A Study of the effects of Sulfur in Electro-codeposited MCrAlY Coatings
Demands for higher efficiency and lower emissions require higher operating temperatures in aircraft, land-based, and nautical power generation gas turbines. Gas turbine operating temperature is increasing due to advances in knowledge, materials development and cooling techniques. The superalloy technology alone cannot provide metals with the high-temperature performance necessary to sustain operation. The key to meeting these new demanding goals is to provide an insulating thermal barrier coating (TBC) to lower the surface temperature of the superalloy underneath. MCrAlY overlay coatings have been used as the bond coat for TBCs, which form a protective oxide scale during service. This scale allows the substrate to withstand the high temperatures while also increasing the corrosion resistance. Electrolytic codeposition is a promising alternative process for fabricating these MCrAlY coatings. Compared to current coating processes, electrolytic co-deposition has many advantages such as low cost, non-line-of-sight, consuming much less energy with little waste, and the fabrication of dense, adherent coatings. Traditionally, a “Watts Bath” solution has been used to produce these coatings. While these coatings have had success, they can still be improved. The “Watts Bath” contains traces of sulfur in the solution which can adversely affect the coating oxidation performance. The use of a sulfur-free solution is investigated in this study. If the results are positive, this innovative approach to synthesizing these multiphase coatings will expand the knowledge and usage of the electro-codeposition technique in the area of high-temperature protective coatings.