Plastic Deformation of Nanocrystalline Zinc Investigated by Positron Annihilation Lifetime Spectroscopy

The plastic deformation of nanocrystalline Zn is investigated by positron annihilation lifetime spectroscopy. The deformation is carried out by exerting a pressure on the surface of the samples, which causes a thickness reduction of the samples. The different behavior of the relative thickness reduction with the increasing pressure between the nanocrystalline sample and the conventional bulk sample indicates that a distinct plastic deformation mechanism is operating in the nanocrystalline sample. The positron lifetime results confirm indirectly that the mechanism is grain boundary based, such as grain boundary sliding. Once the nanocrystalline sample is annealed at high temperature, the changes in the thickness reduction and the positron lifetime results become similar to those of the conventional bulk sample. Furthermore, vacancy clusters inside the nanocrystalline sample are found to be an impediment to the plastic deformation process.