Fracture toughness of thermal barrier coatings determined by micro cantilever bending tests
October 1-6, 2017
To investigate the local fracture toughness of thin coatings new small scale methods like FIB milling of micro cantilever are used. Webler et al. used this technique for measuring the fracture toughness of NiAl bond . This method can also be used to investigate the local fracture toughness of thermal barrier coatings. The fracture toughness of ceramic coatings can be determined by different indentation techniques . The drawback of these methods is the analysis of the KIc-value without the specific knowledge of the crack front propagation, which can only be determined after the experiment. By using micro-cantilever produced by ion beam milling it is possible to measure the local fracture toughness with freestanding micro-cantilever independent of the substrate. Therefore two yttrium stabilized zirconia (YSZ) top coats with a thickness of 250μm, which were deposited by suspension plasma spraying on a layer of Amdry 9954 bond coat and IN 738 substrate with different standoff distances of about 70 and 100 mm, were investigated. Figure 1. shows the micro-cantilever with the initial crack (a) before testing.
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Sven Giese, S. Neumeier, M. Göken, and R. Vaßen, "Fracture toughness of thermal barrier coatings determined by micro cantilever bending tests" in "Nanomechanical Testing in Materials Research and Development VI", Karsten Durst, Technical University of Darmstadt, Germany Eds, ECI Symposium Series, (2017). http://dc.engconfintl.org/nanomechtest_vi/17