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V. Dalbauer, J. Ramm, S. Koloszvári, C.M. Koller, P.H. Mayrhofer:
"Adjusting the Oxidation Behaviour of arc evaporated Al1-xCrx Intermetallics and Substoichiometric Oxides";
Poster: 45th International Conference on Metallurgical Coatings and Thin Films (ICMCTF) 2018, San Diego, CA; 2018-04-23 - 2018-04-27; in: "45th ICMCTF", (2018), 108.

Initiated by our recent works on intermetallic Al-Cr-Fe droplets [1-3], which indicate the ability to trigger the nucleation of corundum-structured (Al,Cr,Fe)2O3 crystallites, the oxidation behaviour of intermetallic Fe-doped Al0.70Cr0.30 coatings and corresponding substoichiometric oxides was investigated. The structure and composition of the outermost oxide scale and the oxidation temperature at which it forms is determined by the initial microstructure. Columnar intermetallic coatings, for instance, oxidise via an outermost metastable Al2O3 scale, which transforms into the thermodynamically stable corundum-phase starting at 1000-1050 °C. However, nano-composite-like structures, present in substoichiometric coatings, show a more diverse oxidation at the surface and complex elemental separation within the unoxidised material
In the present work, we extent our studies on the oxidation and oxide phase formation to intermetallic and substoichiometric coatings prepared from powder-metallurgically produced Al1-xCrx cathodes with nominal compositions of x=0.10, 0.25, 0.30, 0.50, and 0.75. The structural evolution of the outermost scale and coating underneath-studied by X-ray diffraction and cross-sectional electron microscopy-is related to the Cr content, oxygen flow rate during the synthesis process and the oxidation conditions.

[1] C.M. Koller, J. Ramm, S. Kolozsvári, J. Paulitsch, P.H. Mayrhofer, Role of droplets and iron on the phase formation of arc evaporated Al-Cr-oxide coatings, Surf. Coatings Technol. 276 (2015) 735-742. doi:10.1016/j.surfcoat.2015.05.012.
[2] C.M. Koller, R. Hahn, J. Ramm, S. Kolozsvári, P.H. Mayrhofer, Microstructural modifications in powder-metallurgically produced Al0.675Cr0.275Fe0.05 targets during cathodic arc evaporation, J. Vac. Sci. Technol. A Vacuum, Surfaces, Film. 34 (2016) 21603. doi:10.1116/1.4938407.
[3] C.M. Koller, A. Kirnbauer, R. Hahn, B. Widrig, S. Kolozsvári, J. Ramm, et al., Oxidation behavior of intermetallic Al-Cr and Al-Cr-Fe macroparticles, J. Vac. Sci. Technol. A Vacuum, Surfaces, Film. 35 (2017) 61601. doi:10.1116/1.4986928.