Characterization of helium implanted Fe–Cr alloys by means of positron annihilation methods

Doppler broadening spectroscopy and positron lifetime measurements have been used for the characterization of radiation damage and helium effects on the microstructure of the ferritic Fe–Cr alloy with 12% (wt.) chromium content. Severe displacement damage (up to 100 dpa) was introduced by the implantation of helium ions with fluence 1.25 × 1018 cm−2. The temperature during the implantation process was below 80 °C. Positron lifetime spectra obtained from slow positron beam experiments confirmed the presence of large voids in the region of the displacement peak. Further investigation by Doppler broadening spectroscopy in the conventional and slow positron beam setups revealed a strong retention of helium in this region, which contributes to the broadening of the momentum peak and at the same time it reduces the positron lifetime in radiation-induced vacancy clusters. The measured Doppler broadened profiles of the implanted materials reasonably correspond with the calculated data showing the helium effect range within 5–12 × 10−3 m0c. Both experimental techniques show empty vacancy clusters to be a dominant type of defect in the first 400 nm region, while helium filling of these defects occurs further in depth. This is in a good agreement with the results of SRIM simulation.