Monitoring of Self-Annealing in Ultrafine-Grained Silver Using Nanoindentation

The self-annealing of an ultrafine-grained (UFG) microstructure in pure silver produced by severe plastic deformation (SPD) was studied by nanoindentation and X-ray line profile analysis. Both recovery and recrystallization of the UFG structure take place during long-term storage at room temperature as a result of the extremely high dislocation density which acts as a driving force in self-annealing. Nanohardness mapping revealed that self-annealing occurred inhomogeneously, and the higher strain imposed in SPD processing leads to faster recrystallization in severely deformed silver. This behavior of self-annealing can be explained by the enhanced contribution of twinning which facilitates the formation of recrystallized embryos.