Homogeneity of ultrafine-grained copper deformed by high-pressure torsion characterized by positron annihilation and microhardness

Spatially resolved positron annihilation was employed for mapping lateral defect distribution in Cu deformed by high-pressure torsion. Parameters describing Doppler broadening of the annihilation peak were used for mapping the spatial distribution of defects. In comparison with microhardness showing a clear development towards homogeneity, positron annihilation revealed that spatial distribution of defects was far from uniform, even after 25 turns. This was mainly due to a higher concentration of deformation-induced vacancies at the periphery compared with the center.

► Doppler broadening (DB) of annihilation radiation was used as a novel technique for two dimensional mapping of lateral defect distribution in ultra fine grained Cu produced by high pressure torsion. ► This paper introduces DB mapping and compares it with standard microhardness (HV) characterization. ► DB mapping enables to visualize lateral distribution of dislocations and in particular deformation-induced vacancies which are invisible in HV mapping. ► Hence, DB mapping can be considered as a complementary technique to standard HV characterization.