of the compacted materials were studied. It was found that the bulk density and hardness of the compacted material increased with shock pressure. Increasing compaction temperature resulted in increases in compact hardness and bonding, and reductions in cracking within the compacted specimens. The results suggest that dense, well bonded, crack free nanocrystalline ceramics may be fabricated more effectively using hot shock compaction, than by room temperature shock compaction followed by sintering or room temperature static compaction followed by sintering.

次世代超硬質材料の超高圧合成とナノ組織制御 ナノダイヤモンドセラミックス合成 ＩＩ 動的合成法 極短時間の核生成・粒成長の制御

Shock compaction methods for diamond powder can produce nanocrystalline diamond ceramics consisting of particles a few tens of nanometers in diameter. However, by using these methods, it is difficult to consolidate nanocrystalline diamond powder of only a few nanometers in diameter because heat localization, which is essentially important for the shock compaction process, can not be achieved. On the other hand, the SCARQ (shock compression and rapid quenching) method can produce transparent, nanocrystalline and/or amorphous diamond films 5-μm thick by controlling the nucleation and growth process in the phase transition from fullerene to diamond. The stability of the diamond phase dependent on their size is also discussed.

Production of bulk materials of an Nd/sub 4/Fe/sub 77.5/B/sub 18.5/ alloy and their magnetic properties

Amorphous melt-spun ribbons of an Nd/sub 4/Fe/sub 77.5/B/sub 18.5/ alloy were consolidated into bulk materials by shock compaction. The resultant bulk materials showed a low coercivity as expected for amorphous Nd-Fe-B materials. Heat treatment of the bulk materials above the crystallization temperature resulted in the formation of metastable Fe/sub 3/B phase together with Nd/sub 2/Fe/sub 14/B phase. The resultant bulk magnets showed a coercivity as high as 2.7 kOe as was the case for the annealed melt-spun ribbons.

Discrete Element Modelling on a Cluster of Workstations

2 , a state-of-the-art discrete element modelling technique for simulating the behaviour of energetic materials and modelling shock compaction phenomena. The underlying computational approach is derived from particle methods, where short-range interactions, both mechanical and thermochemical, determine individual particle movement and state. Using spatial decomposition, a client-server software architecture distributes the computations and, at the language level, Berkeley sockets enable communication between conventional Unix processes on workstations connected by an Ethernet. We evaluate the performance of the system in terms of overall execution time and efficiency, and develop a simple model of computational and communication costs that enables us to predict its performance in other contexts. We conclude that distributed implementations of short-range particle methods can be very effective, even on non-dedicated communication networks.

Characterization of the surface of shock-compacted YB 2C 3O y particles

The shock compaction effects on the structural and superconducting properties of high- T c YB 2C 3O y particles are investigated. YB 2C 3O y particles with an average size of 960 nm were prepared by the dry-type jet mill. The lattice constants of the orthorhombic cell with a=0.383 nm, b=0.390 nm and c=1.17 nm for as-shocked YB 2C 3O y particles are calculated just after the shock compaction under 5.71 GPa. In the measurements of susceptibility by SQUID magnetometer, ΔM is obtained. It is found that ΔM(0.00232 emu/g) for as-shocked YB 2C 3O y particles after annealing at 870°C for 10 h is larger than ΔM(0.00047 emu/g) for as-shocked YB 2C 3O y particles, which seems to indicate the new pinning centres created around the grain boundaries during annealing. From scanning electron microscopy observations, the surface of the specimens for as-shocked YB 2C 3O y has large grains of 4–15 μm in length partly with large growth-steps caused mainly by heats generated in shock compaction. Also from the section analysis of atomic force microscope image, the vertical distance of about 30–80 nm is obtained around the edge area in annealed YB 2C 3O y grains.

Characterization of shock-compacted bulk YBCO by magnetic torque measurements, X-ray diffraction analysis and AFM-image

The as-shocked specimen showed an oriented crystal structure with the lattice constants of the orthorhombic cell with a=0.3830nm, b=0.3899nm and c=1.1693nm for as-shocked bulk YBCO calculated by XRD(X-ray powder diffraction analysis) just after the shock compaction under 5.71GPa. Also from magnetic torque measurements, it is found that c-axis orientation is perpendicular to the pellet disk plane.

