Orbiting dynamic compression laboratory

In order to examine the feasibility of carrying out dynamic compression experiments on a space station, the possibility of using explosive gun launchers is studied. The question of whether powders of a refractory metal (molybdenum) and a metallic glass could be well considered by dynamic compression is examined. In both cases extremely good bonds are obtained between grains of metal and metallic glass at 180 and 80 kb, respectively. When the oxide surface is reduced and the dynamic consolidation is carried out in vacuum, in the case of molybdenum, tensile tests of the recovered samples demonstrated beneficial ultimate tensile strengths

Shock Consolidation of Powders – Theory and Experiment

A recently proposed model of shock consolidation of powders quantitatively predicts regimes of input energy and shock duration required to produce well-bonded compacts. A growing data base from shock experiments in which the shock wave and powder parameters of importance are controlled allows evaluation of the model. Rapidly solidified crystalline AISI 9310, and microcrystalline Markomet 3.11, as well as amorphous Markomet 1064 and crystalline Mo powders, have been consolidated by shocks up to 2 μsec duration. The formation of amorphous layers on Marko 3.11 particle surfaces indicates that surface melting and rapid solidification occurred. Decreasing amounts of amorphous structure are retained in Marko 3.11 and 1064 powder compacts with increasing shock energies. Significant improvement in Mo particle bonding is achieved by reducing surface oxides prior to shock consolidation

Temperature kinetics during shock-wave consolidation of metallic powders

Powders (60 ..mu..m diam) of constantan and pure copper were compressed statically into cylindrical greens (20.3 mm diam, 5.3 mm long) with a flat interface separating the two powders. A 20-mm propellant gun was used to accelerate a flyer of Lexan, copper, or aluminum, and generate in the green a shock wave with front parallel to the Cu/constantan interface. The voltages between opposite ends of the greens were measured as a function of time and for shock pressures between 1.3 and 9.4 GPa. When the shock wave arrives at the Cu/constantan interface, the voltage signal shows an abrupt increase, which lasts between 45 and 81 ns and leads to a peak temperature T/sub p/. After this, the hotter and cooler parts of the compact equilibrate and the temperature decreases to a value T/sub h/. With increasing shock pressure, T/sub h/ increases from 425 to 1215 K. The measurements of T/sub h/ are in excellent agreement with the temperatures calculated from the measured flyer velocity, the Hugoniot for copper powder, and thermodynamic data for the flyer and powders

The Effect of Shock Duration on the Dynamic Consolidation of Powders

A recently advanced model for the shock consolidation of powders predicts, for a powder of given distension, the regimes of shock pressure and shock duration expected to yield fully densified compacts of near optimum strength. The model is evaluated in terms of UTS measurements in compacts of rapidly solidified powders of AISI 9310 alloy, shocked to initial shock pressures between 3.6 and 17.9 GPa and to shock durations between 0.23 and 2.1 μs. We find that in powders of distention 1.7, shock durations > 1 μs are required at 10 GPa to properly solidify the melt

A theory for the shock-wave consolidation of powders

A model for the shock consolidation of powders is developed which predicts, for a given powder density, the regimes of shock pressure P and shock duration t_d expected to yield fully densified compacts of near optimum strength. Most of the densification work is assumed deposited near particle boundaries, leading to partial melting. The model gives an upper bound to the amount of melt. The condition that the melt between particles must exceed a critical thickness and must solidify within the duration of the shocked state leads to necessary conditions for P and t_d.These requirements are presented in “maps of shock consolidation,” using normalized parameters. The model predicts that for a shock energy (normalized to that required to heat iron to the melting point) of 0.7, a minimum shock duration of 2μs is required to consolidate 60μm diameter iron-based powder

