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R. Raab, C.M. Koller, H. Riedl, S. Kolozsvári, J. Ramm, P.H. Mayrhofer:
"The influence of synthetic air flow on the properties of arc evaporated Al-Cr-O-N coatings";
Thin Solid Films, 688 (2019), 137252; 1 - 8.

Various (AlxCr1-x)(O1-yNy) oxynitrides with different nitrogen non-metal fractions y and two different multilayers thereof were developed by varying the synthetic air flow (without any other gas addition) during arc evaporation of powder-metallurgically prepared Al0.70Cr0.30 cathodes. The (AlxCr1-x)(O1-yNy) oxynitride coatings crystallize with a single-phase face centred cubic (fcc) (Al,Cr)N-based structure for y ≥ 0.8, and with a phase composition of fcc-(Al,Cr)2O3-like and corundum type α-(Al,Cr)2O3-based structures for y < 0.8. Two different multilayers, one with a steep and one with a smooth transition between the constituting (Al0.66Cr0.34)(O0.85N0.15) and (Al0.62Cr0.38)(O1.0N0.0) layers are prepared by periodically varying the synthetic air flow while arc evaporation the Al0.70Cr0.30 cathodes, leading to a bilayer period of ~20 nm. The hardness of our as-deposited (AlxCr1-x)(O1-yNy) oxynitrides, decreases from ~33 to 15 GPa with decreasing y from 0.8 to 0, while both multilayers demonstrate hardnesses of ~26 GPa. The onset temperature Tonset for thermally induced dissociation of Cr-N bonds of our oxynitrides, to finally form Cr under N2-release, significantly increases from ~1000 to 1300 °C with decreasing N-content y from 0.8 to 0.15. The multilayer with a smooth layer-transition shows no mass loss up to the maximum temperature of 1500 °C, whereas that with a steep layer-transition shows a mass loss due to N2-release with Tonset ~1250 °C. Dynamic oxidation treatments of our coatings in synthetic air up to 1500 °C indicate increased structural stability with decreasing nitrogen content y. Based on our results we can conclude, that by varying the synthetic air flow during arc evaporation of Al-Cr cathodes (here, Al0.70Cr0.30), (AlxCr1-x)(O1-yNy) oxynitrides with y ≤ 0.8 can be prepared, having excellent mechanical properties and thermal stabilities.

Aluminium chromium oxynitride; Synthetic air; Thermal stability; Cathodic arc evaporation;

http://dx.doi.org/10.1016/j.tsf.2019.04.027