Microstructures and oxidation behavior of sputter-deposited overlay coatings based on â-NiAl

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University of Alabama Libraries

Nickel-based superalloy components in the hot sections of commercial gas turbine engines are often protected by aluminide coatings due to their ability to function in oxidative and corrosive environments. However, the microstructures of these coated systems are metastable and change in service due to interactions with the environment and interdiffusion with the underlying substrate. The extent of these changes depends critically upon coating microstructure, chemistry, and the environment that the coated component operates in. This thesis highlights the influences of chemical composition, post-deposition annealing, and isothermal oxidation at 1050°C on the microstructures and properties of NiAl-Zr and NiAl-Cr-Zr overlay bond coatings. In particular, the results indicated that in slightly Ni-rich NiAl-based coatings, coating/substrate interdiffusion and Al-depletion within the coating could be inhibited by increasing the Zr content from 0.3 at.% to 1.0 at.% Zr. However, subsequent additions of 5 at.% Cr to coatings containing 1 at.% Zr, resulted in interdiffusion and Al-depletion levels more similar to low Zr or Zr-free coatings. Results are discussed relative to conventional coating systems.

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Materials science