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.