ABSTRACT
Nanocrystalline materials are single-or multiphase polycrystalline solids with a grain size of the order of a few nanometers (1 nm = 109 m = 10 A˚), typically 1-100 nm in at least one dimension. Since the grain sizes are so small, a significant volume of the microstructure in nanocrystalline materials is composed of interfaces, mainly grain boundaries. This means that a large volume fraction of the atoms resides in the grain boundaries. Consequently, nanocrystalline materials exhibit properties that are significantly different from, and often improved over, their conventional coarsegrained polycrystalline counterparts. Compared to the material with a more conventional grain size, i.e., larger than a few micrometers, nanocrystalline materials show increased strength, high hardness, extremely high diffusion rates, and consequently reduced sintering times for powder compaction. Several excellent reviews are available giving details on different aspects of processing, properties, and applications of these materials [1-7].
