Explanation for deviations from the Hall-Petch Relation based on the creep behavior of an ultrafine-grained Mg-Li alloy with low diffusivity

Deviation from the normal Hall-Petch relationship was observed in an ultrafine-grained Mg-Li alloy at low strain rates where plastic flow was governed by power-law creep. Based on the deformation analysis, the abnormal Hall-Petch relation for many metals often observed at nanograin sizes could be explained in terms of a transition from power-law breakdown to a grain-size-independent creep mechanism or a transition from a grain-size-independent to a grain-size-dependent mechanism, the condition of which depends greatly on strain rate and diffusivity. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.