Excessive concentrations of deformation-induced vacancy type defects were found in nanometals processed by severe plastic deformation but not in others. This suggested that they were responsible for severe plastic deformation-specific properties: i.e., appreciable ductility and the existence of particular phases. Methods of annealing resistometry as well as of calorimetry proved to be good for determining the concentration of these defects, with their activation enthalpy being typical of both the defect type and the actual diffusion mechanism. For the identification of complex vacancy defects, comparisons with results from X-ray line profile analysis for the dislocation density revealed them to be indispensable. The vacancy concentrations measured in severely plastically deformed metals markedly exceeded that of conventionally deformed ones, because of the presence of enhanced hydrostatic pressure, as shown by systematic investigations using various pressures. Whereas in severely plastic deformation-processed Cu only vacancy agglomerates were found, in severely plastic deformation-processed Ni single/double vacancies were also present, and the total concentration of vacancy type defects was higher. These effects were suggested to arise from the higher stacking fault energy of Ni, and its higher enthalpy for vacancy migration.

The Presence and Nature of Vacancy Type Defects in Nanometals Detained by Severe Plastic Deformation. D.Setman, E.Schafler, E.Korznikova, M.J.Zehetbauer: Materials Science and Engineering A, 2008, 493[1-2], 116-22