Fracture behavior and grain boundary cohesion of alumina scales formed on ion-irradiated FeCrAl-ODS alloy

• Irradiation on fracture behavior of alumina scales formed on FeCrAl ODS alloy has been investigated. • Preferential intergranular fracture dominates the fracture of irradiated alumina scales in nanoindentation. • Irradiation induced REs segregation and Ti/TiC precipitation on alumina grain boundaries. • Cohesion strength of alumina scales formed on FeCrAl ODS alloys has been efficiently evaluated by DNS compression tests. The design of FeCrAl ferritic oxide dispersion strengthened (ODS) alloys is based on the formation of a stable alumina scale, which is expected to protect the alloys from extreme heat and corrosion in nuclear applications. To ensure reliable alumina protection in nuclear environment, it is indispensable to concern the radiation tolerance of the alumina scales formed on the FeCrAl ODS alloys. The present study investigates the effect of Fe ions irradiation on fracture modes and grain boundary cohesion of the alumina scales in conjunction with nano-impact tests and micro-double notch shear (DNS) compression tests. Pre-oxidation was carried out in air at 1000 °C to form an α-alumina layer on the surface of Fe-15Cr-7Al-0.5Y 2 O 3 –0.4Zr (wt.%) ferritic ODS alloy, followed by 6.4 MeV Fe 3+ ion beam irradiation at 500 °C. Based on the microstructural characterization of the cross-sectional micrographs of nanoindentation imprints on the alumina scales, it was confirmed that the irradiation on the alumina scales resulted in significant intergranular fracture in nanoindentation, whereas the unirradiated alumina scales showed transgranular fracture. The elemental distribution around the alumina grain boundaries was elucidated with the aid of scanning transmission electron microscopy (STEM) and atom probe tomography (APT) observations, and obvious segregation of reactive elements (REs) and intergranular Ti/TiC precipitation were observed after irradiation, indicating the link between the microstructural evolution and the fracture behavior of the alumina scales. The detailed grain boundary cohesion of alumina scales before and after irradiation was accurately measured by the micro-DNS compression tests, and the results showed that the cohesion strength of the alumina decreased significantly after the Fe ions irradiation.