The ferrite/perovskite interface and helium partition in nano-structured ferritic alloys from the first-principles

Abstract

Nano-oxides are largely responsible for the excellent mechanical properties and irradiation tolerance of nano-structured ferritic alloys (NFAs) for nuclear reactor applications. In this work, the roles of perovskite YTiO₃ and its interface in trapping helium in NFAs were investigated from the first-principles. Similarly as other two Y-Ti-oxide phases (Y₂TiO₅ and Y₂Ti₂O₇), bulk YTiO₃ can trap insoluble helium at its interstitial sites, but with a lower trapping ability that is only comparable to matrix vacancies. The ferrite/YTiO₃ interface phase diagram was constructed based on the experimental orientation relationship and the calculated interface formation energy, and the lowest-energy interface structure was predicted as the ns-Ti or the stoichiometric. Helium always prefers to consume individual interfacial vacancies and interstitial sites to the extent possible, before forming higher-order helium-vacancy clusters at the interface. Similarly as Y₂Ti₂O₇, YTiO₃ preferably traps helium at its interface, followed by its bulk interior and the ferritic matrix. However, in view of all the bulk and interface results, perovskite YTiO₃ cannot compete with pyrochlore Y₂Ti₂O₇ in trapping helium in NFAs.