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Change of Cr atoms distribution in Fe85Cr15 alloy caused by 250 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 viz. 5, 10 and 30 dpa was investigated by means of conversion electrons Mossbauer spectroscopy. The redistribution was expressed in terms of the Warren-Cowley short-range order parameters alpha1, alpha2 and alpha12 pertaining to the first, second and both neighbor 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, alpha1 is positive, hence indicates an under population of Cr atoms in 1NN with respect to the random case, alpha2 is negative, giving evidence thereby that 2NN is overpopulated by Cr atoms, and alpha12 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 two-shells 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.