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L. Zauner, R Hahn, M Alfreider, O Hunold, P. Polcik, D. Kiener, H. Riedl:
"Influence of the Bonding Nature on the Fatigue Resistance of Cr-based Thin Films";
Talk: 47th International Conference on Metallurgical Coatings and Thin Films, ICMCTF, San Diego, CA, USA; 2021-04-26 - 2021-04-30.

Innovative coating materials and architectural concepts extending the fatigue-life of modern high-performance
components throughout their operating spectrum by controlled, and hence predictable crack propagation are of
major interest for various industrial fields. Consequently, a fundamental knowledge on the decisive failure criteria
of PVD deposited coatings - generally associated with an intrinsic lack in ductility - under long-term mechanical
and/or thermal loading is paramount in order to enhance the limited bulk material properties utilizing protective
thin films. Literature reports on fatigue resistance, of especially hard ceramic coating materials [1] but also thin
films in general, are relatively rare. Thus, an in-depth analysis of different coatings - meaning prevalent bonding
states, i.e. altered ratio of ionic, covalent, and metallic bonds - with respect to fatigue phenomena (e.g. LCF, HCF,
strain rates or extrusion formation) is of great interest.
Within this study we present a methodical approach towards a general understanding on the failure behaviour of
PVD deposited thin films from the aspect of the bonding structure between the atomic constituents making use of
a model system containing Cr and Cr-based compounds, respectively. The DC magnetron sputtered thin films have
been analysed with respect to phase formation, thermo-mechanical properties, and morphology by means of
nanoindentation, X-ray diffraction, as well as electron imaging techniques. The influence of the stress state was
quantified through high-temperature wafer-curvature measurements. Microcantilever tests were used to calculate
the fracture toughness K IC and the fracture stress σ f by introducing a pre-notch as well as bending the cantilevers in
the as received state, respectively. Low (LCF) and high cycle fatigue (HCF) tests of unstrained micro-cantilever
geometries were subsequently performed under various loading conditions based on the critical stress intensities
observed during quasi static tests. Through this comprehensive approach we are able to identify the most critical
aspects with respect to fatigue life of different coating material classes.

Project Head Helmut Riedl:
CDL-SEC