DEPENDENCE OF GRAIN-BOUNDARY CHEMISTRY ON THE IRRADIATION DOSE IN LOW-ACTIVATION FERRITICS

Grain boundary chemistries in low activation 9%Cr-2%Mn-1%W and 12%Cr-6%Mn-1%W steels were measured by means of Auger electron spectroscopy (AES) after irradiations in the FFTF/MOTA at 638 K up to doses of 10 and 25 dpa. In 12%Cr-6%Mn-1%W steel, grain boundary concentration of Si increased with an increase in the irradiation dose from 10 to 25 dpa. Segregation of Mn, however, appeared to saturate or even decreased with the increase. The average size of grain boundary precipitates was increased during the irradiation from 10 to 25 dpa. It is considered that beyond the 10 dpa irradiation, Mn-rich precipitates at grain boundaries absorb Mn atoms segregated at grain boundaries, resulting in the growth of grain boundary precipitates and the reduction of segregated Mn atoms in elemental form at grain boundaries. It is possible that Si atoms which may compete site with Mn atoms at grain boundaries begin to segregate at grain boundaries. In contrast, no significant change in grain boundary chemistry was recognized in 9%Cr-2%Mn-1%W alloy with the increase in irradiation dose from 10 to 25 dpa.