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L. Zauner, R Hahn, M Alfreider, P. Polcik, O Hunold, D. Kiener, H. Riedl:
"Fatigue testing of protective coatings: New insights on Cr-based ceramics";
Talk: 2020 MRS Virtual Spring/Fall Meeting, Boston, MA, USA; 2020-11-27 - 2020-12-04.

Thermo-mechanical fatigue phenomena and related crack propagation strongly limit the capabilities of modern high-performance components and therefore demand innovative coating materials for extending their life-time. Consequently, an in-depth knowledge of the decisive failure criteria of ceramic-based thin film materials - generally associated with an intrinsic lack in ductility - under cyclic loading is important to enhance limited bulk material properties. Literature reports on the fatigue resistance, especially of hard coatings but also thin films in general, are relatively rare, yet the pool of testing procedures appears vast and undirected. Thus, an extensive analysis between the methodology and 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 of the failure behaviour of PVD deposited thin films from the aspect of the bonding nature between the atomic constituents using a model system of Cr and Cr-based ceramics, respectively. The DC magnetron sputtered thin films were analysed regarding structure, thermo-mechanical properties, and morphology using micro-mechanical testing, X-ray diffraction, as well as electron imaging techniques. Static fracture characteristics such as fracture toughness KIC and -stress σf have been evaluated during bending of pre-notched microcantilever beams. Fatigue testing was subsequently performed on unstrained micro-geometries (i.e. cantilever or pillar) under various loading scenarios based on the critical stress intensities observed during quasi-static tests. The obtained results were further correlated with dynamic-mechanical analysis to get additional insights on size effects during fatigue testing of thin films. Through this comprehensive approach, we want to highlight the critical aspects for the fatigue life - and the evaluation of related measures - of thin film materials.

Fatigue resistance; Thin films; Cr-based compounds; Micromechanical testing; LCF; HCF

Project Head Helmut Riedl:
CDL-SEC