A New Approach for the Relationship Between the Yield Strength of Nanocrystalline Materials and Grain Size

The experimental results showed that the Hall-petch slope in the nanocrystalline domain is lower than in the microcrystalline (conventional) range of grain sizes [1-4]. Furthermore, in some cases we face with another not well known phenomenon: when the grain size of nanostructure materials is smaller than a certain critical value, the Hall–Petch slope is zero or even negative [5-7]. In short, the relationship between the yield strength of nanocrystalline materials and grain size is not well known. Finding a solution for this shortage is the major aim of this paper; we will try to introduce a simple relation between the yield strength and grain size in nanocrystalline domain