Interfacial microstructure and adhesion evaluation of pre-oxidized alumina scales on FeCrAl ODS alloy under ion irradiation

Zr-added FeCrAl oxide-dispersion-strengthened (ODS) alloys have been developed as promising candidates for accident-tolerant fuel claddings, which can spontaneously form protective alumina scales at elevated temperatures and provide excellent oxidation resistance in harsh nuclear environments. To clarify the effect of irradiation on scale adhesion, alumina scales were pre-formed on FeCrAl ODS alloy via oxidation at 1000°C and subsequently irradiated with 6.4 MeV Fe³⁺ ions at 500°C at the Dual-Beam Facility for Energy Science and Technology, Kyoto University. Irradiation-induced segregation of reactive elements (REs), including Zr and Y, together with Ti/TiC precipitation at the grain-boundary triple junctions (GBTJs) of the alumina–alloy interface, was confirmed via scanning transmission electron microscopy. Atom probe tomography analysis further revealed irradiation-induced depletion of Ti, Zr, and Y, accompanied by Si impurity segregation at the oxide/alloy interface. The adhesion strength of the alumina scales before and after irradiation was quantitatively evaluated via micro double-notched shear compression tests, which indicated a slight increase in the interfacial adhesion strength after irradiation. This study suggests that the segregation of Ti/TiC and REs at the interfacial GBTJs under Fe-ion irradiation enhances the anchoring effect and improves the interfacial adhesion strength by promoting mechanical interlocking.