On the nucleation of partial dislocations in nanoparticles

Abstract

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

Keywords:

• nanoparticles
• dislocations
• stacking faults
• nucleation