An angle-resolved XPS study of the in-depth structure of passivated amorphous aluminum alloys

Angle-resolved X-ray photo-electron spectroscopy (ARXPS) measurements were performed in order to characterize the in-depth structures of the passive film and underlying alloy below the passive film for sputter-deposited corrosion-resistant amorphous aluminum alloys. Titanium cation is enriched throughout the passive film formed on an amorphous Al-36Ti-7Mg alloy, while chromium cation is enriched in the exterior of the passive film formed on an amorphous Al-36Cr-9Mo alloy and is deficient in the interior. The analyses of the in-depth distribution of constituents in the passive films indicate that the field-assisted outward migration of chromium cation in the passive film is faster than that of aluminum cations though the corrosion resistance of chromium is apparently higher than that of aluminum in 1 M HCI. The protective ability of the passive film is attributed to the stability of the chromium-enriched surface layer of the passive film. The outward migration of titanium cation is slower than that of aluminum. The investigation of the structure of the underlying alloy below the passive film shows that chromium and titanium are enriched in the underlying alloy surface and the composition gradually approaches the alloy composition with depth. The thickness of the chromium-or titanium-enriched region estimated is less than 1 nm.