Shock Consolidation of a Glass-Forming Crystalline Powder

Plane shock waves were employed to consolidate a microcrystalline Markomet 1064 alloy powder (~50 μm particle size, Ni_(55.8)Mo_(25.7)_Cr_(9.7) B_(8.8)) with shock energies ranging from 210-595 kJ/kg. Metallurgical examination of the compacts reveals amorphous regions at particle junctions and interparticle boundaries which formed from shock melted material. A fine microcrystalline region was observed near the center of the larger amorphous regions. The volume fraction of the melt (amorphous + fine microcrystalline regions) increases from 0.006 to 0.28 over the energy range employed. The maximum metallic glass fraction retained was approximately 20% at energies near the maximum employed. The thermal history of spherical particles flux during the shock rise time was calculated. melt fraction, assuming all of the shock energy subject to constant energy The numerically predicted was input at the particle surface, is large than the experimentally measured melt fraction at low energies. TEM observations on the consolidated powder indicate extensive slip and deformation by twinning. The present melt fraction measurements indicate that while the shock energy is preferentially deposited near particle surfaces, a significant fraction of shock energy is also dissipated in plastic deformation of particle interiors

Shock wave consolidation of an amorphous alloy

Irregular flakes prepared from ∼ 50 μm thick melt spun ribbons of an amorphous Markomet 1064 alloy (Ni_(55•8)Mo_(25•7)B_(8•8)) were consolidated by shock waves produced from stainless steel flyer plate impact in the 0.9 to 1.4 Km/s velocity range. Recovered samples were observed to have a bulk density of 8.9±.2 g/cm^3. The compacts remained amorphous for shock energies of less than 450 KJ/Kg. Metallographs indicate that moderately good interparticle bonding can be achieved with shock waves at stress levels below those which can induce recrystallization from shock heating

Microstructural Characteristics of a Shock-Consolidated Glass-Forming Alloy Powder

An irregularly shaped, microcrystalline Markomet 1064 alloy powder (Ni_(55.8)Mo_(25.7)Cr_(9.7)B_(8.8), ~50 µm diameter) was consolidated by plane shock waves with energies ranging between 210 and 595 kJ/kg. The recovered compacts were analyzed to determine structural changes which occurred within the particles (due to deformation), and at particle boundaries (due to deformation and localized melting). The crystalline regions of the particles exhibit deformation twins, with dislocation networks and tangles within individual crystals (grain size ~0.4 µm). Localization of plastic strain along shear bands was also observed in the interior of the particles. Recrystallization of some of the heavily deformed grains occurred near the interface between unmelted particle interiors and melted particle surfaces. The melted and rapidly solidified interparticle regions were confirmed to be amorphous. Large Mo-rich precipitates (0.15 µm diameter) present in the annealed powder, were not melted and remained as isolated particles in the amorphous regions of the compact. A dispersion of fine spherical Cr- rich amorphous phase (~0.03 µm diameter) was observed randomly distributed in tile amorphous material. Nucleation and growth of fine crystallites occurs in some of these spherical regions

Shock consolidation of a rapidly solidified steel powder

Rapidly solidified AISI 9310 steel powders were consolidated by shock waves produced from the impact of high velocity flyers. Dependence of the microhardness and the ultimate tensile strength of the compacts on the initial shock pressure (from 3.6 to 17.9 GPa) and the maximum shock pressure (from 6 to 37 GPa) was measured for an initial powder density 0.6 of the bulk density and a shock duration of 2–3 s. Photomicrographs and SEM fractographs were used to study the interparticle bonding in the compacts. Results show that for initial shock pressures below 4 GPa, the compacts have negligible strength. However, above this threshold the strength of the compact rises rapidly until a maximum value of 1.3 ± 0.1 GPa is reached for an initial shock pressure of 12.4 GPa. The strength then remains constant before decreasing at the highest initial shock pressure. In marked contrast, with increasing shock pressure, the diamond pyramid hardness increases very gradually from a value of about 340 for the powder to about 500 at the highest shock pressure. The maximum strength obtained correlates reasonably well with the strength-expected from microhardness measurements