Crystallite size-dependent metastable phase formation of TiAlN coatings.

It is well known that surface energy differences thermodynamically stabilize nanocrystalline γ-AlO over α-AlO. Here, through correlative ab initio calculations and advanced material characterization at the nanometer scale, we demonstrate that the metastable phase formation of nanocrystalline TiAlN, an industrial benchmark coating material, is crystallite size-dependent. By relating calculated surface and volume energy contributions to the total energy, we predict the chemical composition-dependent phase boundary between the two metastable solid solution phases of cubic and wurzite TiAlN.