Effect of Zr and Al addition on nanocluster formation in oxide dispersion strengthened steel - An ab initio study

Abstract

Conventional oxide dispersion strengthened steels are characterized by thermally stable, high density of Y–Ti–O nanoclusters which are responsible for their high creep strength. Ti plays a major role in obtaining a high density of ultrafine particles of optimum size range 2–10 nm. In Al containing ODS steels developed for corrosion resistance, Y–Al–O clusters formed are of size range 20–100 nm and Ti fails in making dispersions finer in presence of Al. Usage of similar alloying elements like Zr in place of Ti is widely considered. In this study, binding energies of different stages of Y–Zr–O–vacancy and Y–Al–O–vacancy complexes in bcc Iron matrix are studied by first principle calculations. It is shown that in all the stages of formation, Y–Zr–O–vacancy clusters have higher binding energy than Y–Al–O–vacancy clusters. Hence in a ferritic steel containing both Zr and Al, Y–Zr–O clusters are more stable and favored to nucleate over Y–Al–O clusters. The bonding nature in each stage is analysed using charge density difference plots to help establish the plausible reason for the higher stability of Y–Zr–O clusters.