ABSTRACT
In the conventional polycrystals at the mesolevel, the hardened zone occupies a small fraction of the grain body. This fraction increases with a decrease of the average grain size and at the microlevel may reach half the grain size, and in the region of the nanocrystals it can include the whole grain. All the hardening mechanisms, which operate in the conventional polycrystals at the mesolevel, also operate in the polycrystals at the microlevel. The high density of the grain boundaries creates additional resistance to the movement of dislocations and increases the yield point of the UFG materials. To this it is necessary to add the high initial density of dislocations distributed at the grain boundaries and at their junctions. The high level of the internal stress fields in the UFG materials also increases the yield point. The relationships governing the deformation of the crystalline material become similar to the relationships of the formation of the amorphous material.
