Effect of chromium on void swelling in ion irradiated high purity Fe–Cr alloys

The concentration of chromium (Cr) plays an important role on the radiation induced microstructure of the binary Fe–Cr alloys, in particular on the formation of cavities leading to void swelling of the material. Many fast neutron irradiations were performed in the past to understand the swelling variation as a function of the Cr content. However, due to some contrasting results in the literature, the trend is not yet clear. For that purpose, we have performed self-ion irradiations to high doses (>100 dpa) at 773 K, in single beam mode (damage by 2 MeV self ions) and dual beam mode (damage by 2 MeV self-ions and co-implantation of 2 MeV helium ions with continuous energy degradation) on a wide range of high purity Fe–Cr alloys with Cr level ranging from 3 wt.% to 14 wt.% and a reference body centred cubic (bcc) iron (Fe). Conventional transmission electron microscopy (TEM) analysis revealed a strong swelling suppression by the addition of 3 wt.% Cr to the Fe matrix. The analysis of the dual beam irradiated samples revealed that the variation of void swelling as a function of the Cr content is non-monotonic, with a local swelling maxima around 9–10 wt.% Cr. Overall, all the Fe–Cr alloys up to 14 wt.% Cr show much reduced swelling as compared to bcc Fe. No cavities, and hence, swelling, was noted in the single beam irradiated Fe–Cr alloys, while the same in bcc Fe remained high. This elucidates further the large magnitude of swelling reduction by Cr.