Deformation twinning in nanocrystalline Pd

Abstract

Defect structures of plastically deformed nanocrystalline Pd investigated by high-resolution transmission electron microscopy are presented. Material with an average grain size of about 15 nm was prepared by inert-gas condensation, and this was plastically deformed by cold rolling up to a true strain of 0.32 at a strain rate of about 0.3 s⁻¹. Abundant deformation twinning on {111} planes was found and Shockley partial dislocations identified. Remarkably, in each grain, twinning occurs only on a single set of parallel planes. This implies that only one out of the five independent slip systems required for the general deformation of a grain is active, a finding which suggests that grain rotation and grain-boundary sliding must be active together with twinning.