Diffusion Based Aluminide Coatings for High-Temperature Corrosion Protection of Stainless Steels

Since 2008, the United States has experienced a fundmental shift in energy resources and policies that are now changing the power generation industry. New Federal EPA regulations and State renewable energy portfolio standards have increased the pressure on coal-fired power plants to reduce pollutants and implement clean-coal technology, through ultra-supercritical (USC) and advanced ultra-supercritical (A- USC) plants. The USC plant operates at temperatures of 600 C, using ferritic and austenitic stainless steels. A-USC plants raise the operation temperature to 700 C, requiring new nickel alloy materials for the turbine and critical steam piping. In addition, the higher operating temperatures create more corrosive steam and fireside environments. In advanced steam cycles coal-ash corrosion is a critical problem for superheater and reheater tubes that needs to be resolved before A-USC can be deployed. In this proposed Phase I SBIR effort, NexTech Materials will develop a protective aluminide/alumina coating for steel alloys used in power generation applications. NexTechs demonstrated aluminide coating process relies on a simple process of spray deposition and heat treating to replicate the microstructure and corrosion resistance of more complex vapor- and pack-aluminization processes. The coating process has potential in a range of applications including steam turbines, combustion chambers, boilers, heat- exhanger and waste incineration. NexTech will build upon the corrosion resistance of aluminide coatings by tailoring the microstructure and properties of its simultaneously deposited aluminum oxide overlay coating. The thickness, density and mechanical properties of these coatings can be tailored by controlling the precursor composition and morphology as well as the process conditions.