Anelastic behaviour of nanocrystalline aluminium prepared by mechanical attrition

Nanocrystalline aluminium was prepared by mechanical attrition with different equipment and in different thermodynamic conditions. The milled powders were characterized by X-ray diffraction and mechanical spectroscopy measurements. A coarse grained aluminium sample was measured as well. An internal friction peak, attributed to a grain boundary sliding mechanism, was observed in all samples. The results indicate that the activation energy for grain boundary sliding is lowered in nanocrystalline samples, due to the enhanced grain boundary diffusion. A significant decrease of the high temperature elastic energy dissipation was observed too. This is a consequence of the reduced dislocation density and activity in the nanograins.