| With the current focus on finding future energy sources, land-based power gas turbines offer a desirable alternative to common coal-fired steam power generation. Ni-Cr-Al-X alloys are the material basis for producing overlay bond coats for the turbine blades used in sections of the turbine engine experiencing the most extreme environments. These overlay coatings are designed to provide environmental protection for the blades and vanes. While the oxidation of such alloys has been investigated and modeled in-depth, the concurrent sulfidation attack has not. This corrosion mode is now being heavily researched with the desire to use gasified coal, biomass, and other renewable fuel sources in gas turbines that often contain significant amounts of sulfur. The purpose of this dissertation was to use thermodynamic calculations to describe and predict the oxidation/sulfidation processes of two Ni-Cr-Al model alloys regarding phase evolution, composition, and component activities. These calculations, in the form of potential and phase fraction diagrams, combined with sulfidation experiments using kinetic measurements and materials characterization techniques, were able to describe and predict the simultaneous oxidation and sulfidation that occurred in these alloys. |
