Precipitation Behavior of Irradiated Reduced-Activation Ferritic Steels

抄録

In order to study the effects of small additional elements on precipitation behavior in reduced-activation ferritic steels under neutron irradiation, analytical transmission electron microscopy was used to examine the microstructure and the precipitation of the extraction replica of several reduced activation ferritic/martensitic steels which have different contents of small additional elements after 60 displacements per atom (dpa) irradi-ation at 693, 698 and 733 K in the Fast Flux Test Facility (FFTF)/Materials Open Test Assembly (MOTA). All of reduced-activation ferritic/martensitic steels were found to have a good phase stability after irradiation. Micro-voids were observed in both materials of Fe-9Cr-2W with or without boron, the density of micro-voids in the steel with boron is larger than that without boron, and the mean size of micro-voids is smaller than that without boron. However void swelling was less than 1%. Most of the precipitates in the irradiated specimens were found to be M₂₃C₆ which consists of mainly Cr. The remainder of the precipitates were found to be Ta-rich M₆C. Laves phase was observed only at 733K. Several precipitates which were Ti-rich including Si and W were also observed at grain boundary in Ti addition steels at 733 K irradiation. Several Y₂O₃ particles were observed in an yttrium containing alloy. No precipitation including Al was observed in an Al containing alloy. Ti addition decreased precipitation of Ta-rich M₆C in 9Cr and 12Cr steels in this irradiation condition.