Segregation of alloying elements on small-angle grain boundaries in ferritic-martensitic steels under ion irradiation

Segregation of chemical elements was studied in ferritic-martensitic steels RUSFER-EK-181 and ChS-139—promising structural materials for fast neutron reactor core. To simulate the radiation effects, Fe ions with an energy of 5.6 MeV at temperatures of 250–400°C to damage doses of ~6 dpa and at temperatures of 350–450°C to a damage dose of 30 dpa were used. RUSFER-EK-181 steel was also studied after thermal aging at 450°C for 5000 h. Z-contrast analysis of the irradiated steels revealed the segregation of alloying elements on dislocations at small-angle tilt and mixed grain boundaries. Atom probe tomography of the ion-irradiated ChS-139 steel showed that clusters enriched in Ni, Si, and Mn were formed on the dislocations, including dislocations of small-angle grain boundaries. Clusters enriched in Si were formed on dislocations in the RUSFER-EK-181 steel. In the aged state of RUSFER-EK-181 steel, segregation of Cr, V, Mn, Si, and N was shown at dislocations of the small-angle grain boundary. The calculated misorientation angles of the small-angle grain boundaries were ~1°–3°, and the twist angle of the mixed boundary was ~3°.