Energetic balance and kinetics for the decomposition of supersaturated Ti1−xAlxN

Ti1−xAlxN films have been shown to exhibit superior mechanical and thermal properties and are thus widely used for industrial applications. We have recently reported, that metastable NaCl-structure (c) Ti1−xAlxN decomposes to form c-TiN and c-AlN domains, and that the chemical requirement for spinodal decomposition is fulfilled over a broad composition and temperature range. Ab initio calculations showed that the maximum metastable solubility limit of AlN in c-TiN is in the range of 0.64–0.74, depending on the configurational entropy. The enthalpy change for decomposition of supersaturated c-Ti1−xAlxN into c-TiN and c-AlN has a maximum of ∼0.146 eV/at (28.18 kJ/mol) at x ∼ 0.61. Here, we use continuum mechanical investigations in addition to ab initio calculations to consider also the previously not described contribution of strain and surface energy on the energetic balance for this decomposition process. Based on these results a simple kinetic model for the decomposition process of c-Ti1−xAlxN can be developed.