Vacancy concentrations determined from the diffuse background scattering of X-rays in plastically deformed copper

The background intensity of X-ray diffraction patterns is analysed in terms of point defects, especially vacancies, in poly- and single-crystalline copper specimens. The samples have been deformed by compression in-situ in a synchrotron peak profile experiment. Systematic comparative analysis of X-ray, electrical resistivity, and calorimetric measurements indicate that (i) point defects, especially vacancies, are produced during plastic deformation and (ii) that the point defect concentration is increasing concomittantly with the actual dislocation density. The point defect production rate in poly- and single-crystalline specimens is observed to be drastically different. This difference is interpreted as different vacancy production rates in the grain interior and in the grain-boundary regions. With increasing deformation, the vacancy concentration in the grain-boundary regions is found to approach the equilibrium values corresponding to the melting temperature of copper. This result would support the assumption that in severely deformed metals the grain boundary region is a highly distorted, almost amorphous phase of the material.