Effective values of critical resolved shear stress for slip in polycrystalline magnesium and other hcp metals

Critical resolved shear stresses (CRSSs) for slip on different types of slip systems in single-crystal hexagonal close-packed metals show very wide variations. Values derived from measurements and modelling on polycrystals show much less variability and there is often evidence for activation of "hard" slip modes from dislocation observations in transmission electron microscopy. We show that this discrepancy originates in the hardening processes that take place in polycrystals, which must be treated as a term that is additive to the true CRSS. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.