Diffusion in Nanocrystalline Materials

Abstract

This chapter discusses the diffusion in nanocrystalline materials, which are polycrystals with an ultrafine grain size and a high volume fraction of atoms located in interfaces. Nanocrystalline materials have gained considerable interest due to high prospects for their attractive potential applications arising from improved mechanical and magnetic properties compared to their coarse-grained counterparts. With respect to both the structure and the physical properties of nanocrystalline solids, the understanding of the atomic transport properties in these materials represents a key research issue. In general, the atomic transport in nanocrystalline materials differs substantially from that in coarse-grained or single-crystalline materials. This is due to the fact that, in nanocrystalline solids, the crystallite interfaces provide paths of high diffusivity, whereas in more coarse-grained crystals, volume self-diffusion or substitutional diffusion dominates at least at temperatures higher than approximately half of the melting temperature. Interface diffusion, in combination with a high fraction of atoms in interfaces, gives rise to modified physical properties of nanocrystalline solids. © 2007 William Andrew Inc. Published by Elsevier Inc. All rights reserved.