Systematic study of radiation-induced segregation in neutron-irradiated FeCrAl alloys

Abstract

This work systematically reports grain boundary radiation-induced segregation (RIS), and insights into RIS mechanisms, in FeCrAl alloys. Recently, FeCrAl alloys have received significant attention as direct replacement accident tolerant fuel (ATF) claddings for light water cooled nuclear reactors, because of their corrosion and high-temperature oxidation resistance characteristics. One degradation method not studied in detail is RIS, which could sufficiently alter grain boundary chemistry, potentially compromising the superior aqueous corrosion resistance. This study focuses on candidate ATF FeCrAl alloys C06M, C35M, C36M, and C37M that are neutron irradiated to 1.8 displacements per atom (dpa) at 357°C. Grain boundary Cr enrichment and Al depletion are observed in all irradiated alloys that span the 10-13 wt.% Cr and 5-6 wt.% Al composition space. Fe will either enrich or deplete at grain boundaries to balance the grain boundary composition. The Cr enrichment is attributed to interstitial diffusion, consistent with that in body centric cubic 9-12 wt.% Cr steels. The depletion of Al occurs through the same mechanisms as α−α′ phase partitioning previously observed in FeCrAl alloys. This study underscores the need for FeCrAl alloy design to consider RIS implications on corrosion and oxidation susceptibility.