Spinodal decomposition of cubic Ti1–xAlxN: Comparison between experiments and modeling

Abstract

Annealing of cubic (c) Ti1–xAlxN, possessing NaCl structure, leads to decomposition into the stable constituents c-TiN and hexagonal (h) AlN (ZnS wurtzite structure) via the formation of metastable c-TiN rich and metastable c-AlN rich phases. In this paper, we describe the influence of sizes of the newly formed particles and strain energy due to their different lattice parameter and elastic constants with respect to the remaining matrix on decomposition processes and energetics. Good agreement between the enthalpy output obtained from differential scanning calorimetry and values derived from ab-initio and continuum mechanical based calculations for the decomposition and transformation processes occurring is obtained. Based on the comparison between experiments including X-ray diffraction and small-angle neutron scattering of annealed samples and modeling we can conclude that spinodal decomposition is present in c-Ti1–xAlxN coatings with x = 0.50 and 0.66, whereas the alloy with x = 0.25 is outside the spinodal.