Critical assessment of Cr-rich precipitates in neutron-irradiated Fe–12 at%Cr: Comparison of SANS and APT

Neutron irradiation at 300 C up to 0.6 dpa of an industrial purity Fe–12at%Cr alloy gives rise to the formation of Cr-rich precipitates of radii of about 1 nm. Small-angle neutron scattering (SANS) and atom probe tomography (APT) applied to the same material should reveal consistent characteristics of the irradiation- induced features. They roughly do so with respect to size and volume fraction, but they do not with respect to the composition of the precipitates or clusters. The discrepancy was expressed in terms of the Porod invariant of nuclear SANS. This quantity can be determined directly by integrating the measured nuclear difference scattering cross section or, alternatively, estimated from the APT results. Both estimates were compared taking into account all potential sources of deviation including error propagation. We have found that the deviation is significant and can be progressively removed by artificially reducing the Fe fraction in the Cr-rich clusters with respect to the measured value. A well-known effect of this kind is the different evaporation fields of Cr-rich clusters and the Fe-rich matrix and resulting ion trajectory overlaps in APT. State-of-the-art consideration of this effect indicates, however, that it is not sufficient to remove the observed discrepancy.