Analysis of isothermal and isochronal annealing in deformed Zn and Zn-Ag

Abstract

Zn and Zn-Ag polycrystals have been deformed by rolling at 293 K to true strains e=0.05–3.8. After deformation, samples were subjected to isothermal and isochronal anneals, and thereby investigated by intermittent measurements of strength, electrical resistivity, and TEM. Along the isotherms at 293 K, quite unusual hardening effects were observed, which turned out to be strongly affected by the applied prestrain and alloy content. The experimental results can be consistently ascribed to loop formation and loop coarsening from deformation-induced vacancies whereas other explanations, such as loop formation by oxidation and/or phase transformations, can be largely ruled out. Saada's model accounts satisfactorily for the vacancy concentrations measured. In the framework of a loop-hardening theory by Kirchner, the experimentally found values of vacancy concentration and loop density/size yield the right order of magnitude for the strength effects observed. With the isochronal anneals, three stages could be found which are related to loop annealing, dislocation rearrangement, and dislocation annealing.