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 distributi on of the grain size in nanocrystals is simulated with a logarithmic n ormal distribution, and one dislocation per grain is assumed. The plas tic yielding for nanocrystalline materials is considered to be control led by the stress required to attain dislocation loops (the Frank-Read source) in a set of larger grains with their critical semicircle conf iguration. The dislocations in the rest of the smaller grains are cons idered to be in the subcritical configuration, which produces a revers ible 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 met als exhibit a negative Hall-Petch slope and two a positive Hall-Petch slope. The model also predicts a decrease in Young's modulus with dimi nishing grain size, which is in agreement with experimental results fo r nanocrystalline copper and palladium.