A simple dislocation model of deformation resistance of ultrafine-grained materials explaining Hall-Petch strengthening and enhanced strain rate sensitivity

A model is presented where the properties of ultrafine-grained (UFG) materials are explained in terms of the influence of high-angle boundaries on the rates at which dislocations are stored and recovered at the boundaries. The model reproduces the experimental observations that UFG materials reach a steady state where the deformation resistance is independent of strain. that the strain rate sensitivity, of flow stress is relatively high and that the steady-state flow stress increases inversely with the square root of,rain size. The model results are compared to experimental data for UFG Cu and nanostructured Ni. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.