Vacancy-type defects in cold-worked iron studied using positron annihilation techniques

Positron annihilation lifetime (PAL) and coincidence Doppler broadening of the annihilation radiation (CDBAR) measurements have been investigated on cold-worked iron with different percentages of a deformation up to 40%. The PAL spectra were analyzed into two lifetime components. The shorter lifetimes were explicitly smaller than the monovacancy lifetimes, which were possibly caused by deformation-induced dislocations and vacancy-impurity complexes. The longer lifetimes showed that, the deformation introduces also larger vacancy clusters (consisting of five to ten vacancies) as a result of a cold-working. The behavior of the S-parameter (extracted from CDBAR) with the rolling deformation was analogous to the mean positron lifetime. It increased at up to 5% rolling deformation and leveled off above this percentage of the rolling deformation. The CDBAR ratio curve with respect to pure iron showed that, above the 5% rolling deformation the nature of the defects trapping the positron changed.