Consolidation of Bi-Sr-Ca-Cu-O superconductors by the shock-loadingmethod

Shock compaction experiments were carried out for Bi2223 to prepare adense, oriented bulk specimen. The shocked specimen exhibited a high degree ofcrystallographic orientation and a high density, above 96%. The optimalcondition of the crystallographic orientation was attained at a shock pressureof 5 GPa and at annealing temperatures between 750 and 800 °C. The postannealing of a specimen shocked at 5 GPa was effective in increasing ΔM,indicating the introduction of pinning sites. The magnetic torquemeasurements showed that a high degree of orientation was attained and manypinning centres were induced by the shock loading.

Synthesis and characterization of mechanically alloyed and shock-consolidated nanocrystalline NiAl intermetallic

The synthesis, microstructural characterization and microhardness of nanocrystalline B2-phase NiAl intermetallic are discussed in this paper. Nanophase NiAl powders were prepared by mechanical alloying of elemental Ni and Al powders under an argon atmosphere for different times (0–48 h). The alloyed nanocrystalline powders were then consolidated by shock compaction at a peak pressure of 4–6 GPa, to 83% dense compacts. Characterization by transmission electron microscopy (TEM) revealed that the microstructure of the shock-consolidated sample was retained at the nanoscale. The average crystallite size measurements revealed that mechanically alloyed NiAl grain size decreased from 48±27 to 9±3 nm with increasing mechanical alloying time from 8 to 48 h. The long-range-order parameters of powders mechanically alloyed for different times were determined, and were observed to vary between 0.82 for 5 h and 0.63 for 48 h of milling time. Following shock compaction, the long-range-order parameter was determined to be 0.76, 0.69 and 0.66, respectively, for the 16, 24 and 48 h alloyed specimens. Both the mechanically alloyed nanocrystalline NiAl powder and the shock-consolidated bulk specimen showed evidence of grain boundary dislocations, subgrains, and distorted regions. A large number of grain boundaries and defects were observed via high resolution TEM (HRTEM). Shear bands were also observed in the mechanically alloyed NiAl intermetallic powders and in the shock-consolidated compacts. Microhardness measurements of shock-consolidated material showed increasing microhardness with increasing crystallite size refinement, following Hall–Petch behavior.

Shock wave fabricated ceramic-metal nozzles

Shock compaction was used in the fabrication of high temperature ceramic-based materials. The materials' development was geared towards the fabrication of nozzles for rocket engines using solid propellants, for which the following metal-ceramic (cermet) materials were fabricated and tested: B4C-Ti (15 vol.-%). B4C-Al, and TiB2-Al, with an Al content typically between 15-20 vol.-%. Here, the B4C-Ti was only shock-compacted, while the other two cermets were shock compacted followed by melt infiltration with Al. The materials were subjected to gradually more severe testing conditions. Slabs of the materials were first tested for thermal shock resistance in an acetylene flame, followed by testing in the exhaust gas stream of a rocket propellant, and thereafter as a cylindrical insert in a nozzle of TZM alloy. The B4C-Ti composite showed erosion and cracking after the first test in the propellant flame, while the B4C-Al composite failed the insert tests. The TiB2-Al composite performed well under all conditions. A venturi nozzle of that material was formed during compaction. This real, shaped nozzle was shown to function well, even during repeated 3-6 s tests. This could be explained by the resistance of TiB2 to molten Al, the high thermal conductivity of the TiB2-Al cermet and the in situ formation of a protective layer, consisting mainly of Al2O3.

Preparation of Alloy in the Sm-Fe System by Combustion Synthesis and the Effect of Shock Compaction on Their Magnetic Properties.

Preparation of Alloy in the Sm-Fe System by Combustion Synthesis and the Effect of Shock Compaction on Their Magnetic Properties.

