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R Hahn, M. Bartosik, S. Koloszvári, H. Bolvardi, P.H. Mayrhofer:
"Fracture toughness enhancement of epitaxially grown CrN/TiN superlattice thin films";
Talk: 2017 MRS Fall Meeting, Boston; 2017-11-26 - 2017-12-01.

Coherently grown nanolayered thin films, referred to as superlattice thin films, are known for their superior hardness as compared with their monolithically grown constituents. Recently we have shown -by employing in-situ micromechanical cantilever bending tests- that also the fracture toughness (in addition to the hardness) shows a significant bilayer period dependent behaviour *. While mechanisms based on dislocation activity explain the hardness-peak versus the bilayer-period, the linear elastic deformation of the micro-beams during the micro-fracture experiments suggests that these explanations are not directly applicable to describe the enhancement in fracture toughness. Consequently, an underlying, bilayer-period dependent intrinsic property has to be responsible for this behaviour. The present work represents a detailed experimental study of epitaxially grown CrN/TiN superlattice thin films with bilayer periods ranging from 4 to 160 nm deposited on MgO (100) substrates by unbalanced reactive magnetron sputtering. Possible explanations for the excellent mechanical properties, like peak hardness values of ~34 GPa and fracture toughness of ~3 MPa√m are discussed. The careful analysis of the experimental results unveils an excellent correlation between mechanical properties, interface constitution (e.g., interface width, misfit dislocations), and coherency strains.

* R. Hahn, M. Bartosik, R. Soler, C. Kirchlechner, G. Dehm, and P.H. Mayrhofer, Scr. Mat. 124, 67 - 70 (2016).