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A Kirnbauer, S. Kagerer, P. Polcik, P.H. Mayrhofer:
"Improved Ti-Al-Ta-N coatings by doping with LaB6 and CeSi2";
Talk: 47th International Conference on Metallurgical Coatings and Thin Films, ICMCTF, San Diego; 2021-04-26 - 2021-04-30.

The ever-growing need for improved mechanical and thermal resistance of protective coatings ask for their continuous enhancement and optimization. Recently, we showed that CeSi2 or LaB6 doping (<2 mol%) of well-known and used Ti-Al-N coatings leads to a considerable enhancement of their thermomechanical properties and oxidation resistance. The very positive effects of Ta for Ti-Al-N (with Ta/Ti ratios of ~1/3) are already well documented. Within this study, we further follow the alloying concept by preparing sputtered nitride coatings using Ti0.45Al0.45Ta0.10 composite targets alloyed with 2 mol% CeSi2 or 1 mol% CeSi2 plus 1 mol% LaB6. The thereby developed single-phase face centered cubic LaB6 and CeSi2 doped Ti-Al-Ta-N coatings outperform the previously studied Ti-Al-Ta-N coatings considerably.
In their as-deposited condition, the LaB6+CeSi2-doped Ti0.44Al0.42Ta0.13N coatings exhibit a hardness (H) of 37.81.5 GPa and an indentation modulus (E) of 498±14 GPa (on polished sapphire substrates). Although the hardness after vacuum-annealing at 1100 °C is with 30.71.8 GPa below that of the solely LaB6-doped Ti0.43Al0.57N (39.61.3 GPa), the oxidation resistance is simply outstanding. Even after exposure to ambient air at 900 °C for 25 h, the oxide scale thickness is only 800 nm. Thus, easily outperforming the solely LaB6-doped Ti0.43Al0.57N, but also the already excellent oxidation resistance of Ti0.44Al0.44Ta0.12N and Ti0.43Al0.42Ta0.14Ce0.01N, which showed 2.4 and 1.9 µm thick oxide scales after 25 h exposure at 900 °C in ambient air, respectively.
Based on our results we can conclude that knowledge-based alloying design is a powerful tool to meet the ever-growing demands of highly-sophisticated applications.