Lateral and depth distribution of defects in ultra fine grained copper prepared by high pressure torsion

Ultra-fine grained copper prepared by high-pressure torsion has been studied by means of positron annihilation techniques (slow positron implantation spectroscopy,conventional positron lifetime and Doppler broadening measurements) combined with transmission electron microscopy, X-ray diffraction and microhardness measurements. Dislocations in distorted regions along grain boundaries and microvoids of size 3-4 vacancies inside grains were identified and their lateral distribution and depth profile were investigated in detail. The concentrationof microvoids has been found to decrease with depth and to vary slightly with the distance from specimen axis, being lowest in the centre of the specimen disc. No position dependence of the concentration of dislocations was observed.