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C.M. Koller, A Kirnbauer, V. Dalbauer, R. Raab, S. Kolozsvári, J. Ramm, P.H. Mayrhofer:
"Challenges and Recent Progress in the Development of Arc Evaporated (Al1-xCrx)2O3";
Talk: 45h International Conference on Metallurgical Coatings and Thin FIlms, San Diego (invited); 2018-04-22 - 2018-04-27; in: "Book of Abstracts", B4-2-3 (2018), 85.

Ceramic Al2O3-based coatings have been utilised for technical and functional purpose for decades. Their popularity with respect to protective applicability is based on the excellent combination of mechanical integrity, thermal stability, and chemical resistance. Physical vapor deposition (PVD) belongs to synthesis techniques of choice for industry, as process conditions allow for the utilisation of temperature sensitive substrate materials. Crystalline Al2O3 films can be grown at 600 °C and below, but the phase composition is in many cases dominated by metastable Al2O3 polymorphs and not the more favourable thermodynamically-stable corundum (α) structure. Among different alloying elements investigated with respected to their ability to stabilise the α-phase, Cr appears to be the most promising candidate. Only recently studies on (Al1-xCrx)2O3 films were extended to cathodic arc evaporation. In order to develop protective coatings with an optimised property spectrum it is imperative to have a comprehensive knowledge of interdependencies of the synthesis procedure. This in first place includes process parameters and structure-property relationships, but it also implies a profound understanding of arc-induced modifications at the cathode surface and the ability to link these to the coating performance. We therefore study on the structural evolution of Al1-xCrx-based coatings grown in intermetallic state and their transition to stoichiometric oxides, both as a function of the Cr content and oxygen flow rate, and in further consequence examine cathodes and macroparticles with different compositions. Monolithically-grown and gradient-structured (for which the oxygen flow-rate was gradually increased during the synthesis), coatings were prepared by Al0.75Cr0.25, Al0.70Cr0.30, Al0.50Cr0.50, or Al0.25Cr0.75 cathodes and investigated with respect to their mechanical properties, thermal stability and oxidation behaviour. By the example of stoichiometric Al0.70Cr0.30-based oxides, the impact of alloying elements on either a promotion of the hexagonal corundum structure the stabilisation of transient phases is discussed and the significance of an optimised microstructure is demonstrated by multilayer architectures containing α-structured (Cr,Al)2O3 seed layers.
By taking different aspects of the cathodic arc evaporation process into account-i.e., cathode surfaces, droplets, oxide phase formation during synthesis-we could provide a further understanding towards the controlled synthesis of Al1-xCrx-based coatings and thus introduce new concepts for their industrial application.