Formation of Amorphous Oxide Layer on the Crystalline Al-Ni-Y Alloy

Abstract

The oxidation behavior of the crystallized <TEX>$Al_{87}Ni_3Y_{10}$</TEX> alloy has been investigated with an aim to compare with that of the amorphous <TEX>$Al_{87}Ni_3Y_{10}$</TEX> alloy. The oxidation at 873 K occurs as follows: (1) growth of an amorphous aluminum-yttrium oxide layer (~10 nm) after heating up to 873 K; and (2) formation of <TEX>$YAlO_3$</TEX> crystalline oxide (~220 nm) after annealing for 30 hours at 873 K. Such an overall oxidation step indicates that the oxidation behavior in the crystallized <TEX>$Al_{87}Ni_3Y_{10}$</TEX> alloy occurs in the same way as in the amorphous <TEX>$Al_{87}Ni_3Y_{10}$</TEX> alloy. The simultaneous presence of aluminum and yttrium in the oxide layer significantly enhances the thermal stability of the amorphous structure in the oxide phase. Since the structure of aluminum-yttrium oxide is dense due to the large difference in ionic radius between aluminum and yttrium ions, the diffusion of oxygen ion through the amorphous oxide layer is limited thus stabilizing the amorphous structure of the oxide phase.