MODEL FOR THE PREDICTION OF THE MECHANICAL-BEHAVIOR OF NANOCRYSTALLINE MATERIALS

A model is proposed in the present paper to account for the mechanical behaviour of nanocrystalline materials. In this model, the distribution of the grain size in nanocrystals is simulated with a logarithmic normal distribution, and one dislocation per grain is assumed. The plastic yielding for nanocrystalline materials is considered to be controlled by the stress required to attain dislocation loops (the Frank-Read source) in a set of larger grains with their critical semicircle configuration. The dislocations in the rest of the smaller grains are considered to be in the subcritical configuration, which produces a reversible deformation and only contributes to an inelastic deformation. The model presents a very good agreement with the sigma(y) vs. D(av) -1/2 relationships for five nanocrystalline materials; of these, three metals exhibit a negative Hall-Petch slope and two a positive Hall-Petch slope. The model also predicts a decrease in Young's modulus with diminishing grain size, which is in agreement with experimental results for nanocrystalline copper and palladium.