Change of Cr atoms distribution in Fe85Cr15 alloy caused by 250Â keV He+ ion irradiation to different doses

Redistribution of Cr atoms in a Fe85Cr15 alloy caused by its irradiation with 250 keV He+ ions to different doses, D = 8 ⋅ 1016, 16 ⋅ 1016 and 48 ⋅ 1016 ions/cm2 was investigated by means of conversion electrons Mössbauer spectroscopy. The redistribution was expressed in terms of the Warren-Cowley short-range order parameters α1, α2 and α12 pertaining to the first (1NN), second (2NN) and both i.e. 1NN + 2NN shells, respectively. Clear evidence was found, both for non-irradiated and irradiated samples that the actual distribution of Cr atoms is characteristic of the shell, and for a given shell it depends on the irradiation dose. In particular, α1 is positive, hence indicates an under population of Cr atoms in 1NN with respect to the random case, α2 is negative, giving evidence thereby that 2NN is overpopulated by Cr atoms, and α12 is weakly positive. Under the applied irradiation the number of Cr atoms in both neighbor shells decreased signifying thereby a clustering of Cr atoms. The underlying decrease of Cr concentration within the 1NN-2NN volume around the probe Fe atoms was estimated at 1.5 at.% ranging between 2.1 for the lowest and 0.8 at.% for the highest dose.