Effect of 0.25 and 2.0 MeV He-Ion Irradiation on Short-Range Ordering in Model (EFDA) Fe-Cr Alloys

The effects of He+ irradiation on a distribution of Cr atoms in Fe100-x Cr (x) (x = 5.8, 10.75, 15.15) alloys were studied by Fe-57 Conversion Electron Mossbauer Spectroscopy (CEMS). The alloys were irradiated with doses up to 12 x 10(16) ions/cm(2) with 0.25 and 2.0 MeV He+ ions. The distribution of Cr atoms within the first two coordination shells around Fe atoms was expressed with short-range order parameters alpha (1) (first-neighbor shell, 1NN), alpha (2) (second-neighbor shell, 2NN), and alpha (12) (1NN + 2NN). In non-irradiated alloys, alpha (1) > 0 and alpha (2) < 0 was revealed for all three samples. The value of alpha (12) ae0, i.e., the distribution of Cr atoms averaged over 1NN and 2NN, was random. The effect of the irradiation of the Fe94.2Cr5.8 alloy was similar for the two energies of He+, viz., increase of number of Cr atoms in 1NN and decrease in 2NN. Consequently, the degree of ordering increased. For the other two samples, the effect of the irradiation depends on the composition, and is stronger for the less energetic ions where, for Fe89.25Cr10.75 alloy, the disordering disappeared and some traces of Cr clustering appeared. In Fe84.85Cr15.15 alloy, the clustering was clear. In the samples irradiated with 2. 0 MeV He+ ions, the ordering also survived in the samples with x = 10.75 and 15.15, yet its degree became smaller than in the Fe94.2Cr5.8 alloy.