Microstructure and vacancy-type defects of high-pressure torsion deformed Al-3 wt%Cu alloy

The influence of high-pressure torsion (HPT) on the microstructure and free-volume type defects of supersaturated Al-3 wt%Cu was studied. By means of HPT, grain refinement down to sizes of 100 nm could be achieved. Positron annihilation spectroscopy was applied for the characterization of deformation-induced defects and of vacancy-solute interaction. The chemical sensitive method of two-dimensional Doppler broadening spectroscopy reveals predominantly deformation-induced defects. In comparison to undeformed supersaturated Al-3 wt%Cu, the fraction of Cu-decorated free-volume type defects is strongly reduced and Al2Cu-precipitates with equilibrium structure occur rather than metastable semi-coherent Al-Cu precipitates. These precipitates stabilize the nanocrystalline structure and give rise to a rather different aging behaviour compared to the undeformed state.