Effect of Cr on metastable phase equilibria and spinodal decomposition in c-TiAIN coatings: A CALPHAD and Cahn-Hilliard study

Metastable c-TiAICrN is a new generation quaternary hard protective coating that is of interest due to its excellent performance. Based on limited experimental phase stability data together with the first-principles computed free energies, a thermodynamic evaluation of the pseudo-ternary c-TiN/c-AIN/c-CrN system was first performed using the CALculation of PHAse Diagram (CALPHAD) technique, allowing the construction of the metastable phase equilibria. This thermodynamic description was used in combination with the Cahn-Hilliard model to perform numerical simulation of the microstructure evolution in c-Ti0.45Al0.47Cr0.08N coating during spinodal decomposition. The simulated results showed that Cr atoms were distributed in both c-TiN- and c-AIN-rich domains with preferential location at the interface regions. This enrichment at the interface can decrease the lattice mismatch and lead to a smaller driving force for spinodal decomposition compared with Cr-free coatings. Overall, the simulated composition wavelengths after 7200 s agree well with the experimental results. (C) 2017 Elsevier B.V. All rights reserved.