The aim of the study was to compare polycrystalline and coherent, single crystal TiN/NbN multilayer thin films with respect to the deformation mechanisms during indentation. TiN/NbN films with different combinations of single layer thicknesses, 4/9 nm (80 periods) for single crystal and 25/25 nm (20 periods) for polycrystalline coatings were deposited in the sputtering process. Single layer reference coatings of TiN and NbN (1 µm thick) were synthesized for comparison in both cases. Hardness was determined by nanoindentation (TriboIndenter, Hysitron, Inc.) using a Berkovich indenter tip. In order to assess toughness, adhesion and deformation modes (pile-up, sink-in or crack propagation) of the coatings, a Hysitron PicoIndenter® integrated into a high resolution scanning electron microscope (SEM) was employed. We have observed a very different mechanical behavior of the reference coatings compared to the multilayer composition of same thickness. Also differences between polycrystalline and single crystal multilayers were observed. In order to get a complete understanding of the fundamental deformation phenomena occurring within the layers, transmission electron microscopy (TEM) observations on the cross-sections of the indented regions were carried out  using a focus ion beam (FIB) technique. TEM images revealed that deformation mechanisms strongly depend on the microstructure of the coating. For polycrystalline multilayer films grain boundary sliding was identified as one of the acting mechanisms, while for coherent samples shear band formation and cracks perpendicular to the substrate were predominant. The difference in deformation mechanisms observed will be discussed and linked to the features observed  on the load – displacement curves.

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