Effects of aluminum concentration on the oxidation behaviors of reactively sputtered TiAlN films

Polycrystalline TiAlN films were deposited on a substrate of high-speed steel via a radio-frequency-bias reactive-sputtering process. The effects of aluminum concentration (0-60 at.%) on the high-temperature oxidation behavior of TiAlN films were explored by using in situ thermogravimetric analysis and high-temperature X-ray diffractometry. The composition and distribution of the oxidizing layers over TiAlN films were investigated. Results indicated that the oxidation resistance increased as the aluminum concentration increased. The type and location of oxidizing phases also were dependent on the aluminum concentration. Three major oxides - i.e., Al₂O₃, TiO₂, and TiO - were observed. The thickness of the Al₂O₃ layer increased and the TiO₂ gradually changed to TiO as the aluminum content increased. Thermodynamic calculations were compared to experimental observations, and they showed good agreement.