Vacancy clustering in quenched Al-Li solid solution alloys studied by Doppler broadening spectroscopy

Abstract

The clustering of vacancies in severely quenched Al-Li solid solution alloys, with Li content between 230 and 2760 ppm, has been studied using Doppler broadening spectroscopy. The alloy samples were initially annealed at 873 K in dry air or dry, pure nitrogen. The onset temperature for vacancy clustering in samples initially annealed in air was found to be 150 ± 10 K, 40 ± 15 K lower than for the nitrogen-annealed samples. This result is consistent with the migration of divacancies, formed as a result of the significant increase in vacancy concentration caused by Li migration to, and oxidation at, the surfaces of samples annealed in air. Li-vacancy binding may also contribute, to a lesser extent, to the retardation of vacancy migration in the nitrogen-annealed samples. No dependence on Li content was seen in the results for the two sets of samples.