Influence of the Al distribution on the structure, elastic properties, and phase stability of supersaturated Ti1-xAlxN

Ti1-xAlxN films and/or their alloys are employed in many industrial applications due to their excellent mechanical and thermal properties. Synthesized by plasma-assisted vapor deposition, Ti1-xAlxN is reported to crystallize in the cubic NaCl (c) structure for AlN mole fractions below 0.4-0.91, whereas at larger Al contents the hexagonal ZnS-wurtzite (w) structure is observed. Here we use ab initio calculations to analyze the effect of composition and Al distribution on the metal sublattice on phase stability, structure, and elastic properties of c-Ti1-xAlxN and w-Ti1-xAlxN. We show that the phase stability of supersaturated c-Ti1-xAlxN not only depends on the chemical composition but also on the Al distribution of the metal sublattice. An increase of the metastable solubility limit of AlN in c-Ti1-xAlxN from 0.64 to 0.74 is obtained by decreasing the number of Ti-Al bonds. This can be understood by considering the Al distribution induced changes of the electronic structure, bond energy, and configurational entropy. This may in part explain the large variation of the metastable solubility limit reported in the literature. (c) 2006 American Institute of Physics.