A coherent polycrystal model for the inverse Hall-Petch relation in nanocrystalline materials

A coherent polycrystal model for the abnormal grain size dependence is presented. It treats the nanocrystalline material as a coherent precipitate strengthened two-phase alloy in which all the grain boundaries merge into a whole continuous matrix acid each of the grains embeds in the matrix coherently. According to this model, the transition from the normal to the inverse Hall-Fetch relation corresponds to thr role-exchange of the grain bulk and the grain boundary in the deforming mechanism. Theoretical formula based on this model is compared with the available experimental data. Thr results indicate that the model gives an excellent description of the so-called inverse Hall-Petch relation in the nanocrystalline materials. (C) 1999 Acta Metallurgica Inc.