DYNAMIC RECOVERY OF THE MICROSTRUCTURE OF SCREW DISLOCATIONS IN HIGH-PURITY BCC METALS

The dynamics of screw dislocations in high purity b.c.c. tantalum, plastically deformed at low temperature, has been studied by a subresonance internal friction method at very low frequency. In the temperature range where the mobility of screw dislocations is controlled by thermally activated kink-pair formation, the dynamic recovery of the microstructure gives rise to a highly complex relaxation phenomenon, which can be observed through an irreversible dissipation peak in the sample's response. The complexity of the relaxation derives from the disorder introduced into the process by the dynamic formation of jogs. The relaxation of the entire dislocation arrangement, leading to a partial recovery of the microstructure, follows the stretched exponential function, as shown by energy measurements on microstructures of different degrees of complexity.