The attractive mechanical properties of ultrafine-grained metals prepared by severe plastic deformation (SPD) are initimately related to the high fraction of lattice defects, such as grain boundaries, dislocations, and vacancies. And, this also means that SPD metals are highly suitable for studying basic issues of defect physics. This talk will summarize recent dilatometer studies of SPD metals prepared by high-pressure torsion (HPT-Ni, -Cu) [1,2] or equal angular channeling pressing (ECAP-Ni) . Measuring by time-differential dilatometry the irreversible length change upon annealing in the wake of crystallite growth allows for instance the direct determination of the grain boundary excess volume, i.e., a most relevant structural property parameter determining grain boundary energy or grain boundary diffusivities [1,2]. Moreover, the vacancy relaxation volume is accessible if an orientation dependence in the defect annealing due to anisotropic grain shape is taken into account . The dilatometry studies are complemented by neutron diffraction, in order to assess the length change anisotropy , by kinetic modeling of vacancy annealing and recrystallization upon time-linear heating , and by positron annihilation for studying free volume-type defects on an atomistic scale .
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