New insights into the mechanism of yttrium changing high-temperature oxide growth of Fe-13Cr–6Al–2Mo–0.5Nb alloy for fuel cladding

The oxidation behavior and microstructure evolution of Fe–13Cr–6Al–2Mo–0.5Nb alloys with various yttrium contents ranging from 0 to 0.23 wt.% have been investigated at 1200 °C for 4 h in steam environment. The oxide weight gain decreased with minor addition of yttrium, but this tendency was lost with excess addition. The grain boundary migration was hindered due to high binding energy of yttrium atom and vacancy. The combination of yttrium with vacancies and a large number of fine Laves phases at grain boundaries suppressed the outward diffusion of Al³⁺, resulting in the change of oxide growth mechanism and oxide scale adhesion.