ABSTRACT
Various modified properties like enhanced reactivities and solid solubilities or reduced elastic moduli of nanocrystalline metals (see references in [2]) as well as improved sintering characteristics [6, 7] and an enhanced plastic deformability [8] of nanocrystalline ceramics in comparison with the respective bulk crystalline materials are presumably a direct consequence of the low-density structure of the interfaces of nanophase materials. An understanding of these properties requires a detailed study of the atomic structure of the interfaces, particularly of their structural free volumes, and of the atomic transport behavior of the interfaces. After some introductory remarks on the preparation and characterization of nanocrystalline materials (section 11.2) a summary will be presented on the positron annihilation studies of the structural free volumes of nanophase materials (section 11.3) as well as on the diffusion data available at present for nanocrystalline materials (section 11.4 ). The results of a recent desorption study of He after implantation into nanocrystalline metals will be described in section 11.5 as another example of atomic transport phenomena in nanocrystalline metals.
