Radiation-induced precipitation in a ferritic model alloy: An experimental and theoretical study

The radiation embrittlement of low-alloyed reactor pressure vessel steels is partly due to the formation of nanometer-sized solute clusters (Mn, Si, Ni, Cu and P). In order to determine if radiation-induced mechanisms can take part in the solute clustering, an under-saturated binary Fe-1 at.% Mn alloy was irradiated with Fe ions at 400 degrees C. After irradiation, atom probe tomography experiments revealed that a high density of Mn-rich clusters is formed. This observation clearly demonstrates that, under these irradiation conditions, Mn clustering in this model alloy is radiation-induced and not radiation-enhanced. Mn-rich clusters were not distributed homogeneously in the analyzed volume but were heterogeneously precipitated on a planar object, suggesting a grain boundary (GB) or a dislocation loop. In parallel, a rate theory model calibrated on the population of point defect (PD) clusters measured by transmission electron microscopy has shown that the dominant sinks for mobile PDs are PD clusters. Thus Mn clustering could be explained by Mn atoms dragged by mobile PD fluxes towards sinks such as PD clusters or GBs. According to the model, most of the dragging occurs via isolated interstitials. These results are in very good agreement with previous studies, suggesting a correlation of position between solute-rich clusters and sinks. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.