Effects of yttrium on the oxidation behavior of Fe13Cr6AlY alloys under 1200 °C steam

Abstract

FeCrAl alloys are a candidate material for accident-tolerant fuel cladding in nuclear power plants owing to their high-temperature oxidation resistance, which can be further enhanced by the addition of Y. The main objective of this study was to investigate the effects of Y on the oxidation behavior of Fe13Cr6Al alloys in a 1200 °C steam environment with varying Y concentrations. Initially, Y was present as intermetallic particles in the matrix, which were identified as YFe4Al8. Once the oxidation process began, Y-rich intermetallics served as Y reservoirs and caused two conflicting effects: Y segregation at the oxide grain boundaries and Y-rich oxide formation. The Y segregation caused the inward diffusion of oxygen to be dominant, which changed the oxide growth mechanism and led to enhanced oxidation resistance and oxide adherence. On the other hand, Y formed Y2O3 at the grain boundaries near the oxide/metal interface, which eventually became Y3Al5O12. The Y3Al5O12 pegs allowed rapid oxygen penetration into the metal substrate and caused internal oxidation. Therefore, there is an optimal Y content as a result of these conflicting effects of Y addition. The reticular structure was also carefully analyzed to determine any relationship with the Y-rich oxide pegs. The reticular structure observed on the oxidized surface was identified as Y3Al5O12, which was formed at the grain boundaries of the metal or buried in the Al oxide. The size of the reticular structure coincided with the grain size of the metal near the surface. Data AvailabilityThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also form part of an ongoing study.