Phase stability and elastic properties of titanium aluminum oxynitride studied by ab initio calculations.

The impact of oxygen additions on phase stability and elastic properties of titanium aluminum nitride is studied by ab initio calculations. Fcc-Ti0.5Al0.5N and fcc-Ti0.5Al0.5O show a negative energy of mixing with an interaction parameter ΩTiAlNO of -37.6 kJmol-1. The lattice parameter of Ti0.5Al0.5N1-xOx increases with increasing x while the bulk modulus decreases by 35%. The reason is the metallic bonding character which increases at the expense of the covalent character with increasing oxygen content. It is shown that the incorporation of oxygen in Ti0.5Al0.5N1-xOx on interstitial sites is energetically favourable. This can be understood based on the compensation of metallic bonding as the population of metal-oxygen bonds that are similar to a-Al2O3 and rutile-TiO2 is increased. Based on the oxygen incorporation-induced stability increase of Ti0.5Al0.5N1-xOx+y, a new design concept for transition metal oxynitride based hard coatings is developed. [ABSTRACT FROM AUTHOR]