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, pla stically deformed at low temperature, has been studied by a subresonan ce internal friction method at very low frequency. In the temperature range where the mobility of screw dislocations is controlled by therma lly activated kink-pair formation, the dynamic recovery of the microst ructure gives rise to a highly complex relaxation phenomenon, which ca n 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 rela xation of the entire dislocation arrangement, leading to a partial rec overy of the microstructure, follows the stretched exponential functio n, as shown by energy measurements on microstructures of different deg rees of complexity.