Modeling of metastable phase formation for sputtered Ti_1-xAl_xN thin films

Metastable titanium aluminum nitride coatings are widely applied in cutting and forming applications. Although it is generally accepted that the phase formation of metastable TiAlN is governed by kinetic factors, modeling attempts today are based solely on energetics. In this work, the metastable phase formation of TiAlN is predicted based on one combinatorial magnetron sputtering experiment, the activation energy for surface diffusion, the critical diffusion distance, as well as thermodynamic calculations. The phase formation data obtained from further combinatorial growth experiments varying chemical composition, deposition temperature, and deposition rate are in good agreement with the model. Furthermore, it is demonstrated that a significant extension of the predicted critical solubility range is enabled by taking kinetic factors into account. Explicit consideration of kinetics extends the Al solubility limit to lower values, previously unobtainable by energetics, but accessible experimentally.