Oxidation kinetics of the quasicrystalline i-AlCuFe phase compared with that of crystalline ω-AlCuFe and pure aluminum

The oxidation of the quasicrystalline alloy i-AlCuFe has been compared with that of tetragonal ω-AlCuFe and that of pure aluminum. At 600 °C, for low exposure to oxygen in UHV conditions (up to 5000 L), much smaller thicknesses of oxide have been observed on i-AlCuFe by AES and depth profiling. After oxidations of 105 L, oxide crystallites are clearly observed by SEM on the surface of ω-AlCuFe and pure aluminum, in particular in the center of the grains. Such is not the case on i-AlCuFe grains. These oxide crystallites give rise after ion etching to cones structure on the surface of ω-AlCuFe and pure aluminum whereas the i-AlCuFe surface remains very smooth. However when oxidation is performed at 700 °C, oxide crystallites also appear on the whole icosahedral grains. These results show that the crystalline and the quasicrystalline phases have a different kinetics in the oxide growth, due to, in particular, a delay in the nucleation and growth rate of the oxide on the quasicrystalline phase. It is assumed that this difference is linked to the impossible epitaxial growth of the γ-Al2O3 oxide on the aperiodic lattice of the i-AlCuFe phase.