Enhanced diffusion in shock activated Be-Al interfaces

Enhanced diffusion of aluminum in shock activated beryllium has been observed. Cylindrical samples of aluminum coated beryllium rods were axisymetrically loaded up to 40 GPa and a total residual strain of up to 6.7%. The defect microstructure produced by both the shock wave and strain enabled the transport of aluminum in beryllium to exceed its equilibrium solid state saturation. This {open_quotes}super saturated{close_quotes} aluminum, upon heating exsolves out at relatively low temperatures and forms very strong interfaces with pressure mated components

Enhanced Diffusion in Shock Activated Be-Al Interfaces

Une augmentation de la diffusion de l'aluminium dans le beryllium activé par choc a été observée. Des échantillons cylindriques de barreaux de beryllium revêtus d'aluminium ont été soumis de manière axisymétrique à un choc jusqu'à 40gpa et une déformation résiduelle totale jusqu'à 6,7%. Les défauts dans la microstructure dûs à la fois par l'onde de choc et la déformation permet au transport de l'aluminium dans le beryllium de dépasser la saturation de son état solide à l'équilibre. Cette super saturation en aluminium apparaît, après chauffage, à une température relativement faible et forme des interfaces très résistants.Enhanced diffusion of aluminum in shock activated beryllium has been observed. Cylindrical samples of aluminum coated beryllium rods were axisymetrically loaded up to 40 Gpa and a total residual strain of up to 6,7%. The defect microstructure produced by both the shock ware and strain enabled the transport of aluminum in beryllium to exceed its equilibrium solid state saturation. This "super saturated" aluminum, upon heating exsolves out at relatively low temperatures and forms very strong interfaces with pressure mated components

Shock wave effects and metallurgical parameters

This review summarizes results from some principal investigations of shock-strain effects in metals. The strain contribution indeed plays a role in residual microstructures, particularly, if the strain becomes dominant as in ''under trapped'' experiments of low or moderate pressure or for that matter, of ''well trapped'' high pressure experiments. Not only does this strain contribution affect the microstructure by increasing deformation, a concommitant strain heat is generated and absorbed by the shocked material. This strain heat, if large enough (relative to the homologous temperature of the material), can and does have an annealing effect on the residual microstructure. This strain heat is over and above the values typically calculated for materials implying little or no strain. Although the accumulative effects of associated strain are not completely definite, the collective picture presented is one in which shock-induced strains, when large enough, have a significant effect on the residual microstructure. 43 refs., 20 figs

PRESSURE-STRAIN-TEMPERATURE RELATIONSHIP IN SHOCK LOADED CYLINDRICAL SAMPLES OF 304 STAINLESS STEEL

On décrit l'évolution de la température résiduelle déduite des relations pression-déformation pour un échantillon cylindrique axisymétrique d'acier inoxydable 304. Des explosions axisymétriques conduisent à des relations non uniformes entre pression déformation et température encore incomplètement comprises. Cet article décrit chaque contribution de la température et l'effet notable induit sur l'échantillon.The residual temperature resulting from pressure-strain relationships in an axisymmetric cylindrical sample of 304 stainless steel are described. Axisymmetric implosions result in nonuniform pressure-strain-temperature combinations that need to be better understood. This paper describes each temperature contribution and the net effect on the sample

Experimental approach to shock synthesis using pressure-temperature-strain data

An understanding of the shock conditions that optimise true shock synthesis, not shock initiation, must be understood. Simply the mixing of powdered materials and shock loading them is at best a hit and miss proposition. A shock loading technique, using an axi-symmetric radial implosion technique that produces a Mach-stem region upon convergence of the shock wave results in pressure-temperatures that for the most materials exceed their melting temperatures. As the shock wave passes through, the resultant melt is pressure/temperature quenched. This technique has produced metastable concentrations of several alloys. Various parameters utilizing high pressure-temperature data are assessed towards increasing solubility beyond equilibrium. This paper will describe the current understanding and basic premise as well as the experimental technique used to obtain these conditions

Measurement of strain heat in shock-loaded 304 stainless steel: Implications to powder consolidation

Over the past decades there have been numerous papers on the shock response of materials and more specifically towards metal powder compaction and consolidation. In general, the shock process for powdered materials has utilized the traditional pressure-volume shock relationships proportioned to the initial packing densities of the powders. However, this approach and its resulting data are in controversy due to the lack of knowledge of its associated particle strain and strain temperature uncertainties. This paper will describe the current understanding as well as the experimental technique used to obtain the shock response for distended materials. The above parameters are described within a pressure-strain-temperature interdependence. It was found that the experimentally measured strain heat was not only a function of initial packing density but also a function of powder size and distribution

Technique for megabar controlled strain experiments

This design allows in one shot one experiment a range of pressures from 12 to 170 GPa and a selectable strain range (0 to 55%) in 304 stainless steel with 100% recovery. Development of the application of griding has enabled correlation, locally, of pressure and strain with structure and properties at a strain rate of 10/sup 6//s. Appropriate variations in momentum trap design can control strain in cylindrical implosion shock experiments. Pedestal type traps have shown significant improvement in the reduction of strain in cylindrical implosion experiments. Such design would seem to be appropriate for experiments on brittle and ceramic materials. In cylindrical designs the degree of macro-strain is a function of trapping and is the result of reflected waves not the primary shock pulse

High strain rate approx. 10/sup 6//s response of 304 stainless steel at various strains

The effect of high strain rate at controlled strain levels has been investigated on 304 stainless steel. This study implements a radial shock loading design with a reliable specimen recovery. Strains were measured by plating circle grids on a split anvil design and measured after shock loading. The strain levels were controlled by varying the momentum trap geometries. The shock wave profile impinging and traveling through the specimen as obtained by hydrocode calculations is in fact a shear wave. This shock loading design yields a specimen with a gradient of shock levels up to 1.7 Mbars at a pulse duration of less than one microsecond. The pressure range is achieved nominally independent of the strain level. With this strain pressure independence we were able to study the amount of strain induced ..cap alpha..'-martensite generally associated with 304 stainless steel deformation experiments

Controlled powder morphology experiments in megabar 304 stainless steel compaction

Experiments with controlled morphology including shape, size, and size distribution were made on 304L stainless steel powders. These experiments involved not only the powder variables but pressure variables of 0.08 to 1.0 Mbar. Also included are measured container strain on the material ranging from 1.5% to 26%. Using a new strain controllable design it was possible to seperate and control, independently, strain and pressure. Results indicate that powder morphology, size distribution, packing density are among the pertinent parameters in predicting compaction of these powders

Mach stem characterization in Mbar designs using RSR powder

Suitable selection of powders can be used as a modeling device for complicated experimental designs. The powder melt zone is clearly defined and the RSR-834 powder is reasonably well behaved. This experiment was with only one composition, size and distribution. However, it is believed that other morphologies, composition, and size distributions could result in a more complete modeling of the compaction process that would enable heuristic calculations of the combined effects of adiabatic temperature rise and entropic heating (strain/deformation)