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T. Glechner, S. Fritze, E. Lewin, V. Paneta, D. Primetzhofer, S. Kolozsvári, D. Holec, P.H. Mayrhofer, H. Riedl:
"Novel ultra-high temperature Ta-C and Ta-C-N coatings: From ab initio calculations to PVD depositions";
Talk: 64. Metallkunde Kolloquium, Lech am Arlberg; 2017-04-18 - 2017-04-21.

In the field of ultra-high temperature applications, the choice of materials is very limited due to highly demanding requirement profiles. Major characteristics are highest melting temperatures (TM > 3000 °C), single-phase structures as well as low tendency for recrystallization effects. These requirements are most likely fulfilled by refractory ceramics such as transition metal carbides (TMCs). However, the field of use for TMC based structural components is very limited to specific applications in aerospace industry due to different aspects. In principle, ultra-high temperature ceramics (UHTCs), such as Ta-C, are known to be harder but tremendously lower in ductility compared to metals. The typical fracture appearance transition temperature for Ta-C is about 0.5·Tm. Improving their ductility while retaining high hardness is highly desired for a variety of structural applications.
Therefore, we applied a combinatorial approach between DFT calculations and PVD based synthesis techniques to explore new possibilities for enhancing the ductile character of Ta-C based thin films. In relation to our theoretical prediction, we could prove that exchanging carbon with nitrogen on the metallic sublattice lead to a drastically increase of the fracture toughness accompanied by a smooth decrease in hardness. In addition, the influence of structural defects, such as vacancies, and chemical variations (C to N ratios) was investigated with respect to thermo-mechanical properties. For the detailed evaluation of these structure property relationships, we utilized a set of various characterization techniques such as XRD, XPS, ERDA, SEM, HR-TEM, as well as micro-mechanical testing methods.

Ultra-high temperatures; Non-reactive sputter deposition; Ta-C; vacancies; Ta-C-N;