LOCAL FRACTURE TOUGHNESS AND RESIDUAL STRESS MEASUREMENTS ON NiAl BOND COATS BY MICRO CANTILEVER AND FIB-BASED BAR MILLING TESTS

摘要

The mechanical behavior of bond coats depends on their chemicalcomposition. Important for the mechanical behavior is the Alcontent of β-NiAl based coatings. Additionally, internal stressesare present and change during thermal cycling. Therefore bondcoats with different Ni and Al content in the as-coated andthermally cycled state are investigated. For the first time, newsmall scaled methods are used to obtain fracture toughness andinternal stresses of real bond coat systems. Micro cantileverbending and stress relaxation tests were performed on a local scaleby employing focused ion beam milling. Additionally, theinfluence of NiAl composition on Young’s modulus and hardnessis studied by nanoindentation. Results show an increase ofYoung’s modulus with Al content. In off-stoichiometric NiAl ahigher hardness and fracture toughness than in binary NiAl isfound. The internal stresses change from tensile in as-coated tocompressive stresses in thermally cycled bond coats, respectively.