Nanocrystalline face-centred-cubic materials showed unique mechanical properties. In this regard, an interesting but controversial discovery was that nanocrystalline face-centred-cubic materials with high stacking-fault energy, such as Al, exhibited a novel mechanism of deformation. In particular, both molecular dynamic simulations and high-resolution transmission electron microscopy observations showed that for nanocrystalline Al mechanical twinning played an important role in the deformation process. Yet these results were surprising, as the presence of partial dislocations in high stacking-fault energy face-centred-cubic metals were expected to be unstable. The purpose here was to offer a plausible explanation for the occurrence of stacking faults and deformation twins in nanocrystalline Al. A simple model was developed for the nucleation of both perfect and partial dislocation half-loops in individual single-crystal nanoparticles of Al and Cu with different sizes subjected to shear stress. The model showed that as the size of the nanoparticles decreased, partial dislocations were more likely to occur. Moreover, for a constant applied stress, there was a critical size for which the nucleation of partial dislocations occurred was more probable, compared to that of perfect dislocations.

On the Nucleation of Partial Dislocations in Nanoparticles. C.E.Carlton, L.Rabenberg, P.J.Ferreira: Philosophical Magazine Letters, 2008, 88[9-10], 715-24