Annealing dynamics of interstitial complexes in a dilute Al-Li alloy with Fe

Previous ultrasonic measurements of a dilute Al-Li alloy irradiated by 2.3-MeV electrons gave strong evidence that self-interstitial atoms trapped by Li atoms form mixed dumbbells with tetragonal symmetry. The dumbbell is detected through its relaxation, which anneals away by 130 K. In this work, Fe is added to the alloy to determine whether this annealing stage represents migration of the defect to a trap or its dissociation. Fe atoms are known to trap self-interstitials, forming a complex stable to stage III that gives a set of relaxations different from the Al-Li relaxation. If Al-Li complexes dissociate, then self-interstitials would be released and captured by Fe atoms, resulting in larger Al-Fe relaxations. This result is not seen for this annealing stage. Furthermore, it is unlikely that the annealing is due to a change of configuration of the defect, since the anisotropy of the diaelastic effect remains constant during the annealing. Therefore, the Al-Li complex migrates as a unit without dissociating during this annealing stage. However, Al-Li complexes are observed to dissociate at 200 K, or about 20 K below stage III