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MM: Fachverband Metall- und Materialphysik

MM 49: Topical Session: Fundamentals of Fracture - Novel Experimental Techniques I

MM 49.3: Vortrag

Donnerstag, 14. März 2013, 11:00–11:15, H4

Micro Cantilever Bending Tests and Nanoindentation on NiAl Bond Coats and SX-NiAl — •Ralf Webler, Steffen Neumeier, Karsten Durst, and Mathias Göken — Lehrstuhl Allgemeine Werkstoffeigenschaften, Department Werkstoffwissenschaften, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Deutschland

Typically, turbine blades in aero engines and stationary gas turbines are coated with bond coats or environmental barrier coatings that are based on beta-NiAl. NiAl is an attractive intermetallic compound due to its high melting point and high Al content, which provides supreme oxidation resistance. A drawback, however, is that beta-NiAl is very brittle below the ductile to brittle transition temperature. The mechanical behavior of bond coats depends on their chemical composition, particularly important is the Al content of beta-NiAl based coatings. During service, these coatings are exposed to thermal cycling, their chemical composition changes and the mechanical properties accordingly. To determine the influence of chemical composition on hardness, Young's modulus and especially fracture toughness, bond coats with different Ni and Al content in the as-coated and thermally cycled state as well as SX-NiAl were investigated with nanoindentation and new small scaled methods. Micro cantilevers were cut by employing focused ion beam milling and subsequently in-situ bending tests were performed. This method allows to study fracture mechanics on a local scale of individual phases present in bulk materials. Results show an increase of Young's modulus with Al content and a higher hardness and fracture toughness is found in off-stoichiometric NiAl compared to binary NiAl. Furthermore, fracture surfaces differ significantly between high Ni and high Al containing samples which shows a clear influence of composition on the fracture behavior of NiAl.