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H. Asanuma, F. Klimashin, P. Polcik, S. Kolozsvári, H. Riedl, P.H. Mayrhofer:
"Impact of lanthanum and boron on the growth, thermomechanical properties and oxidation resistance of Ti-Al-N thin films";
Thin Solid Films, 688 (2019), 137239; 1 - 8.

State-of-the-art machining applications require new developments in the field of protective coatings, to guarantee for excellent dimensional accuracy and effective processes. Recently, we showed an enormous enhancement in deposition rate, mechanical strength, and thermal stability of Ti-Al-N when using Ce-alloyed Ti-Al composite targets. Within this study, we further follow the concept of alloying lanthanides to nitride-based coatings, by sputtering Ti0.5Al0.5 composite targets alloyed with 2 mol% LaB6 in mixed Ar/N2 atmospheres. This allowed us to produce coatings that outperform not only Ti-Al-N (significantly) but also Ce-alloyed Ti-Al-N coatings. Compared with coatings prepared from non-alloyed Ti0.5Al0.5 composite targets (Ti0.43Al0.57N), we achieved an impressive increase in deposition rate from 77 to 139 nm/min. Furthermore, we observed an increase in hardness from 34 to 40 GPa (on polished polycrystalline Al2O3 substrates) in the as-deposited state, accompanied by a delayed spinodal decomposition, and an additional TiB2 precipitation, allowing for still 40 GPa after annealing at 1100 °C. Also the oxidation resistance could be significantly improved through the addition of LaB6. After exposure to ambient air at 850 °C for 10 h or 950 °C for 1 h, the oxide scale thickness is only 500 nm for the LaB6 alloyed coatings, whereas the Ti0.43Al0.57N counterpart was already fully oxidized after 10 h at 850 °C or 1 h at 950 °C.

TiAlN; Lanthanum hexaboride; Sputter rate enhancement; Thermal stability; Oxidation resistance;

http://dx.doi.org/10.1016/j.tsf.2019.04.014