Ferritic steel is one of the most promising materials for fuel cladding of fast breeder reactors and fusion first wall. However, not enough data on microstructural evolution under irradiation have been obtained, especially at high doses. In the present study, microstructural changes in several ferritic steels under ion irradiation up to 200 dpa were investigated.
The specimens were irradiated with 200 keV C+ or 3 MeV Ni2+ ions between 698 and 898 K. Post irradiation microstructures were observed with transmission electron microscopes. Few voids were detected in MA957. Dislocation structure and dispersed oxide particles (Y2O3) were found to be stable under irradiation up to 200 dpa. Uniform distributions of fine voids were observed in HT-9, Fe-12Cr-2Mo, and pure Fe-12Cr alloy irradiated with 200 keV C+ ions to 150 dpa. However, 3 MeV Ni2+ irradiation of HT-9 between 748 and 848 K caused heterogeneous nucleation of voids near lath boundaries. As-received metallic compound-strengthened steel consisted of martensitic and ferritic phases. Large voids were formed in limited region in martensitic phase during ion irradiation, whereas few voids were found in the ferritic phase. Radiation-enhanced formation of Laves phase (Fe2Mo) was observed in ferritic phase.