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L. Zauner, R Hahn, P. Polcik, O Hunold, D. Kiener, H. Riedl:
"Advances in fatigue testing of protective coatings: A case study on Cr-based ceramics";
Talk: AVS 67 Virtual Symposium, Online; 2021-10-25 - 2021-10-28.

Thermomechanical fatigue phenomena strongly limit the life time of modern high-performance components and therefore demand innovative coating materials extending the life-time through predictable crack propagation. Especially, an in-depth knowledge on the decisive failure criteria of ceramic thin film materials - generally associated with an intrinsic lack in ductility - under long-term mechanical loading is paramount to enhance limited bulk material properties. Literature reports on fatigue resistance, especially of hard coatings but also thin films in general, are relatively rare. Thus, an extensive analysis of different coatings - meaning prevalent bonding states, i.e. altered ratio of ionic, covalent, or metallic bonds - with respect to fatigue phenomena (e.g. LCF, HCF, 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 nature between the atomic constituents using model systems - Cr and Cr-based ceramics, respectively. The DC magnetron sputtered thin films were analysed with respect to structure, thermo-mechanical properties, and morphology by means of micro-mechanical testing, X-ray diffraction, as well as electron imaging techniques. The influence of the stress state was quantified through high-temperature wafer-curvature measurements. Static fracture characteristics such as fracture toughness KIC and -stress σf have been evaluated during cantilever bending of pre-notched beams. Low and high cycle fatigue tests of unstrained micro-cantilevers were subsequently performed under various loading scenarios based on the critical stress intensities observed during the quasi static tests. These results are also correlated with dynamic-mechanical analysis to get insights on the size effects during fatigue testing. Through this comprehensive approach we are able to identify the most critical aspects with respect to fatigue life of these protective coating materials.