Aluminide Coatings for Power Generation Applications

In order to form model aluminide coatings for studying critical issues related to their high temperature oxidation and corrosion performance, a laboratory chemical vapor deposition (CVD) procedure is being used to more rigorously control the coating process in terms of composition, purity and microstructure. One ferritic (Fe-9Cr1Mo) and one austenitic alloy (304L) were selected as substrate materials. CVD aluminizing parameters such as temperature, time, and aluminum activity were varied to fabricate an iron aluminide coating with suitable thickness and composition. One of the specific goals of the present research is to increase the thickness of the outer aluminide layer of Fe-Al coatings to improve sulfidation resistance of these alloys. It was found that raising the CVD coating temperature alone was not sufficient to increase the outer-layer thickness. Instead a higher Al activity in the CVD aluminizing process was used. However, the aluminide coatings produced in the high-Al activity process tended to crack or spall after deposition. An in situ post-coating diffusion treatment was included after CVD aluminization to improve coating adhesion. Finally, a Pt plating system has been set up at Tennessee Technological University (TTU) and initial Pt plating runs have been conducted for future study of Pt-modified aluminide coatings on Ni-base superalloys.