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J. Buchinger, N. Koutná, Z. Chen, Z. Zhang, P.H. Mayrhofer, D. Holec, M. Bartosik:
"Toughness Enhancement in Transition Metal Nitride Thin Film Superlattices";
Talk: Euromat 2019, Stockholm; 2019-09-01 - 2019-09-05.

Exploring the origin of the toughness enhancing superlattice (SL) effect in transition metal nitride thin
films, we analyse and compare the properties of elastically and structurally disparate SL systems.
Based on density functional theory (DFT) data, we select TiN/WN, a system in which the elastic
moduli differ substantially between the layers, and TiN/Cr-Al-N SLs, for which we modify the
composition of Cr-Al-N to match the elastic moduli of TiN. Thereby, we simultaneously ensure a
sizeable lattice mismatch between the layers, to contrast with the miniscule differences in TiN/WN.
We use DC reactive magnetron sputtering to synthesise TiN/WN and TiN/Cr-Al-N SL coatings and
employ x-ray diffraction, as well as electron microscopy techniques for structural evaluations. To
shed light onto the mechanical characteristics, we conduct nanoindentation and single-cantilever
bending tests.
Our results uncover a pronounced dependence of all tested mechanical properties of TiN/WN SLs on
the bilayer period. These include a hardness peak of 36.7 GPa, a maximum fracture toughness of 4.6
MPa√m, and a tripling of the fracture energy to 49 J/m 2 compared to monolithic TiN (15 J/m 2 ). We
consult DFT-based models and compare the TiN/WN results with the contrasting TiN/Cr-Al-N.
Following this approach, we ascertain the contribution of coherency stresses and misfit dislocations
and elastic disparities on the toughness enhancement.

Project Head Paul Heinz Mayrhofer:
Hard coating materials