The effect of copper and manganese on magnetic minor hysteresis loops in neutron irradiated Fe model alloys

Changes of magnetic minor hysteresis loops in pure Fe, Fe–1 wt% Mn, Fe–0.9 wt% Cu, and Fe–0.9 wt% Cu–1 wt% Mn model alloys after neutron irradiation have been studied. Minor-loop coefficients which are obtained from scaling relations between minor-loop parameters and in proportion to internal stress, were found to decrease in all model alloys after the irradiation to a fluence of 3.32 × 1019 n cm−2. The decrease of the coefficients is larger for alloys including Cu and is enhanced by 1 wt% Mn addition. Such decrease implying the reduction of internal stress during irradiation is in contrast with changes of yield strength after the irradiation that increase with Cu and Mn contents. A qualitative explanation was given on the basis of the preferential formation of Cu precipitates along pre-existing dislocations which reduces internal stress of the dislocations.