Origin and stability of the core-shelled Y–Ti–Zr–O nano-oxides in oxide-dispersion-strengthened ferritic alloys

Quaternary Y–Ti–Zr–O nano-oxides form in preference to other ternary nano-oxides in Y+Ti+Zr micro-alloyed FeCr- oxide-dispersion-strengthened (ODS) ferric alloys. In this study, bulk substitution and interfacial segregation were calculated from the first-principles to explore the formation and stability of core-shelled Y–Ti–Zr–O nano-oxides. Our results were validated with previous electron microscopic characterizations. The major findings that were obtained are as follows. Quaternary Y–Ti–Zr–O nano-oxides are most likely formed as a consequence of Zr substitution of Ti in Y–Ti–O nano-oxides. Ti segregation from the matrix interior to the Y2Ti2O7 interface is a self-limiting process, and the resulting Ti-shell at Y2Ti2O7 nano-cores can hardly be thermally stable. In contrast, the Y2(Ti,Zr)2O7 nano-core due to Zr substitution can strongly trap the Zr-substituted Ti at its interface. The resulting Ti-shell can be more stable at high Zr-content Y2(Ti,Zr)2O7 nano-cores but will reduce the interface adhesion strength. The gained insights help to clarify the experimental observations and achieve a better understanding of micro-alloying effects and mechanisms in FeCr-ODS ferric alloys.