The high temperature oxidation resistance of FeCrAlalloys, which is a candidate material for ATF cladding, isfurther enhanced by the addition of yttrium in the alloys.Yttrium in FeCrAl alloys is present as YFe4Al8intermetallic particles and uniformly distributed in thematrix. At the 1200 °C steam/Ar environment, YFe4Al8near the oxidized surface becomes Y_2O_3 at the grainboundary of the metal below the uniform aluminum oxideand eventually becomes Y_3Al_5O_(12). Y_3Al_5O_(12) peg allowsrapid oxygen penetration into the metal substrate andcause internal oxidation. In the case of yttrium undopedFeCrAl alloys, most of the oxide spalled out during airquenching but not in yttrium doped FeCrAl alloys. Oxideadhesion could be explained by the change in the growthmechanism of the oxide by yttrium segregation at thegrain boundary. The reticular structure with high yttriumconcentration observed on the oxidized surface wasobserved as Y_3Al_5O_(12) peg formed in grain boundary ofmetal and Y_3Al_5O_(12) precipitate buried in aluminum oxide.The size of the reticular structure coincides with theinitial grain size of the metal near the surface.
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