Investigation of defects (migration and formation) in metals by positron annihilation lifetime

In the present work a discussion of the possibilities to study defect in solids is presented. Generally, positron behavior in metals is simpler than in insulators. Migrations and formations of defects (point defects, dislocation) in metals have been studied in detail by using position annihilation lifetime technique. Samples of Pb, Bi, Al, Mg, Ag. and Cu were deformed to 20% thickness reduction then annealed at different temperature 1 h before quenched lair cooling). In each pair of samples, lifetime spectrum was accumulated, as a function of the annealing temperature and measured at room temperature. For each metal, two stages were observed with a minimum at T=(0.52-0.62)T-m. This seems to be due to the compensation of two different processes; one for recovery and the other for defect formation. This observation of two processes is clear only on the metals have face center cubic structure such as (Al, Pb, Ag and Cu). (C) 1999 Elsevier Science B.V. All rights reserved.