Microstructural effects in FCC alloys after small charge explosions

Effects on metal targets after an explosion include: fracture, plastic deformation, surface modifications, microstructural crystallographic alterations with ensuing mechanical properties changes. In the case of small charge explosions, macroscopic effects are restricted to small chargeto- target distances, whereas crystal alterations can still be observed at moderate distances. Microstructural variations, induced on gold alloy disk samples, as compared to previous results on AISI 304Cu steel samples, are illustrated. The samples were subjected to blast wave overpressures in the 0.5 to 195 MPa range. Minimum distances and peak pressures, which could still yield observable alterations, were especially investigated. Blast-related microstructural features were observed on the explosion exposed surface and on perpendicular cross-sections. X-ray diffraction analyses were performed to identify modifications of phase, texture, dislocation density, and frequency of mechanical twins, before and after the explosions. Optical and scanning electron microscopy observations evidenced partial surface melting, zones with recrystallization phenomena, and crystal plastic deformation marks. The latter marks are attributed to mechanical twinning in the stainless steel, and to cross-slip (prevalent) and mechanical twinning (possibly) in the gold alloy.