Thermal stability and oxidation resistance of arc evaporated TiAlN, TaAlN, TiAlTaN, and TiAlN/TaAlN coatings

Our research demonstrates that the quaternary Ti0.45Al0.36Ta0.19N and the multilayered TiAlN/TaAlN coatings feature enhanced mechanical properties and thermal stability as compared with their monolithically grown constituents Ti0.54Al0.46N and Ta0.89Al0.11N. All coatings synthesised exhibit as-deposited hardness values of 32 ± 1 GPa, but only the quaternary Ti0.45Al0.36Ta0.19N and the multilayered TiAlN/TaAlN coatings demonstrate pronounced age-hardening with peak hardness values of 37 ± 2 and 35 ± 2 GPa for annealing temperatures of ~ 1000 and 1100 °C, respectively. Complementary X-ray diffraction and differential scanning calorimetry confirm their enhanced phase stability. Even though, also the multilayered design shifts the formation of wurtzite-structured AlN to higher temperatures, only quaternary Ti0.45Al0.36Ta0.19N could withstand ambient air oxidation at 850 °C for 20 h. This is based on the ability of forming a nearly single-phased dense protective mixed oxide scale, having an outermost Al-rich composition. Approximately 70% of this quaternary nitride remained unaffected from oxidation. With the present study we conclusively demonstrate that thermomechanical properties of cathodic arc deposited TiAlN coatings can significantly be enhanced by either forming a quaternary compound or sophisticated architectural design with tantalum, both allow for wide-ranged industrial applications.