Plane-wave shock-loaded Ni exhibited {111} micro-twins which increased in frequency with increasing peak shock pressure above a critical twinning pressure of about 30GPa. Micro-bands which coincided with traces of {111} were produced below impact craters in Ni targets by stainless steel projectiles at velocities of up to 3.5km/s. The micro-band widths were ten times the 0.02μm twin widths and were characterized by misorientations of roughly 2°. Shock-loaded and impacted Ni had similar dislocation cell structures which decreased in cell size with increasing pressure or equivalent stress. The exclusive formation of micro-bands in connection with impact craters in Ni was expected on the basis of its stacking-fault energy of about 130mJ/m2. A simple dislocation model was developed for the microtwin-microband transition, based upon graphical summaries which included shock (stress) geometry and stacking-fault energy effects in fcc metals and alloys.

Comparison of Microstructures for Plane Shock-Loaded and Impact Crater-Related Nickel: the Microtwin-Microband Transition. E.V.Esquivel, L.E.Murr, E.A.Trillo, M.Baquera: Journal of Materials Science, 2003, 38[10], 2223-31