Schennach, Friederike (2012)
Ph.D. thesis, University of Birmingham.
Two different Pt-aluminised bond coats, with varying thicknesses and Pt-contents were examined, regarding the in uence of bond coat phases on the oxide growth. This was done in a series of short term (3, 7 and 10 minutes) oxidation experiments at 1100°C. These clearly showed different types of oxide growing on Ni3Al and NiAl phases in the low Pt specimens. It could also be shown that the transition from NiAl to Ni3Al already occurs at these early stages of oxidation. On the high Pt specimens the same types of oxide are growing on Ni3Al and PtAl2.
In addition, the high Pt specimens were examined after longer times at temperature (up to 100 hours), to gain information on the bond coat phase transformations happening at high platinum contents. It could be shown that the chromium content plays an important role with regards to phase stability fields in the ternary Ni-Al-Pt diagram. Oxidation kinetics on these samples show that the oxide is not growing at a parabolic rate, but is characterized by a time exponent of 0.145, which may be attributed to a theta to alpha a transformation in the oxide.
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