The hall-petch relationship in nanocrystalline materials

Abstract

As a new type of material, the nanocrystalline material has drawn world-wide attention in recent years. As a challenge subject, much work has been done concerning the grain size dependence of mechanical properties, e.g., on the Hall-Petch relationship of these new materials. The currently-known Hall-Fetch relations in the nanocrystalline material were examined in this work with an emphasis on crystallized nanocrystalline materials. Nanocrystalline materials usually show decreased microhardness compared with the prediction from the Hall-Petch relationship and even a negative Hall-Petch slope. The possible mechanisms for above phenomena were analyzed in relation to the quantitative measurements on the microstructures of crystallized nanocrystalline materials by means of positron annihilation spectroscopy and X-ray diffraction.