Positron annihilation studies of microstructure of ultra fine grained metals prepared by severe plastic deformation

In the present work, positron annihilation spectroscopy (PAS) is employed for microstructure investigations of various ultra fine grained (UFG) metals (Cu, Ni, Fe) prepared by severe plastic deformation (SPD), namely high-pressure torsion (HPT) and equal channel angular pressing (ECAP): Generally, UFG metals prepared using both the techniques exhibit two kinds of defects introduced by SPD: dislocations and small microvoids. The size of the microvoids is determined from the PAS data. Significantly larger microvoids are found in HPT deformed Fe and Ni compared to HPT deformed Cu. The microstructure of UFG Cu prepared by HPT and ECAP is compared and the spatial distribution of defects in UFG Cu samples is characterized. In addition, the mircrostructure of a pure UFG Cu prepared by HPT and HPT deformed Cu+Al2O3 nanocomposite (GlidCop) is compared.