Principles of self-annealing in silver processed by equal-channel angular pressing: The significance of a very low stacking fault energy

Experiments were conducted to evaluate the long-term microstructural stability of silver after processing using equal-channel angular pressing (ECAP). The results show that an ultrafine-grained microstructure is produced by ECAP at room temperature but there is self-annealing in the form of recovery and recrystallization during long-term storage at room temperature. In practice, the very low stacking fault energy of silver results in a high degree of dislocation dissociation and thereby hinders recovery by cross-slip and climb. The experiments examine the evolution of microstructure and the mechanical behavior as a function of the storage time after different numbers of ECAP passes. The results demonstrate that the degree and kinetics of self-annealing depend upon the number of passes imposed in ECAP.