Fracture toughness of alpha-Cr / NiAl bond coats determined by micro cantilever bending testsWednesday (28.09.2016) 11:45 - 12:00 Part of:
To investigate the local fracture toughness of thin coatings new small scale methods like FIB milling of micro cantilevers are used. This method is applied on bond coats consisting of NiAl and Cr. For this, two bond coats with a low and a high amount of Cr were investigated. These coatings are applied on a Ni-based superalloy for protection against oxidation and are investigated after thermal cycling for 192 h at 1100°C in ambient air. The chemical compositions of the α-Cr and β-NiAl phase were analyzed by EDX measurements after the heat treatment. Using micro cantilever beams, produced by FIB milling, the local fracture toughness of the α-Cr and β-NiAl phase was measured. The α-Cr phase coarsed during the heat treatment, so that micro cantilevers could be milled out of the α-Cr phase. Apparently α-Cr has a higher fracture toughness than β-NiAl, which has, depending on the Al/Ni ratio a fracture toughness of about 1.6 - 2 MPa√m in soft orientation. Therefore α-Cr shows a ductile fracture behavior with plastic deformation in front of the FIB milled crack in comparison to β-NiAl, which fails in a brittle fracture mode.
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