  The effect of He+ ion irradiation on a distribution of Cr atoms in model
(EFDA) Fe(100-x)Cr(x) (x=5.8, 10.75, 15.15) was studied by means of conversion
electrons Mossbauer spectroscopy. The alloys were irradiated to the dose of
1.2E16 ions per cm2 (7.5 dpa) with He+ of 0.25 and 2.0 MeV. The distribution of
Cr atoms within the first two coordination shells around the probe Fe atoms was
expressed in terms of the Warren-Cowley short-range order parameters alpha1
(first-neighbour shell, 1NN), alpha2 (second-neighbour shell, 2NN) and alpha12
(1NN+2NN. In non-irradiated alloys alpha1 was positive and alpha2 was negative
for all three samples which indicates an ordering of Cr atoms. Yet, the value
of alpha12 were close to zero, i.e. the distribution of Cr atoms averaged over
the first two coordination shells around the probe Fe atoms, was random. The
effect of the irradiation of the Fe5Cr sample is similar for the two energies
of the He+ projectiles viz. increase of number of Cr atoms in the 1NN and
decrease in the 2NN shell. Consequently, the degree of the ordering increased.
For the other two samples, the effect of the irradiation depends on the
composition, and it is stronger for the less energetic ions where, in the case
of Fe10Cr, the disordering disappeared and some traces of Cr clustering
(alpha12 weakly positive) can be seen. In the Fe15Cr sample the clustering is
clear. In the samples irradiated with 2.0 MeV ions the ordering also survived
in the samples with x=10.75 and 15.15, although its degree became smaller than
in the Fe5Cr sample. Small changes in the magnetic texture were revealed.
