Abstract
Plane-wave shock-loaded Ni exhibits {111} microtwins which increase in frequency with increasing peak shock pressure above a critical twinning pressure of ∼30 GPa. In contrast, microbands coincident with traces of {111} are produced below impact craters in Ni targets by stainless steel projectiles at velocities up to 3.5 km/s. The microband widths are ten times the 0.02 μm twin widths and are characterized by misorientations of roughly 2°. Both shock-loaded and impacted Ni have similar dislocation cell structures which decrease in cell size with increasing pressure or equivalent stress. The exclusive formation of microbands in connection with impact craters in Ni is expected on the basis of its high SFE (∼130 mJ/m2), and a simple dislocation model is developed for the microtwin-microband transition based on graphical summaries which include shock (stress) geometry and SFE effects in FCC metals and alloys.
