Formation of barrier-type anodic films on sputtering-deposited Al–Ti alloys

The formation of amorphous anodic films at constant current is investigated for sputtering-deposited Al–Ti alloys containing from 3–30 at.% Ti. The films were grown at high efficiency in a borate electrolyte and comprised a main region containing units of Al2O3 and TiO2, with a thin surface region enriched in titanium species. The formation ratios of the films increased with increase of titanium content of the alloys. The presence of the outer region is explained by the faster migration of Ti4+ ions relative to that of Al3+ ions through the films.

Research highlights
► Amorphous anodic oxides form on Al-Ti alloys - compositions similar to alloys.
► Oxides growth by migration of Al3+, Ti4+ and O2- ions.
► Faster migration of Ti4+ ions than Al3+ ions results in Ti4+-rich surface layer.