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T. Glechner, R Hahn, D. Primetzhofer, H Zaid, S. Kodambaka, D. Holec, P.H. Mayrhofer, S. Kolozsvári, J. Ramm, H. Riedl:
"Tuning fracture characteristics of superhard TM carbide coatings by nitrogen alloying";
Talk: 47th International Conference on Metallurgical Coatings and Thin Films, ICMCTF, San Diego; 2021-04-26 - 2021-04-30.

Cubic transition metal (TM) nitrides and carbides are well-established protective coating materials due to their specific combination of remarkable thermo-mechanical properties but also chemical inertness. Nevertheless, their unique bonding nature - in particular combination of strong covalent and metallic bonds - is also the origin for their lack in fracture tolerance compared to metals and metallic alloys.
To overcome these limitations the formation of carbonitrides by substitutional alloying of the non-metallic sublattice exchanging C with N atoms is an interesting approach. The so obtained adjustment of the valence electron concentration has strong consequences on intrinsic material properties, e.g. Young´s modulus, melting temperature, phase decomposition as well as fracture toughness. Therefore, within this study the impact of non-metallic alloying - exchanging C with N atoms - has been explored systematically for two model systems, TaC and HfC, respectively. TM-C thin films were deposited via non-reactive magnetron sputtering, while ternary TM-C-N coatings have been deposited in mixed Ar/N2 atmospheres. We combined ab initio calculations (DFT by VASP) with experimental studies to correlate predicted properties such as fracture tolerance enhancement with increasing VEC (due to nitrogen alloying). The mechanical characteristics have been assessed by micro cantilever bending, pillar compression or splitting tests in correlation to well-established nanoindentation to gain a comprehensive view on the mechanical characteristics - also at elevated temperatures. Furthermore, detailed insights on the phase formation during coating synthesis (also considering influence of structural defects such as vacancies), and hence morphology as well as chemical composition has been studied via ERDA and SEM/HR-TEM, respectively.

Project Head Helmut Riedl:
CDL-SEC