The Hall-Petch law, that accounted for the effect of grain size on the plastic yield stress of polycrystals, was revisited in terms of the collective motion of interacting dislocations. Sudden relaxation of incompatibility stresses in a grain triggers aftershocks in the neighboring ones. The Hall-Petch law resulted from a scaling argument based upon the conservation of the elastic energy during such transfers. The Hall-Petch law breakdown for nanometric sized grains was shown to stem from the loss of such a collective behavior as grains start deforming by successive motion of individual dislocations.

Hall-Petch Law Revisited in Terms of Collective Dislocation Dynamics. F.Louchet, J.Weiss, T.Richeton: Physical Review Letters, 2006, 97[7], 075504 (4pp)