Microstructural characterization of Ag shock-loaded at high pressure

The substructure evolution in Ag shock-loaded tp 48.6 GPa has been characterized. Under the influence of large dynamic strain and local heating, the substructure evolution of Ag consists of deformation twins, twin-faults, stacking-faults and microbands, all on {111} planes, with dislocation tangles, loops and a small number of shear bands distributed in between. Twins were observed to occur in bundles with twin-faults and stacking-faults occasionally intermingling with each other. Frequently only one variant of twins were present within one grain and the possible reasons are discussed. Microbands were also observed with a local misorientation with the surrounding matrix of 1-3⁰. Evidence of shock- heating-induced recovery was surmised by observation of collapsed and segmental stacking-faults, large numbers of dislocation debris and loops and equiaxed recrystallized grains. One example of a "micro-shear-band", 1 μm in width and containing many small elongated crystals, was found. The finding of such a shear-band-like feature, coupled with the observation of significant shearing at the intersections of two sets of crosscut microbands, indicate that the bands in shock-loaded Ag to a 30% dynamic strain are most likely an early stage of macroscopic shear band development. It is argued that only under extreme shock pressure where shock heating is significant of where shock deformation occurs to large dybamic strains can shear bands begin to play a role in shock deformation.