Low-temperature fission-neutron disordering of Fe-Co and Fe-Co-X (X=Mn,V,Ti) ordered alloys

Four B2-type Fe/50 at.% Al, Fe/49 at.% Co/2at.% X (X = Mn, V, Ti) alloys have been irradiated with fission neutrons (E > 1 MeV) at liquid-hydrogen temperature, either in the ordered or the disordered state. Radiation damage rates have been continuously investigated using electrical resistivity measurements at 22 K and the behavior of every alloy is compared for both states of order. In the disordered state, the resistivity increase is only attributed to point-defect production. The displacement cross-sections for Fe sigmasub(d)sup(Fe) and Co atoms sigmasub(d)sup(Co) are calculated; the specific Frenkel-pair resistivities rhosub(F) and the effective recombination volumes V0 are determined. These results are in good agreement with previously reported values obtained from electron irradiation experiments. In the ordered alloys, resistivity damage curves reveal both the defect production and disordering process. Radiation-disordering kinetics exhibiting a linear dependence of the disordering rate with the long-range degree of order are verified experimentally. The comparison between the displacement and the disordering rate suggests that replacement collisions along <111> directions are the dominant disordering mechanism. The average lengths of replacement sequences are estimated and it is observed that they are strongly reduced in the ternary alloys. (orig.)