Positron annihilation studies on the migration of deformation induced vacancies in stainless steel AISI 316 L

Positron lifetime measurements were carried out at room temperature before and after isochronous annealing of cylindrical, machined fatigue specimens and of round slabs of austenitic stainless steel AISI 316 L deformed in com pression. Annealing experiments are evaluated in terms of vacancy migration and sinking to grain boundaries and dislocations. The model assumes spheri cal grains with a homogeneous initial distribution of vacancies. A vacancy migration enthalpy of H-V(M) = (0.9 +/-0.15) eV was found. It is concluded that positron trapping at dislocation lines does not significantly contribu te to positron lifetime measurements at room temperature and that single va cancies are the dominating positron traps. Positron annihilation depth prof iling on cross-sectional areas prepared from machined specimens using a pos itron microprobe with 10 mum spatial resolution shows that machining of cyl indrical specimens creates vacancies up to 5 mm below the surface.