Formation of crystalline Al–Ti–O thin films and their properties

The article reports on the effect of addition of Ti into Al2O3 films with Ti on their structure, mechanical properties and oxidation resistance. The main aim of the investigation was to prepare crystalline Al–Ti–O films at substrate temperatures Ts ≤ 500 °C. The films with three different compositions (41, 43 and 67 mol% Al2O3) were reactively sputtered from a composed Al/Ti target and their properties were characterized using X-ray diffraction (XRD), X-ray fluorescent spectroscopy (XRF), microhardness testing, and thermogravimetric analysis (TGA). It was found that (1) the addition of Ti stimulates crystallization of Al–Ti–O films at lower substrate temperatures, (2) Al–Ti–O films with a nanocrystalline cubic γ-Al2O3 structure, hardness of 25 GPa and zero oxidation in a flowing air up to ∼ 1050 °C can be prepared already at low substrate temperature of 200 °C, and (3) the crystallinity of Al–Ti–O films produced at a given temperature improves with the increasing amount of Ti. The last finding is in a good agreement with the binary phase diagram of the TiO2–Al2O3 system.