Spatial distribution of defects in ultra-fine grained copper prepared by high pressure torsion

A study of ultra-fine grained copper produced by high-pressure torsion is presented. Positron annihilation spectroscopies (slow-positron implantation, lifetime and Doppler broadening spectroscopies), transmission electron microscopy, X-ray diffraction spectroscopy and micro-hardness measurements have been employed in order to identify defects and their spatial dis-tribution, i.e. lateral distribution and depth profile, in the specimens. Two types of defects could be identified: dislocations in the distorted regions along grain boundaries and micro-voids of size of 3-4 vacancies inside the grains. No change in grain size as a function of the distance from the center of the sample disk was observed. The mean coherent domain size close to the surface was found to be 80 ± 20 nm and it slightly increases with depth. The con-centration of microvoids has been found to decrease with depth and it slightly varies with the distance from the center of the disk, being lowest in the center. No position dependence of the concentration of dislocation was observed.