Reversal from depletion to enrichment of solute elements in radiation-induced segregation at grain boundaries

Ni⁺⁺ ion irradiations of a Nb-stabilized steel of type 1.4981 were performed at 400, 500, and 600°. Dislocation loop evolution with increasing dose and radiation-induced segregation at grain boundaries were observed by transmission electron microscopy. At low doses the typical radiation-induced segregation behaviour at grain boundaries, as commonly observed in steels and Fe-Ni-Cr alloys, is confirmed. At high doses the segregation behaviour at grain boundaries was found to be completely inverted, i.e. elements which were radiation-enriched at the grain boundaries at low doses were now depleted and vice versa. This is attributed to the formation and growth of radiation-induced precipitates with increasing dose. The precipitates were only found after irradiation at 500 and 600°C and to doses higher than 5 dpa. They are rich in Ni, Si, and Nb. The effect of inverse radiation-induced segregation at grain boundaries could possibly be useful for solving the problems arising from radiation-assisted sensitization and stress corrosion cracking.