Are rate sensitivity and strength effected by cross-slip in nano-twinned fcc metals

Synthesis of nano-twinned pure Cu by Lu et al. [L. Lu, R. Schwaiger, Z. W. Shan, M. Dao, K. Lu, S. Suresh, Nano-sized twins induce high rate sensitivity of flow stress in pure copper, Acta Mater. 53 (2005) 2169-2179] has produced materials with extremely attractive properties of combined high strength, strain rate sensitivity, and ductility adequate for applications. This note explores the underlying mechanistic reasons for this via a model analysis of dislocation interaction with nano-twinned boundaries. Interestingly, we find that processes like cross-slip, that lead to the absorption and transmission of slip through twin boundaries yet are normally associated with rate insensitive behavior, can lead to high strength and rate sensitivity as observed in experiment. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.