Anelastic relaxation due to clustered self-interstitial atoms in Al

Anelastic processes in Al single crystals present after low-temperature electron irradiation have been investigated using both internal-friction and elastic-aftereffect techniques. Several stress-induced relaxation processes have been observed, one due to the $I_B$ close-pair defect, and six others attributed to small interstitial clusters formed during long-range interstitial migration in recovery stage I. Details are presented concerning the creation, stability, symmetry, and relaxation kinetics of the various defects responsible for the anelastic processes. One of the processes exhibits all the characteristics expected for a configuration of the di-interstitial proposed by Johnson. A model is discussed which suggests how a small interstitial cluster may undergo reorientation without simultaneous migration of the defect center of mass.