The release of energy during annealing of deformed metals

Abstract

The method described previously for measuring the energy stored in cold-worked metals has now been applied to nickel and arsenical copper as well as to pure copper. Torsion, tension and compression have been used as methods of deformation, and the heating rates were 2, 4 and 6° C/min. For all these materials, for all types of deformation and for all heating rates a sudden release of energy corresponding to recrystallization is observed and this comprises the total stored energy for pure copper. Thus, for pure copper, there is no indication of the two stages in the release of the stored energy reported by Suzuki. However, for nickel and arsenical copper a considerable proportion of the stored energy is released prior to recrystallization. Measurements of electrical resistivity, hardness and macroscopic density have been made on similar specimens, and correlation of these results with the measurements of stored energy suggests that the release of energy prior to recrystallization, in nickel and arsenical copper, should be ascribed to the rearrangement and annihilation of dislocations and also, in nickel, to the disappearance of vacancies produced during deformation. Values are given for the energy stored in specimens deformed to various extents in torsion, tension and compression at room temperature, and it is shown that the energy released on recrystallization is a linear function of the strain . Estimates of the density of dislocations corresponding to this energy are made for various strains. The disappearance of vacancies in nickel releases an amount of energy which is almost independent of the strain, for the comparatively large strains investigated and the density measurements indicate that this energy corresponds to 1·6 eV per vacancy.