Hall-Petch revisited

The necessity to combine analyses of the intragramilar plasticity with the effect of the locking of dislocations close to the grain boundaries is emphasized and shown to describe reasonably well the Hall-Petch behaviour of polycrystals of grain size larger than a few micrometers. Extrapolation of this analysis to crystals of smaller size, particularly to nanocrystals, requires however, a detailed description of the effects which do not play a significant role in standard grain size materials: grain boundary volume, grain boundary sliding, strain localization. A simple scaling analysis reveals the limits of,the relevance of this extrapolation. Mechanisms controlling plastic flow of nanocrystals are suggested. (c) 2005 Elsevier B.V. All rights reserved.