Shock compaction of Al-based nanocrystal materials using an ion-beam device

An ion beam-driven shock loading device has been proposed to make dynamic compaction of non-equilibrium and nano-crystalline powders efficient. Different from the conventional gas/fire guns and the explosive detonation methods, the repetitive application of shock pressure pulse to target materials and the fine control of pressure pulse are both intrinsic features to the present approach. Since the generated plasmoid is electro-magnetically accelerated to launch the flyer, no limitation to flyer velocity can, in principal, be expected. The optical fiber technique was utilized to carry out real time measurement of copper flyer velocity. The efficiency was estimated to be about 6% for conversion from the accumulated energy in the condenser bank to the kinetic energy of a flyer. Al-based nanocrystal powders were used for dynamic compaction.

The double explosive layer cylindrical compaction method

The standard cylindrical configuration for shock compaction is useful for the compaction of composite materials which have some plastic behavior. It can also be used to densify hard ceramics up to about 85% of the theoretical density (TMD), when low detonation velocity explosives (2-4 km s-1) are used. In order to attain higher densities, higher pressures will be needed. With the aid of computer simulations, it is shown that this can be realized without the risk of tensile rarefaction waves, by using two layers of explosives having different detonation velocities. This method has already resulted in a homogeneous B4C compact (87% TMD). After infiltration with Al, a B4C composite having a hardness ranging from 15 to 18 GPa could be obtained with this method. © 1999 Elsevier Science S.A. All rights reserved.

Application of the shock compaction technique for consolidation of hard magnetic powders

A shock compaction technique has been successfully applied for the consolidation of hard magnetic powders without appreciable changes in the phase structure and grain size. Pr–Fe–B and Sm–Fe–N materials, prepared with the application of melt spinning and mechanical alloying, respectively, were shock compacted with a shock wave speed of 1200 m/s and a pressure of 4.4 GPa. We found that the coercivity of high RE containing material, for which the magnetic hardness is controlled by good magnetic separation of magnetic grains by a RE-rich paramagnetic phase, decreases slightly, by ∼5 %, due to the closer proximity of the crystallites in a dense material. For low RE, exchange coupled materials, the densification does not change the coercivity.

Temperature Measurements during Shock Compaction of Powders.

The measurement of the temperature history of a powder during the shock compaction process requires a very fast measuring principle. Since the response time of normal thermocouples is too slow for the extremely fast temperature changes occurring in the shock compression of powders, here thermocouples formed by the powder to be compacted are used. The temperature measurements are performed in the cylindrical configuration. Copper and constantan powders are used in the development of the measuring technique. This resulted in measurements of the temperature history in these metallic materials. To be able to investigate whether the temperature history during the shock compaction of ceramics differs from that of metals, two ceramic materials TiB2 and WC) were selected to be used as a powder thermocouple for future work.

Forming during Shock Compaction.

Methods are presented for the forming of articles during shock compaction of powders in the cylindrical configuration. The forming methods make use of mandrels of either a polymer or a metal, since those materials can easily be machined in the required shape. The polymer mandrel decomposes during the shock compression process, forming a hole in the compact with the dimensions of the mandrel. Aluminum mandrels do not decompose, but may change their shape during the compaction process. The aluminum of the mandrel can also be used for a subsequent melt infiltration of the remaining pores in the compacts. In this way fully dense venturi shaped nozzles of TiB2-Al have been fabricated.

The Effects of Nanostructure on the Strengthening of NiAl

ABSTRACTThe relationship between microhardness and grain size was investigated for nanocrystalline and coarse-grained stoichiometric intermetallic NiAl. The nanocrystalline NiAl specimens were synthesized through mechanical alloying with a high-energy Spex 8000 shaker mill and consolidated by shock compaction at a peak pressure of 4–6 GPa, to 83% dense compacts. The nanocrystalline NiAl compacts were also sintered at 1073, 1173 and 1473 K for 2 h. The Vickers hardness of consolidated and sintered NiAl was determined by microhardness testing, and the grain size and microstructure were investigated with transmission electron microscopy. It was found that the hardness values increased with decreasing grain size of the NiAl alloy. The Vickers hardness values were approximately 650±16, 690±6, 800±43 HV, respectively for NiAl with grain-sizes corresponding to approximately 27±18, 11±6 and 9±6 nm. The possible strengthening mechanisms operating in NiAl are discussed.