TiAlN coatings are today used as wear protection, for example cutting tools. The alloy shows a combination of good oxidation resistance and superior mechanical properties at elevate temperatures as compared to TiN. The good high temperature behavior is correlated to an isostructural spinodal decomposition of the TiAlN solid solution into coherent cubic Al- and Ti-enriched TiAlN domains that results in a hardness enhancement, i.e. age hardening, at 800-1000C. Several subsequent studies have already highlighted different aspects of importance for the understanding of the decomposition and stability of this materials system, such as the influence of nitrogen off-stoichiometry, pressure, and domain growth behavior.
Although the phase stability and performance of TiAlN coatings has attracted much attention, little is known on the fundamental aspect of their elastic properties. Strong compositional-dependent elastic properties have been observed theoretically and experimentally in TiAlN alloys. Increasing the Al-content weakens the average bond strength in the local octahedral arrangements resulting in a more compliant material. On the other hand, it enhances the directional (covalent) nature of the nearest neighbor bonds that results in greater elastic anisotropy and higher sound velocities. The strong dependence of the elastic properties on the Al-content offers new insight into the detailed understanding of the spinodal decomposition and age hardening in TiAlN alloys.