[Zurück]

M. Pfeiler, C. Scheu, H. Hutter, J. Schnöller, C. Michotte, C. Mitterer, M. Kathrein:
"On the effect of Ta on improved oxidation resistance of Ti-Al-Ta-N coatings";
Journal of Vacuum Science & Technology A, 27(3) (2009), S. 554 - 560.

Formation of protective oxide scales is the main reason for the high oxidation resistance of TiAlN
based coatings. Here the authors report on further improvement in the oxidation resistance of TiAlN
by Ta alloying. An industrial-scale cathodic arc evaporation facility was used to deposit Ti-Al-Ta-N
coatings from powder metallurgically produced Ti38Al57Ta5 targets. After oxidation in ambient air,
a significantly reduced oxide layer thickness in comparison to unalloyed TiAlN reference material
was observed. Energy-dispersive x-ray spectroscopy line scans and secondary ion mass
spectroscopy depth profiling showed that the oxide scale consists of an Al-rich top layer without
detectable amount of Ta and a Ti-Ta-rich sublayer. Transmission electron microscopy investigations
revealed -Al2O3, rutile-type TiO2, and anatase-type TiO2 as the scale forming oxides.
Furthermore, the Ti-Ta-rich sublayer consists of a porous layer at the oxide-nitride interface but
appears dense toward the Al-rich top layer. The improved oxidation resistance is explained by
doping the TiO2 lattice by replacing Ti4+ with Ta5+ in the rutile lattice, which decreases the oxygen
mass transport. This leads to reduced oxidation of Ti under formation of TiO2 at the oxide-nitride
interface and is the reason for the excellent oxidation behavior of Ti-Al-Ta-N coatings.

TOF-SIMS, Hard coatings