Nanostructured metals: Less is more

The effect of annealing, which contained no alloying element, on the strength and ductility of bulk nanostructured aluminum was investigated. It was found that the process of annealing leads to hardening of the bulk nanostructured aluminum, while deformation of the bulk nanostructured aluminum results in the softening of the bulk nanostructure. Annealing decreased the density of dislocations in the grain interior of the bulk metal by 60%, resulting in a 10% increase to the strength of the metal. It was observed that on annealing, the elimination of the dislocations renders the material less prone to plastic flow, and hence deformation. It was concluded that fewer dislocations could provide the strengthening of the bulk nanomaterials.