Study of damage in binary Fe85Cr15 alloys irradiated by ions and the effect of an external magnetic field during irradiation

Abstract

Understanding radiation-induced damage in iron-chromium alloys is critical for the use of advanced steels

in future fusion reactors. However, the role of the strong magnetic fields present in such magnetically

confined plasma devices on material damage, though considered important, has not been thoroughly

explored to date. In this work, irradiation experiments of Fe85Cr15 alloy (15% Cr content) by heavy (Feþ) and

light (Heþ) ions have been carried out in order to characterize the damage and, additionally, the influence

of an external magnetic field (B¼ 0.4 T) has been taken into account. The analysis of the data has been

done with different techniques, the distribution of the Cr and/or vacancies around probe nuclei has been

explored by M€ossbauer spectroscopy and the vacancy profile by Slow Positron Annihilation Spectroscopy

(SPAS). Comparison between samples irradiated by Heþ and Feþ, in absence of B, reveals significant differences

in the average hyperfine magnetic field (<DH>¼ 0.8 T). This can be attributed to changes in the

local environment around the probe nuclei (57Fe) where either vacancies or the Cr distribution play a role.

From depth-profiling by SPAS in Feþ irradiated samples, a large concentration of vacancy-type defects is

found with a profile that extends deeper than that predicted by computer simulations. Furthermore,

sequential irradiation by Feþ and Heþ ions indicates that the He atoms tend to fill the vacancy clusters just

in the depth where the Heþ is implanted. On the other hand, small but significant differences in vacancytype

defect profiles are found between the samples irradiated both in the presence and absence of a

magnetic field (B¼ 0.4 T) both independently of single and sequential irradiation. Detailed M€ossbauer

spectroscopy and SPAS analysis seem to point out that external magnetic fields could be a non-negligible

parameter in the material damage due to ion irradiation.