Using ultrasonic shear waves, the kinetics of migration of vacancy to dislocations in Al was studied. Ultrasonic attenuation was sensitive to the effective dislocation length, which was shortened by the segregation of point defects. Two principal measurements were done: (i) measurement of temperature dependence of decay behavior of attenuation after elastic deformation; (ii) continuous measurement of attenuation of a specimen quenched from 573K to cold-water and then to liquid-N temperatures. The specimens were polycrystalline and monocrystal Al with 4N5-purity. The former measurement indicated an activation energy of 0.28eV for the migration of the predominant point defects, via the Granato–Hikata–Lücke theory. The latter measurement revealed the vacancy kinetics: the attenuation coefficient rapidly decreased twice at 125 and 250K, corresponding to activation energies of 0.28 and 0.61eV for migration, respectively. Thus, the same mechanism occurred for the attenuation change after elastic deformation and at 125K after quenching. The 0.28eV migration energy was attributed to the fast diffusion of vacancies along dislocations. The 0.61eV migration energy was consistent with the bulk diffusion of vacancies in Al. The electromagnetic acoustic resonance method was used for making non-contact but highly accurate attenuation measurements.

Acoustic Study of Kinetics of Vacancy Diffusion toward Dislocations in Aluminum. H.Ogi, A.Tsujimoto, S.Nishimura, M.Hirao: Acta Materialia, 2005, 53[2], 513-7