NUCLEATION OF VACANCY LOOPS IN QUENCHED PURE ALUMINUM

摘要

The nucleation of vacancy loops has been studied in nominally 99.999% pure aluminum using transmission electron microscopy and electrical resistivity measurements. The clustering of supersaturated vacancies after quenching was examined with a two-step aging treatment. The temperatures characterizing the nucleation of vacancy loops in aluminum are analyzed. For aluminum quenched from 610℃ into liquid nitrogen and preaged at temperature -60℃ or lower, the rate controlling process for the nucleation of vacancy loops is the migration of single vacancies at the beginning of preaging. Toward the end of preaging, the nucleation rate is dominated by the migration of divacancies. At temperature higher than -40℃, dissociation of subcritical clusters is noticeable. The nucleation rate is found to vary with the concentration of quenched-in vacancies and the aging temperature. The results of this investigation indicate that the migration energy, E_m~2, of a divacancy is E_m~2 = 0.47 +- 0.02 eV.