Deformation mechanisms in nanocrystalline palladium at large strains

The mechanical behaviour and microstructure evolution of nanocrystalline palladium was investigated. Material with an initial grain size similar to 10 nm was prepared by inert gas condensation. Instrumented high-pressure torsion straining was used to characterize the flow stress during plastic deformation to shear strains Lip to 300. A change in primary deformation mechanism was induced by stress-induced grain growth. For grain sizes <40 nm, grain boundary mediated processes (shear banding, grain boundary sliding and grain rotation) controlled the deformation, with dislocation slip, twinning, and grain boundary diffusion providing the accommodation. For larger grain sizes, the operative deformation mechanism was dislocation slip. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.