Explosive Shock Loading Research Articles

Comparison of the substructures and properties of nickel, TD-Ni, chromel-A, inconel 600, and TD-NiCr following explosive-shock deformation

The substructures of Ni, TD-Ni, Chromel-A (80/20 NiCr), Inconel 600, and TD-NiCr following simultaneous explosive shock loading at pressures of 80, 180, 240, and 460 kbars were observed by transmission electron microscopy. Well defined dislocation cells having average diameters of 0.8, 0.3, 0.2, and 0.1 μ for the respective pressure level were observed in pure nickel, but were not developed to the same extent in annealed TD-Ni due to the presence of the ThO2 particles having a mean particle diameter of 340A. Deformation microtwins having an average width of 175A occupied approximately 1 vol pct of the nickel substructure at 460 kbars, while twinning was inhibited by the ThO2 particle distribution in the TD-Ni. Planar dislocation arrays observed in the Chromel-A and Inconel 600 were generally not observed to form in TD-NiCr following shock loading at 80 and 180 kbars. In addition, deformation microtwins having an average width of 150A occupied 5 pct of the Chromel-A microstructure at the same pressure. At 460 kbars, twins occupied 18 pct of the Chromel-A and 24 pct of the Inconel 600 microstructure. No evidence of deformation twinning was observed in the TD-NiCr microstructure because of the inhibition afforded by the ThO2 particle distribution having a mean particle diameter of 145A in the annealed material. A relationship was observed for the residual hardness and dislocation density; and stacking-fault energy and the character of the microstructures.

Electron-Microscope Study of Thermal Recovery Processes in Explosion-Shocked Nickel

A study by transmission electron microscopy was made of the microstructure of pure polycrystalline nickel foil after explosive-shock loading and subsequent heat treatments between 600° and 780°C. In the instance of specimens shocked at 70 and 320 kbar, the deformation substructures resemble those normally caused by cold work, but the recovery process consists mainly in dislocation migration and recombination; no polygonization, nucleation, or grain growth are observed. Nickel shocked at 1000 kbar on the other hand, exhibits an extremely high density of dislocations, point defect clusters, and microtwins arranged in complex patterns. In this instance, heat treatment causes nonuniform polygonization, nucleation, and grain-boundary migration. This results in a significantly lower dislocation density after annealing, particularly at the higher temperatures, and considerably more extensive softening than is the case for nickel shocked at lower pressures.

Thermal Recovery of Explosive Shock-loaded Stainless Steel

Abstract The annealing response of shock-loaded type 304 stainless steel was studied in the pressure range of 120–1200 kbars, and compared with the response of stainless steel cold-rolled 5 and 45%. The annealing kinetics of shock-loaded stainless steel are characterized by a prominent recovery and grain growth stage, with little perceptible recrystallization in the classical sense. The results indicated a pronounoed structural difference between the shock-loaded and cold-rolled materials, as observed by transmission electron microscopy. The structure of stainless steel shock-loaded to 750 and 1200 kbars is observed to be strongly influenced by the transient shock heating effect, and a dislocation cell-type substructure is observed to occur predominantly in (100) grains. The hardness produced over the pressure range 120–1200 kbars by explosive shock-loading is shown to occur by a transition from dense dislocation arraya to twin-faults, and finally to what may be dense point defect concentrations at very high pressures (750–1200 kbars) where transient thermal recovery occurs. Cold-rolled hardening produces a transition from dense dislocation arrays to martensite at large reduction in thickness.

The crystallography of the pressure induced phase transformations in iron alloys

The pressure induced phase transformations produced by explosive shock loading of two groups of iron alloys (Fe-C and Fe-Ni-C) have been investigated using transmission electron microscopy and electron diffraction. The existing phenomenological theories of martensitic transformations have been applied to these pressure induced phase changes and the various theoretical predictions compared with the experimental results. In the case of Fe-Ni-C alloys the high pressure phase was f.c.c. γ, which was retained after the passage of the shock wave. At low pressures (100 kb) the transformation from b.c.c. α-martensite to f.c.c. γ occurred predominantly as a direct reversal of the established System I γ to α transformation in these alloys. At higher pressures (160 kb and over) the transformation followed a different path (System II) and the pressure induced γ showed evidence of internal twinning on {111 } γ. No high pressure phase was retained in the Fe-C alloys, but an analysis of the doubly transformed specimens was consistent with transformation from α. to h.c.p. ε by means of an invariant plane strain on {112} α, followed by re-transformation of the ε to α.

A simple technique for shock deforming metal foils

The merits of a multi-layer sandwich technique for explosive shock loading of metal foils are discussed with special reference to electron transmission studies of microstructure. The conditions are given for the design of the explosive test assembly such that the foil specimens are subjected to a plane compression wave only. Illustrative examples are given of shock-deformation faults produced in nickel and 70: 30 brass as observed by electron microscopy.