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T. Glechner, R Hahn, A. Bahr, T. Wojcik, M. Weiss, J. Ramm, O Hunold, S. Kolozsvári, H. Riedl:
"Alloying of period VI transition metal boride-based coatings for ultra-high temperature oxidation protection";
Talk: AVS 67 Virtual Symposium, Charlotte; 2021-10-25 - 2021-10-28.

Various challenges in the field of environmental sustainability as well as emission reduction in general are closely linked to the usage of ultra-stable materials. Protective coatings sustaining harsh environments, involving highest temperatures accompanied by abrasive and corrosive media, are therefore of great interest. Transition metal ceramics are a suitable class to resist such conditions. Especially, period VI borides, nitrides and carbides stand out due to their extraordinary mechanical properties and highest thermal stability making them interesting for ultra-high temperature applications. However, their high temperature stability is strongly limited due to their strong tendency to form volatile oxides.
In particular, to improve the oxidation resistance of period VI based transition metal diborides, it is important to first have a profound knowledge on the scale formation of the binary systems - such as HfB2-z, TaB2-z and WB2-z, in oxidative environments. Here, especially the influence of the stoichiometry and constitution of the grain boundary interior is of major interest. Based on that knowledge, we developed alloying strategies which tremendously enhance the oxidation resistance of these coating materials and enable temperature regimes up to 1600 °C. The coating materials were deposited using an unbalanced magnetron sputtering system and consequently oxidized in a DTA/TG setup (using coatings on substrates) to study the oxidation kinetics. These results were verified with long-term oxidation tests at 1200 °C (various time periods up to 60 h) using a conventional chamber furnace. To gain a comprehensive insight on the relation between chemical composition, crystal structure, as well as morphology, we applied a broad set of high-resolution characterization techniques (e.g. HR-TEM, APT, SIMS, as well as XRD) to correlate the as deposited with the annealed states.

Project Head Helmut Riedl:
CDL-SEC